1. Eutrophication Status of the Wadden Sea Justus van Beusekom Wadden Sea Station Sylt Alfred-Wegener-Institute for Polar and Marine Research List/Sylt

2. Overview Recent Trends (QSR 2004) – Trends in River Input – Trends in Eutrophication Proxies Seasonal Cycle of NH 4 + NO 2 Summer Phytoplankton Biomass Historic levels

3. Trends in River input: Discharge

4. Trends in River Input Total Nitrogen - Input

5. Trends in River Input Total Phosphorus - Input

6. Trends in River Input Specific TN Input

7. Trends in River Input Specific Phosphorus Input

8. Trends in River input: Conclusions Interannual Difference related to Variation in Riverine Freshwater Discharge Decreasing trend in the specific nutrient loads – All areas show similar Trends – TP decrease faster than TN decrease TN decrease: 2.1 - 2.2% year -1 TP decrease: 3.3 - 2.5 % year -1

9. Indicators of Eutrophication Eutrophication Criteria: Changes in the seasonal cycle of nitrogen (NH 4 + NO 2 levels in autumn) QSR 2004 Summer Chlorophyll

10. Changes in the seasonal cycle of nitrogen (NH 4 + NO 2 levels in autumn) Sylt Rømø Bight Mean Annual Cycle

11. Changes in the seasonal cycle of nitrogen (NH 4 + NO 2 levels in autumn) Multiple regression analysis dependent: – Autumn NH 4 + NO 2 independent: – Riverine input (Rhine Meuse; Dec-Aug) – Chlorophyll (autumn) – Temperature (autumn)

12. Changes in the seasonal cycle of nitrogen (NH 4 + NO 2 levels in autumn) Significant effect of Rhine/Meuse in the Southern Wadden Sea Western Dutch Wadden Sea Eastern Dutch Wadden Sea Norderney No significant relations in the Northern Wadden Sea

13. Changes in the seasonal cycle of nitrogen (NH 4 + NO 2 levels in autumn) Western Dutch Wadden Sea

15. Trends in Summer Chlorophyll (Common Driver: Rhine/Meuse) AreaPeriodMeanTrend/FactorCorrelation Western Dutch Wadden Sea1976-200218.0Yes/2.7r²=0.43; n=27; p=0.0002 Eastern Dutch Wadden Sea1976-200219.9No Trend Lower Saxon Wadden Sea (Norderney) 1988-200216.6Yes/2.1r²=0.308; n=18; p=0.008 Southern Schleswig-Holstein1990-200214.2No Trend*r²=0.002; n=13; p=0.868 Northern Schleswig-Holstein1990-20027.4No Trend*r²=0.12; n=13; p=0.245 Sylt-Rømø-Bight1984-20026.3Yes/2.7r²=0.345; n=19; p=0.008 Danish Wadden Sea1990-20028.6No Trend*r²=0.18; n=12; p=0.15

16. Spatial Trends in Summer Chlorophyll 18.0 19.9 16.6 14.2 7.4 6.3 8.6

17. Contrasting Eutrophication Status of the Northern and Southern Wadden Sea?

18. Conclusions Large Interannual Differences in Nutrient Discharge Decreasing Trend in Nutrient Loads Decreasing Trends in Eutrophication Status No Universal Indicator (yet) – Southern Wadden Sea: NH 4 + NO 2 – Entire Wadden Sea: Summer Chlorophyll (some areas) Presently: about 5 Times above Pre- Industrial Levels Southern Wadden Sea more Eutrophic the Northern Wadden Sea

19. Relative Importance of Rivers Influencing the Wadden Sea Mean relative contribution of major fresh water sources to nutrient input into the southern (1977-2002) and central Wadden Sea (1980 to 2002). For the Eider and Danish rivers, data since 1990, resp. 1995 were used as reported to OSPAR (Hereira, pers. comm.). Southern Wadden Sea SourceDischargeTotal NitrogenTotal Phosphorus Haringvliet27.5%27.2%22.1% Maassluis47.4%47.2%57.2% Noordzeekanaal3.0%2.9%4.6% IJsselmeer19.3%17.6%13.8% Ems2.8%4.6%2.3% Central and Northern Wadden Sea SourceDischargeTotal NitrogenTotal Phosphorus Weser31.1%31.7%30.1% Elbe62.0%61.9%64.3% Eider 2.5%2.2%2.5% County Ribe 3.4%3.2%2.1% Jylland 0.9%1.0%0.9%