Effectiveness of the European Natura 2000 network to sustain a specialist wintering waterbird population in the face of climate change.

Analysis of coordinated Greater Scaup (Aythya marila) count data from the last 30 years showed a 38.1% decrease in wintering numbers in North-West Europe, from 309,000 during 1988-1991 to c.192,300 individuals during 2015-2018. Annual trends in wintering numbers differed throughout the range. Numbers decreased in the UK, Ireland, and in the Netherlands, while numbers were stable in Denmark. Germany, Poland, Sweden, and Estonia showed increasing numbers, suggesting a shift in the distribution of the species within its wintering grounds towards the east and north. Higher temperatures in northern and eastern areas were correlated with the range shift of the wintering distribution. Deaths from bycatch drowning of Scaup in fishing gear have significantly decreased in recent decades in the Netherlands, where currently the greatest threat is considered the deterioration of food resources. The increasing concentration of wintering Scaup in coastal Poland and Germany (where lack of effective implementation of conservation measures fail to protect the species from the impacts of bycatch and declining food quality) pose major threats to the entire population.

Nitrogen and phosphorus dynamics of a re-wetted shallow-flooded peatland.

Minerotrophic peatlands play an important role in the regulation of water quality and quantity but due to drainage and agricultural land use most of these systems have lost this function. In Central Europe, many re-wetting projects have been implemented to restore wetlands for multifunctional purposes during the last years. The Pohnsdorfer Stauung (Northern Germany) is a eutrophic fen which was used for intensive agriculture for 40 years. The peatland is divided in two subareas by a small stream. In the scope of re-wetting measures, one subarea (westpolder) was flooded by blockading the main drainage ditch in 1996/97, a second subarea (eastpolder) was re-connected to the stream by an inlet and outlet in 2001. Nitrogen and phosphorus dynamics were investigated in the surface water of these systems over a 5-year (westpolder) and 3-year (eastpolder) period, and balances were calculated. In both polders high dynamics of nitrogen and phosphate concentrations were observed in the surface water. Nitrate peaked in the winter months, whereas ammonium, phosphate and organically bound nitrogen (N(org)) revealed highest values during summer. Daily balances for the eastpolder and annual balances for both polders were calculated. In both polders nitrate was retained but phosphate and N(org) were exported. Differences of the nutrient dynamics and the absolute and relative balances between the polders were due to the different hydrology: the eastpolder received a high nitrate load by the stream, in the westpolder nutrient loads are low and internal nutrient cycles are dominating. During the summer months, high ammonium concentrations, oxygen depletion, and phosphate release occur in the warm, stagnant water of both polders. Normally, high phosphate and ammonium concentrations did not coincided with discharge phases from the polders. However, in August 2002 after heavy rainfall high phosphorus and ammonium discharge was observed. One important factor influencing the detected nutrient dynamics and balances is the change from a drained and fertilized peatland to a flooded wetland in only a few years. We conclude that continuous water flow and stable water levels are desired for flooded peatlands to prevent high concentrations of ammonium and phosphate and to utilize the potential for nitrate retention. In degenerated peatlands, flooding should only be regarded as an easy technological solution in order to conserve the peat mineralization, and to form the foundation for the further development of the peatland to a more efficient nutrient retaining system.