Responses of Phytoplankton Photosynthesis and Phosphorus Kinetics to Resuspended Sediments in Copper Sulfate‐Treated Ponds

Abstract

AbstractSix farm ponds (dugouts) and one lake that differ in the history of copper 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 eutrophic. Effects of sediment resuspension on phytoplankton photosynthesis were assessed by changes in the photosynthesis‐irradiance (P‐I) curve parameters, Pmax and a, after addition of sediment at 2% v/v to lakewater samples; the effects on phytoplankton P‐state were assessed by changes in 32P‐PO4 turnover time. Copper concentrations in sediments of Gour no. 4, the dugout that had received the largest dosage of CuSO4, 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 a were not correlated with Cu concentrations in the sediments. Instead, the prevailing P‐state in lakewater could better explain the observed trends in Pmax after sediment addition. Pmax values decreased at sites where phytoplankton were P‐limited (32P‐PO4 turnover time <63 min) and increased at more P‐sufficient sites (32P‐PO4 turnover time >63 min). Stimulation of Pmax and increase in 32P‐PO4 turnover time were positively correlated. With the exception of Gour no. 4, values of a increased in all treatments. Similar changes in Pmax and a in response to sediment addition occurred in laboratory experiments with P‐sufficient cultures of Anabaena flos‐aquae. We suggest that, with the exception of grossly Cu‐polluted sediments, resuspension of sediments in waters previously treated with CuSO4 will enhance phytoplankton photosynthesis by increasing P availability, and possibly by supplying Cu at trace metal levels.