Effects of Water Level Fluctuation on the Structure and Function of the Littoral Zone

Abstract

Water level fluctuations (WLFs) are most pronounced in impoundments, but are also observed in natural lakes over a wide size range, both on a seasonal and on an interannual time scale. In small and/or shallow lakes, WLFs can affect the metabolism and structure of the entire lake system. In most cases of large deep lakes, only the littoral region is affected. The effects on the biota, either beneficial or adverse, depend on local conditions. In Section 8.1, effects of WLFs on the physical and chemical environment and on the community of the littoral are described in general. Thereafter, we examine the effects of long-term WLFs in Lake Kinneret, Israel. The relatively large amplitude of WLFs in this lake results in periodic changes of the littoral slope and of the substrate composition. This latter factor affects the breeding of the dominant fish species of the lake. At lower water levels, semi-aquatic vegetation that grows well in the exposed littoral provides vegetative habitats after it is inundated. WLFs should be looked at as an environmental disturbance maintaining the temporal and spatial heterogeneity, which, in general, is characteristic of the littoral zone.