LONG-TERM EFFECTS OF LOW CADMIUM CONCENTRATIONS ON A NATURAL PHYTOPLANKTON COMMUNITY

Experimental additions of cadmium (Cd) raised concentrations of Cd in the epilimnion of Lake 382 from background levels (0.0016 mu g . L(-1) ) to averages as high as 0.185 mu g . L(-1) for 150 days from 1987 to 1993. The effects on the algal community were assessed on the basis of 9 years of premanipulation data and 7 years of experimental data on p hytoplankton population, phytoplankton photosynthesis, and epilimnetic chemistry. In addition, trends in the Lake 382 data were compared wit h those from two reference lakes over the full 16-year period. Cd addi tions to Lake 382 had no significant effects on the phytoplankton comm unity. Phytoplankton biomass was relatively stable, and small changes were related to nutrient inputs. Species diversity and community size structure were not affected. Species described in the literature as be ing sensitive to Cd did not respond significantly in Lake 382. Cd addi tions did not significantly affect phytoplankton photosynthesis. Chang es in photosynthesis were related to nutrient inputs and phytoplankton biomass.