PRIMARY PRODUCTION AND PHYTOPLANKTON IN LAKE KINNERET - A LONG-TERM RECORD (1972-1993)

The long-term (22 yr) record of primary production in Lake Kinneret, I srael, has been examined, together with chlorophyll and microscopicall y determined algal biomass, in order to discern whether there have bee n any significant changes in these parameters during this period. Duri ng the period 1972 through 1993, annual averages have ranged from 1,22 3 to 2,311 mg C m(-2) d(-1) for primary production, from 127 to 246 mg m(-2) for chlorophyll, and from 39.3 to 98.5 g m(-2) for algal wet we ight. The annual peak of these parameters was in April-May. Over 22 yr , variability in primary productivity was more closely related to chan ges in chlorophyll than to changes in algal biomass. No evidence was f ound for consistently increasing long-term trends in primary productio n, chlorophyll concentrations, or algal wet weight biomass from 1972-1 993. Although the annual and semiannual averages of algal biomass were significantly higher in the past 11 yr than those in the previous dec ade, this pattern could arise from a long-term cyclical but self-compe nsating trend. The extended record indicates that despite population g rowth and intense economic development around the lake and in its catc hment area, there has been no extreme eutrophication of Lake Kinneret from 1972 to 1993. We suggest that this relative resiliency of the Kin neret ecosystem is due to high ambient levels of alkalinity, calcium, and pH in the lake water acting to limit phosphorus availability, whic h in turn restricts the outgrowth of phytoplankton.