Lake Kinneret (Israel) Ecosystem: Long-Term Instability or Resiliency?

Abstract

The Kinneret ecosystem has undergone significant man-made modifications. These include, among others: construction of the south dam (1932); drying of Hula Lake and swamps (1950s); salty springs diversion (1964); lake water salinity decline from 395 (1961) to 210 ppm chlorid; deepening of the Jordan River near Bnot-Yaacov bridge (1971) with consequent high loads of suspended matter; National Water Carrier (NWC) operation (1964); sewage removal and fishpond restriction in the catchment; implementation of the Hula Project (1994–1998); introduction of native and exotic fishes; an amplitude of water level fluctuations of 4.8 m. Natural fluctuations occurred as well: heavy floods with high nutrient loads in 1968/69 and 1991/92 and droughts in 1973, 1989–1991 and 1998–1999; 4.6 m water level fluctuations; low temperatures (12.3°C) and fish kill in 1971/72 and 1991/92; no mixing period in 1984; low (1975, 1996–1997) and high biomass of Peridinium (1994, 1998); N₂-fixing cyanobacterium bloom (1994, 1995); high stock of Lavnun (Acanthobrama) fishes (1990s); Zooplankton biomass decline (1969–1993) and increase afterwards. Although man made changes and natural environmental changes were significant, the lake ecosystem did not deviate from the level of resilient fluctuations and the classification of long-term instability in Lake Kinneret is probably an overestimation. In this paper I use long-term (31 years) distribution data of plankton, nutrients, and water level in Lake Kinneret to distinguish between resiliency and instability.