The role of hydrological regime in structuring macrophyte assemblages in gravel pit lakes along the Drina river floodplane (Serbia)

Abstract

Hydrological regime plays an important role in structuring macrophyte vegetation in highly connected fl oodplain lakes, such as gravel pit lakes connected to the main river channel. If the dominant hydrological drivers are known, an optimal selection of gravel excavation location, relative to the main river channel, may create favorable hydrological conditions for aquatic biota. The aim of this study was to determine the most significant and relevant hydrological variables for structuring macrophyte assemblages in newly formed gravel pit lakes along the lower course of the Drina River. Field research was carried out on 49 survey sectors (14 gravel pit lakes), during the summer months of 2015 and 2016. Vegetation data was collected in accordance with the Pan-European standard for the sampling of macrophyte vegetation in lakes, using the UKTAG LEAFPACS (Lake Assessment Methods, Macrophyte and Phytobenthos). Hydrological variables (frequency, duration and amplitude of the flooding events during the 4-year period prior to the vegetation survey) for each lake were extracted from the Republic Hydrometeorological Services according to the relative shore height to the Badovinci water-level station on the Drina River. The role of hydrological variables in structuring macrophyte assemblages was tested using partial Canonical Correspondence Analysis, while Generalized Linear Model was performed to test the ability of selected hydrological attributes to predict the macrophyte quantitative metrics (Shannon diversity index, species richness, total macrophyte cover, number of macrophyte functional groups, number of charophyte taxa and relative charophyte cover). The analyses showed that species richness, Shannon diversity index, total macrophyte cover and number of macrophyte functional groups were negatively predicted by the frequency of flooding events during the summer seasons in the past 4-year period. However, these macrophyte indices, including the number of charophyte taxa and the relative charophyte cover, were positively correlated with the frequency of flooding events during the spring periods. These results suggest that the frequency of fl ooding periods during vegetation season may affect macrophyte vegetation structure by direct biomass removal. However, the frequency of spring flooding events influences the water trophic conditions which may increase macrophyte diversity and richness.