A COMPARISON OF FENS IN NATURAL AND ARTIFICIAL LANDSCAPES

Fens depend on inputs of groundwater or surface water. In Western Euro pe especially soligenous fens, receiving groundwater, are threatened b y human hydrological intervention. We demonstrate the impact of artifi cial versus natural hydrologies on such fens by comparing 3 case areas : the Biebrza valley (reference) and the Gorecht and Vecht river plain s (both reclaimed and drained). The patterns found in the fairly undis turbed Biebrza area suggest local water quality is governed by a stron g regional groundwater flow emerging in the fen near the valley margin s and seeping through it down to the river. Hence water quality gradie nts are smooth: there is little variation in water type over large dis tances. The pattern is determined by the natural geomorphology. In the reclaimed Vecht and Gorecht river plains large differences exist at s hort distance. Regional water flow from the adjacent ridges into the p lains is weak here and governed primarily by water management (polders and pumping wells). However, the relations between specific water typ es and fen species and communities in this artificial pattern are quit e similar to those found in the natural landscape. Low-productive rich fens are fed by calcium-rich and base-rich, nutrient-poor groundwater in both cases. While conservation of such rich fens is served best by maintaining the natural groundwater flow, some opportunities for rest oration with an artificial hydrology are discussed.