A whole-lake basin analysis of the spatial distribution of total- and methylmercury in relation to the sediment matrix using WD-XRF and FT-IRS

• The aim of this study was to try and identify some of the factors controlling the spatial distributions of total- and methyl-Hg across a single whole-lake basin. In order to achieve this we analyzed the geochemical composition of 83 surface sediment samples from the lake Stor-Strömsjön using WD-XRF and FT-IRS. Our results show that in the north-western basin (i.e., the main recipient of the dominant inlet) total-Hg distribution is controlled by fine-grained mineral matter, while the eastern basin (which lacks major inlets) the main controlling factor is organic matter. There is only a weak correlations between methyl-Hg concentrations and either total-Hg (r2=0.12) or organic matter (r2=0.15) concentrations. Instead the distribution of methyl-Hg is largely controlled by water depth and sulfur (59 %). The spatial patterns for total-Hg concentrations vs. inventories (mass per unit area) are rather different. Even if total-Hg concentrations are about the same in locations controlled by organic matter and fine-grained mineral matter, the total-Hg inventories are much higher in the latter. For methyl-Hg the spatial distribution is patchy both for concentrations and inventories, and the highest methyl-Hg inventory was found in a shallow location with coarse-grained minerogenic sediment. The large variations in the controlling factors, even within a single whole-lake basin, suggest that lake type and surrounding catchment have an effect on the behavior of Hg. This needs to be recognized both when studying Hg loading on ecosystems, and when using lake sediments to reconstruct atmospheric Hg deposition.

Ämnesord

NATURVETENSKAP  -- Geovetenskap och miljövetenskap -- Miljövetenskap (hsv//swe)

NATURAL SCIENCES  -- Earth and Related Environmental Sciences -- Environmental Sciences (hsv//eng)

Nyckelord

Mercury

Methylmercury

Lake sediment

Spatial distribution

Sediment composition

WD-XRF

FT-IRS

Environmental chemistry

Miljökemi

Environmental Science

miljövetenskap

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