New estimates indicate that diffuse sources outweigh point sources in most sub-catchments. The main cause of unsatisfactory water quality in Ireland is excess phosphorus and nitrogen emissions that can come from sewage discharges, agricultural land, and other sources. Recent EPA-funded research, the CatchmentTools project, has produced estimates of the nutrient losses to Irish surface waters from nine main sources using geospatial modelling. The sources were grouped into point discharges (municipal wastewater treatment plants, industry and septic tank systems) and non-point, or diffuse, sources (pasture, arable, diffuse urban, forests, peatlands, and deposition on water). The results were used by the EPA Catchments Unit to support the identification of significant pressures for the development of the River Basin Management Plan.

Main sources of phosphorus and nitrogen in Irish rivers These new estimates indicate that over 50% of phosphorus and over 80% of nitrogen losses to surface water are from ‘non-point’ sources.

View News feature Nutrient modelling indicates most nutrient losses to surface waters are from diffuse sources