Ken Maximilian Mauser

• Agricultural intensification and climate change increase pressure on biodiversity, with pesticides dispersing beyond treated fields into non-target areas. This thesis investigated three major stressors relevant to aquatic-terrestrial ecosystems: pesticide contamination, altered hydrological regimes, and the mosquito control agent Bacillus thuringiensis israelensis (Bti). It addresses the lack of data on the environmental presence and spatio-temporal dynamics of pesticide contamination and on how different environmental stressors influence trait development in aquatic-terrestrial organisms, with potential consequences for reproduction and higher trophic levels. This thesis combines multi-scale mapping of pesticide residues with computer-vision analysis of morphological traits of a damselfly under controlled exposures to each stressor. It uses a tiered approach linking field observations, experiments, and validation across scales for mechanistic and ecological insight. Large-scale pesticide monitoring across the Upper Rhine Valley in Germany revealed pronounced spatial gradients and pervasive background contamination. Prediction maps identified regional hotspots of mixture complexity, and contamination of conservation areas far from agricultural land. Temporal monitoring demonstrated chronic contamination in soils and seasonal peaks in vegetation during periods of high biological activity. At finer scales, riparian non-target buffer zone assessment showed high contamination regardless of buffer width, challenging their function as effective buffers or refuges for non-target organisms. Together, these studies showed pesticide mixtures to be a widespread and persistent characteristic in non-target habitats. Experimental exposures of damselfly larvae to an insecticide, Bti, and altered hydrology produced distinct trait signatures in wing morphology, including size, structure and asymmetry indicating changes in developmental stability. In two damselfly populations, morphological predictors of short-term mating success varied between sites, indicating that trait-fitness relationships are environmentally mediated. Furthermore, changes in emerging insect prey quality influenced higher trophic levels by affecting the developmental stability in riparian spiders. This research reveals that environmental stressors can alter morphological traits in aquatic organisms that are linked to important terrestrial processes such as mating success and predator-prey interactions. The widespread detection of pesticide mixtures in non-target areas suggests exposure pathways that current regulatory frameworks may not adequately address. The findings also emphasize the need for integrated management approaches that consider cross-ecosystem connectivity when assessing the ecological implications of micropollutants and climate change.