Contributions and dynamics of pesticide loads from riparian crop fields in the Luxembourg Sandstone catchment Kielbach
Owing to the dynamic character of pesticide emissions to surface waters from arable fields it is useful to make overall yearly balances of the parent compound and the metabolites of a pesticide to capture the multiple phases of mobilisation: surface runoff of parents shortly after application and, with advancing time, metabolites in interflow of flood waves. Passive samplers are ideally suited to continuously sample pesticide concentrations in surface waters. Loads can be calculated and normalized to arable surface or even specific crops if the information is available. This exercise has been successfully carried out within the PestList2 project, comparing (sub-)catchments across geologies in western Luxembourg. However, the question remains to what extent all the arable surfaces contribute equally to the measured loads independently of their distance and hydrological connectivity to surface water. This question is especially relevant for the Luxembourg Sandstone area, where large agricultural plateaus are elevated above the valleys with rather long flow paths to receiving rivers.
This project aims to quantify the contributions of individual maize fields to the overall balance in the catchment of the Kielbach, a 19 km2 large catchment in the Luxembourg Sandstone area with a special focus on riparian arable fields in the marly parts (li3) of the catchment. The difference between these load contributions and the overall balance will yield the proportion of pollutants that can be attributed to the plateaus. It is expected that there is a strong mismatch in sources between parent compounds and metabolites, owing to their contrasting flow paths.
The monitoring strategy relies on both passive samplers that isolate relatively small stretches of the stream in which maize fields are adjacent, combined with high resolution hydro-/chemographs at the catchment outlet that will allow attribution of the loads to flow components (autosampling assisted by continuous probes). Passive samplers have been previously used in an urban hydrology context to track industrial emitters in the sewer network in the SourceControl project. This is the same concept transferred to more diffuse inputs in the landscape.
Being able to physically track sources of loads in a longitudinal profile over a whole season is extremely useful in evaluating the impact of arable fields according to their closeness to the stream and implicitly in relation to their overland or underground hydrologic connectivity. This case study will allow evaluation of the necessity and pertinence of runoff mitigation as compared to metabolite inputs through underground flow paths. It is therefore of great interest to the implementation of the national pesticide reduction plan and of the Water Framework Directive.
<p>T. Gallé, M. Bayerle, D. Pittois, and V. Huck</p>
<p>Water Research, vol. 173, art. no. 115533, 2020</p>
<p>T. Galle, M. Frelat, V. Huck, M. Bayerle, D. Pittois, and C. Braun</p>
<p>Environmental Science: Processes & Impacts, vol. 22, no. 2, pp. 294-304, 2020</p>
Carafa R., Gallé T., Massarin S., Huck V., Bayerle M., Pittois D., Braun C.
Environmental Toxicology and Chemistry, vol. 41, n° 11, pp. 2667-2678, 2022