First results from Blue Estuaries

The project Blue Estuaries (BluEs) is characterized by an ambitious field program to assess the simultaneous loading of eutrophication and pollutants in the two largest German estuaries of the Elbe (North Sea) and the Odra (Baltic Sea) on an annual basis, as well as the effects on food webs and stock-forming organisms in the benthos and fish fauna. Despite Covid-19 restrictions in 2021, nearly all planned campaigns could be conducted aboard various vessels or from shore using small boats.

Working on the assessment of sediment toxicity, the Applied Aquatic Toxicology group of HAW is conducting ecotoxicological studies in the Odra and Elbe estuaries. In the Stettiner Haff and along the Peenestrom water and sediment samples were taken at 5 stations, along the Lower Elbe from Drage to Otterndorf sediment samplers were laid out at 6 stations in the tidal flat area. Preliminary results show large differences in sediment toxicity between estuaries, with the Odra estuary appearing much less polluted than the Lower Elbe, where pollutants from upstream industrial facilities accumulated over decades. When we compare our data collected in BluEs with those from previous projects, the impact on our deployed test organisms appears to be less. Next year will show whether these positive findings can be confirmed. Key fish species of smelt, herring, finfish, walleye, ruffe, perch, flounder and blackmouth goby were also caught in both estuaries and samples of these were taken for food and growth analyses. In addition, 37 different fish species were quantitatively recorded in spring, summer and autumn campaigns on board the vessel "Ostetal" in the Elbe estuary in order to assess the diversity of the fish fauna as well as the abundance and biomass of all species. The degree of eutrophication was recorded with the help of a chamber lander at several stations of the Odra outflow. It was found that near the bottom the consumption of oxygen and the production of ammonium are highest in summer and inversely correlated. The released nutrients can, for example, favor the strong growth of microalgae, which can lead to increased turbidity and thus decreased water quality.

Next year, all field work will continue to ensure seasonal coverage of findings.

Photos of BluEs work in 2021. Left: Mats in the Elbe silt to collect sedimentary material, Middle: Chamber lander with programmable sampler, Right: Fish were mostly caught in cooperation with local fishermen (right photo: R. Koll).