A hydrologically informed agricultural land use intensity index for assessing ecological impacts on streams and rivers

Abstract The concept of land-use intensity has been widely used to quantify human impacts in terrestrial systems, yet such approaches fail to capture the cumulative effects of land use on connected river networks. Here, we introduce the Land Use Intensity Index for Stream Ecosystems (LUIS), a spatially explicit, hydrologically informed index that integrates crop-specific inputs of nitrogen, phosphorus, and pesticides with river network structure. To evaluate the relationship between agricultural pressures and water quality, we used logistic regression and a random forest classification model to assess overall ecological status and biological quality elements across Germany. Pesticide pressure showed the strongest association with ecological status, exhibiting the highest effect sizes, R² values, and predictor importance across both low- and high-order streams. These associations were especially pronounced in low-order streams and the central highlands, likely due to their limited dilution capacity and direct exposure to runoff. Phosphorus showed secondary relevance, particularly in higher-order streams, while nitrogen’s effects were less distinct. LUIS is a valuable tool for assessing the compound-specific and combined pressures of agricultural land use on stream ecosystems. Its mechanistically informed yet conceptually flexible framework provides a solid basis for future development and integration into operational monitoring and management contexts.