The Elbe is one of the major rivers of Central Europe near Geesthacht, a weir separates the river from the estuary.  Hamburg harbor is situated about 20 km downstream of the weir in the Elbe estuary. There, the depth of the estuary strongly increases from about 4 m to about 17 m due to dredging to accommodate for large ships.

The river used to be heavily polluted. Industrial pollution has been strongly reduced especially after the German unification. Although nutrient concentrations decreased by about 50% since the early 1990s, they still remain high. Low toxicity and high nutrient concentrations enable massive phytoplankton blooms. When these blooms enter the Hamburg harbor, light limitation induces the collapse of these blooms leading to high organic matter degradation rates and extreme low oxygen levels in summer. We will develop safe ecological limits for the Elbe estuary based on local system functioning focusing on oxygen depletion and translate these into nutrient concentrations and riverine loads. We will combine long time- series observations, the Elbe model (UFZ) for nutrient loads with an estuarine model (Hereon) to investigate nutrient reduction necessary to bring the O₂ levels within safe ecological limits, considering the combined effects of climate change and dredging.