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 ranging from 8 to 70 ha in surface area, 6 to 20 m in maximum depth, 5.2 to 7.0 in mean epilimnetic pH, and 1.7 to 6.8 mg.L-1 in dissolved organic carbon. Within 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 sediments, which increased with water depth. Volumetric concentrations (i.e., mass per volume of met sediment) were correlated with water depth in only one lake, and they more accurately represented the spatial distribution of sedimentary 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 the strong correlation between lake area and whole-lake burdens of cadmium in the surface sediments (range, 625-5785 g/lake). Hence, cadmium in these lakes appears to be derived largely from atmospheric deposition. When normalized 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 cadmium and organic matter to the sediments.