Water level control over submerged macrophyte development in five shallow lakes of Mediterranean Turkey

Abstract

The functioning of shallow lakes is supposedly very sensitive to water level fluctuations (WLF). Relationships between WLF and submerged macrophyte development were investigated in five Turkish shallow lakes located in a semi-arid to arid Mediterranean climate where the hydrological event of WLF is a common phenomenon. In all lakes, WLF emerged as a major factor determining submerged plant development. High submerged plant coverage was observed in four of the study lakes, Lake Beysehir, Lake Uluabat, Lake Marmara and Lake Mogan when the water level was low throughout the year or during growing season, submerged plants expanded; however, in Lake Isikli extensive submerged plant development was observed at high water levels during winter. In Lake Isikli, an increase of 25 % in the surface area was recorded, which, in turn, might have resulted in an increased potential for expansion of submerged plants. Furthermore, in all the lakes excluding Lake Beysehir, high submerged plant coverage coincided with a significant decrease in the amplitude of intra-annual water level fluctuations. The depth profile, expressed as the morphometry index (Z mean /Z max ), appeared to be critical for the development of extensive vegetation. Expansion of vegetation coincided with either an increased morphometry index or a flatter bottom profile. However, the impact of hydrology on lake morphometry differed between the lakes. In Lake Isikli, the high water level generated a slightly flatter, albeit not significantly so, bottom; however, in the remaining lakes the same effect was observed at low water level. Differences in the morphometry index in response to WLF appeared to depend on the original bottom profile, which is either conical or ellipsoid. Therefore, the impact of hydrology on the bottom profile of a lake may profoundly affect the extent of the littoral zone. Biomass of carp (Cyprinus carpio) had a strong inverse correlation with vegetation development in Lake Marmara and Lake Uluabat, therefore, carp might also have been important in macrophyte development. It may be concluded that littoral plant communities in shallow lakes located in semi-arid to arid regions appear to be particularly susceptible to water level fluctuations.