Loss potential and retention efficiency of pesticides and their transformation products in a small drained agricultural catchment

The overall objective of this thesis is the elaboration of the impacts to the aquatic environment of pesticides and their transformation products (TPs) in tile-drained agricultural headwater catchments. To identify retention measures for impacted areas, the hydrology of a catchment and the pesticide transport pathways were analysed. For a spatial comparison, monitoring was carried out at the field and catchment scale in different environmental compartments. Environmental conditions such as soil moisture and temperature, and the behaviour of fluorescent tracers in the soil were elucidated to derive new conclusions on the transport and transformation behaviour of pesticides in soil and leaching to shallow groundwater at the field scale. Field investigations at field and catchment scales were used to analyse the influence of physico-chemical properties, hydroclimatic and agricultural factors on pesticide transport in tile drainage. A drainage pond system was investigated regarding its pesticide retention capacity. The drainage pond system was modified to increase the flow paths and residence time of the pesticides and TPs in the ponds. In this dissertation, it was shown that high loads of pesticides occur at field and catchment scales in the short and long term under both dry and wet climatic site conditions. In particular, the permanent detection of mobile and persistent TPs poses a risk. Future efforts should focus on improving regulatory monitoring strategies, such as monitoring of tile drainages and setting limits for TPs in the Surface Water Regulation. In summary, existing drainage ponds can serve as retention measures if the temporal loads for pesticides and TPs, as well as the hydrological characteristics are recorded and, on this basis, pond modifications are made to improve retention. Hence, the need to promote small-scale agricultural retention measures close to field was demonstrated to improve downstream water quality.


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