Abstract
Results from the biogeochemical mapping (roots of aquatic plants and Fontinalis antipyretica) conducted by the Geological Survey of Sweden (SGU) reflects the metal load of surface waters draining acid sulphate (AS) soils in Sweden. In this study, results from the biogeochemical, soil geochemical and Quaternary mapping programmes at SGU were used to investigate the impact of fine-grained deposits hosting AS soils on stream water trace element chemistry in two separate areas. In the area around Lake Mälaren, postglacial sediments contain the highest levels of most trace elements studied. Owing to the low pH of AS soils and subsequent leaching, levels of nickel (Ni), cobalt (Co), copper (Cu), sulphur (S), yttrium (Y), uranium (U), tungsten (W), and molybdenum (Mo) were significantly elevated in aquatic roots. Levels were lower in the Skellefteå area, which may be explained by lower concentrations in source deposits. Concentrations of arsenic (As) and lead (Pb) were normal or impoverished in biogeochemical samples from postglacial, finegrained sediment areas. Maps based on ratios (Ni:Pb or Y:Pb) in biogeochemical samples can, together with results from Quaternary mapping, be used to predict areas with AS soils in Sweden.;
Highlights
Introduction acid sulphate soilsThe exact extent of such soils has not been mapped in Sweden, but has been estimated from the extent of gyttja-containing soils in the soil map of the country, scale 1: 2 000 000 (Ekström 1953).There are two main processes whereby sulphide-bearing, fine-grained sediments in Fennoscandia are exposed to atmospheric oxygen (Åström 1996)
As was evident from the comparison of median concentrations in this study (Table 1). This is assumed to be explained by precipitation of Mn hydroxides onto the plants, a hypothesis supported by concurrently elevated levels of Co, Ba and Zn
It is noteworthy that water moss had the lowest loss on ignition
Summary
Results from the biogeochemical mapping (roots of aquatic plants and Fontinalis antipyretica) conducted by the Geological Survey of Sweden (SGU) reflects the metal load of surface waters draining acid sulphate (AS) soils in Sweden. Results from the biogeochemical, soil geochemical and Quaternary mapping programmes at SGU were used to investigate the impact of fine-grained deposits hosting AS soils on stream water trace element chemistry in two separate areas. Fine-grained sediments of marine/lacustrine origin occur below the highest shoreline in Sweden and Finland Some of these sediments contain significant amounts of iron sulphides, and develop into acid sulphate (AS) soils on oxidation. Most studies have focused on case studies from limited areas, e.g. Andersson et al (1988), Manngård (1997), Öborn and Andersson (1999) These studies show that fine-grained sulphide-containing soils in Sweden cause elevated levels of several elements, e.g. As, Cd (cadmium), Co, Cu and Ni, in minor streams. Quaternary and soil geochemical mapping programmes have been used to classify the terrestrial sediments and investigate their general trace element geochemistry
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