Lake Kinneret: planktonic populations during seasons of high and low phosphorus availability

Summary

Lake Kinneret (Lake Tiberias) in Northern Israel is a warm monomictic, eutrophic lake having extensive phytoplankton blooms annually after the onset of homothermy in January. The main bloom-forming algae are generally Pyrrhophyta (Peridinium cinctum fa. westii) although occasionally Cyanophyta (Microcystis spp.) have predominated. Among zooplankton, maximum numbers of Copepoda, Cladocera and Rotifera are observed at this season and phosphorus appears to be abundant. However, by late summer a shortage of epilimnic phosphorus may be limiting algal growth. By then the main phytoplankton biomass consists of Chlorophyta and Cyanophyta and zooplankton numbers are minimal.

Phosphorus availability was assessed by several methods: 1. relative phosphatase activities with p-nitrophenyl phosphate and endogenous substrates, 2. hot water extraction of orthophosphate from plankton, and 3. nutrient enrichnent experiments. Despite seasonal changes in planktonic populations, alkaline phosphatase activities were always predominantly associated with small organisms, presumably algae and bacteria.