Soil Survey and Databases in Iceland lafur 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 (19
  61). The first comprehensive map of of Icelandic soils was printed in 1959 at a scale of 1:750,000 (Nygard and Johanesson 19
  59). Other soil survey efforts were localized and this map together with Johannessons monograph on Icelandic soils (19
  60) 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 1:500,0
  00. Soil Mapping in the Past The pioneer work by Johannesson (19
  60) 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 (19
  60). The monograph was reprinted in Icelandic by the Agricultural Research Institute in 19
  88. The underlying basis for Johannessons and Nygards work was the US soil classification system (Baldwin et al., 19
  38). 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 Johanessons 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; 19
  68). Two Ph.D. dissertations added considerable knowledge on the basic characteristics of Icelandic soils in the eighties by lafsson (19
  74) and Gumundsson (19
  78). 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, 19
  96). Several attempts have been made to map soils in localized areas (e.g. Helgason and Gudbergsson, 1977; Gudbergsson and Olafsson, 19
  78), drawing much from the basis Johannesson provided. Gudbergsson (19
  82) made an outline for the classification of wetland soils (Histosols). 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., 19
  92). 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; 19
  90) and Gudmundsson (19
  91) 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, 19
  98) rather than Histosol classification (Arnalds et al., 19
  99). 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, 19
  98) 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. This can also be judged as a benefit, demonstrating the dominating influence of andic soil properties of Icelandic soils. Applying the FAO soil classification (FAO, 19
  98) 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 (19
  94) found that the FAO legend
  88) provided a good framework 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, 19
  94) does not fully correlate with the FAO World Reference Base (FAO 19
  98) 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 1:500,0
  00. 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., 19
  87. Soil descriptions generally follow US methods (eg., USDA-NRCS 19
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 Icelands 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.
  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. 19
  99). 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., 19
  97). 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
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 1:25,0
  00). 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. These categories are divided into 14 associations and about 100 mapping elements. Deserts are mapped separately. The methods were described in detail in a special issue of the Journal of Agricultural Research in Iceland (Thorsteinsson, 19
  82). Much of this data has been digitized and the Institute of Natural History has rece



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