A review of the nature and source of nutrient impairment in small streams: a desk based characterisation for targeted mitigation measures

Recent research has highlighted the need to refocus research and management on small streams to address wider catchment water quality and biodiversity concerns, together with the sustainable management of ecosystem services. A novel and transferable method for the characterisation of nutrients in non-compliant small streams in Ireland is presented. The method is based on the analyses of several, publicly available datasets, including historic water quality data, coupled with temporal correlations of hydro-meteorological data, and evaluations of biological index data, urban wastewater issues, and potential impacts across major catchment typologies. The study was able to identify priority areas for mitigation and propose potential mitigation strategies. Many of the small stream study sites were nutrient impaired, with more than half exceeding Water Framework Directive concentration thresholds for molybdate reactive phosphorus and total ammonia, and almost one-quarter exceeding non-statutory total oxidised nitrogen levels emerging from multiple sources and pressures. Mitigating these inputs is a priority. There is a clear need to address declining water quality in river networks in Ireland, and globally, and refocussing attention to the headwaters of fluvial systems, should make a significant contribution to this goal.