GEOCHEMISTRY OF SURFACE WATERS IN THE BURREN REGION, WESTERN IRELAND

The Burren in western Ireland is a 500 km² karstic terrain comprising both an upland and a lowland component, dominated by Carboniferous limestones. The area is bounded to the west by the Atlantic Ocean and to the east by the Slieve Aughty uplands that are largely siliciclastic sediments of Ordovician to Devonian age. In general, the drainage in this coupled Slieve Aughty-Burren area reflects bedrock type. An exception is the Caher River in the NW corner of the Burren: it flows almost entirely on the surface of a karst topography. In this presentation we show geochemistry data from surface features within the broad Burren area. The sampled features include the Caher River, a series of small rivers draining the Slieve Aughty, and two turloughs, which are surface depressions in karst regions that are seasonally flooded. Samples have been analyzed for major cations and anions, nutrients (N, P, Si), and stable water isotopes. We have compared our surface water data with previously published groundwater information collected from the Burren subsurface. This comparison highlights the differences which are clearly defined by rock-water interactions. The differences in geochemical signatures allow for the evaluation of the geochemical evolution of the water as it moves through the surface water-karst system. In general, our results reveal that waters draining the Slieve Aughty have higher H₄SiO₄ (43–61 µM) but lower magnesium (194–240 µM), calcium (640–1180 µM), potassium (27–34 µM), sulfate (25–33 µM), nitrate (<4 µM), and alkalinity (1600–2800 µM), than does the groundwater, reflecting differences both in lithology and in landuse. Previously published groundwater values clearly reflect input of solutes from CaCO₃ dissolution and from agricultural inputs. Dissolved organic carbon in Slieve Aughty rivers ranged from 380 to 710 µM. The geochemistry of the two turloughs reflects different proportions of surface and groundwater to them, supporting previous groundwater modeling work by others. The geochemistry of the Caher River shows the influences of precipitation and of limestone chemical weathering. Our geochemical results will be discussed in terms of what is currently understood about the karst hydrogeology of the region.