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|Kalbitz, K; Rupp, H; Meissner, R: N-, P- and DOC-dynamics in soil and groundwater after restoration of intensively cultivated fens in Broll, G; Merbach, W.; Pfeiffer, E.-M.: Wetlands in Central Europe: Soil organisms, soil ecological processes and trace gas emissions, Springer Verlag, 99-116 (2002)|
Most areas of fenland soils in Northeast Germany have been drained since the late 18th century with a consequent increase in intensity of agricultural land use until the early 1990s. This cultivation resulted in severe peat degradation. Nowadays schemes are introduced to restore such degraded wetland sites. However, nothing is known about the impact of these restoration schemes on nutrient dynamics in soil and water.
We investigated the effects of changes in land use and an increase in groundwater table on nitrogen, phosphorus, and carbon in soil, soil solution, and groundwater at six sites with variable land use and management in the "Droemling" fen area. Changes in land use from intensive crop production to unimproved pasture reduced nitrogen and phosphorus leaching from soil into ground water. An alder swamp forest site contained much higher inorganic nitrogen and dissolved organic carbon contents in soil and water than a site under grassland because of enhanced degradation of the peat layer under this forest. Increasing groundwater tables partly decreased mineral nitrogen content of the topsoil. However, peat decomposition due to a lawering of the water water table in summer and slow re-wetting in autumn caused high N mineralization peaks followed by temporarily high nitrate contents in groundwater at sites with an existent peat layer. Higher water tables increased phosphorus and carbon contents in the groundwater due to a decreased redox potential, which increased phosphorus solubility and intensified leaching of dissolved organic matter from the peat. The results show that variation in water table levels are an important factor controlling the concentration of N, P and DOC in soil solution and groundwater.