Soil Survey and Databases in Iceland

EUROPEAN SOIL BUREAU  RESEARCH REPORT NO. 6
Soil Survey and Databases in Iceland
Ólafur Arnalds
Agricultural Research Institute, Keldnaholt, 112 Reykjavik, ICELAND
Introduction
Icelandic agriculture is characterized by the use of
extensive rangelands for grazing and the making
of hay for winter feeding. Cultivated land is of
limited extent. Iceland has therefore traditionally
put more emphasis on mapping vegetation
resources rather than the soils.
The history of soil science in Iceland is relatively
young. Geologic aspects of the soils received
considerable attention early on with the study of
volcanic ash layers, but dating of soils by volcanic
ash layers was pioneered by the Icelandic
geologist Sigurdur Thorarinsson (1961).
The first comprehensive map of of Icelandic soils
was printed in 1959 at a scale of 1:750,000
(Nygard and Johanesson 1959). Other soil survey
efforts were localized and this map together with
Johannesson´s monograph on Icelandic soils
(1960) remained the only complete survey of
Icelandic soils until this year.
In response to request made by the European Soil
Bureau and other international agencies, the
Agricultural Research Institute is now completing
a soil map in the scale of 1:500,000.
Soil Mapping in the Past
The pioneer work by Johannesson (1960)
established a framework for the classification of
Icelandic soils that is still valid. The soil map that
was included in his monograph is attributed to Ivar
Nygard who started this work in 1951, but after
Nygard’s death, Johannesson completed the map
in co-operation with the US Soil Conservation
Service. The map was printed by the U.S.
Geologic Survey in 1959, but was included with
both the Icelandic and English versions of
Johannesson’s monograph on Icelandic soils
(1960). The monograph was reprinted in Icelandic
by the Agricultural Research Institute in 1988.
The underlying basis for Johannesson´s and
Nygard´s work was the US soil classification
system (Baldwin et al., 1938).
Johannesson established a classification system
based on 23 mapping units, but the soils were
devided into three major groups, the freely drained
soils (silt loams), poorly drained soils (peat soils)
and the soils of the deserts (stony alluvial, aeolian,
lag gravel, etc). At the time of Johanesson´s
studies, the unique properties of Andosols were
only beginning to be realized, which limits the
present applicability of this work. It is noteworthy,
however, that Johannesson wrote in his
monograph: “…is the fact that many silt loam soils
have some characteristics like those of the
volcanic ash soils in other countries, for instance
those of Japan, and thus perhaps might be
considered as close relatives to or even as
members of the so-called Ando soil group..”
After the work of Johannesson, emphasis was
mainly on agronomic aspects of Icelandic soils,
such as fertilization of hay fields and draining of
wetland soils. Noteworthy is Helgason’s
comprehensive account of soils of South-west
Iceland (1963; 1968). Two Ph.D. dissertations
added considerable knowledge on the basic
characteristics of Icelandic soils in the eighties by
Ólafsson (1974) and Guðmundsson (1978). The
Agricultural Research Institute is still involved in
soil evaluation for fertilizer recommendations, and
has carried out extensive research related to soil
fertility. The results have been reported both in
specialized reports and as scientific papers (e.g.,
Palmason et al., 1996; Palmason and Helgason,
1996).
Several attempts have been made to map soils in
localized areas (e.g. Helgason and Gudbergsson,
1977; Gudbergsson and Olafsson, 1978), drawing
much from the basis Johannesson provided.
Gudbergsson (1982) made an outline for the
classification of wetland soils (Histosols).
Soil Survey and databases in Iceland. Ólafur Arnalds
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EUROPEAN SOIL BUREAU  RESEARCH REPORT NO. 6
This can also be judged as a benefit, demonstrating
the dominating influence of andic soil properties
of Icelandic soils.
Current Soil Mapping
Activities
Soil Taxonomy and FAO World
Reference Base
Soil mapping needs to be based on a suitable soil
classification system. The Agricultural Research
Institute collaborated with Texas A&M University
and the USDA-NRCS to provide a new
perspective on Icelandic soils for this purpose,
with detailed analyses of several representative
soil pedons (Arnalds, 1990; Arnalds et al., 1995;
Arnalds and Kimble, unpublished data; Wada et
al., 1992). These studies show that Icelandic soils
are Andosols and Andic integrates of other soil
groups to a large extent. More recent overview of
Icelandic soils was published by Arnalds (1999a).
The soils of the barren areas in Iceland are quite
different from the typical Andosols and Histosol
that cover other parts of the country. Arnalds
(1988; 1990) and Gudmundsson (1991) have
published studies on these soils. Arnalds and
Kimble conducted a detailed analysis of ten
representative pedons of Icelandic desert soils but
the results are still being analyzed.
A steady input of eolian materials and occasional
tephra additions cause the organic carbon content
to be lower than 25% in many of the wetland soils,
resulting in Andisol (US-Soil Survey Staff, 1998)
rather than Histosol classification (Arnalds et al.,
1999). The desert soils are also often classified as
Andisol because of their high volcanic glass
content.
The current edition of the US Soil Taxonomy (US
Soil Survey Staff, 1998) has therefore the
disadvantage in relation to the classification of
Icelandic soils that it fails to distinguish between
some of the major soil types at the highest level
because of dominating andic influences.
Applying the FAO soil classification (FAO, 1998)
system involves similar problems as for the US
system in that many contrasting soils are classified
the same at the highest level as Andosols. The
wetland soils often do not meet the cryterion for
Histosols because of relatively low organic content
and the dominance of volcanic glass in desert soils
often excludes Arenosols, Fluvisols, Cambisols
and Regosols as soil groups. However, Thorsteinn
Gudmundsson (1994) found that the FAO legend
(FAO-UNESCO, 1988) provided a good framwork
for mapping soils in Iceland. He translated and
adapted the FAO system for use in Iceland.
The Icelandic adoption of the FAO scheme for the
soil groups (Gudmundsson, 1994) does not fully
correlate with the FAO World Reference Base
(FAO 1998) for reasons stated above. Its use may
therefore cause problems in relating Icelandic soil
information at an international level although, with
modifications, it is well suited for domestic use.
Current soil mapping effort
The Agricultural Research Institute is currently
making an effort to produce a soil map in
1:500,000. Soil classification issues have not been
resolved yet. A preliminary version of this map is
published with this paper (Figure 1). The soil
information underlying the map is drawn from
published and unpublished literature on Icelandic
soils, which currently is being compiled for a
databank and an overview publication. Some
general characteristics are presented in Table 1.
Soil analysis generally follows standard methods
designed for Andosols such as described by
Blakemore et al., 1987. Soil descriptions generally
follow US methods (eg., USDA-NRCS 1998).
Table 1. General characteristics of major soil classes in Iceland. Common ranges.
Soil Class
km2
43 770
8 600
1 8600
4 540
15 090
Depth
m
0.5-1.5
0.5-5
0.2-0.5
OC
%
2-10
5-30
0.5-1.5
pH
in H2O
5.5-6.5
4.5-5.5
6.5-7.0
Oxalate
Al+1/2Fe%
Clay
%
15-40
?
5-15
Brown Andosols
3-8
Organic Andosols
>2
Vitric Andosols
1-2
LeptosolsÀ
0-2
0.2-2
6.5-7.0
0.3-0.8
1-5
Sandy Andosols‚
À No data available
‚ Area (km2) includes both Sandy Andosols and Sandy Andosols/Leptosol complex.
92
Soil Survey and databases in Iceland. Ólafur Arnalds
CEC
10-40
30-60
5-15
H2O
15 bar
30-60
60-120
5-15
2-10
1-10
Meq/100g
EUROPEAN SOIL BUREAU  RESEARCH REPORT NO. 6
Figure 1: Soil map of Iceland at 1:500,000 scale.
Soil Survey and databases in Iceland. Ólafur Arnalds
93
EUROPEAN SOIL BUREAU  RESEARCH REPORT NO. 6
The geographic information is mainly drawn from
three sources:
1. Vegetation maps. Vegetation reflects soil
conditions, especially the distinction between
wetlands (organic soils), freely drained
vegetated Andosols and the deserts.
2. Soil Erosion digital databases (see later in the
paper). This information gives a good
geomorphological overview of the desert
surfaces, and is the primary source for their
geographic information.
3. Infrared satellite images (LANDSAT TM).
They are used where there is a lack of
vegetation information. The images also
provide the base map, correlated with
Iceland´s current map projection system.
The map was constructed using Arc/Info GIS
software. The soil classes used in the map are as
follows (note the class names are only suggestive
at this stage and are subject to further
development):
1. Brown Andosols. These represent the typical
Andosols of Iceland. They are usually freely
drained and have developed in eolian and
tephra materials that typically form a 80-200
cm mantle that has accumulated over an older
surface (usually glacial till or lava). They are
rich in allophane clay minerals, and
ferrihydrate, but volcanic glass is also in
abundance near the most active volanoes.
Distinctive volcanic ash layers are common.
2. Organic Andosols. These soils are found at
poorly drained sites (bogs and myres), and
often grade into Histosols. They most likely
classify as Histosols in areas furthest away
from eolian sources. The Organic Andosols
are typically 50-500 cm thick with 5-30% C
content. Volcanic ash layers are common.
3. Vitric Andosols (or Gravelly Andosols).
These soils are desert soils poor in organic
matter compared to the classes above. They
meet the criterion for Andosols (and Andisols)
because of abundance of volcanic glass
materials and other andic characteristics. The
Vitric Andosols grade into Regosols (away
from eolian tephra sources) and Leptosols.
4. Leptosols. These soils are found on scree
slopes, recent lava surfaces, and on lava
surfaces where erosion processes have
removed Brown or Organic Andosols from
the top.
5. Sandy Andosols. Sandy surfaces are common
in Iceland near glacial margins and on glaciofluvial floodplains. Eolian processes have
often carried sandy materials long distances
from their sources, increasing the size of
sandy areas. The sand is largely composed of
volcanic glass.
94
6.
Leptosol/Sandy Andosol complex. This is a
special class as this combination is very
common in Iceland. It occurs where there is
an abundance of sand on lava surfaces (due to
eolian processes and volcanic ash fall). The
sand covers the depressions while bedrock
(lava surface) sticks out where the surface
rises.
Two other soil classes can readily be applied into
this system, but can not be included on a map at
such a coarse scale. These are Gleysols and Fluvic
Andosols (which grade into Fluvisols, Gleysols
and Regosols).
Andosols in Iceland cover all together about
80,000 km2 and therefore make up a substantial
proportion of the Andosols in the world. The areal
extent of Brown Andosols represents an
overestimate for two reasons. One is that desert
areas /patches are common within areas dominated
by the Brown Andosols. The second is that the
land classification system used includes some
areas within this class where the soils are too
shallow to meet the criteria for Andisol/Andosol.
At this point, it is not possible to account for this
error.
The three desert soil classes dominate about
38,000 km2, (actual extent is somewhat larger for
the reason given above). They have vast potential
for carbon sequestration associated with ecosystem
restoration (Arnalds et al. 1999). No data is
available for the Leptosols yet.
National Soil Erosion
Database
Soil erosion and degradation has been a major
problem in Iceland since the arrival of man about
1100 years ago. The extent and severity of soil
erosion in Iceland has been mapped at a scale of
1:100,000, by the Agricultural Research Institute
and the Icelandic Soil Conservation Service.
Erosion processes in Iceland are extremely varied
and conventional methods designed for estimating
erosion in cultivated areas are of little use.
The erosion assessment is based on classification
of erosion forms that can be identified in the
landscape (Arnalds et al., 1997). The ARI-SCS
erosion database is made of about 18,000
polygons. Each polygon is characterized by one or
more erosion forms. Erosion severity for each of
the erosion forms was estimated on a scale from
zero to five, five being considered extremely
severe erosion (Table 2).
Soil Survey and databases in Iceland. Ólafur Arnalds
EUROPEAN SOIL BUREAU  RESEARCH REPORT NO. 6
Table 2. Overview of soil erosion in Iceland.
Erosion severity/map units
Km2
% Iceland
0 No erosion
4 148
4
1 Slight erosion
7 466
7
2 Moderate erosion
26 698
26
3 Considerable erosion
23 106
23
4 Severe erosion
11 332
11
5 Very severe erosion
6 375
6
High mountains
9 794
10
Glaciers
11 361
11
Waters
1 436
1.4
Other
1 010
1
TOTAL
102 721
$: High mountains, glaciers, waters and ‘other’ excluded.
The overall results indicate the severity of erosion
in Iceland, the scale of which is comparable only
to very degraded, arid areas of the world. The
combined total of considerable to very severe
erosion is >50% of the country when high
mountains and glaciers have been excluded. Much
of this severe erosion occurs within the deserts, but
severe erosion is also degrading large tracts of the
remaining vegetated areas (see Arnalds et al.,
1997; Arnalds, 1999b).
Soil erosion continues to be monitored and
mapped by the Icelandic SCS, in areas where it is
most severe, but now at a larger scale (1:5,000 to
1:25,000).
Vegetation Mapping
Although detailed soil maps have not been made
for Iceland, much effort has been made to make
vegetation maps. It was concluded around 1960
that vegetation maps would give more information
about Icelandic nature than would soil maps,
bearing in mind the major use of the land for
grazing. It was expected that each of the
vegetation mapping elements reveal information
on the underlying soils.
Mapping of the vegetation was conducted by the
Agricultural Research Institute but the programme
has recently been relocated at the Institute of
Natural History. Vegetation mapping has been
completed for about 2/3 of the country at a scale of
1:40,000 in the highlands and 1:25,000 in lowland
areas. Icelandic vegetation was split up into five
major categories where drainage is the most
influential factor.
%$
5.2
9.4
33.7
29.2
14.3
8.1
100
detail in a special issue of the Journal of
Agricultural Research in Iceland (Thorsteinsson,
1982). Much of this data has been digitized and the
Institute of Natural History has recently published
a new vegetation map for all of Iceland in the scale
of 1:500,000.
Outlook
A central database for Icelandic soils is being
established. The main use for soil data is related to
soil fertility for hay production. Detailed soil
research has also provided fundamental
understanding to explain why the soils are
extremely vulnerable to erosion. The national
erosion database is used for various purposes such
as land use planning, reclamation strategies, and
policy-making.
Soil science is still a young science in Iceland.
Few Icelandic scientists have higher degrees in
soil science. This is reflected in all too sparse
research efforts. The Agricultural Research
Institute has plans to increase its current research
on the formation and basic properties of Icelandic
soils.
Currently, there is no systematic monitoring of soil
fertility and quality, but plans have been made for
such activities. Mapping of soil resources will
become more important with increased emphasis
on GIS databases for land capability assessment
and land use planning in Iceland. Improved basic
understanding of soil behaviour will also become
important in the near future for maintaining soil
quality and for monitoring pollution.
These categories are divided into 14 associations
and about 100 mapping elements. Deserts are
mapped separately. The methods were described in
Soil Survey and databases in Iceland. Ólafur Arnalds
95
EUROPEAN SOIL BUREAU  RESEARCH REPORT NO. 6
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