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.

Habitat use and preference of adult perch (Perca fluviatilis L.) in a deep reservoir: variations with seasons, water levels and individuals

“…These results, based on the entire lake, are in agreement with other studies (Gasith & Gafny, 1990;Gasith & Gafny, 1998), and mean that lowering WL correspond to fewer refuge areas and probably fewer food resources for perch (Zohary & Ostrovsky, 2011;Zohary & Gasith, 2014). They also confirmed the trends observed by Logez et al (2016) with a point sampling on the same lake, but brought additional information as the stable availability of littoral tree stumps with WL and the rise of the relative availability and surface of the littoral area when the WL dropped.…”

Environmental drivers of fish spatial distribution and activity in a reservoir with water level fluctuations

“…The precise quantification of changes in the availability and quality of littoral habitats induced by the lowering of water level that we described here confirmed a general trend towards a reduction in habitat complexity with the lowering of water level. Similar studies are rare but our results confirmed the observations made in Lake Kinneret (Gasith & Gafny, 1990, 1998 and Lake Tahoe (Beauchamp et al, 1994). Considering the interest of the littoral zone for fish fauna (Schiemer et al, 1995;Schmieder, 2004;Lewin et al, 2014), alterations of littoral habitats due to water level decrease are likely to affect fish community.…”

“…The overall functioning of lake ecosystems is closely dependent on the littoral zone, which is under strong pressure induced by WLF (Wetzel, 1990;Schindler & Scheuerell, 2002;Strayer & Findlay, 2010). Several studies observed impacts of a water level drop with an alteration of littoral habitats availability and a decline in littoral habitats complexity (Gasith & Gafny, 1990;Beauchamp et al, 1994;Zohary & Ostrovsky, 2011). Nevertheless, to our knowledge, none quantified precisely composition changes at a whole reservoir scale.…”

Macroinvertebrate communities associated with littoral zone habitats and the influence of environmental factors in Malilangwe Reservoir, Zimbabwe

“…Human exploitation of water resources can lead to increased annual and inter-annual water level fluctuations, at times, far beyond natural amplitudes and/or irrespective of the natural hydrological cycle. A range of natural features of the water level regime are often impacted, not only the amplitude of fluctuation but also the timing of the minimum and maximum water levels and the rates of water level increase and decline (Gasith and Gafny, 1990;Zohary and Ostrovsky, 2011). Aquatic macroinvertebrate assemblages and communities can act as good indicators of the prevailing hydrological regime and water quality in aquatic systems.…”