Our ecosystems are threatened by the consequences of the global biodiversity crisis: habitat loss and fragmentation, overexploitation, pollution, and climate change drive species, ecosystem, and genetic diversity losses. Freshwater ecosystems are highly diverse, harboring 12 % of all described species (fungi, plants, invertebrates, and vertebrates) condensed on just 2 % of the world's surface (Albert et al. 2021). Yet, they are also among the most endangered and vulnerable ecosystems. Globally, aquatic insects have declined by 33 % (Sánchez-Bayo and Wyckhuys 2019). Ponds, in particular, host high macrophyte and macroinvertebrate diversity as well as high numbers of rare and endangered species, making them biodiversity hotspots (Williams et al. 2004). However, ponds are highly susceptible to biotic and abiotic stressors and remain understudied compared to larger water bodies (Ulrich et al. 2022). Addressing this research gap is urgent given accelerating freshwater biodiversity loss (Sánchez-Bayo and Wyckhuys 2019; Darwall et al. 2018; Kelly-Quinn et al. 2017; Reid et al. 2019). To support effective conservation and management, this thesis focuses on assessing water and habitat quality of small water bodies (SWBs) in agricultural landscapes, given that the main causes of biodiversity loss include pollution and the destruction and fragmentation of habitats, using benthic macroinvertebrates as indicator organisms.
The first publication focuses on pesticides, showing their presence in SWBs across large spatial and detailed temporal scales. Eight pesticides were frequently detected regionally, and it was determined that a constant herbicide contamination negatively affects ecosystems. The second publication focuses on the biology and it was found that habitat type most strongly shapes community composition, while structural biodiversity indices are insufficient for depicting the influence of agricultural stressors. Thus, the third publication links indirect pesticide effects to benthic macroinvertebrate diversity, introducing a new multimetric indicator that reveals these impacts. The fourth publication applies a functional approach, using stable carbon and nitrogen isotope ratios to assess agricultural effects on the isotopic niches of six functional feeding groups in ponds and ditches. No differences were found between the two water body types (pond and ditch) and their different exposure to the agricultural stress factor (pesticides) for the isotope niches of the functional feeding groups. The small and unstable systems studied are more affected by strong fluctuations in abiotic and biotic factors. Results from the case study indicate that benthic macroinvertebrates respond to the stressors in complex ways.
By integrating chemical and biological analysis from both taxonomic and functional perspectives, this thesis aims to provide a more holistic and nuanced understanding of biodiversity patterns in SWBs and the challenges of detecting changes in communities due to agricultural stressors, with the ultimate goal of informing conservation policy.
