Whole-lake burdens and spatial distribution of cadmium in sediments of Wisconsin seepage lakes, USA

Cadmium was quantified in the surface sediments of six seepage lakes rangin g from 8 to 70 ha in surface area, 6 to 20 m in maximum depth, 5.2 to 7.0 i n mean epilimnetic pH, and 1.7 to 6.8 mg.L-1 in dissolved organic carbon. W ithin each lake, dry-weight concentrations of cadmium (range, 0.02-7.17 mu g.g(-1)) were positively correlated with volatile matter content of the sed iments, which increased with water depth. Volumetric concentrations (i.e., mass per volume of met sediment) were correlated with water depth in only o ne lake, and they more accurately represented the spatial distribution of s edimentary cadmium within the lakes. Analysis of sediment cores from two of the lakes indicated that surface sediments were enriched with cadmium. The source of cadmium and the within-lake processes controlling deposition to the sediments were presumably similar among the lakes, as demonstrated by t he strong correlation between lake area and whole-lake burdens of cadmium i n the surface sediments (range, 625-5785 g/lake). Hence, cadmium in these l akes appears to be derived largely from atmospheric deposition. When normal ized for lake area, cadmium burdens in the surface sediments ranged from 62 to 92 g.ha(-1) and were strongly correlated with dissolved organic carbon, but not with lake pH, which suggests a link between the transport of cadmi um and organic matter to the sediments.