The overriding role of hydrological factors on zooplankton community: evidence from a shallow tropical reservoir (Koka, Ethiopia).

Due to changes in global climate and local hydrological variability, land-water interactions are considered the prevailing processes underpinning aquatic ecology. Periodic meteorological conditions could have significant effect upon freshwater plankton communities by modifying the relative influences of biotic and abiotic structuring factors. However, the influence of unusual meteorological events, such as the El-Niño Southern Oscillation cycles, and advection on zooplankton communities of tropical shallow lakes and reservoirs are not fully understood. The present study, therefore, aimed to explore the relationship between hydrological factors and zooplankton community structure in Koka Reservoir, Ethiopia. Field measurements and collection of water samples and zooplankton were performed at monthly intervals from January to August 2016 at three sampling sites along a stretch of the reservoir from the river mouth to the center and the outlet (dam). The results showed post-El-Niño hydrological events (i.e., elevated riverine runoff and higher levels of turbidity) and associated advective losses can disrupt zooplankton community structure at the river mouth site, particularly during the rainy period. The results suggest that integrated watershed management activities are important aquatic resource management options in small- and medium-sized lakes and reservoirs.