Linking changes in nutrient load source apportionment to estuarine responses: an Irish perspective

In the Irish environment, anthropogenic pressures have led to widespread nutrient over-enrichment and eutrophication in surface waters. In the past 25 years European Directives have been implemented resulting in significant measures to improve water quality. Multi-decadal monitoring of nutrient inputs from rivers, and response parameters in estuarine and coastal systems, allows for a comparison of the effectiveness of these measures. In this study, trends in nutrient inputs from eighteen river systems and downstream estuarine parameters between 2000 and 2013 are explored. The results are placed in the context of changes in nutrient source load apportionment modelled through a newly developed GIS tool. Measured phosphorus inputs showed a significant reduction from fifteen catchments, with only four rivers showing a concurrent reduction in nitrogen.Significant Parallel improvements in estuarine water quality were evident in eight downstream systems, highlighting the complexity of response mechanisms. Load apportionment illustrated that the effectiveness of measures largely depended on factors such as land use and the proximity of large urban agglomerations to the estuary. The partitioning of nutrient sources could determine the nutrient landscape of the downstream estuary, with possible implications for the ecological health of the system.The results of the study will inform decision makers on the effectiveness of measures to date and the possible response of systems to future controls in the light of targets set out under the Water Framework Directive.