Mitigating pesticide levels in surface waters: Long-term surface water monitoring in an agricultural catchment

While several human activities influence water quality, agriculture remains an important source of water-related problems. The use of pesticides during agricultural production can negatively influence water quality and be a threat to aquatic ecosystems. Pesticides can enter watercourses through different pathways such as runoff, erosion, drift or point losses and be diffused in the environment. Despite the efforts, many European rivers still show pollution from agricultural sources. Targeted mitigation measures in agriculture could reduce the environmental impact of pesticides and help to reach the desired surface water quality at a particular location. Vegetated buffer strips between water bodies and agricultural fields are applied to reduce the export of sediments, pesticides and nutrients from agricultural fields to surface waters. Since 2014, a monitoring campaign has been carried out within a representative catchment in SE Flanders (Belgium), in an area known for its intensive agriculture (>70%) and frequent detection of pesticides in water bodies. The site was selected based on results from geospatial pesticide emission modelling, historical glyphosate concentrations, and land use. The primary objective of this 5-year study (2014-2018) is to evaluate and quantify the effect of implemented mitigation measures on runoff and glyphosate loads into surface water. The monitoring consists of a combination of time-based (to establish baseline concentrations and grasp the direct losses) and event-based (to detect the rainfall-runoff related inputs) automatic sampling during the agricultural season (April to October). Glyphosate and its major metabolite aminomethylphosphonic acid (AMPA) were selected as monitoring substances for this project since glyphosate has been frequently detected in watercourses in Flanders. Following a communication campaign targeted to the farmers with fields in the most critical zones, vegetated buffer strips were implemented within the catchment. Additionally, farmer awareness on risks and good practices related to point losses was raised. We investigated two years before (baseline monitoring) and three years after implementation of the mitigation measures. By analysing the results during base flow and peak flow conditions, the contribution of different pathways to the pesticide loads and the effectiveness of measures is investigated. We will present the setup and the results of the monitoring campaign, with the evaluation of the effect of several mitigation measures within the catchment on pesticide loads reduction