Planktonic blue‐green algae: Production, sedimentation, and decomposition in Lake Mendota, Wisconsin

Abstract

During two annual phytoplankton cycles (1976, 1977), growth, primary production, and sedimentation were measured in Lake Mendota. Blue‐green algal blooms developed after lake stratification in a succession of dominant genera. Aphanizomenon and Anabaena normally dominated early populations with Microcystis becoming more important by midsummer. Periodic declines in blue‐green algal standing crop could be accounted for by a combination of epilimnetic decomposition and sedimentation. For Aphanizomenon and Anabaena, decomposition appeared to be primarily important, whereas sedimentation accounted for more of the decline of Microcystis. Estimates for annual sediment accumulation obtained by correcting the observed sedimentation rates for resuspension agreed fairly well with values calculated from coring data. For the period of blue‐green algal dominance, about 57–67% of the organic carbon was lost from particles during sedimentation due to decomposition. Further decomposition occurred at the sediment surface so that only about 11% of the original organic material was more or less permanently buried. Amounts of blue‐green algal volume, particulate chlorophyll, and particulate phosphorus measured in the traps also indicated that significant decomposition had occurred during sedimentation.