Open access publications in the SLU publication database

Abstract

Pesticide residues in groundwater and surface waters may harm aquatic ecosystems and result in a deterioration of drinking water quality. EU legislation and policy emphasize risk management and risk reduction for pesticides to ensure long-term, sustainable use of water across Europe. Different tools applicable at scales ranging from farm to national and EU scales are required to meet the needs of the various managers engaged with the task of protecting water resources. The use of computer-based pesticide fate and transport models at such large scales is challenging since models are scale-specific and generally developed for the soil pedon or plot scale. Modelling at larger scales is further complicated by the spatial and temporal variability of agro-environmental conditions and the uncertainty in predictions. The objective of this thesis was to identify the soil processes that dominate diffuse pesticide losses at field and landscape scales and to develop methods that can help identify 'high risk' areas for leaching. The underlying idea was that pesticide pollution of groundwater and surface waters can be mitigated if pesticide application on such areas is reduced. Macropore flow increases the risk of pesticide leaching and was identified as the most important process responsible for spatial variation of diffuse pesticide losses from a 30 ha field and a 9 km² catchment in the south of Sweden. Point-sources caused by careless handling of pesticides when filling or cleaning spraying equipment were also a significant source of contamination at the landscape scale. The research presented in this thesis suggests that the strength of macropore flow due to earthworm burrows and soil aggregation can be predicted from widely available soil survey information such as texture, management practices etc. Thus, a simple classification of soils according to their susceptibility to macropore flow may facilitate the use of process-based models at the landscape scale. Predictions of a meta-model of the MACRO model suggested that, at the field scale, fine-textured soils are high-risk areas for pesticide leaching. Uncertainty in pesticide degradation and sorption did not significantly affect predictions of the spatial extent of these high-risk areas. Thus, site-specific pesticide application seems to be a promising method for mitigating groundwater contamination at this scale.