title: Low flow water quality in rivers; septic tank systems and high-resolution phosphorus signals.
abstract: Rural point sources of phosphorus (P), including septic tank systems, provide a small part of the overall phosphorus budget to surface waters in agricultural catchments but can have a disproportionate impact on the low flow P concentration of receiving rivers. This has particular importance as the discharges are approximately constant into receiving waters and these have restricted dilution capacity during ecologically sensitive summer periods. In this study, a number of identified high impact septic systems were replaced with modern sequential batch reactors in three rural catchments during a monitoring period of 4 years. Sub-hourly P monitoring was conducted using bankside-analysers. Results show that strategic replacement of defective septic tank systems with modern systems and polishing filters decreased the low flow P concentration of one catchment stream by 0.032 mg TPL(-1) (0.018 mg TRPL(-1)) over the 4 years. However two of the catchment mitigation efforts were offset by continued new-builds that increased the density of septic systems from 3.4 km(-2) to 4.6 km(-2) and 13.8 km(-2) to 17.2 km(-2) and subsequently increased low flow P concentrations. Future considerations for septic system mitigation should include catchment carrying capacity as well as technology changes.
authors: School of Environmental Sciences, University of Ulster, Coleraine, N. Ireland, United Kingdom.
authors: K A
authors: KA
authors: Macintosh
authors: P
authors: P
authors: Jordan
authors: R
authors: R
authors: Cassidy
authors: J
authors: J
authors: Arnscheidt
authors: C
authors: C
authors: Ward
mesh_terms: D004784:Environmental Monitoring; D007494:Ireland; D009660:Northern Ireland; D010758:Phosphorus / Q000032:analysis*; D045483:Rivers / Q000737:chemistry*; D014865:Waste Disposal, Fluid / Q000295:instrumentation; D014872:Water Movements; D014874:Water Pollutants, Chemical / Q000032:analysis*; D018508:Water Purification / Q000295:instrumentation; D060753:Water Quality
chemical_list: D014874:Water Pollutants, Chemical; D010758:Phosphorus