School of Geography and Environmental Sciences, Ulster University, Coleraine, UK.
Agricultural Catchments Programme, Teagasc, Johnstown Castle, Wexford, Ireland.
Water Res. 2022 Jul 15;220:118654. doi: 10.1016/j.watres.2022.118654. Epub 2022 May 24.
Detection of the agricultural acid herbicide MCPA (2-methyl-4-chlorophenoxyacetic acid) in drinking water source catchments is of growing concern, with economic and environmental implications for water utilities and wider ecosystem services. MCPA is poorly adsorbed to soil and highly mobile in water, but hydrological pathway processes are relatively unknown at the catchment scale and limited by coarse resolution data. This understanding is required to target mitigation measures and to provide a framework to monitor their effectiveness. To address this knowledge gap, this study reports findings from river discharge and synchronous MCPA concentration datasets (continuous 7 hour and with additional hourly sampling during storm events) collected over a 7 month herbicide spraying season. The study was undertaken in a surface (source) water catchment (384 km-of which 154 km is agricultural land use) in the cross-border area of Ireland. Combined into loads, and using two pathway separation techniques, the MCPA data were apportioned into event and baseload components and the former was further separated to quantify a quickflow (QF) and other event pathways. Based on the 7 hourly dataset, 85.2 kg (0.22 kg km by catchment area, or 0.55 kg km by agricultural area) of MCPA was exported from the catchment in 7 months. Of this load, 87.7 % was transported via event flow pathways with 72.0 % transported via surface dominated (QF) pathways. Approximately 12 % of the MCPA load was transported via deep baseflows, indicating a persistence in this delayed pathway, and this was the primary pathway condition monitored in a weekly regulatory sampling programme. However, overall, the data indicated a dominant acute, storm dependent process of incidental MCPA loss during the spraying season. Reducing use and/or implementing extensive surface pathway disconnection measures are the mitigation options with greatest potential, the success of which can only be assessed using high temporal resolution monitoring techniques.
检测饮用水源集水区中农业酸性除草剂 MCPA（2-甲基-4-氯苯氧乙酸）的工作越来越受到关注，这对供水公司和更广泛的生态系统服务具有经济和环境意义。MCPA 在土壤中吸附性差，在水中移动性高，但在集水区尺度上，水文路径过程相对未知，且受到粗分辨率数据的限制。为了有针对性地采取缓解措施，并提供监测其有效性的框架，需要了解这些过程。为了弥补这一知识空白，本研究报告了在爱尔兰跨境地区的一个地表水（源）集水区（384 平方公里，其中 154 平方公里为农业用地）进行的为期 7 个月的除草剂喷洒季节中，河川径流量和同步 MCPA 浓度数据集（连续 7 小时，在暴雨事件期间增加每小时采样）的研究结果。将 MCPA 数据结合成负荷，并使用两种路径分离技术，将 MCPA 数据分配到事件负荷和基流负荷成分中，然后进一步将前者分离，以量化快速流（QF）和其他事件路径。根据 7 小时数据集，在 7 个月内，有 85.2 千克（流域面积为 0.22 千克/平方公里，或农业面积为 0.55 千克/平方公里）的 MCPA 从集水区中输出。在该负荷中，87.7%通过事件流路径运输，其中 72.0%通过地表主导（QF）路径运输。大约 12%的 MCPA 负荷通过深层基流运输，表明这种延迟路径具有持久性，这是每周监管抽样计划中监测的主要路径条件。然而，总体而言，数据表明在喷洒季节中存在一种以急性、依赖于风暴的方式偶然损失 MCPA 的主导过程。减少使用和/或实施广泛的地表路径断开措施是最有潜力的缓解选择，只有使用高时间分辨率监测技术才能评估其成功与否。
