Investigating hydrological and biogeochemical controls on Irish alkaline fen habitats

Alkaline fens are listed under Annex 1 of the European Union (EU) Habitats Directive (Council Directive 92/43/EEC, habitat code 7230) as habitats requiring special conservation measures, including the designation of suitable sites as Special Areas of Conservation (SACs). These fens are peat-forming wetlands predominantly fed by groundwater containing significant concentrations of calcium, magnesium and bicarbonate. The hydrogeological dynamics and hydrochemical signature supports small sedge and brown moss communities in a mosaic of different habitats. Despite fens being an important part of the natural landscape in Ireland as well as one of the most threatened wetland habitats in Europe, there is little information on the hydrology and hydrochemistry that support these habitats. As part of a three year research project (Ecometrics) on GWDTE’s (Groundwater Dependent Terrestrial Ecosystems) an intensive hydrochemical monitoring programme was established on four Irish fen sites, designated as SACs, covering an eco-hydrological gradient from intact to highly degraded conditions. Ground and surface waters monitoring started in July 2018 with spot measurements supplemented by a continuous water table time series collected every two months. Simultaneously ground and surface water samples were taken and analysed for nutrients, mayor ions and metals. Topographical surveys as well as vegetation surveys were carried out in 2019. The hydrological and hydro-chemical evidence from each fen were then collated to build conceptual eco-hydrological models to represent both temporal and spatial variability in each geological setting. In addition, remote sensing was used in order to investigate the relationship between vegetation and water levels. Utilising ground surveyed habitat map and Sentinel-2 (S2) imagery in a Random Forest model a remotely sensed vegetation map was created. This information was then correlated with water level data as follows: hydrological data were interpolated over the entire area of the fen, giving seasonal information for both surface and groundwater levels. Using K-means clustering, the data were divided into clusters which were then matched and correlated with the vegetation map produced through S2 imagery. The strength of the correlation between water level and fen vegetation can further aid the construction of conceptual models for the four research sites. These models will then be used to define appropriate metrics that characterise the environmental supporting conditions in fens, as required for the EU Water Framework Directive. Here, the preliminary conceptual models for fen functioning will be presented as they are continuously updated by the ongoing data collection.