A bioassay to assess the potential effects of sediment resuspension on phytoplankton community composition

A laboratory assay (SAGA or Sediment Ala;al Growth Assay) was developed to assess the potential impact of sediment resuspension on the structure of ph ytoplankton communities, and to evaluate the effectiveness of various sedim ent treatments in decreasing the abundance of blue-green algae in the event of sediment resuspension during storms. In assays with sediment from eutro phic Akanoi Bay, Lake Biwa, Japan, 7-11 species of phytoplankton seeded fro m the sediments grew during the 3-week assay indicating that sediment resus pension has the potential to increase both phytoplankton biomass and specie s diversity. Treatment of sediments with Ca(NO3)(2) substantially decreased phytoplankton biomass (measured as chlorophyll concentration) in assays wi th sediments from Akanoi Bay and the North Basin of Lake Biwa. Further, amo ng various oxidation treatments of sediments, Ca(NO3)(2) was most effective in decreasing or preventing filamentous blue-green algal growth in N- and P-replete media. In contrast, when sediments were added to P-limited phytop lankton dominated by green algae and diatoms, no growth of blue-green algae occurred regardless of sediment treatment.