Defining a good ecological status of coastal waters — a case study for the Elbe plume

The definition of a good ecological status of coastal waters requires a close cooperation between sciences (natural and socio-economic) and decision makers. An argument is presented for the use of ecosystem integrity assessment based on indicators of function and state. Ecosystem integrity is understood to be reflected in energy capture (here expressed as net primary production), storage capacity (as nutrient input/outut balances for coastal sediments), cycling (turn-over of winter nutrient stocks), matter losses (into adjacent water), and heterogeneity (here the diatom/non-diatom ratio of planktonic algae is used). Its feasibility is assessed using ERSEM, an ecosystem model of the North Sea, for the Elbe plume, after prior satisfactory calibration. Three scenarios were applied corresponding to 80, 70 and 60% reduction of the riverine nutrient load into the German Bight, compared to a reference situation of 1995. The modelling effort suggested that drastic nutrient load reduction from the Elbe alone would have a limited effect on the larger German Bight: even a 60% reduction scenario Would only lead to moderate changes in all five indicators. In conclusion, application of functional integrity indicators appears feasible for coastal seas at larger spatial scales (i.e. the German Bight), and, for the coast, would form a useful addition to the indicators presently proposed in the Water Framework Directive (WFD).