Land use practices in the Kimbe bay catchment

Transcription

Land use practices in the Stettin Bay catchment area
and their relation to the status of the coral reefs in Kimbe Bay
Jon Brodie1 and Emre Turak2
1. Australian Centre for Tropical Freshwater Research,
James Cook University, Townsville, Australia
2. CORMEC, 1 r Francois Villon, 95000, Cergy, France
Australian Centre for Tropical
Freshwater Research Report No. 04/01
Land use practices in the Stettin Bay catchment area and their relation to the status of coral reefs – ACTFR Report No. 04/01
Summary
The report concludes that there is damage to coral reefs in Stettin Bay from sedimentation
particularly in the inshore south western section of the Bay, from Kimbe Town to Walindi
with less damage inshore further north of Walindi and to the east of Kimbe Town. Reefs
further offshore are damaged but not primarily from land-based sources but via bleaching and
crown-of-thorns starfish damage. The greatest sources of above-natural sediment export to
Stettin Bay are from logging and oil palm plantation development in the plant crop stage.
Other sources exist such as gardens, mature oil palm plantations, urban and small crops but
these are of lesser significance. Natural sources of sediment to the Bay include episodic
catastrophic events such as landslides and volcanic eruptions and associated lava/ash flows
but the effects of these will also have been exacerbated by deforestation and agricultural
development. Sediment exports associated with logging will have peaked in the 1980s, the
peak logging period, and be now falling with the reduction of logging activity in the Stettin
Bay catchment. Oil palm new development and replanting continues and is now a large
source. There is no clear evidence that nutrients (specifically nitrogen) runoff is causing
problems but any such problems may be masked by the more acute damage caused by
sedimentation. A monitoring program to measure loads of sediments and nutrients entering
Kimbe
Bay
from
different
land
uses
could
assist
in
resolving
this
issue.
The reefs being damaged from sedimentation are fortunately not the premier dive sites for
tourism but are important parts of the coral reef biodiversity of the Bay. Given it is difficult to
implement management in the logging industry, assistance should be given to the Oil Palm
industry to help manage new developments focussing on the plant stage of development as
well as attempting to improve environmental management in logging.
•
Coastal reefs were surveyed at 16 locations including 29 sites in Stettin Bay in late
November early December 2003, in order to assess current status and possible effects
from land runoff.
•
With the exception of one, all reefs showed varying degrees of damage and degradation.
Coastal and near shore reefs showed the maximum amount of degradation. The main
causes appeared to be; coral bleaching, crown of thorns starfish and siltation.
Australian Centre for Tropical Freshwater Research
Page i
•
Highest level of degradation appears to be in the Southwest corner of the bay, on
coastal and nearshore reefs from Kimbe to Numondo. Reefs along the west coast of the
bay showed lesser degradation and reefs at the East around Hoskins peninsula showed
the least degradation.
•
On the heavily degraded coastal and nearshore reefs fine sediment and silt smothered
the surface of dead corals, possibly severely interfering with recruitment and hence the
recovery capacity of the coral communities.
•
Further offshore where there was still coral mortality but none or low levels of silt,
various age cohorts of coral recruits were apparent.
•
It is clear in our opinion that a number of inshore reefs in Kimbe Bay, particularly in
the south-western section, have been severely damaged by sedimentation in recent
times. The damage may be exacerbated by other factors such as bleaching and crownof-thorns starfish in a synergistic way. There is no clear evidence of nutrient enrichment
effects, but these may be disguised by the mortality caused by sedimentation, bleaching
and crown-of-thorns starfish, and cannot be completely ruled out.
•
The area of clear damage from sedimentation is the area from the mouth of the Dagi
River westward to Walindi and to a lesser extent from Walindi to Talasea. Reefs in
most other areas of Stettin Bay have not been damaged by terrestrial sediment discharge
although many of them have been damaged by other factors such as bleaching and
crown-of-thorns starfish.
•
The modelled estimates of sediment and nutrient loads reinforced by anecdotal and
observational evidence suggest the most significant additional loads of sediment above
natural originate from logging operations and the plant stage of oil palm plantation
development.
•
A principal factor in the concentration of reef damage from sedimentation in the south
west section of Kimbe Bay is the poor flushing, low wave action and generally still
conditions in this area. As a result of this low energy regime sediment deposited on
reefs remains for extended periods and is not removed by wave action as occurs in other
parts of Kimbe Bay.
•
Sedimentation from land runoff is not the only threat to coral reef health in Kimbe Bay.
In many other parts of Kimbe Bay damage from bleaching and crown-of-thorns starfish
were evident. At one site damage from a ship grounding was observed.
Page ii
Contents Page
Summary ....................................................................................................................................i
1. Introduction ..........................................................................................................................1
1.1 Kimbe Bay......................................................................................................................................... 1
1.2 Stettin Bay ......................................................................................................................................... 6
2. Background.........................................................................................................................17
2.1 General land use status and history in Kimbe Bay Catchment Area............................................... 17
2.2 Potential runoff ‘pollutants’ from the land uses present in KBCA ................................................. 28
2.3 Potential modes of delivery............................................................................................................. 29
2.4 Habitat modification in wetlands, mangroves, streams & effects on marine fauna ........................ 30
2.5 Other impacts & potential impacts on marine ecosystems & synergism with land runoff ............. 33
3. Methodology .......................................................................................................................33
3.1 Land use information collection...................................................................................................... 33
3.2 Mapping .......................................................................................................................................... 33
3.3 Reef surveys .................................................................................................................................... 34
4. Marine survey results.........................................................................................................36
4.1 Community types ............................................................................................................................ 36
4.2 Status of reef biota........................................................................................................................... 41
4.3 Reef damage and sediment levels ................................................................................................... 44
5. Land use results..................................................................................................................48
5.1 Logging ........................................................................................................................................... 48
5.2 Oil palm........................................................................................................................................... 50
5.3 Copra ............................................................................................................................................... 54
5.4 Subsistence gardens......................................................................................................................... 55
5.5 Small crops...................................................................................................................................... 55
5.6 Sewage Treatment Plants ................................................................................................................ 56
5.7 Oil/Hydrocarbon storage ................................................................................................................. 56
5.8 Oil palm mills and refinery ............................................................................................................. 56
5.9 Natural sources of sediment ............................................................................................................ 57
6. Budgets/modelling ..............................................................................................................57
6.1 Background ..................................................................................................................................... 57
6.2 Model basis ..................................................................................................................................... 58
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6.3 Model calculations for suspended solids......................................................................................... 59
6.3.1 Logging................................................................................................................................................................. 59
6.3.2 Oil palm plantation planting stage ....................................................................................................................... 60
6.3.3 Oil palm plantation juvenile and mature stage..................................................................................................... 60
6.3.4 Oil palm smallholder juvenile and mature stage .................................................................................................. 60
6.3.5 Rainforest (including both primary and secondary forest) ................................................................................... 61
6.3.6 Gardens, small crops, copra................................................................................................................................. 61
6.3.7 Suspended sediments summary ............................................................................................................................. 62
6.4 Model calculations for nitrogen ...................................................................................................... 63
6.4.1 Logging................................................................................................................................................................. 63
6.4.2 Oil palm plantation planting................................................................................................................................. 63
6.4.3 Oil palm plantation mature................................................................................................................................... 63
6.4.4 Oil palm small holders mature ............................................................................................................................. 64
6.4.5 Forest.................................................................................................................................................................... 64
6.4.6 Gardens, small crops, copra................................................................................................................................. 64
6.4.7 Fertiliser losses..................................................................................................................................................... 64
6.4.8 Sewage STP discharges ........................................................................................................................................ 65
6.4.9 Septic and pit sewage systems............................................................................................................................... 65
6.4.10 Nitrogen summary............................................................................................................................................... 66
6.5 Sediment and nutrient losses from different land uses............................................................ 67
7. Conclusions .........................................................................................................................77
7.1 Overall............................................................................................................................................. 77
7.2 Likely loads/sources of SS, nutrients .............................................................................................. 77
7.3 Oceanographic factors..................................................................................................................... 78
7.4 Other reef damaging factors ............................................................................................................ 78
7.5 Effects of reef damage on Stettin Bay resources............................................................................. 78
8. Monitoring program options.............................................................................................82
8.1 Background ..................................................................................................................................... 82
8.2 Methods........................................................................................................................................... 82
8.2.1 Sources and loads ................................................................................................................................................. 82
8.2.2 Transport and exposure ........................................................................................................................................ 83
8.2.3 Biological effects .................................................................................................................................................. 83
8.3 Interpretation................................................................................................................................. 84
9. Recommendations ..............................................................................................................85
9.1 Logging practices ......................................................................................................................... 85
9.2 Land use practices in oil palm. ................................................................................................... 85
9.3 STPs ............................................................................................................................................... 86
9.4 Monitoring program ..................................................................................................................... 86
Acknowledgements & contributors ......................................................................................87
10. References .........................................................................................................................89
Appendix 1. The effect of land use on water quality and aquatic ecosystems ..................99
Page iv
1. Introduction
The ‘Land use practices in the Kimbe Bay catchment area and their relation to the status of
the marine ecosystems in the Bay’ project was established jointly by New Britain Palm Oil
Limited (NBPOL) and The Nature Conservancy (TNC). Its objective was to investigate
whether current land uses in the Kimbe Bay Catchment Area (KBCA) cause runoff of
pollutants to the marine environment and, as a result, cause or contribute to the damage to
marine ecosystems (particularly coral reefs) in Kimbe Bay . The project was commissioned as
a result of previous reports (e.g Munday, 2003), which indicated coral damage within Kimbe
Bay.
The project was carried out by Jon Brodie, Principal Research Scientist, Australian Centre for
Tropical Freshwater Research, James Cook University and Emre Turak, independent
consultant on coral reef studies, with the assistance of the large number of people noted in the
Acknowledgements.
1.1 Kimbe Bay
Kimbe Bay is a large bay on the north coast of New Britain Island (Figure 1) in the West New
Britain Province of Papua New Guinea (PNG). The bay is approximately 120 km across and
is divided into Stettin Bay in the west and Commodore Bay in the east (Figure 1). Extensive
areas of coral reef occur in the Bay (Maragos, 1994; Turak and Aitsi, 2002) (Figure 2) which
form the basis of a dive tourism business (based at Walindi Plantation Resort) and the
resource base for local fishing industries. The KBCA is made up of two small rivers (Kapiura,
Dagi) and a large number of small streams.
Kimbe Bay is in latitude 5ºS and thus in the doldrums with a weak and variable wind climate.
SE winds are common but the Bay is sheltered from these by the main longitudinal range of
New Britain and they produce only minor waves in the available fetch. Ocean swells
approach the bay from the NW at times but the SW of Stettin Bay is sheltered from these. The
waves do break on the reefs and shores of eastern Stettin Bay on the Hoskins Peninsula and in
Commodore Bay. Tidal range in the Bay is small – approximately one metre, and thus tidal
currents are weak.
Page 1
Figure 1 Kimbe Bay
Page 2
The bay is too far north to regularly experience cyclones but this can happen infrequently
such as in Cyclone Justin in 1997. Unusual wind conditions such as from the NE occur
occasionally and have been noted to pool warm water in the SW of the Bay and perhaps thus
be responsible for coral bleaching in that area (Max Benjamin, pers. com.) Overall the bay is
very calm with a low wave climate and weak wind and tidal generated current regime.
River plumes from the major rivers entering the Bay are likely to dispense evenly in the Bay
in low wind conditions as shown by the example from the Kapiura River (Figure 3), which
discharges into Commodore Bay, observed from satellite images or with SE winds dispense
to the west and north-west. Coriolis forces will also tend to drive river plumes to the west in
Stettin bay but these forces are weak in this region. In the Bay plumes from the Dagi River
are most likely to disperse offshore and into the SW and W of the Bay.
The KBCA is made up of two small rivers (Kapiura, Dagi) and a large number of small
streams covering an area of approximately 3000 km2. Geology and soils in the catchment are
dominated by the presence of several active or recently active volcanoes (Figure 4). The
landscape is active with visible landslips on the steeper slopes and active river channels.
Rainfall is high (3000 – 4000 mm see Figure 5) and distinctly seasonal with monthly rainfall
in the December to April period above 500 mm. The KBCA has a relatively large coastal
plain and then the ranges and individual volcanic cones rise to 2000m around the rim of the
watershed (Figure 6). The catchment was until recent times primarily forested with lowland
and montane rainforest, coastal freshwater swamps of several types and coastal mangroves.
Most of the KBCA has been logged (Figure 7), particularly in the period 1965 – 1990,
although logging continues to the present day. The coastal plain and lower slopes of the range
which forms the boundary of the KBCA has been gradually planted to oil palm since the
1960s. The total area of oil palm is now approximately 60,000 ha split between the
plantations of NBPOL with 29,000 ha (Figure 8), Hargy Oil Palms Limited (HOPL) with
10,000 ha and smallholders with a total of approximately 18,000 ha (Ian Orrel, pers. com.).
There are three active volcanoes in East Kimbe Bay, Mt Ulawana, Lolobau and Mt Pago and
Turak and Aitsi (2002) stated that these will undoubtedly have an influence on coral (both in
distribution and condition) and noted that the dark volcanic sand around two of the volcanoes
appeared incompatible with coral growth. Mt Pago erupted on the 28 July 2002.
Page 3
Given the time available for this preliminary assessment of the situation, the study focussed
on Stettin Bay, the site of existing reports on reef degradation. Oceanic and physical
conditions on the eastern side of Kimbe Bay (i.e. Commodore Bay) appear to be quite
different to the west and extrapolation of the results of the current assessment to that area
should be carried out with care. However it was considered that by studying the Stettin Bay
Catchment Area (SBCA) and the reefs in Stettin Bay conclusions could be drawn that, with
care, would be relevant to the whole of Kimbe Bay.
Figure 2 Reefs of Kimbe Bay
Page 4
Figure 3 River plume from the Kapiura River
Page 5
1.2 Stettin Bay
Stettin Bay (Figure 9) is largely composed of open water (scattered with patch reef) with
depth of approximately 400 – 600m but also has a narrow shelf adjacent to the land with
depths of less than 200m. Reefs in the Bay can be conveniently divided into three groups –
(1) the fringing reefs adjacent to the coast (Figure 10), generally within 500m of the shore
and in water depths of less than 50m
(2) the barrier reefs generally just inshore of the 200m isobath and within about 10km of
the coast (Figure 11)
(3) the patch (atoll) reefs towards the centre of the Bay (Figure 12) rising out of deep
(generally > 400m) water.
Seagrass beds and algal meadows are located in shallow water (less than 10m) adjacent to the
coast in parts of the Bay. Mangrove forests can be found in some islands close to the shore
(Figure 13), especially in the SW section of the Bay, and fringing the shoreline in parts of the
Bay (Sheaves, 2002). The Bay is also known for its megafauna including dugongs, orcas,
pilot whales, sharks, tunas and billfish.
The population of Stettin Bay is now 70,000, having risen quickly over the last three decades.
The town and port of Kimbe lies on the coast on the southern shore of Stettin Bay and has a
population of approximately 25,000.
Page 6
Figure 4 Active volcano (Mount Pago) in Kimbe Bay catchment
Page 7
Figure 5 Stettin Bay catchments and rainfall
Page 8
Figure 6 Kimbe Bay elevation and major rivers
Page 9
Figure 7 Logged areas
Page 10
Figure 8 NBPOL plantation areas
Page 11
Figure 9 Stettin Bay
Page 12
Figure 10 Fringing reefs near Walindi
Figure 11 Barrier reefs near Hoskins
Page 13
In recent years studies of the status of the reefs of Kimbe Bay have revealed loss of coral
cover and reef degradation (Jones et al., 1999; 2000; Munday, 2000; 2003; Turak and Aitsi,
2002). This has been widely attributed to the effects of land runoff, crown of thorns starfish
and coral bleaching (Jones et al., 2001 Munday, 2003; Selig et al., 2003; Wilkinson, 2002)
with sedimentation caused by oil palm plantation runoff (Selig et al., 2003) coral bleaching
over the last three years (Jones et al., 2001) and drought initiated erosion (Munday 2003)
being specifically mentioned. Turak and Aitsi (2002) concluded that the whole of Kimbe Bay
has coral reefs in good condition which support reef fish populations which are rich in coral
diversity and very attractive to visitors.
A number of coral reef studies carried out in Stettin Bay in the last ten years have drawn
attention to the continual decline in reef health. Several bleaching events, crown of thorns
starfish (COTS) predation, and increased sedimentation from land runoff have been cited as
possible causes for this decline. Maragos (1994) and Turak and Aitsi (2002) noted the overall
good health of reefs in western Kimbe Bay, despite bleaching at many sites. However
Maragos (1994) did point out that some inshore reefs were exposed to heavy sedimentation as
well as fishing pressure and Munday (2003) stated that coral mortality in the bay is related to
reef position and that inshore reefs are more likely to experience significant impacts of
terrestrial origin (logging, agriculture and natural erosion) as well as to suffer more
substantially from coral bleaching.
Jones et al., (2001) looking at the effects reef closure, noted from 1997 to 2000 a decrease in
total hard and soft coral cover and an increase of total algae cover on 8 reefs on the western
coast of Stettin Bay near Walindi resort and concluded that the decline in coral cover was
largely due to a series of coral bleaching events in September 1998, April 1999 and March
2000. Munday (2003) reported a serious decline in the abundance of acroporid corals and
coral-dwelling fishes in Kimbe Bay from 1996 to 2003. And noted that this decline was most
severe on inshore reefs. He also listed coral bleaching, COTS and coastal sedimentation as
possible causes for this decline. Turak and Aitsi (2002) reporting on surveys carried out at the
eastern side of Kimbe Bay, noted high coral mortality in the western part of Commodore Bay
due to active crown of thorns and, in the South, sedimentation on a length of fringing reef
(restricted to the immediate coastal area) which they associated with development of oil palm
plantations. In general Turak and Aitsi (2002) concluded that reefs in the Kimbe Bay were in
Page 14
Figure 12 Patch (Atoll) reef
Figure 13 Mangroves in south west Stettin Bay
Page 15
good condition and showed little current evidence of natural or human associated stress.
Volcanic activity is present in the area and may be the main cause of natural disturbance to
coral reefs in the whole bay (Turak and Aitsi 2002). They also noted that the reef and coral
communities in their study area appear to be primarily structured by volcanism.
Oil palm plantations are seen by some as a threat to freshwater and estuarine fish fauna in the
KBCA (Jenkins, 2000). Sheaves (unpublished- Mahonia supplied report) found the coastal
habitats of Kimbe Bay to have high densities of fish suggesting a healthy ecosystem and
(Beger et al., 2003) found a reduction in fish species on fringing reefs in the KBCA to be a
result of both natural and anthropogenic processes.
Jenkins (2000) found elevated river temperatures, depressed pH, increased turbidity and high
algal counts in one stream in an oil palm area and attributed this to irrigation demands and
nitrogenous fertiliser leaching. However with an average rainfall up to 4m (see introduction)
irrigation is not practised in oil palm and in his assessment of mangroves systems Sheaves
(unpublished- Mahonia supplied report) found no apparent evidence of contamination.
The oil palm industry in general in PNG is seen by one author as a threat to social and
environmental values (Anderson, 2003). Huber (1994) in his general review of the status of
PNG coral reefs notes that large-scale agricultural projects for oil palm, copra and rubber
have contributed to increased sediment loads on downstream coral reefs. He also notes that
urban drift and increasing coastal population have contributed to soil erosion from intensified
subsistence and market gardening thus contributing to the sedimentation problems. Turak and
Aitsi (2002) believed that good management of potential land based threats can protect these
reefs for the future.
The objectives of the ‘Land use practices in the Kimbe Bay catchment area and their relation
to the status of the marine ecosystems in the Bay’ project are as follows:
1. Provide an assessment of land use practices in the Kimbe Bay Catchment Area by
inspection and assess their potential to deliver pollutants to the marine environment.
2. Assess the condition of reefs in Kimbe Bay in relation to their potential exposure to landsourced pollutants.
Page 16
3. Use the western part of Kimbe Bay i.e. Stettin Bay as a focussed study area.
4. Provide advice on the design of further long-term studies including monitoring.
5. Provide advice on changes in land use practices and land use management which could
reduce pollutant discharge to the marine environment.
2. Background
2.1 General land use status and history in Kimbe Bay Catchment Area (KBCA)
The information in this section was gathered during the 18 days spent by the authors in
Kimbe Bay from written material (reports, records) and through interview with relevant
people. It should be used as only a guide to this type of statistics and subject to further
refinement and correction as better data and estimates become available.
The catchment area of Kimbe Bay (KBCA) is made up of two small rivers (Kapiura, Dagi)
and a large number of small streams. The Stettin Bay catchment area (SBCA) was chosen for
focussed study of land export of sediments and nutrients and reef damage. SBCA is defined
in this study to include individual catchments from the Golo River in the east to Lake
Dakataua in the north west, including the Golo, Gavuvu, Tapipu, Ko, Ganuka, Dagi
catchments and the many small catchments on the eastern side of the Willaumez Peninsula
with total area estimated to be approximately 75,000 ha (Keu, 2003 estimates ‘more than
70,000 ha’ for this basin). The Kapiura and Kulu Rivers also drain country behind (ie to the
south of) Stettin Bay but discharge to other bays, the Kapiura to Commodore Bay and the
Kulu to Riebeck Bay (Figure 1). Geology and soils in the catchment are dominated by the
presence of several active or recently active volcanoes e.g. Mt. Pago (Figure 4). The soils are
young, either unweathered or with low/moderate weathering, with low clay content but some
allophane and halloysite (Bleeker, 1983). Typical of tropical rainforest, soils have low
nutrient status overall, with significant, for example, nitrogen content only present in the top
five cm, falling rapidly to very low content by 500 cm (Bleeker and Healy, 1980; Bleeker,
1983; Keu, 2003)(Table 4). Inceptisols with medium nutrient content are also common in
PNG and specifically in the Kimbe region. The landscape is active with visible landslips on
the steeper slopes and active river channels. Rainfall is high (2881 - 4224mm, Figure 5). The
Page 17
catchment was until recent times primarily forested with lowland and montane rainforest,
coastal freshwater swamps of several types (including sago palm swamps) and coastal
mangroves.
Much of the Kimbe Bay region has been logged, mostly since 1961. Anecdotal records (Mark
Tegal pers. com.) suggest that 10,000 cubic metres per month (cmm) of timber was extracted
in the period 1961 to 1973 and 20,000 cmm in the period 1973 to 1990 from the Kimbe Bay
region and the Kulu catchment (Figure 14). This translates into approximately 400 ha of
worked forest per month from 1961 to 1973 (4800 ha per year) and 800 ha from 1973 to 1990
(9600 ha per year). In the period since 1990 logging activity has fallen substantially with
current rates of approximately 3,500 cmm, equivalent to 1700 ha per year.
Figure 14 Progressive area of logging in PNG (from Bun et al., 2004)
Page 18
Our initial estimates of logging in the SBCA were that the total logging areas in the SBCA
were about one quarter those of the whole Kimbe Bay region i.e 1200 ha/year from 1961 to
1973, 2400 ha/year from 1973 to 1990 and 400 ha/year from 1990 to 2003. This gives a total
logged area of 56,000 ha over the last 30 years, 75% of the catchment area.
A more detailed analysis of logging activity was carried out by Simon Lord (NBPOL) based
on volumes of logs harvested and exported by the Stettin Bay Lumber Company (SBLC) in
the period 1999 – 2002 obtained from the Dami Forestry Office (Table 1). This suggests,
based on 30 cubic metres of log per hectare, that SBLC have been actively logging
approximately 3,191 – 4,263 (mean 3500) hectares per annum in undulating terrain. This
figure is obviously greatly in excess of the original estimate of 400 hectares/year. Lord
suggests that these figures, combined with the estimates for the period before 1999 based on
Tegal (see above), give a logging history for the SBCA as follows:
1961-73 = 12 year x 1200 = 14,400 ha
1973-90 = 17 years x 2400 = 40,800 ha
1990-2000 = 10 years x 400 = 4,000 ha
2001 – 04 = 4 years x 3500 = 14,000 ha
totalling 72,800 ha which represents 100% of the catchment area.
However logging by the SBLC is certainly not only occurring in the SBCA and the estimates
of 3,500 hectares per year in the 1999 – 2003 period are an over-estimate of the logging
occurring in the SBCA.
Table 1 Total SBLC harvest
SBLC - Volume of logs harvested & exported 1999-2002
1999
2000
2001
2002
TTL Volume logs harvested
(c. metres)
117,947 95,761 95,735 127,910
TTL Volume logs exported
(c. metres)
82,776 62,770 69,686
82,867
Source: Dami Forests
Page 19
To try and get better logging figures for just the SBCA and thus separate this figure from
logging occurring in other parts of the Kimbe region outside of the SBCA, Walain Ulaiwi
(The Nature Conservancy) carried out a more detailed analysis. Logging data from the Stettin
Bay Lumber Company (SBLC) for the years 2001 – 2004 inclusive within the SBCA were
collated and are shown in Table 2. The cutting areas listed Amelei/Kaskas Umsipel;
Manseng; KorokoManseng; Amelei/Mendrip Umipeli; Kulu Dagi; Avit/Opun; Marapu;
Bunga Kulu Dagi; Koroko/Manseng; Gimomi K. Manseng; Gimoni Oga; Gimoni;
Gimoni/Marapu; Ania Kapiura are those identified by Ulaiwi to lie mostly within the SBCA.
Logging in the SBCA provides only a proportion of the logging carried out by the SBLC,
approximately one half in 2001 and 2002 as can be seen by comparing Table 2 (SBCA
logging) with Table 1 (total SBLC harvest).
Page 20
Table 2 SBLC monthly and yearly production (cubic metres) in Stettin Bay Catchment Area, 2001- 2004.
March
April
May
1497
Sep.
Oct.
Nov.
Dec.
3140
4772
1795
3747
3695
4772
6794
4208
11002
3465
1795
4810
1301
2111
3747
4740
3758
8498
3695
3695
3332
7027
3204
417
3621
4095
2346
6441
48495
5215
5364
1678
5216
5364
2931
2931
39703
8565
19822
8565
19822
21273
2385
1497
4000(est)
4000(est)
1470
2624
0
1975
2385
357
0
1385
1852
0
1437
1826
0
2468
1635
2624
504
1975
3140
5870
562
6432
2047
762
3983
2793
2001
Not available
Aug.
1470
2003
2002
July
Not available
12550
June
357
2121
3237
3263
4103
2551
3851
4269
3779
4745
2793
4899
6252
3465
2450
2121
2450
3851
4269
3779
4899
6252
Total
53010
1678
17617
17617
Unavailable
Feb.
Unavailable
Jan.
8725
Nil production
Year
2004
Cutting Area
Amelei/Kaskas
Umsipel
Manseng
Koroko Manseng
Amelei/Mendip
Umipeli
Kulu Gagi
Avit/Opun
2001 Total
Kulu Dagi
Marapu
2002 Total
Marapu
Bunga
Kuku Dagi
Bunga
Koroko/Manseng
Gimomi
K. Manseng
Gimoni Oga
2003 Total
Gimomi
K. Manseng
Gimomi
Gimomi/Marapu
Ania Kapiura
Various
2004 Total
5000(est)
5000(est)
83652
Page 21
Approximately 30 cubic metres of timber are extracted per hectare of logged forest in New
Britain (Mark Tegal, pers. com.) and the timber volumes in Table 1 thus translate to the
following logged areas in Table 3.
Table 3 Area logged 2001 – 2004
Year
Cubic metres harvest
Hectares logged estimate
2001
53010
1767
2002
48495
1616
2003
39703
1323
2004
83625
2788
Mean of 4 years
1874
However inspection of Ulaiwi’s figures also suggests that some of the cutting areas listed are
outside of the SBCA e.g. Kulu Dagi and Ania Kapiura and that the mean figure of 1900 ha in
the period 2001 – 2004 may also be an overestimate of SBCA logging.
Given the uncertainty in the logging data for the SBCA (with three estimates for recent years
being 400, 1800 and 3500 ha/year) modelling will be based on the 1800 ha/year figure but
recognizing that this is likely an overestimate. On these estimates the cumulative rate of
logging in the SBCA would be:
1961-73 = 12 year x 1200 = 14,400
1973-90 = 17 years x 2400 = 40,800
1990-2000 = 10 years x 400 = 4,000
2001 – 04 = 4 years x 1800 = 7,200
totalling 66,400 ha which represents 87% of the catchment area.
Logging concession areas are shown in Figure 15. Almost all logging for primarily timber
extraction purposes was selective with specific species and types targeted. In the period 1985
to 1994 about 2000 ha was clear felled. Logging was also carried out before the establishment
of cash crops but this, of course, involved clear felling.
Page 22
In 1987 Judge Thomas Barnett’s commission of Enquiry into the Papua New Guinean
Forestry Sector (1987-1989) (Barnett (1989) found a large number of environmentally
damaging practices. Largely as a result The Papua New guinea logging code of practice
(1996) was introduced in 1997 but unfortunately even today many logging operation do not
adhere to this code of practice. For example Forests monitor and ICRAF (Individual and
Community Rights Advocacy Forum Inc.(1999) case study of logging operation in Vanimo
timber area (Sandaun Province, PNG) showed 14 out of the 24 Key criteria to be totally
ignored.
Page 23
Figure 15 Logging concession areas
Page 24
Considerable areas of the coastal plain and lower slopes of the range which forms the
boundary of the KBCA has been gradually planted to oil palm (Figure 8) since the late 1960s.
The total area of oil palm is now approximately 60,000 ha split between the plantations of
NBPOL with 29,000 ha, Hargi PL with 10,000 ha and smallholders with a total of
approximately 18,000 ha (Ian Orrel, pers. com.). From analysis of recent Landsat images
Selig et al. (2003) estimate plantations to cover 86,808 ha in the Kimbe Bay region but this
includes the catchment of the Kulu River and the western side of the Willaumez Peninsula
and also copra plantations which make up the difference to the 60,000 ha estimate. In the
SBCA NBPOL has (very) approximately 13,000 ha and small holders may have 11,000 ha.
NBPOL plantation areas are shown on Figure 8.
As the oil palm gets taller it reaches a height where it is no longer practically possible to
harvest the fruit (cutting the fruit is manual) and the palms at this stage are cut and replanting
occurs. The average age for this process is 18 - 20 years. Thus in a mature plantation region
such as Kimbe Bay both development of new plantations (from copra plantations (Figure 16)
or primary or secondary forest areas (Figure 17) and replanting of old oil palm plantations
(Figure 18) are occurring simultaneously. It is estimated that approximately 1,500 ha/year of
new and replant oil palm is being planted each year by NBPOL (current for 2003). This figure
would have been less in the first 20 years of development in Kimbe Bay before replanting
commenced. Assuming a figure of 800 ha/year of new plantings gives us the total 29,000 ha
of NBPOL plantations over 36 years. In the SBCA an estimate will give a current planting
rate (new and replant) of 650 ha/year.
Considerable areas of cocoa were observed in the KBCA but no figure could be obtained for
total area. Other small cash crops include vanilla and remnants of the once extensive copra
plantations. Fruit and vegetables (bananas, sweet potato, cassava, taro, pawpaw) are grown
for local markets and for subsistence domestic use.
Population is now approximately 70,000 (see earlier) having risen quickly over the last three
decades. The town and port of Kimbe lies on the coast on the southern shore of Stettin Bay
and has a population of approximately 25,000. Two solid waste disposal sites have been in
use serving Kimbe town in recent times, one at Wandoro used for the last 20 years and one at
Dagi in use for the last year. The sites are used for waste from Kimbe but no separation of
Page 25
waste is performed. The current system serves 4,000 houses, 200 businesses, 32 restaurants
and local schools and the hospital. Hospital medical waste is disposed of near the hospital in
Sandermo Creek. Of the approximately 4000 houses in Kimbe town 60-70% are served by
septic systems and the remainder (1,200 -1,600 by the Sewage Treatment Plant (STP). The
STP east of the town consists of two sequential aerobic lagoons with no pre-treatment before
the first lagoon. Discharge from the second lagoon (stocked with Tilapia sp fish) flows
immediately to a drain and then about 150m to the sea. The STP serves about 1,500 houses,
the high school and the hospital for an equivalent population of about 9,000.
Figure 16 Oil palm development on old copra lands
Page 26
Figure 17 Oil palm development on forest lands
Figure 18 Oil palm replanting on old oil palm plantations (Togulo)
Page 27
2.2 Potential runoff ‘pollutants’ from the land uses present in KBCA
Soil erosion, sediment production and export to the sea are natural processes and will have
been occurring in the Kimbe Bay area long before commercial logging, oil palm plantation
development and commercial cropping began. However modern logging, cropping
development, urban development and road construction increase erosion rates and sediment
inputs to streams, and hence the ocean, dramatically above the natural background rate.
The principal contaminants likely to be increased over natural from the land use activities in
the SBCA are suspended sediment, nitrogen and phosphorus and litter. Suspended sediment is
mobilised through soil erosion and will have increased due to soil exposure during logging
(particularly on roads, log dragging/skidding and loading and operations areas), cropping
(particularly on roads, in the soil preparation, planting and replanting stage and by stream
bank erosion) and gardening (also particularly in the preparation and planting stage). Some
loss of landscape ability to trap sediments will also have occurred through the loss of riparian
vegetation and wetlands associated with agricultural, urban and industrial development.
Nitrogen and phosphorus compounds will also be lost at increased rates due to increased soil
erosion and reduced trapping. This increased nutrient load will primarily be present as the
particulate forms of nitrogen and phosphorus.
Nitrogen and phosphorus content of surface soils of various land uses in the SBCA have been
reported by Keu (2003) and reproduced in Table 4 (summarised from Table 5.0 in Keu,
2003).
Table 4 Nitrogen and phosphorus content of SBCA soils (from Keu, 2003)
Land use
Total P %
Total N %
Range
Mean
Range
Mean
Rainforest
0.037-0.241
0.118
0.52-0.80
0.65
Food garden
0.224-0.404
0.302
0.61-0.94
0.79
Village oil palm
0.194-0.286
0.246
0.45-0.60
0.52
Plantation oil palm
0.152-0.359
0.224
0.27-0.51
0.38
(mechanised)
Page 28
Figures from soil surveys of all 29,000 ha of NBPOL oil palm plantings give Total N as
0.33% (mean ) with a range 0.19-0.65. and P (Olsen method of extraction) as <0.1%
Additional nitrogen will be lost from fertiliser application on crops. Nitrogen is used on oil
palms in plantation cultivation at about 100 kg/ha/year and as in many crop systems up to
50% losses of applied nitrogenous fertiliser may occur (Nelson, 2003). Recent research in
Kimbe suggests that approximately 20 kg/ha/year of N is lost by leaching below the root zone
of the palm (ie at 1.5m) (Nelson, 2003). Phosphorus fertiliser is not generally applied in oil
palm cultivation in the SBCA except for a small quantity at replanting (180 kg / ha) and thus
will not represent an large addition source of phosphorus export.
Nitrogen and phosphorus compounds will also be present in the sewage treatment plant (STP)
effluent from the plant in Kimbe and from septic system effluent drainage throughout the
region. A proportion of the septic effluent is likely to reach streams or the ocean directly
through subsurface water flows.
Their is some pesticide usage in the KBCA primarily of the herbicides glyphosate and
gramoxone but these pesticides in the quantities used and given their biodegradability
capacity pose little threat of reaching the marine environment in significant quantities.
Litter is likely to be a noticeable issue especially near Kimbe town and possibly from the
waste disposal facilities. The area affected is likely to be relatively small and restricted to
areas near human habitation.
2.3 Potential modes of delivery
Material will be delivered to the marine environment from the land in the SBCA through
surface runoff via rivers and streams and through subsurface flows either indirectly via
streams or directly to the ocean. Subsurface flows will only transport material in solution such
as nitrate and soluble pesticides. There is visible evidence of direct discharge of groundwater
to the ocean in the Talasea area.
Most of the loads of materials in overland flow will occur during the largest flow events. This
is similar to rivers worldwide (Walling and Webb, 1985) as in these events concentrations
peak during the period of greatest water flow. In addition this period of high river flow will
Page 29
provide the minimum trapping of dissolved and suspended material in the catchment and the
maximum dispersal in the marine environment. Flood plumes from rivers such as the Dagi
will transport material towards the centre of Stettin Bay. Most suspended sediments and other
particulate matter will be deposited close to the coast and material transported well offshore
will be dissolved eg nitrate or colloidal. Biological activity in the river plume will convert
land-supplied nutrients to phytoplankton and bacteria and these will also travel well offshore
(Devlin et al., 2001). Small streams will not have the capacity to carry material offshore and
loads from these systems will be retained close to the coast.
With catchment clearing and ‘hardening’ i.e. formation of surface conditions with no
infiltration capacity – roads, compacted soils, concrete, houses, and increased drainage less
infiltration (and often evapo-transpiration) occurs and greater surface water runoff results.
With higher runoff comes increased stream volumes and velocities and greater levels of gully
and bank erosion.
2.4 Habitat modification in coastal wetlands, mangroves, streams & effects on marine fauna
The natural vegetation on river banks and floodplains including riparian vegetation,
freshwater wetlands and mangroves, plays an important role in trapping material transported
down rivers and preventing much of the material reaching coastal waters. These vegetation
communities are normally heavily disturbed in the development of land for agriculture, being
cleared, drained and hydro logically modified. The communities are also important habitat for
estuarine and marine species significant in coastal fisheries and especially as juvenile habitat.
Widespread removal of riparian and wetland vegetation has occurred in the Stettin Bay
catchment with oil palm, copra and small crops being planted up to the streambank in many
cases (e.g. Figure 19) and to some extent in wetlands. Newer oil palm plantation
developments have retained significant areas of riparian buffer zone e.g. in Figure 20 on Hark
Creek. An assessment of the state of riparian areas along a number of streams within palm
growing areas has recently been carried out by NBPOL and riparian width, type of vegetation
and land use quantified. The results are listed in Table 5. Many riparian areas have a
significant component of gardens which negates some of the protective value of the riparian
strip. However most areas surveyed did have oil palm development set back some distance
from the stream.
Page 30
Quantification of the effects on loads to the marine environment of the removal of riparian
communities is difficult but estimates can be made and have been used in the model in
Section 5.
Figure 19 Streambank erosion Hark Creek
Figure 20 Riparian buffer re-established Ru Creek
Page 31
Table 5 State of riparian areas in the Lameki and Ganuka oil palm plantation areas
Other
Residential
Small
holders
Small
holders
mature
Vegetation
Young
Areas
Cash
crop
OP
Tall
32.2m 18.9m 42º
N-O
O-P
P-Q
Q-R
R-S
A-B
B-C
C-D
D-E
E-F
F-G
G-H
H-I
I-J
J-K
K-L
L-M
27
25
25
40
15
5
5
5
2
5
5
20
30
20
20
15
10
20
10
5
10
5
30
20
30
5
26.4m 2.8m 30º
13
10
16
1
13
12
7
7
6
10
7
8
5
5
5
5
130m 7.5m
15º
20º
40º
37º
80º
30º
2
2
5
5
4 6
3
3 10
10 30
3 5
2
5
3
10
18
20
35
50
27
27
30
67
30
40
27
70
12.2 2.6 35.3 4.2 3.9 4.3 31.8 5.8
60º
28º
25º
20º
15º
6
10
5
6
5
125
180
240
260
125
200
400
2
4
3
3
2
5
13
40
20
50
10
50
40
20
20
60
40
60
Trees
80
5
20
20
10
25
15
15
10
5
6
10
5
Trees
3
Abandone
d
in use
2
25º
27º
24º
80º
50º
30º
34º
40º
45º
27º
60º
65º
Garden
5
short
45m 30º
36
15
17
17
22
17
22
17
10
15
22
17
Garden
80
n2-n3
150
25
15
20
10
20
30
30
15
18
35
20
grass
3
45
grass
2
Slope
Average
5
n1-n2
B-C
C-D
D-E
E-F
F-G
G-H
H-I
I-J
J-K
K-L
L-M
M-N
Average
Ganuka R
Ganuka R
Ganuka R
Ganuka R
Ganuka R
Ganuka R
Ganuka R
Ganuka R
Ganuka R
Ganuka R
Ganuka R
Ganuka R
230
230m
Average
1112-13A
1112-13A
1112-13A
1112-13A
1112-13A
30º
River
A-B
Average
Lameki R
Lameki R
Lameki R
Lameki R
Lameki R
Lameki R
Lameki R
Lameki R
Lameki R
Lameki R
Lameki R
Lameki R
Zone
Areas
Water course
Dagi R
20
25
20
10
10
25
2
20
10
20
16
20
5
5 15
5
5 20
10 25
45
25
40
50
50
6
12
42
5
2
2
5
5
3
3
4
6
4
5
6
7
25 13
10
90
75
70
50
88
48
30
40
22
8
25
25
5
48
2
5
5
10
5
20
30
0.5
8 12
4
10
60
30
30
90
2
10
20
2
5
20 0.83 0.75
Page 32
2.5 Other impacts & potential impacts on marine ecosystems & synergism with land runoff
A complication in any study to determine whether land runoff of contaminants from
agricultural development is damaging coastal reefs is that coral reefs are subject to a range of
impacts besides possible pollution. Currently the major anthropogenic impacts on reefs
worldwide are associated with global climate change and coral bleaching; destructive fishing
methods; outbreaks of the coral-eating crown-of-thorns starfish (Acanthaster planci);
shipping impacts (oil spills, groundings, anti-fouling paint impacts); coral diseases; as well as
pollution from terrestrial runoff (McClanahan, 2002). ‘Natural’ impacts may also occur such
as cyclone damage and volcanic activity damage and natural sedimentation events associated
with landslides.
Determining which of the impacts is the principal cause of a damaged reef is difficult. The
impacts also occur synergistically. Current theory holds that many water quality impacts are
the result of an acute mortality caused by, for example, bleaching, followed by lack of reef
and coral recovery caused by chronic water quality degradation (Kinsey, 1988; Wolanski et
al., 2003; Fabricius et al., 2003, Fabricius, 2005). Such synergisms are quite likely in parts of
Kimbe Bay (the south west area particularly) where acute damage from bleaching and crownof-thorns starfish are combined with chronic poor water quality and sedimentation.
3. Methodology
3.1 Land use information collection
Information on land use was collected through interview with personnel associated with the
different industries and land uses on the SBCA including logging, saw mills, oil palm
plantations, smallholder oil palm, oil palm research workers, fishing, local government and
tourism. Where possible written reports were accessed and, whatever their status, these are
cited in the report and listed in the references.
3.2 Mapping
Geographical information used in the report and to prepare the maps included was provided
by NBPOL (Severina Betitis), TNC (Shannon Seeto) and the Oil Palm Industry Corporation
(OPIC) (Frank Lewis).
Page 33
3.3 Reef surveys
The first objective of the surveys was to establish both the seaward and along-the-coast extent
of influence of land based sources of sedimentation as well as recording all possible types of
impacts on the coral reefs within this zone. Based on the bathymetry and associated probable
hydrodynamic profile in addition to distance from shore and potential maximum loads of
rivers flowing into the bay, the extent of influence was assumed to be as far as the 200 m
depth contour. This is the edge of the coastal shelf area and reefs beyond that are in deep
water.
Sixteen reefs were surveyed (Figure 21), 13 of them at two depths making a total of 29 sites.
This included 7 coastal fringing reefs, 3 mid shelf reefs, 5 shelf edge (outershelf) reefs and
one offshore patch (semi atoll) reef. In order to interpret level of impacts and how reefs in
different parts of the bay vary in their susceptibility and capacity for recovery, the main reef
coral community types were described. Survey methods for this are outlined in Turak and
Aitsi (2002) and further detail can be found in DeVantier et al., (1998, 2000). The survey
basically entailed site lists of coral species and their abundance. Large areas of reef can be
surveyed in relatively limited times using this methodology. In addition for each species data
was collected on levels of damage and size distribution. Site biological characteristics such as
cover estimates of major benthos and physical characteristics such as reef structure and
ranking of sediment levels were recorded.
A hierarchical cluster analysis was used in Statistica software package to define the major
community types present. The distance measure used was Squared Euclidean Distance and
the clustering strategy was Wards Sum of Squares, after Done (1982), who demonstrated their
effectiveness in defining recurrent assemblages within the present type of data set.
Page 34
13
N
10 Km
12
8
6
3
14
10
Stettin Bay
Walindi
Walindi
15
2
Hoskins
Hoskins
4
1
9
11
7
5
16
Kimbi
Kimbe
Figure 21 Distribution of identified community types in Stettin Bay (colours linked to Figure 22)
Page 35
4. Marine survey results
As a result of surveys two main coral community types were recognized with each having
two subtypes (Figure 22). In addition there is a third distinctive community found in a
different type of habitat, though it is representative of only two reef locations and shows
characteristics between the other two types (Table 6). There was a strong link between
community type and reef status, particularly damage level and siltation rates.
Moderately damaged
coastal reefs with some
silt
High damage
1
3
A1
6
A
2
Very damaged coastal
reefs with high silt
7
A2
16
5
Offshore reefs with low
damage and no silt
8
14
B1
15
9
Offshore reefs with none
to low damage and no silt
Low damage
B
11
12
B2
4
Coastal reefs with low to
high damage and sand and
silt
C
10
13
0
200
400
600
Linkage Distance
Figure 22 Dendrogram of cluster analysis that identifies two main community types with two
subtypes each and an indistinct cluster of intermediate type.
4.1 Community types
Community type A is characteristic of coastal and nearshore (Figure 21) reefs where
branching Porites was relatively more common, as well as Astreopora and the fleshy algae
Padina (Figures 23 and 24). A large colony of Plerogyra simplex was recorded in this
community type (Figure 25). Acroporid coral were rare in this community type where dead
hard coral cover was the highest (Figure 26) and silt levels high (Table 6). The large and
hardy favid Diploastrea heliopora was most common on these reefs, though colonies were
Page 36
mostly either severely damaged or dead (Figure 27). Hard coral species richness was
relatively lower, especially in subtype A2 (Table 6).
Community type B was found on mostly shelf edge and offshore reefs as well as one
nearshore reef on Hoskins peninsula where the reef front dropped to clear well flushed deep
water (Figure 21). Reefs in this group had lowest dead coral cover and lowest silt levels
(Table 6). Pocilloporids and acroporids, particularly Anacropora and Acropora species were
most common on reefs with this community type. The agaricid coral Pavona cactus in some
locations formed extensive stands covering substantial tracts of reef. Coral species richness
was high with subtype B2 having the highest value (Table 6).
The main outstanding characteristic of tentative community type C was that the reef with this
type appeared subjected to powerful surge from offshore swells as well as being relatively
shallow with coarse terrigenous sand, perhaps of volcanic origin (Figure 21). They typically
had characteristics somewhere in between types A and B. Though silt levels were relatively
high and live hard coral cover low (Table 6), perhaps because of the wave action, shallow
water areas were relatively cleaner and some new coral recruitment was visible. No
particularity in terms of coral species richness and abundance, though Acropora diversity was
higher than other coastal reefs.
Page 37
Table 6 Physical and biological characteristics of sites found in two main and 5 sub community types.
Community type
Number of sites
A
A1
3
B
A2
4
B1
3
B2
4
C
C
2
Site
Max. depth (m)
Min. depth (m)
Slope (degrees)
Hard Substratum (%)
16
6
37
78
19
7
27
84
20
3
35
82
23
6
47
87
12
5
14
78
Benthos
Hard coral (%)
Soft Coral (%)
Macro-algae (%)
Turf-algae (%)
Coralline algae (%)
Dead coral (%)
11
1
13
22
5
33
12
3
2
22
10
35
32
2
1
12
13
13
28
7
4
13
13
11
10
3
2
15
8
23
Substratum
Continuous pavement (%)
Large blocks (%)
Small blocks (%)
Rubble (%)
Sand (%)
58
12
8
16
7
68
10
6
5
11
63
10
8
12
7
73
8
6
11
4
53
13
13
8
15
Silt (rank 1-5)
3.0
3.0
1.2
1.3
3.0
28 23
30.0 29.8
4.0 4.0
2.8 2.5
121 158
8
30.3
3.5
2.5
150
Visibility (m)
Water temperature
Reef development (1-4)
Exposure to waves (1-4)
Average no. of species
7
8
30.2 30.3
3.7 3.7
1.5 1.7
131 73
Page 38
Figure 23 Padina at Site 6
Figure 24 Padina at Site 1
Page 39
Figure 25 Plerogyra simplex colony at Site 6
Figure 26 Dead fungid corals on Anacropora ruble at Site 6
Page 40
Figure 27 Silt damaged Diploastrea heliopora at Site 2
4.2 Status of reef biota
Zooxanthelate scleractinian corals formed the greatest part of coral biodiversity that was
recorded and also was responsible of a large portion of bottom cover. No species of the
azooxanthelate scleractinian the dendrophyllid genus Tubastrea was recorded. This was quite
unusual, though very few Tubastrea was recorded on the eastern side of the bay during
surveys in late 2002 (Turak and Aitsi, 2002). Non-scleractinian hard coral species records
were also very low, in numbers as well as abundance. There was little of the fire coral
Millepora. However this coral is quite susceptible to bleaching and may have been severely
affected by the several bleaching events in the bay. There was very little of blue coral
Helliopora and the organ pipe coral Tubipora musica.
Page 41
80
70
60
Percent cover
50
40
30
20
10
0
1
3
6
West coast mid
shelf
Coralline Algae
2
5
7
16
SW corner Coastal
Turf Algae
8
14
15
4
Offshore and shelf
edge
Macro Algae
9
11
12
shelf edge and low
damage
10
13
Sand &
strong surge
Soft Coral
Figure 28 Percent cover of other major reef benthos grouped in community sub-types
Overall soft coral diversity was low, though some genera were quite common and abundant at
a limited number of sites. The most common were the alcyonid corals, in particular Sinularia
sp. Clavularia was abundant at a couple of sites, where at one site they were observed to be
spawning. Nephtheid diversity and abundance was low and xeniid’s were totally absent. With
an exception of a couple of sites where there were a number of large colonies overall
gorgonian fan coral diversity and abundance was low (Figure 28).
Sponge diversity and abundance was overall moderate with some sites having higher
abundance of particularly rope (or string) and tubular growth forms. Tridacnid giant clams
numbers were very low and the larger species were never seen. Of the fleshy macro algae
Padina was the most abundant at several sites. At some reef flat sites a number of seagrass
species (Figure 29) were recorded, Enhalus (Figure 30) having the highest abundance score
for one site.
Page 42
Figure 29 Seagrass at site 1
Figure 30 Enhalus sp seagrass at Site 5
Page 43
Interestingly two coastal reefs, one with coral community type A and most damaged of all
reefs visited, and the other with type B and relatively clean, had the highest numbers of large
fish including commercially targeted species. The shelf edge reefs furthest offshore also had
relatively higher fish numbers and diversity. Midshelf and coastal reefs had low to moderate
diversity.
4.3 Reef damage and sediment levels
Overall damage levels were relatively high, for example in comparison to sites surveyed in
east Kimbe Bay (Turak & Aitsi, 2002). Close to half the sites surveyed showed moderate to
severe damage (Figure 31). However the visual evidence of damage to reefs in Stettin Bay
(Figures 26, 27, 54) has been occurring over the last 10 to 15 years and is a result of several
events, some acute, some chronic and some of them quite severe. As a result it was not
possible to record total injury level to coral colonies. Since species of colonies that were
totally killed, especially after a certain time usually cannot be identified. Therefore such
mortality is severely underestimated in the graph in Figure 31.
Increasing colony damage
1
0.8
0.7
Increasing site damage
Proportion of species damaged
0.9
0.6
0.5
Serious damage
0.4
Moderate damage
0.3
Minor
damage
0.2
0.1
0
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Average damage per species
Figure 31 Levels of damage at survey sites
Page 44
On the other hand percent cover estimates of dead coral, which has been killed in the not-toodistant past and could possibly be attributable to damage causing events, shows much clearer
evidence and trends in reef degradation (Figure 32). Surveys reported in average ~ 40% of
hard coral cover of which at the time of surveys in average about half was dead. Lowest live
hard coral cover (avg. ~10%) and highest level of dead hard coral cover was found in coastal
and midshelf reefs, particularly in the southwest corner of Stettin Bay (Figure 32).
80
70
5
60
Percent cover
40
3
30
2
20
1
10
Rank of silt levels
4
50
0
0
1
3
West coast
mid shelf
6
2
5
7
16
SW corner Coastal
Dead Hard Coral
8
14
15
Offshore and shelf
edge
Live Hard Coral
4
9
11
12
shelf edge and low
damage
10
13
Sand & strong
surge
Silt / fine sediment
Figure 32 Ranking of silt levels in relation to percent of live and dead coral cover.
There was a strong positive relation between rank estimates of silt levels and dead hard coral
cover (Figure 33). Offshore and shelfedge reefs with low silt levels had proportionally lower
dead coral cover and midshelf and coastal reefs with high silt levels had proportionally high
dead coral cover.
Page 45
5
2
16
4
13
R 2 = 0.6015
5
Silt level
3
3
1
6
10
2
7
11
8
9
15
1
14
12
4
0
20
40
60
Percent dead coral cover
Figure 33 Silt ranking and percent dead coral cover. Numbers are sites that were surveyed
There also appeared to be a difference in size class distribution of coral colonies between sites
near and offshore, and community types (Figure 33). Highly damaged coastal reefs in the SW
corner of Stettin Bay with community type A2 and high silt levels had proportionally more
smaller colonies (<10cm) and less large colonies (>50cm). Medium size colonies (10-50 cm)
were perhaps marginally lower than in other community types (Figure 34). This was
somewhat similar for community type C. On the other hand all other community types (A1,
B1 and B2) had a relatively lower proportion of small colonies and community types B1 and
B2 had higher proportions of large colonies.
Reefs near Kimbe Town (Site 5) showed widespread litter accumulation (Figure 35) probably
reflecting a combination of stormwater discharge and discards from ships and boat traffic.
Page 46
10.2
Type C
10.1
13.2
13.1
12.2
12.1
11.2
11.1
Type B2
9.2
9.1
4.2
4.1
15
Type B1
14
8.2
8.1
16
5.1
5.1
Type A2
7.2
7.1
2.2
2.1
6.2
6.1
Type A1
3.2
3.1
1.2
1.1
0
0.2
0.4
0.6
0.8
1
Proportion of population
>50 cm
10-50 cm
<10 cm
Figure 34 Proportion of size classes for each site grouped in community types
Page 47
Figure 35 Litter on reef near Kimbe Town
5. Land use results
5.1 Logging
Logging in the SBCA started in the coastal plain areas, moved to the lower slopes of the
surrounding ranges and is now carried out in residual primary forest areas, in oil palm
development areas and in plantation forest areas (Mark Tegal, pers. com.). In the 1990s
major logging activity moved out of the SBCA to the south coast and other areas of West
New Britain as shown in Figure 14 (adapted from Bun et al., 2004). Logging has been
primarily selective. There are no soil erosion measurements or measured losses of suspended
sediment from logging operations in the SBCA and estimates for modelling will have to use
data from similar situations elsewhere.
Logging, even selective logging as compared to clear felling, causes great increases in soil
erosion in tropical forest areas compared to undisturbed forest (Douglas, 1999). The main
sources of erosion are the logging roads (Figure 36), skid trails (the paths used by bull dozers
Page 48
to drag logs to the road) and landings (or yardings), the log storage and loading areas (Sidle et
al., 2004; Ziegler et al., 2000; Baharuddin et al., 1995; Rice, 1981; Motha et al., 2003).
Roads act as linearly connected systems and large volumes of high velocity overland flow
may travel down slope to stream networks. Traffic increases sedimentation on unpaved roads
(Ziegler et al., 2001). Roads have a seven fold higher conveyancy efficiency than agricultural
land in South East Asia and although were found to occupy only 0.5% of land, contributed
the same sedimentation rates as agricultural land which occupied 12% of the catchment area
(Ziegler et al., 2000). Over 60% of gully erosion and 67% of slump erosion in logged areas is
due to roads (Rice, 1981).
Figure 36 Steep newly formed roads in the Goruru area
In Palawan (Philippines) erosion rates measured from cut forest plots were four times the rate
from virgin forest and the rate from road surfaces was 240 times the virgin forest rate
(Hodgson and Nixon, 1988; 2000). The suspended sediment load in streams in catchments
with logging was 100 times that in the stream draining virgin forest. Suspended sediment
loads increase dramatically in streams in logged areas compared to streams in undisturbed
catchments. In California total suspended solids in a river increased from between 89 -212 %
over natural in a six year period (1963-86) (Lewis, 1998).
Page 49
After logging ceases remnant erosional landforms such as haulage road gullies, road culvert
collapses and eroding skid trails continue to contribute to an above-natural sediment load
(Chappell et al., 1999). In a study in a small catchment in Borneo (Malaysia) Chappell et al.
(1999) measured suspended sediment fluxes of 1600 tonnes/km2/year during logging and in
the first year post logging and 592 tonnes/km2/year six years after logging compared to 312
tonnes/km2/year in an undisturbed control catchment. Chappell et al. (2004) in a review of
studies comparing logged catchments against controls in south-east and southern Asia
reported the following ranges of control versus logged: 300/1600; 100/431; 54/2600; 70/1400
tonnes/km2/year i.e. increases of erosion in the range 4 – 50 times. Baharuddin et al., (1995)
measured surface erosion on small plots on logging roads and skid trials in Malaysia. In the
first year after logging soil losses were 1330 tonnes/km2/year from logged roads and 1010
tonnes/km2/year from skid trails but by the second year post-logging rates had dropped to 310
and 210 tonnes/km2/year respectively.
Logging operations cause the construction of a large road and trail network. Sidle et al.,
(2004) found roads represented 3.2% by area of their study catchment in Malaysia, skid trails
6.5% and landings 1.5% for a total of 11%. Pinard et al., (2000) found skid trails covered
11.9% of a logging study area in Sabah. Similar figures (total 11.7%) had been found by Rice
(1981) in Pacific Rim steeplands. In Papua New Guinea there are, on average, 122 linear
metres of roads for every hectare of logging (i.e. 5% by area) excluding landings (Mark
Tegal, pers. comm.).
Logging may also exacerbate the occurrence of landslides. Although they are a feature of an
unstable landscape such as in Kimbe, their frequency may be increased through landscape
disturbance. In Oregon a total of 186 landslides were found after storm events in February
1996 and of these 114 were in logged areas. 68 were road-related and 3 originated in natural
forest (Arial Landslide Survey, 1996). A case study in Vanimo, PNG showed sediment in
streams to be a direct result of logging roads (Forests Monitor & ICRAF, 1999).
5.2 Oil palm
Oil palm (Elaeis guineensis) is the most productive crop of any of the vegetable oil producing
crops producing between 10 and 35 tonnes of FFB and on average 3 tonnes of oil per ha per
year (Corley, 2003) or 0.3 ha of land needed to produce one tonne of oil (0.3 ha/tonne). This
Page 50
compares to other crops such as rapeseed (1.7 ha/tonne), sunflower (2.1 ha/tonne), soyabean
(2.6 ha/tonne), coconut (3.0 ha/tonne) and cotton (5.4 ha/tonne) (Henson, 2003).
The conversion of tropical forests to oil palm plantations has been the most widespread land
use change in a number of SE Asian countries over the last 50 years including Malaysia and
Indonesia but more recently PNG. Few studies have been published on the effects of the
conversion of tropical forests to oil palm plantations but impacts on soil erosion and water
ecosystems are likely to be much greater on slopes greater than 20% (Sidle, 2002). Sidle
(2002) notes that ‘most impacts appear to occur during the land clearance process and in the
initial 2-3 years following plantation establishment, with much rapid storm runoff and
sediment produced on roads and connected disturbed areas (e.g. terrace cuts) within the
plantation’. A study of the conversion of forest land to oil palm plantation in one case and to
cocoa in the second in Pahang, Malaysia is described in Douglas (1999) using data from the
Malaysian Drainage and Irrigation Department. Douglas notes:
‘Predictable, clear-felling and replacing the forest cover with cocoa and oil palm resulted in
marked increases in stream sediment loads. In catchment B (selected for oil palm),
clearfelling was followed by an annual sediment load of 414 tonnes/km2/year in contrast with
values of 20, 25 and 39 tonnes/km2/year for the three preceding years. Substantial increases
were also recorded in catchment A (selected for cocoa), ranging from 10 to 35
tonnes/km2/year prior to logging but rising to 50 and 125 tonnes/km2/year following
clearfelling. Clearfelling was immediately followed by the planting of cocoa and oil palm in
catchments A and B, respectively. By the time the oil palms were two years old, sediment
loads had returned to predevelopment levels reflecting the effectiveness of the ground cover
crop that was established. In contrast, sediment levels in the catchment planted with cocoa
had not returned to near predevelopment levels some three years after planting clearly
indicating that the shade trees that were planted did not provide as effective a cover as do
ground crops’.
Keu (2003) determined average annual soil losses from different land uses in the SBCA using
the Universal Soil Loss equation (USLE). The results are for hillslope erosion only and do not
include gully and streambank components. The results do not also include periods of
catastrophic loss during episodic floods or return interval above three years. The results are
reproduced in Table 7 summarised from Table 17.0a, 17.0b and 17.0c in Keu (2003).
Page 51
Table 7 Estimated soil losses under different land uses (from Keu, 2003)
Land use
Average annual soil loss (tonnes/ha/year)
Rainforest (Kulungi)
Zero
Rainforest (Kimbe)
Zero
Rainforest (Morokea)
Zero
Coconut plantation (Numondo) – some slope
2.81
Oil palm plantation (Numondo) – some slope
1.40
Oil palm plantation (Bebere) – low slope
0.70
Oil palm plantation (Mosa) – low slope
2.1
Village oil palm (Kulungi) – some slope
1.8
Food garden (Kimbe) – high slope
5.3
Food garden (Morokea) – lower slope
2.3
These losses are relatively low and may be compared to the measured losses in other tropical
systems and from PNG cited in Keu (2003), Tables 19.0 and 20.0. The estimates of Keu
(2003) do not include an analysis of the different potential losses in the plant stage of oil palm
(bare earth, no canopy, Figure 37) versus the juvenile plantation stage (cover crop established
but canopy not closed, Figure 38) versus mature plantation (canopy closed and some cover
crop and trash retention on surface, Figure 39). As the focus of Keu’s study was sustainability
within the plantation it also considers primarily losses from hillslope erosion and not drain,
gully or stream bank erosion or catastrophic loss in major floods. In oil palm there are 50
linear metres of roads for every ha (2%) (NBPOL Standard policy on roads within
plantations). Oil palm roads are surfaced two years after development NBPOL roads conform
to the standards set out by the Norwegian standards (Akre, 2004).
Most of the oil palm grown in the SBCA is grown on ‘coarse textured soils that are freely
draining, have high hydraulic conductivity and are located in areas of high rainfall.
Consequently nitrogen losses are likely to be very high due to one or a combination of
leaching, surface run-off and denitrification.’ (Orrel, 2003). Fertiliser accounts for 60% of
the fixed costs of oil palm production (Simon Lord and Ian Orrel, pers.com.) and thus efforts
to make fertiliser use more efficient and minimise losses off-farm present powerful
opportunities for both agronomic and environmental improved performance.
Page 52
Figure 37 Bare earth in oil palm development stage
Figure 38 Juvenile oil palm
Page 53
Figure 39 Mature oil palm plantation
Significant nitrate concentrations above natural have been detected in the ground and surface
waters within oil palm plantations in the KBCA (Nelson, 2003). The sites sampled included
still surface water at Haella containing 0.03 mg/L NO3-N in the dry season and 1.12 mg/L in
the wet, creek water at Haella containing 0.06 mg/L in the dry season and 0.43 mg/L in the
wet, creek water at Dami containing 0.29 mg/L in the dry season and 0.26 mg/L in the wet
and bore water at Garu with 1.34 mg/L in the dry season and 2.76 mg/L in the wet. None of
these values are outrageously elevated but are indicative of some level of fertiliser
contamination.
5.3 Copra
Copra exists as residual plantation areas throughout the KBCA and SBCA but is being slowly
replaced in many places by oil palm. Soil erosion from these established coconut areas are
probably low with Keu (2003) estimating potential losses of 2.8 tonnes/ha/year from a
plantation at Numondo – see Table 7 which can be compared to his estimate for mature oil
palm of 1.4 t/ha/year. Inorganic fertilisers and pesticides are not commonly used on the
plantations.
Page 54
5.4 Subsistence gardens
Slash and burn shifting gardening has been practiced in the SBCA for many thousands of
years. However recent population increases due to both increasing local indigenous
population and settlement from other parts of PNG have sharply increased the area of
gardens. Gardens are also being planted on much steeper slopes as flat land become scarce
(due to increasing use of land for oil palm, other cash crops, urban and industrial development
and roads) such as on the range behind Kimbe town (Figure 40). Soil erosion from garden
areas may be considerable on steep slopes with Keu (2003) estimating potential losses of 5.3
tonnes/ha/year from a garden area at Kimbe – see Table 7. However gully erosion/ landslips
are probably also common as can be seen in Figure 40 and soil loss from these events will be
much higher than from the general hillslope losses estimated by Keu. Inorganic fertilisers and
pesticides are not commonly used on the gardens.
Figure 40 Eroded slopes and gardens behind Kimbe Town
5.5 Small crops
The principal small cash crops observed were cocoa and vanilla. No estimates were available
as to area but as both are grown as a small tree crop, cocoa directly and vanilla as a vine
attached to and shaded by a small tree soil erosion will only be significant at planting. As
grown in West New Britain both crops are minimal users of fertilisers and pesticides. Sidle
Page 55
(2002) notes that ‘ the conversion of native forests to permanent agriculture and other
plantations (e.g. coffee, rubber, fruit trees) has also created problems for soil and water
conservation (in South-east Asia). …..Where crops are grown as a monoculture, soils are
typically more susceptible to erosion compared to forest cover’.
5.6 Sewage Treatment Plants
One small sewage treatment plant (STP) is located in Kimbe to the east of the town. The STP
consists of two sequential aerobic lagoons with no pre-treatment before the first lagoon.
Discharge from the second lagoon (stocked with Tilapia sp fish) flows immediately to a drain
and then about 150m to the sea. The rest of the population in the catchment is served by
septic or pit toilets.
5.7 Oil/Hydrocarbon storage
Storage of hydrocarbon fuels occurs at the port of Kimbe with BP and Shell having storage
facilities. The facilities are only partially bunded and present some risk of spillage to the
marine environment. No overt oil pollution was observed in coastal waters adjacent to these
facilities.
5.8 Oil palm mills and refinery
Several oil palm mills occur in the Stettin bay catchment including Numundo, Kumbango and
Mosa and one refinery at Kumbango all operated by NBPOL. While mills and refineries
generate considerable organic waste, NBPOL facilities have advanced programs of waste
treatment and recycling which minimise releases to the off-facility environment (Lord et al.,
2002; 2003). One example of this is the composting of Empty Fruit Bunches (EFB) and Palm
Oil Mill Effluent (POME) together to produce a fine humus-like compost suitable for
spreading back on plantation fields (Lord et al., 2002). Similarly EFB and Palm Kernel Cake
(PKC) have been composted to produce a nursery potting mix for use in the oil palm
nurseries (Lord et al., 2003). However not all mills have been converted to this zero effluent
discharge system yet. All water released from these mills is however subjected to checks and
pollution control devises under the Government DEC regulation for water use and NBPOL’s
own standards under ISO 14001 (1996). While mill effluent may still be a problem for
freshwater habitats in streams it is unlikely to be a major threat to marine habitats.
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5.9 Natural sources of sediment
Soil erosion, sediment production and export to the sea are natural processes. Erosion occurs
across hillslopes, in gullies and on streambanks. These forms of erosion occur gradually in
‘normal’ weather conditions but catastrophic events such as cyclonic rain-driven floods,
landslides and volcanic eruptions can cause massive soil loss in a short period. Landslides are
a natural process on steep forested slopes in South-east Asia and PNG and may be relatively
common (Day, 1980; Douglas, 1999). In normal conditions many observations and
measurements have shown that soil losses from rainforested slopes are low (Sinun et al.,
1992; Douglas, 1999). Areas of bare earth are uncommon and eroding gullies rare. The main
source of sediment in rainforest streams is probably derived from eroding stream banks
(Douglas, 1999). Large proportions of total river sediment loads are transported during severe
storm events, for example, Hatch found that 57% of the sediment transported from a natural
forest plot in Sarawak over a 12 month period was lost in a single month (cited in Douglas,
1999).
Seismicity is a major landslide trigger and in PNG 40-67% of fluvial sediment discharge was
derived from earthquake-induced landslides (Adams, 1980). Similarly Sheng (1990) showed
that 88% of soil loss from a forest control plot occurred in six storms in studies in Thailand
and many other similar case studies are reviewed in Douglas (1999). Kimbe Bay will be
prone to such extreme events due to its active volcanoes, earthquakes, high rainfall, steep
slopes and young, unconsolidated soils (Keefer, 1994). These episodic events in the KBCA
will lead to enhanced runoff of sediment. Separating this natural pattern of periodically
enhanced sediment input from increased sediment input due to logging and agricultural
activities is difficult.
6. Budgets/modelling
6.1 Background
Budget modelling is a valuable tool to estimate the patterns of delivery, catchment sources
and relative amounts from different land uses of contaminants from a catchment area to the
ocean. The models used can vary from sophisticated numerical models based on extensive
water quality and land use information where available (see for example Alexander et al.,
2002); to models based on catchment process information, land use data and limited direct
Page 57
water quality data (see for example Brodie et al., 2003); to very simple models based on
export coefficients for different land uses and essentially no water quality data (see for
example Moss et al., 1993).
In the case of SBCA only estimates of land use in any particular year are available, export
coefficients for each land use are not available from local data but can be estimated from
similar situations in comparable parts of the world and no reference water quality data is
available. Under these circumstances the model becomes more of an example of what could
be done with better data and the interpretation of the results of the modelling must be used in
association with other data to have explanatory power.
6.2 Model basis
For this report the SBCA has been modelled for 2003 for suspended solids and total nitrogen
discharge to the ocean. The land uses in 2003 have been extracted from the information
discussed in Section 2.3 and summarised in Table 8.
Table 8 2003 land uses in the Stettin Bay catchment
Land use
Area (ha)
Logging
1,900
Logged area in recovery
3,600
Oil palm plantation planting
650
Oil palm plantation mature
13,000
Oil palm small holder mature
11,000
Primary and secondary forest (some logged in past)
30,000
Gardens, small crops, copra
15,000
Total
76,550
A simple model is used which only assumes overall erosion rates, not individual rates for
hillslope, gully and streambank. Nitrogen modelling uses soil analysis of %N with data from
local soils, estimated fertiliser losses from known fertiliser application rates and human
sewage calculated discharges.
Page 58
6.3 Model calculations for suspended solids
6.3.1 Logging
The assumptions for logging operations are:
In the current year:
1. 1,900 ha area per year (2003)
2. 10% of logged area is bare earth including roads, skid trails and yardings ie 190 ha (See
Section 5.1 for 10% of area).
3. Erosion rates on gentle to moderate slopes on bare earth are 200 tonnes/ha/year (i.e. 2000
tonnes/km2/year for the whole logging area similar to values found by, for example Chappell
et al., 1999).
4. Delivery ratio (ie proportion of eroded material which reaches the river mouth) is 0.7. This
high delivery ration is justified by the shortness of the rivers and the intensity of major flow
events (Chappell et al., 2004).
Thus 38,000 tonnes per year of erosion (190 x 200tonnes /ha/year) and delivery to the ocean
of 26,600 tonnes
Recovery period:
1. Assume two year recovery to secondary forest status (e.g as in Baharuddin et al.,
1995)
2. Thus 3,600 ha recovering on a rotational basis, 1,800 in first year of recovery and
1,800 ha in second year.
3. For first year of recovery (year after logging) assume 50 tonnes/ha erosion on the
disturbed areas (old bare earth, 10% of logged area); for second year of recovery
assume 30 tonnes/ha erosion on the disturbed area (estimates of erosion in postlogging situation from Baharuddin et al., 1995; Chappell et al., 2004)
4. Delivery ratio same as for logging (0.7)
Thus in first year recovery soil loss is 1,800 x 0.1 x 50 = 9,000 tonnes.
In second year of recovery soil loss is 1,800 x 0.1 x 30 = 5,400 tonnes.
Total loss in recovering areas = 14,400 tonnes with delivery to ocean of 10,100 tonnes.
Page 59
6.3.2 Oil palm plantation planting stage
Assumptions are:
1. 650 ha per year (2003)
2. Of the 650 ha approximately 32% is covered by logging debris pushed into windrows. (Fig
15 / Fig 18) leaving 68% primarily bare earth. Therefore bare earth total is 68% of 650 ha =
442 ha. This bare earth stage lasts for approximately six months and is the period of
maximum risk of catastrophic soil loss (see Sidle, 2002; Douglas, 1999).
3. Erosion rates on gentle or no slope are 100 tonnes/ha/year giving six months erosion at this
rate.
4. Second half of year is after considerable growth of the cover crop (Figures xc) and erosion
rates in this period assumed to be 50 tonnes/ha/year on the non-windrow area.
5. Delivery ratio of 0.5 based on low slope land and more catchment trapping.
Thus 22,100 tonnes per year of erosion (100 x 442 x 1/2) in the first 6 months and 11,000
tonnes in the second 6 months giving a total of 33,100 tonnes and delivery to the ocean of
15,000 tonnes
6.3.3 Oil palm plantation juvenile and mature stage
Assumptions are:
1. 13,000 ha per year (2003)
2. Erosion rates on gentle or no slope are 6 tonnes/ha /year including streambank, gullies and
floods
3. Delivery ratio of 0.1 based on low slope land and high rates of catchment trapping due to
extensive ground cover and riparian buffer strips.
Thus 78,000 tonnes per of erosion (6 x 13,000) and delivery to the ocean of 7,800 tonnes
6.3.4 Oil palm smallholder juvenile and mature stage
Assumptions are:
1. 11,000 ha per year (2003)
Page 60
2. Erosion rates on gentle or no slope are 4 tonnes/ha/year
3. Delivery ratio of 0.1 based on low slope land and high rates of catchment trapping due to
extensive ground cover and riparian buffer strips.
Thus 44,000 tonnes per year of erosion (4 x 11,000) and delivery to the ocean of 4,400 tonnes
6.3.5 Rainforest (including both primary and secondary forest)
Assumptions are:
1. 31,400 ha per year (2003)
2. Erosion rates are 2 tonnes/ha/year including streambank, gully and flood erosion (i.e. 200
tonnes/km2/year which can be compared to values of 312 tonnes/km2/year in Chappell et al.,
1999 and 300, 100, 54 and 70 tonnes/km2/year from 4 studies cited in Chappell et al., 2004)
3. Delivery ratio of 0.05 based high rates of catchment trapping due to forest cover and these
areas being in back of the catchments
Thus 62,800 tonnes per year of erosion (2 x 31,400) and delivery to the ocean of 3,140
tonnes.
6.3.6 Gardens, small crops, copra
Assumptions are:
1. 15,000 ha per year (2003)
2. Erosion rates are 4 tonnes/ha/year including streambank, gully and flood erosion.
3. Delivery ratio of 0.2 based on moderate slopes and moderate trapping
Thus 60,000 tonnes per year of erosion (4 x 15,000) and delivery to the ocean of 12,000
tonnes.
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6.3.7 Suspended sediments summary
Table 9 Suspended sediment losses and discharge to the ocean
Area (ha)
Erosion in
2003
(tonnes)
SS Discharge
to ocean
(tonnes)
% of total
SS discharge
Logging
1,800
38,000
26,600
34%
Post logging
3,600
14,400
10,080
13%
650
48,100
15,000
19%
13,000
78,000
7,800
10%
Oil palm small holder
mature
11,000
44,000
4,400
6%
Primary and secondary
forest
31,400
62,800
3,140
4%
15,000
60,000
12,000
15%
Total
76,450
345,300
79,020
Land use
Logging
Post logging
Logging and post
logging
Oil palm plantation
planting
Oil palm cultivation
Oil palm plantation
mature
Oil palm small holder
Natural forest
Natural forest
Gardens, small crops,
copra
copra
a.
b.
Figure 41 a. SS delivery to ocean modelled from different land uses and practices
b. Modelled SS delivery to ocean from individual land uses
Page 62
It is also possible to make an estimate (albeit crude) of pre-development sediment loads from
the catchment. If we assume the whole of the catchment ie 76,000 ha was exporting
suspended sediment at the rate of present primary and secondary forest we obtain an estimate
of 7,600 tonnes for the whole catchment in the period before say about 1900. Thus sediment
loads have increased by about 8 times since then. This is a similar factor as found in many
catchments worldwide (without major dams) due to the introduction of modern agricultural
and urban development (Walling and Fang, 2003).
6.4 Model calculations for nitrogen
6.4.1 Logging
Assumptions are:
1. 36,700 tonnes SS delivered to ocean from logging and logged recovery areas
2. Soil nitrogen content of 0.65% (Keu, 2003 for rainforest soils)
Thus 0.65 x 36,700/100 = 240 tonnes N/year delivered to ocean
6.4.2 Oil palm plantation planting
Assumptions are:
1. 15,000 tonnes SS delivered to ocean from new developments
2. Soil nitrogen content of 0.65% (Keu, 2003 for rainforest soils)
6.4.3 Oil palm plantation mature
Assumptions are:
1. 7,800 tonnes SS delivered to ocean from mature plantations
2. Soil nitrogen content of 0.35% (Keu, 2003 gives 0.38% and recent NBPOL survey 0.33%)
Page 63
6.4.4 Oil palm small holders mature
Assumptions are:
1. 4,400 tonnes SS delivered to ocean from oil palm smallholders
2. Soil nitrogen content of 0.5% (Keu, 2003)
Thus 0.5 x 4,400/100 = 22 tonnes N/year delivered to oceans
6.4.5 Forest
Assumptions are:
1. 3140 tonnes SS delivered to ocean from logging areas
Thus 0.65 x 3140/100 = 20 tonnes N/year delivered to ocean
6.4.6 Gardens, small crops, copra
Assumptions are:
1. 12,000 tonnes SS delivered to ocean from gardens etc
6.4.7 Fertiliser losses
Assumptions are:
1. 13,000 ha of plantation using 100 kg N/ha/year
2. 11,000 ha of small holder using 40 kg N/ha/year
3. 50% of fertiliser lost from field
4. 10% of applied fertiliser reaches ocean (from similar studies in north Queensland)
Thus oil palm plantation usage is 1,300 tonnes and delivery to ocean of 130 tonnes. Small
holder usage is 440 tonnes and delivery to ocean of 44 tonnes.
Page 64
6.4.8 Sewage STP discharges
Assumptions are:
1. Kimbe STP treats sewage from approximately 9,000 residents who each excrete 5 kg of
nitrogen per year to the STP i.e. total of 47 tonnes of N.
2. STP removes 33% of the N and delivers 67% of the N to ocean.
Thus 31 tonnes of N discharged to ocean.
6.4.9 Septic and pit sewage systems
Assumptions are:
1. 70,000 as per your earlier statement persons in Stettin Bay catchment not on STP. Each
excretes 5 kg of N per year giving total of 350 tonnes of N.
2. With dispersed nature of much of the settlements good absorption and trapping in soil
should occur and delivery ratio will be low, say 10%.
Thus 35 tonnes of N discharged to the ocean.
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6.4.10 Nitrogen summary
Table 10 Delivery of nitrogen to the ocean from various land uses
Source
Delivery of
Delivery
Land
Delivery
Delivery
N to ocean
% of total
use
of N to
% of total
lumped
ocean
(tonnes)
(tonnes)
Logging and
240
32
Logging
240
32
98
13
Oil palm
321
43
27
4
22
3
130
17
44
6
20
3
Natural
20
3
96
13
66
9
post logging
Oil palm
plantation
planting
Oil palm
plantation
mature
Oil palm small
holder mature
Oil palm
plantation
fertiliser
Oil palm small
holder fertiliser
Forest
Forest
Gardens, small
96
13
crops, copra
Other
crops
Kimbe STP
31
4
Septic/pit
35
5
Sewage
sewage
Total
743
743
Page 66
Logging
Oil palm
Natural forest
copra
Sewage
Figure 42 Sources of nitrogen export to sea from various land uses
6.5 Sediment and nutrient losses from different land uses
The modelling in Sections 6.3 and 6.4, observational evidence collected during November/
December 2003, anecdotal evidence and previous research (e.g. Keu, 2003) in total show that
the largest sources of increased-over-natural suspended sediments export to Stettin Bay are
logging and oil palm plantation development, particularly in the plant stage. Enhanced soil
erosion and increased sediment exports from logging will have started in the 1950s, risen
through the 1960s and 1970s, peaked in the 1980s and be declining through the 1990s and
2000s. Sediment exports from oil palm plantation development, including small holder
development, will have started in the 1960s, reached a plateau in the 1970s and remained
relatively stable through to the present as new land is developed for oil palm and existing
plantations are cut and replanted on the 20 year cycle. Other sources of above-natural
sediment export include gardens on steep slopes, mature oil palm plantations, small crop
areas (copra, vanilla, cocoa), urban development and roads but these are individually less
significant.
In logging areas soil loss from roads is a major issue with roads built on steep slopes (Figure
36) subject to severe erosion. This problem continues for some years after the harvesting of
logs has finished and roads are seldom surfaced. Surfacing roads can lead to a 20 fold
reduction in erosion (Foltz, 2003). Improvements to logging practices which, among other
things, seek to minimise soil erosion and sediment delivery to waterways have been
Page 67
developed. One system known as reduced-impact logging (RIL) (e.g. Bolz et al., 2003)
includes the following practices related to erosion minimisation (Pinard et al., 1995):
1. Include optimising skid trail networks given a knowledge of the exact location of each
tree to be felled.
2. Minimise stream crossings
3. Minimise skid trail earthworks
4. Maintain canopy cover over skid trails
5. Construct water-bars on unused haulage roads
6. Careful supervision of all forestry operations
7. Enrichment planting of trees in areas where natural regeneration has been poor
RIL techniques, as practiced in a Sabah, Malaysia, pilot programme, include the following:
1:5,000 or 1:10,000 Mapping; pre-selection and marking of marketable timber; Pre-harvest
cutting of climber vines; slope and riparian restrictions on logging; Weather restrictions on
logging; Lowering the impact of access roads through planning; Use of directional felling
techniques; Planning of skid trails; No use of bulldozer blades on skid trails (Pinard et al.,
2000).
Research into RIL methods have shown that they can reduce impacts to the soil from heavy
logging machinery by 25%. In some RIL experiments in lowland tropical forests, the amount
of damage to the soil and to advanced regeneration was reduced by about 50% relative to
conventional logging (Holmes et al., 2002).
PNG has formally adopted a Logging Code of Practice (LCOP) in 1996 (PNG 1996) however
there is widespread cynicism about its implementation (Taupa, 2003; PNG Eco-forestry
Forum, 2004). On-ground studies of its implementation in Vanimo Timber Area (Forests
Monitor Limited & ICRAF, 1999), Manus (Pwesei, 2001) and Aitape (Barcelona Field
Studies Centre, 2005) found numerous violations of the LCOP standards. Some studies have
been carried out in the Kimbe Bay area (FAO, 1998) with the Stettin Bay Logging Company
into logging practices and comparison to the LCOP but little quantitative information on area
of roads and skid trails and hence potential soil erosion is available from these.
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In oil palm plantation developments on moderate and high slopes eg parts of Talasea soil loss
from roads is also significant (Figure 43) but in oil palm roads are surfaced within two years
of operations. However even surfaced roads can lose large amounts of soil in high rainfall
events (Figure 44). Methods such as grassing such roads, as is being trialled near Dami
(Figure 45) or more rapid laying of road surface metal may reduce this problem.
A number of factors contribute to high soil losses in the plant stage of oil palm plantation
development and similarly when the crop is replanted after the 20 year crop cycle. Most
significant is a period of bare earth lasting from the clearing of the land (forest, old copra
land, old oil palm land) until the cover crop is well established and the juvenile oil palm trees
also begin to produce a significant canopy. This stage lasts for approximately six months and
is the period of maximum risk of catastrophic soil loss. Such losses can be seen in the images
from the Kulu-Dagi Project area (note not discharging to Stettin Bay) flood where massive
soil loss occurred (Figures 44, 46). Losses from the plant stage will be greatly increased if
plantings occur on high slopes. The outstanding example of this potential situation was
observed in the Talasea area where a small area of high slope land was recently planted
(Figure 47). Planned developments in the Goruru area are also on very steep slopes (Figure
36). Growing oil palm on terraced steep slopes may also be undesirable from a productivity
perspective due to soil fertility problems (Hamdan et al., 1999).
It is clear that methods to minimise soil losses in the plantation development stage will have
the most significant effects on overall sediment exports for this crop. These include
promoting rapid cover crop establishment (Marfo-Ahenkora and Nuertey, 1999) (Figure 48),
retaining vegetation buffer strips on streams and drains, planting vegetation buffers on
constructed drains (such as the Guatamala grass already in use) and leaving steeper slopes
unplanted as buffers as practiced in the Waississi development (Figure 49).
Smallholder oil palm development appears to pose less of a soil erosion threat as less
mechanized clearing is used, more ground cover retained and there is less clearing of ground
cover in the mature crop stage.
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Figure 43 Plantation road erosion in Talasea area
Figure 44 Erosion in flooding in Kulu-Dagi Project area
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Figure 45 Grassed road trial near Dami
Figure 46 Flooding in the Kulu-Dagi Project area
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Figure 47 Oil palm development on extreme slopes in Talasea
Figure 49 Forest strips on slopes left undeveloped (background) in Waississi
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i. 2nd June, 2004
vi. 6th July 2004
ii. 9th June, 2004
vii. 12th July 2004
iii. 16th June, 2004
viii. 19th July 2004
iv. 23rd June 2004
ix. 26th July 2004
v. 28th June 2004
x. 2nd Aug 2004
Figure 48 Cover crop growing NBPOL trials (i – x shown at weekly intervals over a 9 week period)
Page 73
In mature oil palm plantations soil erosion is far less of an issue than in the plant or replant
stage. Canopy closure, moderate ground cover and vegetated drain banks reduce erosion and
sediment loss. Stream bank erosion is still an issue as plantations have been planted right to
the streambank (Figure 19) or coastline (Figure 50). Practices to restore a streambank
vegetation buffer are now being implemented in replanting schemes as seen on Ru Creek
(Figure 20) where two rows of mature oil palms next to the creek are being left while the rest
of the plantation is cleared and replanted.
The intercropping of oil palm and beef grazing as practiced at Numundo also leads to good
ground cover and potentially low erosion rates in the mature phase (Figure 51). However
anecdotal reports suggest that massive soil erosion occurred in the establishment phase of this
development when bare earth was present (a satellite image available to NBPOL also shows
the bare earth zone). The potential for such losses in the development stage can still be seen in
the intercrop areas at present under development (Figure 52). Streams in the intercrop
development, while grassed have little riparian tree or shrub buffers.
Soil losses from subsistence and market gardens on steep slopes are also an issue in the
Stettin Bay catchment. With increasing population and increased areas of oil palm
development on flat lands pressure for garden development on steep lands increases. This is
very noticeable on the hills behind Kimbe Town (Figure 40) where significant landslips are
obvious.
Stormwater flows from Kimbe urban area are an obvious source of litter to the inshore marine
environment (Figure 35) but not an easy issue to practically address.
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Figure 50 Oil palm planted to coastline
Figure 51 Beef and oil palm intercropping
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Figure 52 Beef/oil palm intercropping new development
Table 11 Delivery of suspended solids and nitrogen to the ocean from various land uses
Land use
% of total
Delivery of N to
SS
ocean (%)
Logging
34%
23%
Post logging
13%
9%
19%
13%
10%
4%
Oil palm small holder mature
6%
3%
Primary and secondary forest
4
3%
15%
13%
Oil palm plantation fertiliser
17%
Oil palm small holder fertiliser
6%
Kimbe STP
4%
Septic/pit sewage
5%
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7. Conclusions
7.1 Overall
It is clear in our opinion that a number of inshore reefs in Stettin Bay, particularly in the
south-western section, have been severely damaged by sedimentation in recent times. The
damage may be exacerbated by other factors such as bleaching and crown-of-thorns starfish
in a synergistic way. There is no clear evidence of nutrient enrichment effects, but these may
be disguised by the mortality caused by sedimentation, bleaching and crown-of-thorns
starfish, and cannot be completely ruled out. The presence of thick sediment layers covering
reefs in this area implies that even if sedimentation was not the primary cause of coral
mortality the presence of the sediment layer will prevent any recovery of these reefs through
coral recruitment and juvenile growth.
The area of clear damage from sedimentation is the area from the mouth of the Dagi River
westward to Walindi and to a lesser extent from Walindi to Talasea. Reefs in most other areas
of Stettin Bay have not been damaged by terrestrial sediment discharge although many of
them have been damaged by other factors such as bleaching and crown-of-thorns starfish.
7.2 Likely loads/sources of SS, nutrients
The modelled estimates of sediment (and nutrient) loads from Section 6 reinforced by
anecdotal and observational evidence suggest that the most significant loads of sediment
originate from primary logging operations and then oil palm new developments . Oil palm
plant and replant activity remains at a high levels and is most likely to remain a source of
increased-above-natural suspended sediment exports. Episodic events such as the 1998 wet
year following the dry (drought) 1997 (with fires in the catchment) and the volcanic eruption
of 2002 and associated ash flows will cause large spikes in delivery but these are seminatural. However the potential impact of these natural episodic events has been exacerbated
by logging and cropping development in the catchments.
It is the additional chronic delivery of sediment due to soil disturbance from logging and
agriculture which is likely to be responsible for the damage to reefs seen in south western
Stettin Bay. Losses will be especially severe on plant areas of high slope as seen at Talasea
(Figure 47). The major sedimentation damage to the reefs appears to have occurred since
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1994 as Maragos (1994) noted some sedimentation damage in 1994 but generally healthy reef
conditions.
7.3 Oceanographic factors
A principal factor in the concentration of reef damage from sedimentation in the south west
section of Stettin Bay is the poor flushing, low wave action and generally still conditions in
this area. This area is (1) sheltered from the south easterly wind regime (2) subject to a low
ocean wave climate as waves from the north west do not propagate around Cape Hollman on
the Willaumez Peninsula (3) has a low tidal range and resulting small tidal currents and (4) is
sheltered from wave action by the line of barrier reefs stretching from Walindi to east of
Kimbe town. As a result of this low energy regime sediment deposited on reefs remains for
extended periods and is not removed by wave action as appears to occur in other parts of
Kimbe Bay.
7.4 Other reef damaging factors
Sedimentation from land runoff is not the only threat to coral reef health in Kimbe Bay. In
many other parts of Kimbe Bay damage from bleaching and crown-of-thorns starfish (Figure
53 and 54) were evident. At one site damage from a ship grounding was observed (Figure 55).
7.5 Effects of reef damage on Stettin Bay resources
Major damage caused by land-sourced sedimentation is restricted to near shore reefs in the
west and south-west section of Stettin Bay. Fortunately these are not the premier dive sites for
tourism (Figure 56), which are generally further offshore. These reefs are however an
important component of the coral reef biodiversity of Kimbe bay and deserve some level of
protection from such impacts.
The effect of loss of reef on fisheries resources is probably real but difficult to quantify given
the data available from Kimbe Bay. Overseas loss of reef associated with sedimentation
(McClanahan and Obura, 1997) has led to algal dominance of reefal areas and reductions in
fish biomass and diversity (McClanahan et al., 1999). Similar patterns of fisheries effects are
likely in Kimbe Bay. Munday (2003) notes the serious decline in the abundance of coraldwelling fishes in Kimbe bay associated with declines in the abundance of acroporid corals.
Page 78
Figure 53 Crown of thorns starfish scars at Site 4
Figure 54 Dead coral at Site 7
Page 79
Figure 55 Ship grounding scar off Kimbe Town
Page 80
Figure 56 Premier dive sites in Kimbe Bay
Page 81
8. Monitoring program options
8.1 Background
To detect reef damage due to poor water quality, monitoring of reefs using standard ‘reef
health’ methods may be used. However it is often very difficult to separate the various
possible causes of the damage and change eg bleaching, destructive fishing, natural change,
cyclones and coral disease. If it is suspected that water quality is an issue then a monitoring
program to measure sources of the pollutants, their transport to the reef areas and thus the
exposure of the reefs to pollutants should be established. Such a monitoring program will
complement the monitoring program set up to detect biological effects on the reef system.
8.2 Methods
8.2.1 Sources and loads
Generally land-based pollutants are delivered to the marine environment through essentially a
point source. The point source may consist of a pipe carrying sewage effluent or industrial
wastewater or even more commonly be a river, stream or drain carrying pollutants from a
catchment area. As all of these can be sampled at a single point, monitoring is, in principle,
straightforward. However important considerations in the design of the monitoring program
are:
1. The pattern of flow. Effluent pipes often have fairly regular flows and so can be monitored
at any time. In contrast rivers and streams, especially in the tropics, have very variable flows.
Most pollutants are transported in the wet season and sampling of rivers and streams must be
concentrated at this time.
2. Pollutants to be measured. As the range of possible pollutants from a catchment or
wastewater discharge is large it is essential to narrow the range of pollutants measured to
those likely to be the cause of the problem. Pollutants which can stress coral reefs include
suspended sediment, nutrients (nitrogen and phosphorus compounds), toxic metals (eg lead,
cadmium and copper), petroleum hydrocarbons (lubrication oils and fuels), pesticides,
organochlorine wastes and organic matter. It is prohibitively expensive to sample and analyse
Page 82
for all these materials. It is thus essential to target for analysis only those pollutants which
may be causing the problem and have a known source in the catchment area.
3. Estimate loads. The actual amount (mass) of pollutant being discharged is important to
know as well as the concentration of the pollutant in the water. To measure loads it is
necessary to know the volume of the discharge as well as the concentration of the pollutant at
a number of times through the discharge event.
4. Catchment source identification. To be able to manage the pollutants it will probably be
necessary to identify the actual source areas or activities within the catchment which result in
the majority of the pollutants. This may involve monitoring ‘up the catchment’ as well as at
the river or stream mouth. ‘Proxy’ data may also be of use such as pesticide sales in the
catchment, fertiliser use data and sewage treatment plant discharges to the river.
8.2.2 Transport and exposure
As pollutants are discharged into the marine environment from an outfall or river processes
occur which cause the pollutant concentrations to decrease. The processes include
sedimentation, evaporation and biological and chemical transformations as well as simple
dilution through mixing with seawater. It is often important to know whether sufficient
pollutant (either load or concentration) is reaching the reef system to cause biological effects.
Monitoring pollutants in the marine environment whether in the water column or perhaps in
sediment or biota is far more complex than monitoring point source discharges. The threedimensional nature of the marine water body means that many samples are required to
characterise what is happening. Thus a much more rigorously designed sampling program is
necessary to generate conclusive results. Hydrodynamic modelling may be of use in
predicting transport, dilution, dispersion and sedimentation but such models are also complex
and need competent design. Some simple techniques such as sediment traps on coral reefs
may give comparative information on sources and exposure of reefs to sediment.
8.2.3 Biological effects
The actual reef monitoring program must also focus on indicators which are relatively
specific to water quality impacts. Many traditional reef monitoring indicators such as coral
cover and fish counts are not very useful in detecting water quality impacts. Indicators such as
Page 83
coral recruitment, recruit survivorship, algal abundance and dynamics, immunoassay methods
and photosynthetic performance (PAM) may be more useful indicators for many pollutants.
8.3 Interpretation
Monitoring must focus not just on change in the system in question but also the causes of the
change. If pollution is to be managed then the sources of the pollutants must be identified.
Thus an integrated water quality monitoring program should measure sources, transport and
effects so that an assessment of management options can be made. Management initiatives to
solve water quality problems can also be tested through such an integrated program to assess
their effectiveness.
Page 84
9. Recommendations
9.1 Logging practices
Given that logging will continue in the SBCA, albeit at levels lower than in the past, and in
the wider Kimbe Bay region it would be desirable to ensure that future logging in the area is
carried out under reduced-impact logging (RIL) practices. Other environmentally beneficial
practices, such as enhanced natural reforestation, have been trialled in West New Britain
(KGIDP, 1993) and could be promoted in the Kimbe region. Overall the following practices
within the RIL framework are likely to minimise sediment delivery to the marine
environment:
(a) 1:5,000 or 1:10,000 Mapping; pre-selection and marking of marketable timber;
(b) Include optimising skid trail networks given a knowledge of the exact location of each
tree to be felled. Lowering the impact of access roads through planning;
(c) Slope and riparian restrictions on logging;
(d) Weather restrictions on logging;
(e) Minimise stream crossings;
(f) Minimise skid trail earthworks. No use of bulldozer blades on skid trails;
(g) Maintain canopy cover over skid trails;
(h) Construct water-bars on unused haulage roads;
(i) Careful supervision of all forestry operations;
(j) Enhanced natural reforestation. Enrichment planting of trees in areas where natural
regeneration has been poor.
9.2 Land use practices in oil palm.
Accepting that oil palm is an expanding agricultural entity in the SBCA it would be prudent
to examine current practices with a view to developing sustainable programs from an
economic, social and environmental perspective. The following are possible areas for
research initiatives:
(a) Buffer management, auditing of buffer condition, buffers as traps for sediments (and
nutrients) as well as for biodiversity;
(b) Avoid small areas of steep land;
Page 85
(c) Cover crop planting pattern research to get better coverage of the cover crop in the
shortest possible time in the critical time for bare earth soil erosion;
(d) Investigate methods of leaving more of the windrowed material in the plant stage on the
bare earth in the planting rows;
(e) Road management. Metal roads as soon as possible or use grassed roads where appropriate;
(f) Vegetate drains as soon as possible eg Guatemala grass, natural shrub growth;
(g) In-field streams (drains) to have remnant or planted low buffer strips;
(h) Vegetate streams in oil palm/cattle intercrop areas (Numondo). May need temporary
exclusion of cattle to do so;
(g) Restore buffer zones along the sea and near major streams and on steep slopes in the crop
replant process.
9.3 STPs
Better sewage treatment facilities for Kimbe town. Reuse of effluent on land rather than
release to marine environment.
9.4 Monitoring program
A monitoring program to establish to link between land development, increased loads of
sediments and nutrients in streams, delivery of suspended sediments and nutrients to reefs
and the effects on reefs should be established. This program should consist of elements
including (1) measurement of SS and nutrients in flow conditions in the Kimbe Bay
catchment stream network (2) mapping the extent of river plume influence in Kimbe Bay (3)
measurement of sedimentation rates on selected reefs. Measurement of other reef condition
indicators (eg coral cover, coral diversity, coral recruitment, fish diversity) should be
integrated with other reef health monitoring planned for Kimbe Bay.
Page 86
Acknowledgements & contributors
TNC
Alison Green – Marine Science Coordinator, Asia Pacific - Project initiation, project
administration, marine survey assistance
Paul Lokani – Director, Melanesia Program - Project initiation, project administration
Shannon Seeto – Project administration, GIS information, project information
Joe Aitsi – marine surveys
Stephen Keu – landuse and infrastructure information, reports
Annisah Sapul – Rainfall data
Norma Dobunaba - Project administration
NBPOL
Simon Lord – Head of Technical Services - Project organization, transport provision,
extensive information about the oil palm industry, hospitality, coordination of data from
NBPOL
Jamie Graham – Project manager, Kulu-Dagi Inland Cove Project - Tour of Kulu-Dagi
project, information on floods, information on the development stage of oil palm plantations,
hospitality
Harry Brock – Station manager - Tour of Waississi project
Tony Aromo – NBPOL Environment Manager - Environmental management information for
the NBPOL operations
Walter Tangole – Assistant Manager, Sapun Plantation
Jack Kaeka – Supervisor, Daliavu Plantation
Thomas Betitis – Agronomist – Soils information, oil palm cultivation research and
information
Severina Betitis – Precision agriculture officer – GIS information, geographic information on
the NBPOL operations
Phillip Vovola – Plant scientist – Tour of Talasea area, oil palm cultivation information
John Giru – Superintendent, NBPOL Security - Tour of Talasea area
Nick Thompson – Managing Director – Project discussions
Charlie Ross- Consultant to NBPOL on Best Practice Environmental Management
Other organizations
Joe Loga – Boat driver and dive supervisor – Walindi Plantation Resort
Paul Nelson – Oil Palm Research Association (OPRA)
Ian Orrel – Oil Palm Research Association
Peter Dam – Forcert – sustainable forestry
Shane Richie – Sustainable forestry
Bill McKibbin - Mastamak Limited – Forestry and survey
Frank Lewis – Oil Palm Industry Coorporation (OPIC)
Otto Pukam – OPIC
Nabary Teaku – Kimbe Water Board
Simeon Dakama – Provincial Housing manager
Mark Tegal – Sawmill operator
Alois Ragas – Kimbe Town Authority
Page 87
George and Gina – Curtain University
Titus Waluka – Local councillor, Talasea area
Max Benjamin – Walindi Resort
Phillip Munday – James Cook University
Marcus Sheaves – James Cook University
Zoe Bainbridge- Australian Centre for Tropical Freshwater Research
Mike Webb - CSIRO
Page 88
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Appendix 1. The effect of land use on water quality and aquatic ecosystems
1. Land use and water quality
1.1 Catchment characteristics
Damage to coral reef systems from land-based pollution is one of the worldwide issues facing
the continuing existence of reefs. Well known examples include the Kaneohe Bay, Hawaii
sewage discharge story (Smith et al., 1981) and pollution of Jakarta Bay, Indonesia (Tomasik
et al., 1997). Even very large reef systems such as the Florida Keys, USA (Lapointe & Clark,
1992), the Caribbean (Rawlins et al., 1998) and Australia’s Great Barrier Reef (Brodie,
2002) have been damaged and are further threatened by land-based pollution.
Changed land use on catchments inevitably leads to changes in the amounts, forms and types
of material exported to the marine environment. Changed land use on catchments worldwide,
particularly clearing of forest and woodland and its conversion to grazing, cropping and urban
uses, has led to sedimentation and eutrophication in both fresh and coastal marine waters. The
relationship of land use and sediment and nutrient export has been considered for a long
period eg review of Beaulac and Reckhow (1982). The idea of using the catchment
(watershed) as the explanatory geographic unit also has a long history (e.g. Likens, 2001).
Sediment, nitrogen and phosphorus, along with carbon, iron and silicon, are essential
components in shaping the biotic status of waterways from mountain streams to the ocean.
Site characteristics of catchments are usually not subject to significant change on the time
scale of years to decades. The most prominent static characteristics are:
1. Relief (affects hydrological patterns, storage capacity, transit time).
2. Altitude (vegetation type, air temperature, rainfall).
3. Climatological variables (rainfall, relative humidity, temperature, flood event frequency).
4. Bedrock geology (mineralogy, chemical composition, weathering rates and hence supply of
nutrients).
5. Soil cover (depth, chemical characteristics, particle size, permeability).
6. Vegetation cover.
7. Human impact (atmospheric deposition, land use).
1.2 Export of nutrients from pristine forest systems
The initial studies in what were thought to be forests with no/little anthropogenic inputs in
temperate northern hemisphere forests showed high losses of nitrogen (N) often as nitrate
(refs). However in later studies it was realised that these losses were due to atmospheric
deposition of N from fossil fuel burning (note connection to acid rain) and fertiliser
use/volatilisation and rainout. Further studies in South American temperate forests (mainly in
Chile) with no/little atmospheric N deposition showed low losses of N with what is lost
dominated by dissolved organic nitrogen (DON) (Perakis and Hedin, 2001; 2002). It is now
known from a range of studies, in both temperate and tropical forests (and grasslands and
woodlands), that runoff and subsurface drainage from pristine systems has low concentrations
of N (in range 50 – 200 µg/L) dominated by DON with low concentrations of particulate
nitrogen (PN) and dissolved inorganic nitrogen (DIN made up of nitrate, ammonia and
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nitrite). Much of the N draining forested catchments, with low atmospheric inputs, is in the
form of DON and C:N ratios are high and bioavailability may be low.
Pristine forests on South America are known to export considerable concentrations and loads
in flow events of dissolved inorganic nitrogen and phosphorus (Perakis and Hedin, 2002) but
very low concentrations and loads of dissolved inorganic and particulate N and P (Lewis et
al., 1999). In contrast north American forested ecosystems considered pristine, export
considerable amounts of nitrate but this is now considered to be a result of atmospheric
deposition of nitrogen from fossil fuel burning (Paerl, 1997). Similar patterns of nutrient loss
to the South American examples have been measured in temperate Australia, also with little
anthropogenic atmospheric loading, and have been summarized by Harris (1999; 2001).
The effects of atmospheric deposition are well shown in comparisons of nitrogen exported
from north-east USA forests, with high levels of atmospheric N deposition, and forests in
Argentina and Chile with low levels. In the USA cases nitrogen is found to be exported in
inorganic form (19% nitrate, 2% DON, rest not exported by river). In the South American
cases exports are dominated by DON (70%) with smaller proportions of DIN (13% ammonia
and 4% nitrate) (van Breeman, 2002; Perakis and Hedin, 2002).
1.3 Phosphorus losses and geology
The underlying geology, and its effect on soil type and composition, may have significant
effects on the nutrient status of waters draining the landscape. Volcanic rocks (eg basalts) are
richer in phosphorus than granitic rocks and this factor is evident in the concentrations of P in
water running off areas dominated by one of these rock types (Timperley, 1983; Eyre and
Pepperell, 1999). Dillon and Kirchner (1975) observed that forested watersheds with sandy
soils overlying granitic formations had one half the TP output of forested watersheds with
loam soils overlaying sedimentary formations.
1.4 Runoff changes with catchment development
In general conversion of land from forest to other land uses increases overland flow of storm
runoff and suspended sediment and nutrient exports (Hopkinson and Vallino, 1995). As land
is cleared and landuse changes towards more agricultural and urban uses the total amounts of
N and P exported rise rapidly (Young et al., 1996). Particulate matter exports increase relative
to dissolved loads. Forested catchments lose little N and what losses there are are largely in
the form of DON that is presumed to be largely unavailable for algal growth (in the short
term) (Smith and Hollibaugh, 1997; Aitkenhead and McDowell, 2000; but see Sitzinger and
Sanders, 1997). Land use change however leads to rapid increases in N exports and increases
in N concentrations in receiving waters and the form of N changes from DON to nitrate and
ammonia. These forms are much more bioavailable (Harris, 2001).
Thus DOC:POC ratio is highest in forested catchments and lowest in agricultural catchments
(Harris, 1999). Rivers in tropical areas which have episodic high flows and high turbidity
after intense rainfall (often associated with cyclone systems) tend to export organic matter
with a low labile fraction and thus low bioavailability in the short term.
Fluxes of N from the land via rivers to the coast range from 50 kg N /km2/year in pristine
forested catchments to nearly 1500 kg N/km2/year from catchments draining into the North
Sea from Europe (Howarth, 1998). Rates of atmospheric deposition of N range from 1 to
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nearly 1000 kg N/km2/year (Holland et al., 1997). Atmospheric deposition is highest in the
industrial areas of the Northern Hemisphere (200 – 400 kg N/km2/year) where urban,
industrial and transport sources dominate. Atmospheric deposition is elevated, through
anthropogenic inputs, over all the continents except Australia, but deposition is generally
lower over the Southern Hemisphere continents (50 – 150 kg N/km2/year). Forested
catchments often retain a large proportion of the atmospheric N load.
In rivers affected by anthropogenic nitrogen loading a rise in DIN as a proportion of TN as
the TN increases is found throughout the world (Howarth et al., 1996). Forested catchments
exported mostly DON while urban proportionally more DIN while as catchments were
increasingly affected by deforestation and urbanization the stoichiometry of the more
available forms of N and P rose above Redfield. TN:TP ratio drops towards the Redfield ratio
(16:1) with catchment development.
Landuse change and reduction of forest cover also affects P exports (Harris, 2001). TP is
overwhelmingly associated with the particulate load. A considerable proportion of P exported
downstream may be not available and the proportion of available: non-available varies widely
in waterways depending on geology, soil type, hydrology and P sources (Dillon and Kirchner,
1975; Oliver et al., 1993).
1.5 Losses of sediment and nutrients from different land uses
Extensive studies of loss of sediments, nutrients and pesticide residues from a range of crops
under various management regimes have been reported worldwide. Only a few examples are
given in this review.
Studies have focussed on the losses of suspended solids, nitrogen and phosphorus and of
various forms of N and P from different landuse types including forests, dairy grazing lands,
rangeland grazing lands, cropping lands, urban lands and aquaculture under a large range of
management regimes. The effects of climate, soil type, hydrology, atmospheric deposition of
nitrogen and terrain have been included in the analyses (e.g. Dillon and Kirchner, 1975).
There has also been a large number of studies examining the processing and losses of
suspended solids and nutrients during stream flow and during water passage through riparian
vegetation and wetlands (Arheimer and Wittgren, 1994; Behrendt and Opitz, 2000; Cooper et
al., 1987; Dosskey, 2001; Hillbricht-Ilkowska and Bajkiewcz-Grabowska, 1991; House and
Warwick, 1998). Much of the recent work, particularly in the USA and Europe, has focussed
on using land runoff information from different land uses to model and budget watershed
nitrogen and phosphorus loads and exports (Beaulac and Reckhow, 1982) and the models
have been regularly evaluated (e.g. Alexander et al., 2002).
A good summary of landuse-nutrient export relationships is found in Beaulac and Reckhow
(1982) where results from a large range of cropping (row crops)and grazing studies in the US
are compared. Total nitrogen export values range from 2 to 80 kg/ha/year and phosphorus
from 0.2 to 18 kg/ha/year for cropping systems and 1.5 to 30 kg/ha/year N and 0.1 to 5
kg/ha/year P for grazing systems.
McKee et al., (2000) in their studies on nutrient exports from the Richmond catchment
(northern NSW) summarise factor increases in nitrogen and phosphorus exports from
different land uses using global data. This is reproduced in Table 1. In Table 2 absolute values
Page 101
of erosion and sediment loss from different land uses with examples from the wet tropics of
north Queensland and elsewhere are shown.
Table 1 Comparison of exports of nutrients from different land uses as a factor increase compared to
forest land (from McKee et al., 2000).
Landuse
Crop land
Horticulture
Improved pasture
Pasture
Urban
Forest
Nitrogen (factor increase)
World median
Tropical
Australia
13.7
13.7
20.8
28.9
4.6
5.6
2.8
3.3
6.7
7.3
1.0
1.0
Phosphorus (factor increase)
World median
Tropical
Australia
21.1
23.8
50.7
88.8
7.9
13.8
5.6
1.3
8.5
12.5
1.0
1.0
Table 2 Soil loss from various land uses types (north Queensland)
Paddock scale
Undisturbed rainforest (NEQ)
4.8 tonnes/ha/yr
Selectively logged rainforest
10.9
Cleared rainforest in first year
59.6
Sugarcane - Johnstone R.
– Burnt (Conventional Cultivation)
- Zero tillage, 0% trash
“
50% trash
“
100% trash
150 (70-500)
15
10
5
Sugarcane - Pioneer R.
- Burnt (Conventional Cultivation)
56-390
City average (Victoria)
200
City construction sites
400
Gravelled roads
140-250
Pineapple farms (SE Queensland)
0.1 - 105
Catchment Scale
Rainforest
0.2-0.3
Woodland / Grassland
0.5-1.4
Cleared catchment
20-30
Page 102
1.6 Low intensity land uses (grazing, selective logging)
As catchment development proceeds and low intensity land uses such as grazing (eg
rangeland beef grazing) and selective forestry (not clear felling) replace pristine
forest/woodland/grasslands the fluxes of sediment, N and P lost from the landscape increase
and the forms of N and P change (still excluding large anthropogenic atmospheric inputs).
The principal change is to higher rates of soil erosion and hence considerably higher
concentrations of PN and PP in runoff (but obviously not in subsurface losses). As PN and PP
are mobilized into the water column some desorption of species such as ammonia and
phosphate occurs and so DIN and DIP concentrations rise, albeit, slightly compared to
pristine conditions. Thus runoff from forests under selective forestry has moderate/high
concentrations of PN and PP, moderate concentrations of DON and DOP and low
concentrations of DIN and DIP. Forestry operations increase particulate matter exports
greatly through widespread soil disturbance. Thus suspended solids loads and associated
particulate nitrogen and phosphorus loads increase relative to the natural export of primarily
dissolved organic carbon, nitrogen and phosphorus.
In grazed systems the added factor (besides increased soil erosion) of an increased rate of
mineralization of N and P due to digestion and excretion of vegetation means that increased
losses of dissolved nutrients also occur compared to pristine. Thus in general from grazed
systems runoff has moderate concentrations of PN and PP, moderate concentrations of DON
and DOP and low/moderate concentrations of DIN and DIP.
1.7 Cropping
Modern cropping and fertiliser use, particularly since about 1950 in the developed world and
since the 1970s in the third world (the ‘green revolution’) saw N and P dynamics of cropping
systems dominated by artificial fertilisers (Vitousek et al., 1997; Matson et al., 1997; Holland
et al., 1997).
In general only about one third of fertiliser N and P is incorporated into that part of the crop
removed from the field for use. The other two thirds may be left in the field as crop residues
(stubble, trash), in the plant itself if it is a multi-year crop (sugarcane roots/stalks in ratoon
crops; the trees themselves in tree crops); in the soil; or lost from the field through
volatilisation (mostly of ammonia from N fertilisers); denitrification (loss of nitrogen gas or
nitric oxide); leaching to subsurface or groundwater (commonly nitrate); or as runoff (all
forms of N and P).
Thus cropping systems tend to lose high concentrations and produce large fluxes of N and P
often as DIN and DIP as well as high soil erosion in some cases producing high runoff
concentrations of PN and PP. Thus overall runoff from fertilised cropping contains high
concentrations of PN and PP, moderate concentrations of DON and DOP and high/very high
concentrations of DIN and moderate/high concentrations of DIP. Subsurface water will
contain elevated concentrations of nitrate.
1.8
Urban
The largest source of nutrient input from coastal urban areas is in the form of sewage
treatment plant discharges. Effluent from secondary standard treatment plants has relatively
Page 103
constant composition, while discharge volumes are closely related to population numbers.
Thus estimates of probable nutrient inputs from sewage are relatively easy to calculate.
In general in urban areas people dispose of approximately 500 litres per day per person to the
sewerage system. This includes industrial and other uses. This effluent contains
approximately 1.5kg phosphorus and 5kg nitrogen per person per year (Murdoch, 1971) with
up to half the phosphorus deriving from cleaning agents. Some of the nitrogen and
phosphorus content of the raw sewage is removed in a secondary treatment process but most
can be removed in nutrient-removal tertiary treatment plants. Many smaller coastal
communities still use septic tank systems with absorption or evaporative trenches adjacent to
waterways. These systems have limited ability to remove nutrients from the final effluent but
much of the nutrient may be taken up in plant growth where absorption trenches are
employed. Typical composition of different stages of sewage treatment are shown in Table 3.
Table 3 Effluent composition from various stages of sewage treatment.
Component
Raw Sewage
Biological Oxygen Demand (mg/l) 300
Primary
Treatment
200
Secondary
Treatment
15
Tertiary
Treatment
2
Suspended Solids (mg/l)
300
120
20
2
Total Nitrogen (mg/l)
50
45
20
4
Total Phosphorus (mg/l)
10
9
7
0.6
Surfactants (mg/l)
2
2
1
<1
Pollution of sub-surface waters with nutrients, particularly nitrate, from unsewered rural
residential land uses and subsequent contamination of stream waters after the sub-surface
water leaches into streams has been noted in many catchments. Unsewered residential is a
significant contributor to nitrate loads in the Johnstone River, north Queensland considering
the comparatively small area occupied by this land use (Hunter and Walton, 1997). High
nitrate concentrations in small number of bore waters in the Bundaberg region were
associated with non-sewered settlements (Keating et al., 1996).
Urban stormwater runoff contains significant concentrations of nutrients, sediments, metals,
oil, synthetic organic chemicals and plastics. The nutrient concentrations may be up to 10% of
the concentrations found in sewage effluents.
The quantity of runoff from an urban area depends on the extent of impermeable surface and
the intensity, duration and frequency of rainfall events. The types and concentrations of
pollutants contained in the runoff depend on the types of urban and industrial development
present. In some urban areas sewage overflow from the mains can be a significant source of
contamination to stormwater during intense rainfall. While the actual concentrations of
contaminants in runoff may not be particularly high, the volumes involved may mean that the
mass loadings may exceed sewage loadings in the same area.
Page 104
Nutrients in stormwater flow may derive from garden fertiliser, animal feed lots, land
disturbance during construction activities and pet animal wastes. Trace metals originate from
vehicle emissions (particularly lead), wear metal fallout and industrial activity while synthetic
organic chemicals include pesticides, solvents, paint residues and in harbour areas, antifouling paint residues containing copper and organo-tin compounds.
1.9 River transformations and transport of materials through waterways
All the soil which is lost from a paddock does not reach the main river system or even less to
the coast. The greater part, especially the coarser fractions (sand & silt), is redeposited within
the catchment. This explains the difference in the figures for soil loss measured on a small
area (eg paddock) basis versus a sub-catchment or catchment scale as shown in Table 2. The
percentage of eroded material actually delivered to the river mouth varies with the catchment
size and type and may range from a few percent up to forty percent.
C:N:P ratios and the forms of nutrients vary in downstream transport due to instream
processes such as carbon metabolism, sedimentation, species transformations mediated by
bacterial action and denitrification (Downing, 1997). This will be a minor factor in small wet
tropics rivers due to their fast flow in major events and subsequent lack of time for such
processes to occur. In anoxic conditions (in sediments or bottom waters) DON is converted to
ammonia and then to nitrate and is exported downstream. Reservoirs export nitrate which has
originally entered the reservoir as PN or DON and, in time, been converted to nitrate in the
reservoir (Harris, 2001). Reservoirs thus often export nitrate in far greater concentrations than
the intake water.
Tropical rivers have, in general, highly irregular flow regimes and transport of materials, such
as suspended sediments, nutrients and pesticide residues, in both dissolved and particulate
forms occurs almost completely in major flow events. In these conditions, while some
trapping of coarser washload sediments may occur within the catchment, there is almost no
trapping of the finer sediments, with their PP and PN component, or dissolved nutrients.
Rivers flush fresh to the sea in the major flow events. The salt wedge reaches the coast under
river plumes in major flows but does not penetrate any distance up the rivers. A large
proportion of nutrients mobilised in the catchments in major flood events are completely
exported to the marine environment. Some trapping of finer sediments from the washload
occurs in the estuary of rivers but trapping is minimal compared to temperate rivers and larger
tropical rivers.
1.10 Sub-surface and groundwater
Significant quantities of groundwater often underlie coastal river floodplains. In areas of
significant fertiliser use these groundwaters are often contaminated with elevated nitrate
concentrations (e.g. Brodie et al., 1984; Biggs et al., 2001 in Australia). While natural sources
of nitrate in groundwater do exist, groundwaters with nitrate concentrations > 1 mg/l NO3 – N
are generally a sign of fertiliser or sewage effluent contamination.
The Nutrient Balance project on the Johnstone Catchment, north Queensland showed that a
considerable proportion of applied nitrogen fertiliser passed below the root zone (>0.75m) of
sugarcane and banana crops. For sugarcane the losses to drainage average 30 to 50 kg
N/ha/year and for bananas 70 to 130 kg N/ha/year. (Moody et al., 1996) from fertilser
application rates of 150 – 400 kg/ha/year. This nitrate is believed to be the source of the
Page 105
‘nitrate bulge’ found at some depth (4 - 10 m) in many parts of the Johnstone Catchment (e.g.
Rasiah and Armour, 2001). Concentrations of nitrate in soil of up to 72.5 mg/kg NO3 – N
have been found in this ‘bulge’ under sugarcane compared to concentrations of only up to
0.31 mg/kg NO3 – N under rainforest. High application of nitrogen fertilisers on sugarcane
crops can lead to substantial leaching of nitrate below the root zone (Verberg et al., 1998).
Significant leaching of nitrate in alluvial soils under sugarcane in the Herbert floodplain is
reported (Bohl et al., 2000) and believed to be a significant contribution to elevated levels of
nitrate in streams after horizontal flow of nitrate rich subsurface flow in to streams.
1.11 Acid sulphate soils runoff
Soils containing iron sulphides are commonly referred to as potential acid sulphate soils
(PASS). These soils occur naturally in water logged situations in low-lying areas near the
coast, typically in areas below 5m AHD. Potential ASS is harmless when it remains below the
water table. However, when these soils are drained or disturbed, iron sulphides become
exposed to air, and are oxidised. The soil becomes actively acid forming and is then called
acid sulphate soil (ASS). This oxidation produces sulphuric acid, which may leach into
waterways. The consequences, which can be severe, include acidification of water bodies (pH
as low as 2), lowering of dissolved oxygen (DO), smothering of benthic organisms, and
increased concentrations of toxic metals (iron and aluminium) that are mobilised by the low
pH. The impacts on coastal biota and habitats can be severe, and have been linked to fish-kills
and red-spot disease in fish.
2 Susceptibility of marine ecosystems and specifically coral reefs to runoff
2.1 Pollutants of concern
Sources of coastal pollution in tropical areas can be grouped into several main classes:
agriculture, sewage, industrial discharges, urban stormwater, shipping activities, aquaculture
and mining. The principal contaminant classes which may be present in discharges from these
sources are sediment, nutrients, toxic metals, pesticides, oxygen depleting substances, acid
sulphate runoff (low pH, oxygen depletion and metals), pathogenic organisms, larvae of
exotic species, litter and other toxic chemicals.
The input of many of these contaminants to coastal waters has changed dramatically in many
states over the last few decades. Increased sewage discharges are closely correlated with
population increases while nutrient inputs from agriculture have risen sharply with the
increased fertiliser use in many locations over the last fifty years.
The effects of runoff of sediments and nutrients from agricultural and urban development on
adjacent catchments have been documented in many tropical regions. Edinger et al., (1998)
documented land-based pollution and destructive fishing practices as having led to severe
widespread loss of coral reefs in Indonesia. Similarly, in the Philippines reef destruction is
associated with sedimentation, over-fishing and destructive fishing practices. Increased
nutrient supply can enhance the growth of phytoplankton, turf algae and macroalgae. This
effect has been demonstrated in numerous coral reef systems worldwide such as the Red Sea,
Barbados and Indonesia (Edinger et al., 1998) with the best documented example in Kaneohe
Bay, Hawaii (Smith et al., 1981).
Page 106
2.2 Dispersal and fate of runoff in the marine environment
In the estuarine mixing process as salinity and pH rise clay materials in the river plume
flocculate and tend to settle out close to the coast. For example most of the terrestrial
sediment deposited on the floor of the Great Barrier Reef (GBR) lagoon does so in a band
within 15 km of the coast. However nutrients such as phosphate associated with the sediment
may travel much further offshore than the sediment itself. This occurs as the phosphate
desorbs off the sediment particles in the estuarine mixing process and is then in a dissolved
form able to move greater distances in the prevailing current. Similarly dissolved components
of the river discharge such as nitrate may also travel large distances before biological uptake
or chemical transformation occurs (Devlin and Brodie, 2005).
2.3 Effects of sediment
Increased sediment discharge from land associated with logging, forestry, overgrazing by
stock, cropping on slopped land and urban and road construction may lead to severe effects
on coastal ecosystems including sedimentation, turbidity-related light reduction and
eutrophication.
Benthic communities such as coral reefs and seagrass beds are particularly susceptible to
sedimentation and smothering. Coral reefs in the Ryuku Islands (southern Japan), particularly
on Okinawa and Ishigaki, have been almost destroyed by land runoff of red mud associated
with construction activity and agriculture. Similarly on the Great Barrier Reef (Australia)
general loss of coral on the reef flats of inshore reefs is considered to be associated with a
fivefold increase in sediment discharge from the adjacent coast in the 130 year period since
European settlement. In Westernport Bay (southern Australia) 80% (20,000 ha) of the total
seagrass beds have been lost since 1973, blame being generally ascribed to increased
sediment discharge from the surrounding catchments (Brodie, 1995).
A second impact of sediment discharge is increased turbidity in the water column. Turbidity
cuts light penetration through the water and inhibits the growth of organisms requiring light.
The effects are most severe on benthic communities where the viable depth range for a
community, such as seagrass, may be narrowed by loss of light. Particulate matter in the
water column may also interfere with the feeding behaviour of zooplankton.
In freshwater systems increased sediment leads to muddier rivers with less light for bottom
communities, disturbance to bottom fauna due to siltation and river aggradation. River
aggradation in the lower reaches of the river may lead to increased flooding and boating
problems due to lack of depth. In north Queensland both the Pioneer River and the Johnstone
River have dramatically increased sedimentation and aggradation in recent years blamed in
both cases on land use practices in their catchments.
Seagrasses are more to susceptible to sedimentation damage than mangroves, suffering from
both the lack of light caused by more turbid water and direct smothering from deposited mud.
In recent times large areas of seagrass meadow has been lost in muddy flood events. Over
1000 square kilometres of seagrass were lost in Hervey Bay in February, 1992 following two
large floods in the Mary River. As a result the population of dugongs in the area, dependent
on the seagrass for food, crashed from an estimated 1466 animals in 1988 to 92 in November
1992 with both mortality and migration.
Page 107
Turbid water from sediment runoff causes impacts to coral reefs by reducing light levels.
Corals need light for their symbiotic algae (zooxanthellae) to function. A common response
of corals to prolonged exposure to turbid water is expulsion of the zooxanthellae so that the
coral appears white or bleached. In the long-term, depending on the level of stress, bleached
corals may recover and reestablish their zooxanthellae or die.
Coral reefs may be severely effected by even moderate increases in sedimentation and
turbidity (Fabricius, 2005) but paradoxically some corals thrive in the quite muddy conditions
found on inshore reefs in many parts of the world. This depends on oceanographic conditions
where waves and currents may remove sediment quickly after deposition and the corals
tolerance for low light conditions and their sediment rejection and removal mechanisms.
Corals can live and grow in turbid waters which have previously been assumed to be
incompatible with reef growth and survival, but in high turbidity conditions, these corals may
not accrete significant reef structures.
There is a variety of evidence that increased sediment loading can damage corals (e.g.
Fabricius, 2005). The effects of sediment loading can be exacerbated under conditions where
aggregates of organic matter and fine sediment (‘muddy marine snow’) are formed. However,
at least some coastal reef corals are known to use the organic matter in sediment aggregates as
a food source so that suspended particulate matter may have both positive and negative
implications for corals and other reef animals. Broad-scale distributions of the diversity of
soft corals (Fabricius and De’ath, 2001a) and coralline algae (Fabricius and De’ath, 2001b)
are inversely correlated with the turbidity (suspended particle load) of GBR waters.
2.4 Effects of nutrients, principally nitrogen and phosphorus
Eutrophication occurs when the nutrient supply (particularly nitrogen and phosphorus) to an
aquatic system increases to an amount beyond that useable by the normal photosynthetic
community in the system. The productivity of many aquatic systems is limited by the supply
of a nutrient element, often phosphorus in freshwater systems but more often nitrogen in
marine systems. An enhanced supply of the limiting nutrient will remove the restriction on
plant growth. The definition of eutrophication used by the European Union "The enrichment
of water by nutrients, especially compounds of nitrogen and phosphorus, causing accelerated
growth of algae and higher forms of plant life to produce an undesirable disturbance to the
balance of organisms present in the water concerned" encapsulates the idea.
When enhanced input occurs algae and phytoplankton whose growth is normally limited by
the supply of nitrogen and/or phosphorus flourish, often at the expense of the resident
photosynthetic community. Thus phytoplankton may bloom and the species present change to
'undesirable' types associated with 'red tides' and toxicity in fish and shellfish. In other
ecosystems corals are replaced by macroalgae while seagrass may be overgrown by epiphytic
organisms. With phytoplankton blooms an increase in the presence of filter-feeding
organisms such as boring sponges, tube worms and barnacles which feed on plankton may
replace coral. With enhanced productivity comes increased organic matter in the water
column and the potential for removal of oxygen from the water, particularly near the bottom.
In conditions of zero oxygen (anoxia), anaerobic processes occur producing sulphides and
methane. Fish kills and changes in benthic community structure may then result.
Red tides occur when pigmented algae forms blooms under favourable meteorological and
nutrient supply conditions. These blooms can be natural but may also be enhanced by
Page 108
anthropogenic nutrient inputs. Many such blooms are ecologically benign but others may
consist of algae containing potent toxins. Toxins from algae such as Pyrodinium bahamense
may then be incorporated into bivalve molluscs and pose a serious threat to humans when
consumed. It is believed that toxic red tides are increasing in frequency around the world and
in the Western Pacific.
Effects of runoff, sediment and nutrients on coastal reef communities are complex and
incompletely understood. Reefs and established coral communities can be found at many
sites along the coast, often with naturally high levels of turbidity and sedimentation. At a
number of locations, nearshore reefs or sections of reefs disturbed by various processes (eg.
cyclones or floods) have failed to recover, even after extended periods (e.g. van Woesik et al.,
1999). All occur in locations directly influenced by runoff from agriculturally and urban
developed catchments. Macroalgae are a conspicuous element of nearshore reef communities
near developed and undeveloped catchments and typically exhibit a positive growth response
to nutrient enrichment. Algae were regarded as indicators of eutrophication on coral reefs.
Recent studies however, show that algal dominance is influenced by complex interactions
between nutrient availability, growth and grazing pressure (Fabricius et al., 2005).
The best documented example of the effects of nutrients and organic loading delivered via a
sewage discharge on a coral reef is Kaneohe Bay, Hawaii (Smith et al., 1981). Sewage
discharges into the Bay from the end of the Second World War to 1978 saw the waters
become increasingly rich in phytoplankton and reefs closest to the outfall become overgrown
by filter-feeding organisms, such as sponges, tube-worms and barnacles. Reefs in the centre
of the Bay further from the outfalls were overgrown by the green alga Dictyosphaeria sp.
(Smith et al., 1981). After diversion of the outfalls into the ocean in 1978, the reefs have
slowly recovered.
Page 109

Land use practices in the Kimbe bay catchment

Transcription

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