The unseen threat: indirect pesticide effects are key to realistic ecological assessments of standing small water bodies

Abstract Standing small water bodies are biodiversity hotspots and contribute to landscape-level ecosystem services. Concurrently, they are subject to agricultural land use effects such as pesticide contamination. Holistic assessments of pesticide effects on invertebrate communities in standing small water bodies have, however, not yet been successful. Therefore, we (1) develop an indicator evaluating pesticide impacts on macrozoobenthos communities through indirect toxic effects on aquatic plants ( INPOND ; IN direct P esticide impacts ON D iversity in standing small water bodies); (2) test and compare INPOND against common functional and structural biodiversity indices for ecological status assessment; and (3) provide a holistic assessment of direct and indirect pesticide effects on invertebrate communities in standing small water bodies in Germany. The indicator development process included structural and functional biodiversity indices, tested for correlations with toxic units for invertebrates, algae, and aquatic plants. Our results indicate low direct pesticide toxicity risks for macrozoobenthos in most of the investigated water bodies. However, INPOND reveals a high risk to invertebrates through pesticide-induced changes in aquatic plant communities, an essential habitat component shaping invertebrate assemblages. Consequently, we recommend the combined use of INPOND and toxicity impact indicators to achieve holistic assessments of pesticide risks for macrozoobenthos in standing small water bodies.