DOES SEDIMENT RESUSPENSION HAVE PERSISTENT EFFECTS ON PHYTOPLANKTON -EXPERIMENTAL STUDIES IN 3 SHALLOW LAKES

1. The persistence of effects of sediment resuspension on chlorophyll a, phytoplankton production and plant nutrients was examined by artifi cially resuspending sediment in enclosures in three shallow lakes and monitoring concentrations for 4-8 days. Realism was assessed by relati ng initial suspended solids concentrations to those observed during na tural wind events. 2. Positive effects on the phytoplankton, persistin g for at least 4-6 days were detected in eight of the nine experiments , and similar effects on nutrient concentrations were also common, alt hough suspended solids had normally returned to control levels within 24 h 3. The phytoplankton during the periods of persistence was normal ly dominated by planktonic rather than benthic/meroplanktonic genera. 4. Several of the positive responses appeared to be associated with re lief of nitrogen deficiency in the algae. 5. Persistent effects from p revious resuspension events may cause baseline concentrations of phyto plankton and nutrients in shallow lakes to be overestimated and the ef fects of resuspension on phytoplankton and nutrients to be underestima ted.