Characterizing pesticide fate in the vegetated unsaturated zone and estimating potential impacts to groundwater

Arno Rein1, Fatemeh Shajari1, Florian Einsiedl1
1 Lehrstuhl für Hydrogeologie, Technische Universität München

O 5.5 in Organic pollutants in groundwater

23.03.2018, 10:45-11:00, 3

Maize cultivation is currently intensified in many countries, in the context of food and forage production as well as for the use as energy plants. Pesticides and other agrochemicals are increasingly used, however often posing serious threats to groundwater, human health and non-target ecosystems. In this work we carried out lysimeter studies with four different soils planted with maize. In a five-year study, four pesticides have been applied once a year according to common agricultural practice. Pesticides and some of their metabolites were monitored in the lysimeter outflow water.

Observations revealed, in many cases, considerably high concentration peaks in outflow water shortly after application, and we aim at systematically investigating processes that could explain these findings. The first step is characterizing water flow where we use stable water isotopes as natural tracers. Stable water isotopes were measured in precipitation and lysimeter outflow water, and we use different lumped-parameter models in order to determine the mean residence time of water, dispersion properties and the possible contribution of preferential flow paths. First results, considering a time period 1.5 years, revealed mean residence times of water of about 150 days for a sandy gravel soil and about 250 days for a silt soil. Studies are currently extended to consider longer time periods (3.5 years or more). Next steps focus on chemical transport and fate. Compound-specific isotope analyses gave hints on biodegradation activity occurring in the subsurface to some extent. First mass balance estimates suggest a strong contribution of soil sorption on chemical fate. Modeling studies are currently under way for considering biodegradation under different conditions of bioavailability, as well as for estimating the contribution of plant uptake. Aims include the estimation of process contributions as well as possible consequences in terms of groundwater vulnerability.

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