Artificial wetlands: a device for restoring natural wetland values

In The Netherlands, many oligotrophic and mesotrophic surface waters have been eutrophied. Eutrophication of rivers, streams and lakes is also a major problem in other West European countries (Melzer, 1976; Whitton, 1984; Hoffmann, 1985). The influx of phosphorus into Dutch inland waters can be attributed to three main sources. In 1985, inland sources accounted for 40% of the total influx of phosphorus, while the rivers Rhine and Meuse accounted for 45% and 12% respectively. In 1985, the main sources of nitrogen were inland locations (33%), river Rhine (51%), river Meuse (3%) and other transboundary rivers (11%). Table 12.1 gives the nutrient loading figures in tons per year. Drainage and runoff from manured agricultural areas is the main inland source of eutrophication. Due to high manuring levels, the average nutrient loading of the discharge from the agricultural lands to the surface waters is 2.0 kg P/ha/year and 20 kg N/ha/year. Nutrient emissions are highest in areas of intensive agriculture, situated on sandy soils in the eastern and southern parts of The Netherlands (Vos and Zonneveld, 1993, this volume). Also, in the lowland peat areas used for agriculture nutrient emissions are high.