ARE CLIMATE DYNAMICS REFLECTED IN THE STABLE ISOTOPE HYDROLOGY OF IRISH RIVER WATER DURING 2018?

Research by Frank Schwartz has ranged from studies of groundwater contamination to climate related perturbations of lake-groundwater interactions and uncertainties in predicting river flows in the face of future climate change. We follow his lead in questioning the role of climatic variations on river flow and geochemistry of river waters for our study conducted in Ireland. After a record cold and wet winter of 2017–18, Ireland suffered a drought in the summer of 2018. Stable isotope analyses of stream samples collected in March, May, June, and August 2018 show strong evaporative signals in repeated sampling of multiple locations along the mainstem of the Shannon River and in other major rivers of Ireland. Data reported by Met Éirean show total rainfall at its Athenry, County Galway, synoptic station for January 2018 was 173.2 mm while the mean monthly January total is 116.7 mm. Record wet weather continued through April 2018. In May the weather became warm, sunny, and dry. June 2018 total rainfall at Athenry was 25.2 mm while the 30-year (1981–2010) average for June is 79.6 mm. June rainfalls were below their long-term averages throughout the country and June 2018 was the driest June in Dublin since 1941. Similarly, monthly temperatures were colder in January–April with mean temperature for January 2018 5.3 °C, lower than the 30-year average of 5.5 °C and by June the mean temperature was 15.9 °C, far higher than the 30-year average of 13.7 °C. The highest maximum temperature at Shannon airport was the greatest there since 1946.

We constructed a regional meteoric water line (RMWL) from 558 published δD and δ¹⁸O analyses of samples collected at two locations during 1960 through 2016 and analyzed by the GNIP program. Our samples from seven locations along the main stem of the Shannon River and three of its tributaries in March 2018 clustered tightly together and plotted above both the Global Meteoric Water Line (GMWL) and our calculated RMWL. Samples collected at those same Shannon River locations plus several additional locations along the main stem of the Shannon River in June 2018 all plotted below the GMWL and the RMWL. Calculated d-excess also showed a strong evaporative signal in the June samples. We speculate on both the role of climate and the relationship of the loughs along the rivers in controlling the stable isotopic signals observed.