Internal phosphorus loading in a subtropical lake under extreme water level fluctuation
The water column of Lake Kinneret (LK), a deep warm-monomictic freshwater lake in northern Israel, has been studied intensively since 1969 by a weekly monitoring program. Based on the phosphorus (P) dataset collected at predefined depths at the central lake station we investigated long-term changes in the internal P loading as expressed by the seasonal increase of the integrated phosphate concentrations during the stratified season. Calculations revealed a highly variable annual internal P load that showed an increasing trend during the 1970s and a gradual decline starting from the early 1980s. The latter can be interpreted as response to management measures in the watershed (sewage diversion, partial reflooding of a former swamp area) that caused an overall decrease in the riverine nutrient load. Investigating the critical control parameters for internal P loading in LK we discovered its close dependency on the phytoplankton biomass during the stratified season and on the redox conditions at the sediment water interface. Based on these findings we successfully developed a conceptual model aimed at the quantification of the internal P load in LK with nitrate concentrations, thermocline depth, and hypolimnion temperature as additional drivers.
Host: Hans-Peter Grossart