Ecohydrological analysis of a groundwater influenced blanket bog : Occurrence of schoenus nigricans in roundstone bog, Connemara, Ireland

Since the late 1960s, the occurrence of Schoenus nigricans in Irish blanket bogs has been attributed to inputs of salt spray to the blanket bogs, due to their proximity to the coast and the predominant westerly winds from the Atlantic Ocean. To test this hypothesis we carried out an ecohydrological field study at a large blanket bog in the western part of Connemara, Ireland. We described peat profiles in two transects and sampled pore water from peat at different depths. The water samples were analysed and their macro-ionic composition was used to locate possible inputs of calcareous groundwater to the system. We found clear evidence for inflow of calcareous groundwater at various sites and depths. Inflow of rather base-rich groundwater was indicated by high values of electrical conductivity (EC), high contents of calcium and bicarbonate, and high pH of the pore water. The peat profiles contained macro-remains of reed (Phragmites australis), in most cases only in deeper layers of peat, but at one location throughout the profile. This is another indication that the blanket bog was a groundwater-fed fen for quite some time. We conclude that the occurrence of S. nigricans in the blanket bog studied could be well explained by the hypothesis that S. nigricans is a relic from former more base-rich conditions. Relatively high base saturation could have persisted due to the prevailing groundwater flow in the upper layers preventing decalcification or other loss of cations from the whole soil profile including the topsoil.