PLANKTON AND WATER CHEMISTRY IN LAKE NJUPFATET BEFORE AND AFTER LIMING

Moderately acidified Lake Njupfatet was studied during 2 consecutive y ears, before and after liming (calcite), and compared with correspondi ng data from six reference lakes. After liming, the concentration of t otal phosphorus in the lake water decreased by some 30% as did the con centrations of particulate carbon, particulate nitrogen, particulate p hosphorus, and phytoplankton biomass. Because of significant increases of inorganic nitrogen and dissolved organic carbon, the concentration s of total nitrogen and total organic carbon remained unchanged after liming. Before liming, there was a close balance between phosphorus an d nitrogen limitation of phytoplankton growth, but we conclude that af ter liming the reduced concentrations of phosphorus induced phosphorus limitation of phytoplankton growth. Liming changed the phytoplankton community structure, most importantly causing the complete loss of the dominant species before liming, the cyanophyte Merismopedia tenuissim a. The decrease in total biomass of phytoplankton was not compensated for by a corresponding increase in other species. After liming total b iomasses of bacterioplankton and protozoan zooplankton did not change, while total biomass of metazoan zooplankton increased; hence, total p lankton community carbon remained unchanged. Phytoplankton, protozoan, and metazoan zooplankton diversity (Shannon index) did not change aft er liming. Zooplankton biomass remained heavily dominated by calanoid copepods, typical of acidified lakes.