The effects of drainage on groundwater quality and plant species distribution in stream valley meadows

Conditions in fen meadows in Dutch stream valleys are influenced by both deep (Ca2+-rich) and shallow (Ca2+-poor) groundwater flows. The distribution patterns of phreatophytic (groundwater-influenced) plant species showed distinct relationships with the distribution of different groundwater types. Large fluctuations in the ionic composition of groundwater were observed in the upper peat layers of drained areas. Ca2+-rich groundwater was replaced by precipitation water to a considerable depth (1-1.5 m). These fluctuations in groundwater composition were less pronounced in undrained areas. It was observed that characteristic species of fen meadow communities and rare phreatophytic species were restricted to areas with high water tables, which were nourished by either Ca2+-poor or by Ca2+-rich groundwater. Few species showed a preference for drained areas, where replacement of groundwater types gave rise to the occurrence of an intermediate groundwater type, which was thought to be the result of an increased acidification of the top soil (increased influence of infiltration water). It was argued that the endangered species were best preserved in areas with an undisturbed discharge of natural groundwater flows