Nutrient Concentration and Water Turbidity on Coral Reef Area and

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Nutrient Concentration and Water Turbidity on Coral Reef Area and
Session 2
Biodiversity Conservation
Nutrient Concentration and Water Turbidity on Coral Reef Area
and their Effects on the Living Coral
Koichi KINJO
Okinawa Prefectural Institute of Health and Environment
Coral reef disturbances
Outbreak of crown‐of‐thorns starfish
(Acanthaster planci)
Rise in seawater temperatures
Destruction by typhoons
Widespread of coral diseases
Soil run‐off
Nutrient enrichment
Pesticides・
Heavy metals
Coral reef disturbances
Increasing nutrient loads and soil run-off have been pointed out as the
potential to serious impact on coral reef areas due to urbanization of
coastal areas, growth and development agriculture or livestock farming.
Soil run‐off
Nutrient enrichment
Sedimentation
Overgrowth of algae
Coral death
Decrease of habitat of coral
Objectives
In order to keep the water quality good for coral health, the
environmental water quality guidelines are needed.
If the water quality exceed the limits of environmental guideline, it is
possible to manage the catchment contiguous to the coral reef area,
and to maintain the suitable water quality.
In this study, the suitable water qualities are examined for
conservation and management of coral reef areas.
Topics
In the coral reef areas around Okinawa・・・
• The range of water qualities
• The seasonal variation of water qualities
• The difference of water qualities between the areas
• The thresholds of water qualities required for conservation of coral reef areas
Study area
104 study sites
in the Ryukyu Islands
Sampling periods
・Sep. to Oct. 2009
・Nov. to Dec. 2009
・Feb. to Mar. 2010
・Jun. to Jul. 2010
・Nov. to Dec. 2010
・Feb. to Mar. 2011
Kume Island
5 study sites
Kerama Islands
3 study sites
Okinawa Islands
70 study sites
Yaeyama Islands
20 study sites
Miyako Island
6 study sites
Investigation points
・3 or 4 points set for each study site
Water samples were collected under normal conditions.
River Channel Tidal area†
River mouth
Branching coral
Beach Coral beds
Seagrass beds
Seagrass Moat
study site
(coral reef area)
Reef crest
Parameters water quality
Nutrient parameters
•Total Nitrogen(TN)
•Total phosphorus(TP)
−
−
•Nitrate and Nitrite (NO3 +NO2 )
•Phosphate(DIP)
Turbid parameter
•Water turbidity
•Horizontal transparency
Coral condition
•Coral coverage (%)
Parameters water quality
Nutrient parameters
What is horizontal transparency?
•Total Nitrogen(TN)
•Total phosphorus(TP)
•Nitrate and Nitrite (NO3−+NO2−)
•Phosphate(DIP)
Secchi disk
Turbid parameter
•Water turbidity
•Horizontal transparency
Coral condition
Usual method of transparency has some defects such as difficulties in
measuring at shallow and clean waters in coral reefs.
•Coral coverage (%)
Horizontal transparency is the method of measuring horizontal distances
keeping the Secchi disk perpendicular to seabed.
Parameters water quality
Nutrient parameters
•Total Nitrogen(TN)
•Total phosphorus(TP)
−
−
•Nitrate and Nitrite (NO3 +NO2 )
•Phosphate(DIP)
Turbid parameter
•Water turbidity
•Horizontal transparency
Coral condition
•Coral coverage (%)
Results
Summery of the analyzed water quality data
Mean
Min
Max
n
Achievement rates ※
TN
(mg-N/L)
0.08
< 0.02
1.66
1684
92.8%
TP
(mg-P/L)
0.01
< 0.002
0.190
1682
95.4%
Nitrate + Nitrite
(mg-N/L)
0.005
< 0.005
1.674
1677
Phosphate
(mg-P/L)
0.006
< 0.001
0.094
1681
Water turbidity
(Degree)
0.448
0.012
39.658
1666
Horizontal
transparency
(m)
7.3
0.1
43.0
1781
※ Achievement rates :
The achievement rates of the severest environmental standard values in Japan established by Basic Environmental Law
TN<0.2mg/L, TP<0.02mg/L
Results
(Water quality data for each monitoring period)
75 percentile median
25 percentile ・Each water quality parameters tended to be the maximum in summer and to be the minimum in winter.
Results
(Water quality data for each type of habitat)
・ Each water quality parameters decreased in proportion to distance from the river mouth.
Results (water quality data for 6 areas )
Agricultural area
Urban area
Natural area
・In the coral reef area adjacent to the urban area, each water quality parameters became comparatively high. Results
(Relation between coral coverage (%) and each water quality parameter)
50%
50%
0.08
0.01
50%
50%
0.11
・When nutrients concentration or turbidity decreased or horizontal
transparency increased, coral condition became better.
14.0
Environmental guidelines for coral reef conservation
Thank you very much for your attention

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