Assessment of the eco-hydrology of a groundwater fed wetland in relation to the surrounding gravel aquifer on example of a study from Ireland

Fens are wetlands, which accumulate peat and have ground water as their dominant hydrologic input. Groundwater discharge to a fen is the critical factor controlling its ecology and an understanding of hydro-ecological links is critical in the assessment of likely impacts on a wetland, which typically could arise from groundwater abstraction, drainage or agricultural practice. The significance of groundwater to fens was increased with implementation of the EU Water Framework Directive (WFD), under which fens classify as groundwater dependent terrestrial ecosystems (GWDTE) and must be included in River Basin Management plans. The specific interest of the study was set on the conservation requirements of Vertigo geyeri snail and the habitat it lives in. The snail was chosen as being a sensitive indicator of habitat change in spring-fed wetland of Pollardstown. Very detailed investigations revealed that the preferred environment for existence of the snail is a consistently damp atmosphere with relative humidity varying between 80–95%, very small fluctuations in phreatic level of ±10 cm about a stable mean and soil moisture content within the moss substrate at 80–90% saturation levels. In order to meet these requirements an upward vertical hydraulic gradient is required at a rate sufficient to exceed the counterbalance of evapotranspiration at the fen surface.