Cadmium was quantified in surficial sediments (uppermost 5 cm) of six lakes in north- central Wisconsin. The lakes are small (8 - 70 ha) seepage basins (no surface inlets or outlets) that spanned a broad range of pH (5.2 - 7.0), acid neutralizing capacity (ANC, -5 - 127 ueq l^-1), and dissolved organic carbon (DOC, 1.7 - 6.8 mg l^-1). A random sampling design, stratified by water depth, was used to select 50 sampling sites in each lake, where sediment samples were collected with diver-operated corers. Dry-weight concentrations of cadmium in the sediments (range 0.02 - 7.17 ug g^-1) were significantly (p < 0.001) correlated with volatile matter content (rs ranged from 0.53 - 0.93; Spearman rank order correlation) and water depth (rs ranged from 0.68 to 0.87) in all six lakes. However, when concentrations were expressed on a volumetric basis (i.e., mass per volume of wet sediment), the positive correlation between cadmium content (range 0.004 - 0.067 ug cm^-3) and water depth was significant (p = 0.05) for only one of the lakes. Whole-lake burdens of cadmium in the surficial sediment (range: 625 - 5785 g lake^-1) were strongly correlated (rs > 0.99) with lake surface area, suggesting that atmospheric deposition may be the primary source of cadmium to the lakes. Areal burdens of cadmium varied about 1.5-fold (range: 62 - 92 g ha^-1) and were strongly correlated with DOC (rs = 0.94), but not with pH, indicating that cadmium transport to the sediments may be related to organic matter.

The effect of whole-lake acidification on the bioaccumulation of cadmium by fish was studied in one of the lakes, Little Rock, which is the site of an experimental pH manipulation project. In September 1984, Little Rock Lake was separated with an impermeable curtain into a reference basin (mean pH 6.1) and a treatment basin that was acidified with sulfuric acid for 2 years to pH 5.6, 2 years to pH 5.2, and 2 years to pH 4.9. Age-1 yellow perch (Perca flavescens) were netted annually from each basin in April, after 1 year of residence in the lake, after each year of the pH-5.2 treatment (1988 and 1989) and after each year of the pH-4.9 treatment (1990 and 1991). A random sampling design, stratified by 1-cm total-length groups, was used to sample older yellow perch in April 1989, at the end of the pH-5.2 treatment, and again in April 1991, at the end of the pH-4.9 treatment. Between-basin comparisons of cadmium in whole yellow perch indicated that lake pH significantly influenced cadmium bioaccumulation by fish. After 1 year of residence in the lake, mean whole-body concentrations and burdens of cadmium in age-2 and older fish sampled in 1989 and in 1991 were less in the treatment basin than in the reference basin. The decreased bioaccumulation of cadmium by yellow perch in the acidified treatment basin may reflect increased competition between cadmium and hydrogen ions for binding sites on cell membranes of the gill surface. Estimated cadmium inventories in the yellow perch populations of Little Rock Lake in 1989 were 24 mg in the reference basin and 19 mg in the treatment basin.