Current-use pesticide exposure of riparian ecosystems – stream buffer or non-target habitat?

Riparian non-target buffer zones (RNBZ) are widely implemented to reduce pesticide pollution of surface waters, yet their dual role as protective barriers and semi-natural habitats remains contested, particularly where management targets mitigation rather than conservation. We quantified gradients of pesticide contamination from fields across RNBZ to small streams by sampling vegetation, topsoil, and water at 24 sites spanning RNBZ widths of 10-260 m. At each site we collected samples 1, 2, and 5 m into the RNBZ from both field and stream sides. 93 current-use pesticides (CUPs) were analysed, and residues were detected in all matrices and at every site, demonstrating widespread contamination across riparian zones. On average, topsoil and vegetation contained complex mixtures, with 9.3 and 9.8 CUPs on the field side and 7.7 and 10.7 CUPs on the stream side. Greater RNBZ width significantly reduced CUP numbers in topsoil but not in vegetation. In wine-growing catchments, upstream RNBZ topsoil and vegetation showed higher CUP contamination than downstream, indicating viticulture as a key driver. Contamination increased toward the stream within RNBZ topsoil and vegetation, consistent with accumulation or entry via flooding or infiltration. Jaccard dissimilarities indicated distinct CUP mixture patterns between stream water and riparian soil and vegetation. These findings highlight that RNBZ width alone cannot explain pesticide dynamics and that riparian contamination may reflect a widespread, landscape-scale phenomenon rather than a local anomaly. Effective mitigation should integrate vegetation structure, land-use context, and contamination pathways to strengthen both the protective and habitat roles of riparian zones.