An evaluation of catchment-scale phosphorus mitigation using load apportionment modelling

• Published in: The Science of the total environment 2011-05, Vol.409 (11), p.2211-2221
• Main Authors: Greene, S., Taylor, D., McElarney, Y.R., Foy, R.H., Jordan, P.
• Format: Article
• Language: English
• Subjects: Agronomy. Soil science and plant productions; Applied sciences; Biological and medical sciences; Calibration; Catchments; Continental surface waters; Diffuse; Earth sciences; Earth, ocean, space; effluents; Engineering and environment geology. Geothermics; Environmental Monitoring; Environmental Restoration and Remediation - methods; European Union; eutrophication; Exact sciences and technology; exports; floods; Fresh Water - chemistry; Freshwater; Fundamental and applied biological sciences. Psychology; Hydrology; International trade; Lakes; Load apportionment; Materials requirement planning; Mitigation; Models, Chemical; Natural water pollution; Phosphorus; Phosphorus - analysis; Point; Pollution; Pollution, environment geology; risk reduction; Rivers; runoff; septic systems; sewage; Soil and water pollution; Soil science; soil types; subwatersheds; summer; wastewater treatment; Water framework directive; Water Pollutants, Chemical - analysis; Water Pollution, Chemical - prevention & control; Water Pollution, Chemical - statistics & numerical data; water quality; Water Supply - analysis; Water Supply - statistics & numerical data; Water treatment and pollution
• ISSN: 0048-9697; 1879-1026
• DOI: 10.1016/j.scitotenv.2011.02.016

Functional relationships between phosphorus (P) discharge and concentration mechanisms were explored using a load apportionment model (LAM) developed for use in a freshwater catchment in Ireland with fourteen years of data (1995–2008). The aim of model conceptualisation was to infer changes in point and diffuse sources from catchment P loading during P mitigation, based upon a dataset comprising geospatial and water quality data from a 256 km 2 lake catchment in an intensively farmed drumlin region of the midlands of Ireland. The model was calibrated using river total P (TP), molybdate reactive P (MRP) and runoff data from seven subcatchments. Temporal and spatial heterogeneity of P sources existed within and between subcatchments; these were attributed to differences in agricultural intensity, soil type and anthropogenically-sourced effluent P loading. Catchment rivers were sensitive to flow regime, which can result in eutrophication of rivers during summer and lake enrichment from frequent flood events. For one sewage impacted river, the LAM estimated that point sourced P contributed up to of 90% of annual MRP load delivered during a hydrological year and in this river point P sources dominated flows up to 92% of days. In the other rivers, despite diffuse P forming a majority of the annual P exports, point sources of P dominated flows for up to 64% of a hydrological year. The calibrated model demonstrated that lower P export rates followed specific P mitigation measures. The LAM estimated up to 80% decreases in point MRP load after enhanced P removal at waste water treatments plants in urban subcatchments and the implementation of septic tank and agricultural bye-laws in rural subcatchments. The LAM approach provides a way to assess the long-term effectiveness of further measures to reduce P loadings in EU (International) River Basin Districts and subcatchments. ► Load apportionment models (LAMs) relate phosphorus discharge and concentration. ► LAMs show significant changes of P point and diffuse loadings post P reduction. ► P point sources exist in rural catchments without a WWTP. ► LAMs identify catchments of higher P export risk and sensitive transport pathway. ► Identification of P source magnitude and duration during hydrological year.