Evaluation of stable isotope analysis as a tool to determine nitrate sources in Irish groundwaters

Abstract

This project, which explores combined and δ15N and δ18O analyses on soil-water and groundwater nitrate in conjunction with conventional chemical analysis of water constituents, primarily aims to give a critical evaluation of stable isotope analysis of nitrate as a tool to determine nitrate sources in Irish groundwaters. First, the unsaturated zone was investigated as nitrate leachate samples were collected under small-scale experiments of well-drained soils simulating different agricultural practices. The saturated zone investigations were mainly carried out in the Barrow Valley, south County Kildare and north County Carlow, where unsewered dwellings and farms are scattered in areas of intensive agricultural activities, a significant proportion of tillage land and relatively free- draining soils overlying shallow sand/gravel and Carboniferous limestone aquifers. Research work was also undertaken to a lesser extent at Moorepark Research Centre, north-east County Cork, where an intensive dairy farm and a thin free-draining soil cover overlie a karstified limestone bedrock aquifer. Nitrate was extracted from each water sample using an anion exchange resin technique (Silva et al., 2000), and δ15N and δ18O values were both measured by Continuous-Flow Isotopic Ratio Mass Spectrometry.