River eutrophication: Irrigated vs. non-irrigated agriculture through different spatial scales

► The influence of land use on river eutrophication was scale-dependent. ► Scale based on 1 km radius upstream buffers produced the best results. ► Irrigation turned out to be the main cause of river eutrophication. ► Surpassing 50% of irrigated fields on river sides may cause river eutrophication. ► A new methodological approach to choose the appropriate spatial scale is proposed.