Variations of soil profile characteristics due to varying time spans since ice retreat in the inner Nordfjord, western Norway

摘要

In the Erdalen and B?dalen drainage basins located in the inner Nordfjordin western Norway the soils were formed after deglaciation. The climate inthe uppermost valley areas is sub-arctic oceanic, and the lithology consistsof Precambrian granitic orthogneisses on which Leptosols and Regosols are themost common soils. The Little Ice Age glacier advance affected parts of thevalleys with the maximum glacier extent around AD 1750. In this study fivesites on moraine and colluvium materials were selected to examine main soilproperties, grain size distribution, soil organic carbon and pH to assess ifsoil profile characteristics and patterns of fallout radionuclides (FRNs) andenvironmental radionuclides (ERNs) are affected by different stages of iceretreat. The Leptosols on the moraines are shallow, poorly developed andvegetated with moss and small birches. The two selected profiles showdifferent radionuclide activities and grain size distribution. The sampledsoils on the colluviums outside the LIA glacier limit became ice-free duringthe Preboral. The Regosols present better-developed profiles, thicker organichorizons and are fully covered by grasses. Activity of 137Cs and210Pb_ex concentrate at the topsoil and decrease sharply withdepth. The grain size distribution of these soils also reflects thedifference in geomorphic processes that have affected the colluvium sites.Significantly lower mass activities of FRNs were found in soils on themoraines than on colluviums. Variations of ERN activities in the valleys wererelated to characteristics of soil mineralogical composition. These resultsindicate differences in soil development that are consistent with the age ofice retreat. In addition, the pattern distribution of 137Cs and210Pb_ex activities differs in the soils related to the LIAglacier limits in the drainage basins.