Biodiversity and the health of freshwater ecosystems is strongly impaired by human activities,
compromising the stability of these ecosystems and the ecosystem services they provide. Global
and European efforts to halt the biodiversity decline and protect ecosystem health were not very
successful, especially for rivers, so that for less than ten percent of the German rivers good
ecological status was reached in 2021. Present-day agriculture has been identified as the main
driver for this deterioration, as evident from a multitude of studies. However, the agricultural
effects differ between the organism groups and depending on environmental conditions like soil
and climatic conditions. Moreover, and most importantly, agriculture is not uniform. The
specific agricultural types and practices differ between regions, which in turn leads to
differences in the intensity of agrochemical usage as suggested by many small-scale studies.
Consequently, the magnitude of agricultural effects on biodiversity and health of river
ecosystems most probably depends on agricultural types and practices and differs between
regions. For the effective mitigation of these negative effects, several knowledge gaps need to
be closed, which were addressed in six chapters, shortly described in the following.
First, the current knowledge on the effect of agriculture on river biota was summarized and
analysed in a meta-analysis (Schürings et al., 2022). According to this meta-analysis described
in the first chapter, agriculture has an overall medium to high negative effect on river biota, and
results indicate that the effects of agriculture differ between agricultural types, practices, the
organism groups, and biological metrics considered. Second, a pan-European dataset was used
to establish an agricultural typology, based on agricultural production and agriculture-related
freshwater pressure by nutrients, pesticides, water abstraction and hydromorphological
alterations (Schürings et al., 2023). This chapter identified how agricultural types differ in their
pressures exerted on freshwaters and shows that accounting for agricultural pressure intensity
nearly doubles the correlation with the ecological status. Third, the effects of different
agricultural types on the ecological status according to the EU Water Framework Directive
(WFD) were investigated, using high resolution German-wide land use data, distinguishing
between different crop types (Schürings et al., 2024a). The effects on the ecological status
clearly differed between crop types, which typically are associated with different agrochemical
application rates. Macroinvertebrates and macrophytes were most strongly affected by pesticide
application intensive crops and diatoms were most affected by nutrient intensive crops. Fourth,
the results presented in Markert et al. (2023) provided evidence that urban areas and different
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agricultural crop types with typical agrochemical application rates are indeed related to the
micropollutant concentrations monitored in rivers, which often exceeded Environmental
Quality Standards. Fifth, crop type-specific differences in agrochemical application rates
reported in literature were used to generate an agricultural intensity index (Schürings et al.,
2024b). This index improved the correlative strength between present-day agriculture and the
ecological status with most pronounced relations for macroinvertebrates in small mountain
streams. Sixth, experiences from implementing environmental legislations like the WFD were
used to advice for a successful implementation of the EU Nature Restoration Law (Hering et
al., 2023). This final chapter highlights that joining restoration efforts with a shift to more
sustainable agriculture, whose importance is reasoned in the previous chapters, would offer
unprecedented opportunities for successful protection of ecosystem health.
In conclusion, this thesis provides overwhelming evidence for the negative effects of present-
day agriculture on river biota, portraying influencing factors and highlighting strong
relationships between agricultural effects on river biota and agrochemical application,
particularly of pesticides. Therefore, to mitigate these effects, a transition of present-day
agriculture to more sustainable practices, such as organic farming or agroecology is of vital
importance. Such a transition would be beneficial both for the future viability of agriculture
itself but also for the protection and restoration of healthy ecosystems, including the successful
implementation of the European environmental legislation such as the Nature Restoration Law.