Assessment of cultivation intensity can improve the correlative strength between agriculture and the ecological status in rivers across Germany

Abstract

Agriculture has been identified as a main cause for more than 90% of Germany´s rivers still not meeting good ecological status in 2021. While many large-scale studies observed a negative effect of catchment agricultural land use on river biota, they rarely considered differences in cultivation intensities, although small-scale studies highlight clear differences between the effects of agricultural crops. Here we used Germany-wide and spatially explicit information on crop types to calculate agricultural intensity indices for nutrients and pesticides, weighting different crop types based on average pesticide treatment and nutrient application rates. These indices were then used as explanatory variables for the ecological status of n = 7677 biological sampling sites. Pesticides were more important than nutrient pollution for macroinvertebrates and macrophytes, while diatoms were more sensitive to nutrients. Considering the most relevant intensity index (pesticide or nutrient) slightly increased the correlative strength with ecological status, as compared to the correlation with agricultural land or cropland cover by up to R² = 0.14 for diatoms. Correlative strength of agricultural intensity indices was substantially larger in small mountain and (pre)-alpine streams compared to lowland streams, with an R² up to 0.43 for macroinvertebrates. These results not only confirm previous large-scale studies by demonstrating the detrimental effects of present-day agriculture on river biota, but also shed light on the main pathways involved, particularly highlighting the adverse impacts of agrochemicals. Consequently, to protect river biota, a shift to more sustainable agricultural practices, like reducing pesticide application, is urgently required.