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a Dep. of Natural Resources and Environmental Sciences, Univ. of Illinois, 1102 S. Goodwin Ave., Urbana, IL 61801 USA
b Dep. of Geography, Univ. of Illinois, 607 S. Matthews St., Urbana, IL 61801 USA
c Dep. of Geosciences, Univ. of Arkansas, Fayetteville, AR USA
d Dep. of Physical Geography, Univ. of Stockholm, Stockholm, Sweden
rdarmody{at}uiuc.edu
| ABSTRACT |
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Abbreviations: MAST, mean annual soil temperatures y.b.p., years before present
| INTRODUCTION |
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mark soils. They include common arctic R
mark and arctic Hamada R
mark if they had a stone pavement (Kubiëna, 1953). Soils consisting of a fibrous O horizon of roots and stems over loose rocks essentially devoid of fine particles were called Ranker soils (Kubiëna, 1970). Tamm (1932) described the dominant regional soils in northern Scandinavia to be Podzols on acid materials and Braun waldboden (brown forest soils) on less sandy sites. Tedrow (1977) produced a generalized regional soil map showing "Lithosols" in the mountainous area of Kärkevagge and to the east "podzolized and organic soils, undifferentiated." He described soils in the region as more alpine than arctic with shallow profiles on youthful glacial landscapes. A more recent country-wide map shows the research area mapped as "Entisols, Histosols," with the mapping unit to the east labeled as "Spodosols with E <6 cm" (Olsson and Troedsson, 1990). Arctic soils are dominated by cryogenic processes and display relatively limited chemical alteration (Rieger, 1974; Tedrow et al., 1958; Höfle et al., 1998) while alpine soils are quite variable because of extremes in topography and microclimate (Retzer, 1965; Burns, 1990; Darmody and Thorn, 1997). In both situations, the soils may be relatively young and are often poorly developed because of recent glaciation, cold temperatures, and erosion, particularly in alpine areas (Tedrow, 1977). Recent modifications to Soil Taxonomy (Soil Survey Staff, 1998) altered the classification of soils in cold regions, making permafrost a new criterion to separate soils at the order level. This adds an additional challenge to the classification of arctic-alpine soils given the complexity of soil climate and lack of climatic data. The possible presence of permafrost in our research area is also of interest because global climate change models predict significant warming at high latitudes (Henderson-Sellers, 1994). Melting of permafrost could have an important impact both locally on land use and globally because of methane release.
The objectives of this research therefore, were to: (i) provide data on the morphology, chemistry, and physical properties of the soils of the Kärkevagge watershed; (ii) attempt a preliminary determination of local permafrost distribution; (iii) develop soil-landscape models; and (iv) assign taxonomic classifications to the soils and test the applicability of the new Gelisol soil order in this arctic-alpine environment.
| Materials and methods |
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kko, which rises to an elevation of 1590 m, and on the east by the gently sloping ridge of Mt. Kärketj
rro, which rises to 1400 m. The floor of Kärkevagge is at approximately 600 m at its mouth. It rises to an elevation of 814 m at its head, which is occupied by Lake Rissajaure.
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Below the cliffs are colluvial slopes, which on the west side are soliflucted in the lower portions. In addition to the numerous boulders, the valley floor is rich in fluvial- and glacial-derived land forms. These include slush avalanche fans, a small flood plain along the main valley stream, moraines, eskers, and kame-like features.
Regional deglaciation in the Kärkevagge area occurred about 9000 to 8500 14C years before present (y.b.p.) (Karlén, 1979). The current climate of the region is transitional between the maritime climate along the coast of Norway 80 km to the west and the continental climate to the east. Mean annual air temperature is about -2°C and precipitation averages 1000 mm (Eriksson, 1982). Approximately 50% of the precipitation occurs as snow (
ngström, 1974). Snow cover in the region lasts about 240 d per year and snow depth maximizes at about 1.5 m in MarchApril. Snow cover thickness and duration is locally highly variable, in sheltered positions at high elevations and in areas of deep accumulation within the valley there is nearly continuous snow cover. Because of the prevailing winds, snow tends to accumulate on the west side of the valley. This keeps the soils moist and accounts for the development of the cirques and the solifluction terraces on that side of the valley. Given the cold air temperatures, permafrost could be expected locally. Regionally, active layer thickness above permafrost has been estimated to be 200 to 400 cm at elevations above 1200 m, with sporadic permafrost at lower elevations (King, 1983).
Vegetation in the valley is distributed in a strongly zonal fashion, both on a landform basis and with respect to elevation (Rapp, 1960; Klintenberg, 1995). Subalpine birch (Betula pubescens Ehrh. var. tortuosa Ledeb.) forest extends to about 550 m elevation. Between 550 and 770 m, what is known locally as a "dwarf-shrub heath" dominated by Empetrum hermaphroditum Hagerup, Betula nana L., and Vaccinium myrtillus L., occupies the drier sites on glacial till and glaciofluvial outwash gravels, and dwarf willow (Salix glauca L.) occupies snow-accumulation depressions. Wind-eroded exposed ridges in this zone support a "wind heath" plant community, predominately of stunted Empetrum. From about 700 to 850 m, the vegetation is predominantly grass meadow including forbs [Dryas octopetala L., Cassiope tetragona (L.) D. Don, Phyllodoce coerulea (L.) Bab., Juncus trifidus L.] and patches of dwarf willow shrubs (Salix reticulata L.) covering slopes of colluvium, till, and alluvium. On the wetter, west side of the valley the soliflucted slopes are covered by a meadow of grasses and forbs, with dwarf willows (Salix sp.) and ferns in the wetter margins of the solifluction terraces. Above about 850 m, there are steep slopes and sheer unvegetated rock valley walls leading up to mountain ridges with dwarf shrubs and herbs (Salix herbacea L., Salix polaris L., Ranunculus glacialis L.) in more protected areas and cryptogams on the exposed surfaces.
Field Methods
Thirty-seven sites were selected to determine soil characteristics in the study area (Fig. 2). Sites were chosen to give a representative selection of the variability in landform, plant community, elevation, and aspect. Most of the sites were initially selected on the basis of vegetation communities because our working hypothesis suggested they were related. Soils were examined and described in the field by standard techniques (Soil Survey Staff, 1993). Presence of reduced iron was detected with
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'-dipyridyl (Childs, 1981). Soil pH in the field was measured on a distilled water-soil paste with a solid state electrode. Mineral soils were described in hand-excavated pits at 35 sites. Bulk density samples were retrieved, coarse fragments permitting, with a coring device (Blake and Hartge, 1986) from soil pits at selected locations. Organic soils were described at two locations by means of peat samplers. A total of 215 soil samples were retrieved. Air temperature was recorded in the center of the valley at 760 m a.s.l. Soil temperature loggers were buried at 10- and/or 50-cm depths in 11 selected sites. These recorded temperatures four times daily nominally for 1 yr in 19951996 (Thorn et al., 1999). Field soil temperature data were used to estimate the depth at which 0°C was not exceeded, which served as a proxy for depth to permafrost (Jury et al., 1991).
Laboratory Methods
Soil samples were collected by horizon from excavations for later analyses. The soils were oven-dried in the lab and passed through a nest of sieves to determine gravel content. The <2-mm fraction was saved for further analysis. Particle-size was determined by sieving for sands and by hydrometer for silt and clay (Gee and Bauder, 1986). A 1:1 soil to distilled water suspension was used to determine pH (McLean, 1982). Inductively coupled plasma spectroscopy was used to determine composition of 1:10 soil:Mehlich 3 extracts (Mehlich, 1984). Mehlich 3 extraction has been shown to correlate well with exchangeable cations and Fe and with oxalate extractable Al (Eckert and Watson, 1996; Fernández-Marcos et al., 1998). Cation exchange capacity was estimated by summation of Mehlich 3 extracted cations; to calculate base saturation, exchangeable H was estimated from SMP buffer pH at pH 7.8 (McLean, 1982). Total C and S contents were determined with Leco C and S analyzers; as there were no carbonates in the soil, total C was attributed to organic matter. Conformation of spodic material chemistry was done on selected horizons by 2-amino-2-methyl propanol and KOH extractions (Holmgren and Holzhey, 1984; Holmgren and Kimble, 1984). Mineralogy on the <2-µm fraction was determined on selected samples by x-ray diffraction (Hughes et al., 1994), semi-quantitative estimates of mineral abundance were based on diffractogram peak heights (Darmody et al., 1987; Klages and Hopper, 1982).
| Results and discussion |
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Soils in the main valley are developed on colluvium and alluvium (Table 2) and show evidence of multiple buried A, O, or C horizons, often too thin to sample individually. These are due to instability of the steep valley side slopes and to alluvial processes in the valley floor. The east-facing side of the valley is particularly unstable because of active solifluction. That side of the valley is wetter due to accumulation of snow in the lee of the main ridge.
Organic soils are relatively rare in the valley, perhaps <10% of the watershed, and are confined to bedrock depressions at the lower elevations. The organic soils are made up of sapric and hemic materials derived from sedges and sphagnum mosses. They range in thickness from about 40 to 60 cm and are underlain by bedrock with an occasional overlying thin sandy Cg horizon. Field evidence indicates that these soils have formed in what were shallow ponds in bedrock depressions. Organic materials accumulated in the ponds in an environment with little input of mineral sediments. The bedrock depressions presumably were produced by the main valley glacier that scoured the granite at the mouth of Kärkevagge.
Soil Morphology
The mineral soils were all coarse-textured with generally <5% clay (Table 3)
. Coarse fragments ranged from 5 to 68% by volume and reflect the soil parent materials. On the colluvial slopes, they were primarily channers derived from the local mica schist. In outwash deposits, they were rounded, and at sites near the main valley, they included some granite. Except for the coarse fragments, it was easy to dig in the soils because of the generally very friable consistence and low bulk density, which averaged 1.16 Mg m-3 and ranged from 0.33 to 1.63 Mg m-3. Vesicular pores and very weak platy or subangular blocky structure were common in the upper horizons. Soil color closely reflected the parent materials, typically being shades of gray. The only higher-chroma, bright colors were found at low elevations in Bhs horizons.
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There was little profile development and the soils had multiple buried horizons at most sites within the valley proper (Table 3). The soils on the flood plain and stream terraces (M1-2, W1-4), solifluction terraces (SM 1-8), and colluvial fans (M3, DH1-3), typically displayed a series of thin A or O and C horizons. On more stable sites in the valley at intermediate elevations, horizonation was poorly expressed and reflected the immediate local conditions. The soil on the esker (WH1) for example, has essentially no A horizon and only a thin Bw horizon and no buried horizons. It is on a narrow ridge, protected from deposition and water erosion but is very drouthy due to its coarse texture. It has a surface pavement of coarse fragments because of wind erosion as evidenced by deflation zones around larger boulders. Similarly, only a thin Bw horizon has developed at site MA1 due presumably to cold temperatures and a persistent snow cover. In contrast, a thick mollic epipedon has developed at DH4, despite the 78% slope. This is attributed to an overhanging cliff that protects it from erosion and to the influence of leachate from marble bedrock that gives the soil its high pH and Ca content (Fig. 2, Table 4) .
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Calcium was the dominant extractable base in all the soils followed by Mg, K, then Na. Extractable Fe and Al contents were highest in the Bhs horizons in the birch (B1-3) and heath (H1-3) sites, Al was also elevated at the higher, more stable sites (A1-5) (Table 4). Soil pH for most of the sites was generally low, ranging from about 3.5 to 5.5. In the more stable sites, pH and extractable Ca decreased with depth, but where fluvial or cryoturbation processes were active there were no consistent depth trends. The birch (B1-3), Empetrum heath, and alpine (A1-5) sites (H1-5) tended to have low pH because of production of organic acids and to acidic parent materials, but there were sites with elevated soil pH. On the east side of the valley, for example, sites DH3 and 4 show influence of the nearby marble bedrock and have pH ranging from 6.3 to 7.8, although there were no free carbonates. Dryas heath plant communities are typically associated with soils high in Ca (Rapp, 1960) and this relationship holds in Kärkevagge. Extractable Ca in surface soils associated with Dryas (DH1-4) ranged from 9.5 to 24.9 cmol kg-1. In contrast, soils developed on surfaces above the marble (A1-3) had surface soil extractable Ca ranging from 0.4 to 1.0 cmol kg-1.
Pyrite weathering appears to be important in Kärkevagge (Dixon et al., 1995; Darmody et al., 2000). At two locations, an odor of H2S was noticed, which has been shown to be related to total S content in soils (Darmody and Fanning, 1977). The soils where we detected H2S were relatively rich in total S. The Bog sites had 1.2 to 2.0% total S in the soil. Site W4, a mineral soil with 0.7 to 3.8% total C, had 0.02 to 0.11% total S. This contrasts with the total S content of an excessively drained site such as WH1 that had 0.00 to 0.03% total S, or a poorly drained site, M1, without H2S odor that had 0.01 to 0.06% total S, yet more total C (0.6 to 6.6%) (Table 4).
Soil Mineralogy
Soil mineralogy closely reflects the local geology (Allen et al., 2000), muscovite derived from the mica schist dominated (60 to 95%). This places the soils in the micaceous mineralogy class (Soil Survey Staff, 1999). There was also detectable chlorite (515%) in the <2-µm fraction. A mixed layer mineral was identified in the alpine sites at up to 35% of the <2-µm fraction. It was also identified at depth in colluvial soils that apparently received material from the higher alpine areas. There were no other trends in mineralogy.
Age of Soil Landscapes
Regional deglaciation constrains the maximum land surface age to about 9000 yr (Karlén, 1979), although there is evidence that the highest elevations may be older, preserved under cold-based ice (André, 1995). There is an increasing body of observations indicating the existence of widespread frozen bed conditions in large parts of northern Fennoscandia based on stratigraphic (Kleman et al., 1992) and landform (Kleman and Stroeven, 1997; Kleman and Hättestrand, 1999) evidence. Despite the potential age, soil profile development is minimal at the alpine sites. A sparse vegetation cover, low temperatures, and cryopedoturbation would inhibit soil profile development at these high elevations. However, soils at the alpine sites have a higher content of secondary minerals, which indicates that weathering is more advanced at the alpine sites than elsewhere in the valley (Allen et al., 2000).
On the basis of moraine sequences, apparently there was an active glacier confined to Kärkevagge when the larger valley at the mouth was at least partially ice-free. Therefore, land surface age presumably increases out toward the main valley, away from active erosion and deposition on the slopes and flood plains. This chronosequence is reflected in soil profile development. The best developed soil profiles (B1-3, H1-3) with well-expressed albic E and Bhs horizons are found on large glaciofluvial land forms at the mouth of the valley. These soils are Spodosols which can develop to a recognizable stage in the region within 1000 yr on stable surfaces (Ellis, 1980a). Within the valley, the landscapes are unstable and there is minimal soil profile development. Consequently, the soils on side slopes, flood plains, and terraces have multiple buried surfaces and no or only very weak B horizons. Buried A horizons at site M3 on a colluvial slope were radiocarbon-dated (y.b.p.) to; 130 at 8 cm, 320 at 13 cm, 390 at 15 cm, 1100 at 20 cm, and 1280 at 22 cm which, absent of surface contamination, may indicate that erosion rates are increasing (P. Schlyter, 1998, unpublished data).
Soil Climatic and Taxonomic Classification
Soil Climate
Because of the proximity of the North Atlantic Ocean (Fig. 1), air and soil temperatures recorded were not as cold as might be expected for this high latitude (Table 5)
. In addition, there was not much seasonal range in the temperatures, again due primarily to the moderating influence of the ocean, which does not freeze along the nearby Norwegian coast.
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2 yr in succession (Soil Survey Staff, 1999). It could be expected in soils with MAST <0°C, which our data shows to be above about 1200 m elevation (Fig. 3), the same as regional permafrost estimates (King, 1983). Based on our temperature data, sites A1, A4, A5, and H4 have MAST <0°C and may have permafrost at some depth below the seasonal active layer. Given the limited data, our calculations of depth to permafrost are tentative (Jury et al., 1991). Estimated permafrost depths ranged from 284 cm at site H4 to 154 cm at site A5 (Table 5), similar to independently predicted depths (King, 1983). This allows only site A5 to be classified as a Gelisol because the depth to permafrost is less than 200 cm (Soil Survey Staff, 1998, 1999). Soils with permafrost deeper than 200 cm are excluded from Gelisols even if their MAST is <0°C. The classification of soil temperature has recently changed. In the 7th edition of the Keys to Soil Taxonomy (Soil Survey Staff, 1996), soils with MAST <0°C were placed into the pergelic temperature regime. That regime is no longer recognized, and the soils are now placed in the cryic temperature regime (Soil Survey Staff, 1998, 1999) if they have no permafrost. Soils with permafrost do not now have a defined temperature regime in Soil Taxonomy. The depth to permafrost is unspecified, but is presumably within 200 cm of the surface and implies that the soil is a Gelisol (R. Engel, 1999, personal communication). Soil temperature classes have also changed; hypergelic, pergelic, and subgelic classes have been added for Gelisols in the 2nd edition of Soil Taxonomy (Soil Survey Staff, 1999). Site A5 is in the subgelic temperature class because the estimated depth to permafrost is <200 cm and it is a Gelisol (Table 5). All of the other soils would be in the frigid or isofrigid temperature class, depending on the difference between winter and summer temperatures. There has been a change in the iso prefix. Formerly it referred to soils with a seasonal range of <5°C (Soil Survey Staff, 1996), whereas the limiting range now is <6°C (Soil Survey Staff, 1999). Our recorded seasonal soil temperature range was from 2.1 to 12.1°C, with the majority of soils classed as isofrigid. The isofrigid soils presumably have a deep snow cover, (B1, DH4, MA1), or a thick O horizon (H1 and H4), that limits cooling in the winter and/or heating in the summer. While our temperature data are limited and our interpretations therefore are subject to uncertainty, the years we monitored were not particularly unusual (Thorn et al., 1999).
Soil Classification
Classification of soils in cold regions has recently changed (Soil Survey Staff, 1998, 1999). A new soil order, Gelisols, was introduced on the basis of the presence of permafrost within 200 cm. As discussed above, only site A5 tentatively meets this limitation and is classified as a subgelic Lithic Haploturbel (Table 6)
. Soil temperature regime definitions were also modified as previously discussed. We interpolated the soil temperature data to assign temperature families for all the other soils as either frigid or isofrigid (Table 5).
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The soils in the valley bottom on the flood plains and stream terraces, and on the valley side slopes on alluvialcolluvial fans and solifluction terraces, had characteristics of Cryofluvents such as an irregular decrease with depth of organic C (Soil Survey Staff, 1999). However, there are restrictions on the Cryofluvent great group, slopes must be <25% and gelic materials are not allowed. In addition, soils with aquic conditions dominating classify out before Fluvents. Aquic conditions were difficult to assess as soil colors are almost uniformly gray throughout the area (Table 3), and because of the late-melting snow, ground water was observed in many locations (Table 1). Soils that showed a positive response to
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'-dipyridyl (M1, M2, W4), were all on the flood plain and classified as Typic Cryaquents. Better drained soils on stream terraces were classified as Typic (W1, W2) or Oxyaquic (W3) Cryofluvents. Soils developed on fans with slopes <25% include M3, a Typic Cryofluvent. Where slopes were >25%, the soils were classified as Typic Cryorthents (DH2, DH3, MA1), even though they were essentially similar to those on lesser slopes.
Solifluction is a cryogenic process common in periglacial regions. Soils on solifluction terraces (SM1-8) showed evidence of cryoturbation and contained gelic materials and were classified as Cryorthents. Most of the field and lab pH data from these soils indicates that they tend to be near the border between acid and nonacid, on lower slopes and on the east side they are less acidic. On steeper and upper slopes, they were classified into the Typic subgroup; on gentler and lower slopes, they were placed into Oxyaquic and Aquic subgroups. We estimate that the MAST is >0°C for these soils and that they are all isofrigid based on our field data and their landscape positions. Sites A2 and A3 also showed evidence of solifluction, but their estimated MAST is <0°C. Because the calculated depth to permafrost is >200 cm (Table 5) they also classify as Cryorthents, not Gelisols.
Other soils without an irregular distribution with depth of organic carbon or evidence of fluvial processes, and with essentially no soil development were also classified as Typic Cryorthents (H5, WH1). Site H5 was a thin soil developed directly on one of the weathered boulders in the valley. Site WH1 was on the crest of a gravelly esker where the harsh, dry conditions limit plant growth and soil development. On more stable, less sloping sites at higher elevations, where there were weak cambic horizons, the soils were classified as Typic (A4, A6) or Oxyaquic (A1) Dystrocryepts where the base saturation was <60% (Table 4). Where the base saturation was >60%, the soil was classified as a Typic Eutrocryept (DH1).
At the lowest elevation, on the warmer, presumably older surfaces near the mouth of the valley, the soils showed the most pedogenic development. Well-developed albic E horizons over dark-reddish brown Bhs spodic horizons presented the most contrasting and brightest soil colors in the watershed (Table 3). These soils were classified as Typic Haplocryods. They are coarse-loamy in the till under the Betula forest (B1-3). Under the Empetrum heath, they are sandy-skeletal in the thick outwash (H1-3) or sandy-skeletal over loamy (H4) on thin outwash over loamy materials. Spodosols were found at elevations up to 615 m a.s.l. This elevation is similar to estimates of the "podzol" altitudinal limit in northern Norway at 600 (L
g, 1966) to 800 m a.s.l. (Ellis, 1980b).
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| ACKNOWLEDGMENTS |
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| NOTES |
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Received for publication July 12, 1999.
| REFERENCES |
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ngström A. Sveriges klimat. (Swedish climate). (In Swedish with English summaries). Stockholm: Generalstabens Litografiska Ansyalta Forlag, 1974.
g J. Some general characteristics of the Norwegian soils. Särtryck Grundförbättring 1966;1:3-12.This article has been cited by other articles:
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R.G. Darmody, C.E. Thorn, and J.C. Dixon Pyrite-enhanced chemical weathering in Karkevagge, Swedish Lapland GSA Bulletin, November 1, 2007; 119(11-12): 1477 - 1485. [Abstract] [Full Text] [PDF] |
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C. E. Allen Physical and Chemical Characteristics of Soils Forming on Boulder Tops, Karkevagge, Sweden Soil Sci. Soc. Am. J., January 1, 2005; 69(1): 148 - 158. [Abstract] [Full Text] [PDF] |
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K. Hall, C. E. Thorn, N. Matsuoka, and A. Prick Weathering in cold regions: some thoughts and perspectives Progress in Physical Geography, December 1, 2002; 26(4): 577 - 603. [Abstract] [PDF] |
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