Agricultural Catchments Programme, Teagasc, Johnstown Castle, Wexford, Ireland; Environmental Change Institute, National University of Ireland, Galway, Ireland.
School of Environmental Sciences, Ulster University, Coleraine, N. Ireland, UK.
Sci Total Environ. 2015 Jul 1;520:286-99. doi: 10.1016/j.scitotenv.2015.02.017. Epub 2015 Apr 1.
Faecal indicator organisms (FIOs) can impact on water quality and pose a health and environmental risk. The transfer of FIOs, such as Escherichia coli (E. coli), from land to water is driven by hydrological connectivity and may follow the same flowpaths as nutrients, from agricultural and human sources. This study investigated E. coli transfer in two catchment areas with high source and transport pressures. These pressures were: organic phosphorus (P) loading; human settlement; conduits and fissures in a grassland karst area; and clay rich and impermeable soils in a mixed arable area. The occurrence of E. coli and its transport pathways, along with the pathways of nutrients, were studied using a combination of targeted FIO sampling, during different hydrological phases and events, and high resolution nutrient analysis. The quick flow component in both catchments was found to be a more potent vector for E. coli, and was coincident with the total P flowpaths using a P Loadograph Recession Analysis (LRA). The karst grassland catchment was found to be a transport limited system and the mixed arable catchment a source limited system. Hence, despite the grassland catchment being a potentially higher FIO source, the E. coli loads leaving the catchment were low compared to the mixed arable catchment. E. coli load whole-event comparisons also indicated that the grassland karst transfers tended to be much lower on falling phases of runoff, while the arable catchment, over greywacke and mudstone geology, showed little change between the phases. Furthermore, the arable catchment showed asymptotic decline of sustained E. coli loads towards low flows, which may be indicative of chronic point sources. These results indicate the dominance of transport mechanisms over source mechanisms for mass E. coli loads and also chronic loads during low flow. These will be important considerations for risk assessment and mitigation.
粪大肠菌群（FIO）会影响水质，并对健康和环境构成风险。粪大肠菌群，如大肠杆菌（E. coli），从陆地转移到水中是由水文连通性驱动的，并且可能沿着与营养物质相同的路径流动，这些路径来自农业和人类活动的源头。本研究调查了两个具有高源和传输压力的集水区中大肠杆菌的转移情况。这些压力包括：有机磷（P）负荷；人类住区；草地岩溶区的管道和裂隙；以及混合耕地区富含粘土且不透水的土壤。本研究通过在不同水文阶段和事件中结合靶向 FIO 采样以及高分辨率养分分析，研究了大肠杆菌的发生及其传输途径，以及营养物质的传输途径。发现两个集水区的快速流分量都是大肠杆菌的更有力载体，并且与总 P 流路径一致，使用磷负荷退水分析（LRA）。发现岩溶草地集水区是一个传输受限系统，而混合耕地集水区是一个源受限系统。因此，尽管草地集水区是潜在的更高 FIO 源，但与混合耕地集水区相比，离开集水区的大肠杆菌负荷较低。整个事件的大肠杆菌负荷比较也表明，在径流水位下降阶段，草地岩溶的转移往往要低得多，而在灰砂岩和泥岩地质条件下的耕地集水区，在各阶段之间变化很小。此外，耕地集水区的持续大肠杆菌负荷在低流量时呈渐近下降趋势，这可能表明存在慢性点源。这些结果表明，对于质量大肠杆菌负荷和低流量期间的慢性负荷，传输机制比源机制更为重要。这些结果对于风险评估和缓解措施非常重要。
