Innovative tools for watershed-scale water quality monitoring to identify and quantify micropollutant hotspots in Mediterranean climate first-flush storm waters

Streams worldwide suffer from water quality degradation to an extent that their ecological function has been severely impaired. In Mediterranean climates, runoff generated during short, intense winter rainstorms becomes a major pathway for transporting micropollutants from agricultural areas, especially during early storms when agricultural soils are often bare and most vulnerable to erosion. To address the global imperative of mitigating water pollution, effective strategies are required to pinpoint priority agricultural pollution sources and advance nature-based source control. A watershed-scale sampling approach was designed to characterize stormflows in the Kishon Basin, Israel and identify polluting compounds with high concentrations, aimed at tracing contamination ‘hotspots’ to specific sub basins.  Existing methods often miss variation in hydrochemistry dynamics during storm events and focus only on dissolved chemicals.  We present an innovative tool to characterize sediment-bound pollutants, and combine this with conventional grab sampling and passive samplers, to better represent the whole storm hydrograph. This study investigated polar organic pollutants, including agricultural pesticides and pharmaceuticals derived from treated wastewater used for irrigation. Passive sampler results identified a total of 169 pesticides based on suspect screening and quantified 98, with an average of 32 different pesticides identified in each sampling location. We identified 59 pesticides, 15 pharmaceuticals, and 22 metals using the grab sampling method, with 25 pesticides that were identified and quantified in all three methods. The sediment trap results identified that only one of the 19 tributaries contributed heavy metals to the Kishon River.  Pesticides banned for over a decade, which degrade quickly, were detected throughout the basin, suggesting illegal continued applications. This approach enabled improved understanding of specific chemical transport methods and clear identification of priority tributaries and their chemical contributions, advancing a new approach to watershed management. Application of study findings will support development of strategic plans to improve the farm-stream interface, conserve soil resources, protect water quality, facilitate source control and provide crucial support for decision-makers formulating intervention strategies, demonstrating a model for a national watershed monitoring program.