Assessment of the spatial distributions of total- and methyl-mercury and their relationship to sediment geochemistry from a whole-lake perspective
Résumé
The aim of this study was to determine the spatial variability for total- and methylmercury in surface sediments (0-2 cm) across a single whole-lake basin, and to relate this variability to the sediment's geochemical composition. 83 surface sediment samples from Stor-Strömsjön - a lake with multiple sub-basins located in northern Sweden - were analyzed for geochemical composition as well as total-mercury (total-Hg) and methylmercury (methyl-Hg; 35 samples) concentrations. Our results indicate that variations in fine-grained mineral matter (36%) and organic matter (34%) explain an equal amount of the total-Hg variation, but that their relative importance varies between different parts of the lake. Total-Hg concentrations were similar in locations controlled by organic matter or fine-grained mineral matter (average 109 ng g␣1); however, total-Hg inventories (mass per unit area) were significantly higher in the latter (35 and 53 mg m␣2, respectively). Methyl-Hg concentrations are largely (55% of variance) controlled by water depth and sulfur concentration, which supports the importance of within lake methylation reported from other studies. Both for concentrations and inventories the spatial distribution for methyl-Hg in surface sediments is patchy, and interestingly the highest methyl-Hg inventory (1.4 mg m␣2) was found in a shallow location with coarse-grained minerogenic sediment (very low organic matter). A large spatial variability, even within a single lake, is something that needs to be recognized, e.g., when studying processes affecting mercury cycling, mercury loadings and when using lake sediments to reconstruct historic mercury deposition.
Domaines
Géologie appliquée
Origine : Fichiers produits par l'(les) auteur(s)
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