Has the eutrophic state of German Wadden Sea waters changed over the past 10 years due to nutrient reduction?
For a period of more than 10 years, two basic eutrophication indicators, dissolved inorganic macronutrients and chlorophyll a, have been measured along with physical parameters at a permanent coastal station in the northern German Wadden Sea near Büsum. despite distinctly reduced phosphorus inputs, the data have not revealed any long-term trend in nutrient winter concentrations or algal biomass compared to other available time-series in the area of investigation, i.e. River Elbe nutrient loads and nutrient concentrations in the German Bight near Helgoland. Instead, there are indices of slightly higher winter phosphate concentrations in recent years as well as a decrease in maximum annual N:P ratios due to elevated residual phosphate concentrations in spring. This is in contrast to the situation in the adjacent German Bight, where a declining trend in dissolved inorganic phosphate concentrations is observed. It is suggested that persistent high phosphate concentrations in the northern German Wadden Sea result from local sources of phosphate such as remobilization from the sediments, as well as remineralization of imported organic matter. The comparison with a comprehensive assessment of seasonal light and nutrient availability in the water column indicates that on an annual basis, phytoplankton biomass development in the northern German Wadden Sea is still insensitive to current nutrient reduction measures because of the predominant role of light limitation in this turbid environment.
Article from Marine Science Symposia Vol. 219 - "Hydrobiological variability in the ICES Area, 1990-1999", symposium held in Edinburgh, 8-10 August 2001. To access the remaining articles please click on the keyword "MSS Vol. 219".