RESPONSES OF PHYTOPLANKTON PHOTOSYNTHESIS AND PHOSPHORUS KINETICS TO RESUSPENDED SEDIMENTS IN COPPER SULFATE-TREATED PONDS

Six farm ponds (dugouts) and one lake that differ in the history of co pper sulfate (CuSO4) treatment were selected for studies of effects of sediments resuspension on phytoplankton. All sites are located within 50 km of Peace River, Alberta, and are shallow, hardwater, and eutrop hic. Effects of sediment resuspension on phytoplankton photosynthesis were assessed by changes in the photosynthesis-irradiance (P-I) curve parameters, Pmax and alpha, after addition of sediment at 2% v/v to la kewater samples; the effects on phytoplankton P-state were assessed by changes in P-32-PO4 turnover time. Copper concentrations in sediments of Gour no. 4, the dugout that had received the largest dosage of CuS O4, were 60-times greater than untreated sites but were only 1.5 to 3- times greater at the other treated sites. Changes of Pmax and alpha we re not correlated with Cu concentrations in the sediments. Instead, th e prevailing P-state in lakewater could better explain the observed tr ends in Pmax after sediment addition. Pmax values decreased at sites w here phytoplankton were P-limited (P-32-PO4 turnover time <63 min) and increased at more P-sufficient sites (P-32-PO4 turnover time >63 min) . Stimulation of Pmax and increase in P-32-PO4 turnover time were posi tively correlated. With the exception of Gour no. 4, values of alpha i ncreased in all treatments. Similar changes in Pmax and alpha in respo nse to sediment addition occurred in laboratory experiments with P-suf ficient cultures of Anabaena flos-aquae. We suggest that, with the exc eption of grossly Cu-polluted sediments, resuspension of sediments in waters previously treated with CuSO4 will enhance phytoplankton photos ynthesis by increasing P availability, and possibly by supplying Cu at trace metal levels.