Trophic gradients in a large-river delta: Ecological structure determined by connectivity gradients in the Danube Delta (Romania)

There are over 300 lakes interconnected by riverbranches and man-made canals in the Danube Delta (Romania). A multidisciplinary survey of these riverine lakes situated in large Wetland complexes was made comprising hydrological modelling, remote sensing and monitoring of water quality, plankton, aquatic vegetation and fish communities. Between-lake differences in water quality and aquatic vegetation cover were inferred from satellite image. Based on channel and lake dimensions, hydrological characteristics of the lakes in the delta were determined: hydrological distance from a riverbranch, residence time and impact of reed water. Water-quality and biotic parameters (phyto- and zooplankton, submerged plants and fish) were sampled in a comparative survey in June 1997-1999 in subsets of the lakes. In a follow-up study in 2001-2002, seasonality of aquatic vegetation and fish were recorded.