Does sediment resuspension have persistent effects on phytoplankton? Experimental studies in three shallow lakes

The persistence of effects of sediment resuspension on chlorophyll a, phytoplankton production and plant nutrients was examined by artificially resuspending sediment in enclosures in three shallow lakes and monitoring concentrations for 4–8 days. Realism was assessed by relating initial suspended solids concentrations to those observed during natural wind events. 2. Positive effects on the phytoplankton, persisting for at least 4–6 days were detected in eight of the nine experiments, and similar effects on nutrient concentrations were also common, although suspended solids had normally returned to control levels within 24 h 3. The phytoplankton during the periods of persistence was normally dominated by planktonic rather than benthic/meroplanktonic genera. 4. Several of the positive responses appeared to be associated with relief of nitrogen deficiency in the algae. 5. Persistent effects from previous resuspension events may cause baseline concentrations of phytoplankton and nutrients in shallow lakes to be overestimated and the effects of resuspension on phytoplankton and nutrients to be underestimated