Exporatory Study to assess the impact of climatic anomalies and agricultural yields on water quality from agricultural drainage - INRAE - Institut national de recherche pour l’agriculture, l’alimentation et l’environnement
Master Thesis Year : 2019

Exporatory Study to assess the impact of climatic anomalies and agricultural yields on water quality from agricultural drainage

Abstract

The development of intensive agricultural practices, especially abusive use of mineral and synthetic N-fertilizers, are leading to increased levels of Nitrate pollution of water in regions where anthropologic N inputs are the highest. Strong contamination of water by Nitrate is leading to severe inconveniences for populations and ecosystems, undrinkable water and coastal eutrophication being the main ones. Agricultural drainage is often used for agricultural plots to remove winter excess water in agricultural regions located on “hydromorphic soils” suffering from recurring water saturation damaging crop development. Watersheds with high drainage intensity can be seen as giant reservoirs behaving like lysimeters exporting incoming water and nutrients – including different forms of Nitrogen – from potentially polluted agricultural plots to surface watercourses thanks to the network of tile drains (Minaudo et al., 2019). Therefore, higher Nitrate content in drained soil exposes affected territories to bigger NO3 exports by drainage. In this report, we investigate whether extreme climate events recorded during the last decades in France lowered agricultural yield, which implies bigger quantities of available NO3 for export by drainage during the first months of the following hydrological season. We used a panel of different databases to have access to data on discharge, climate, agricultural yields, and Nitrate concentration for 37 French watersheds selected because of their drainage intensity. We also include the drained watershed of Mélarchez (709ha) – involved in a French research observatory on water quality – to this research. We used the SIDRA-RU model to assess the contribution of drainage to the hydrological behavior of these watersheds, and we performed Anova statistical tests to analyze if there is a decrease of agricultural yields and increase of NO3 concentration when drainage restarts in winter after the watersheds experienced climatic anomalies. Our results show that drainage has a big influence on the hydrology of studied watersheds. We also observed that extreme climate events affect significatively agricultural yields in these studied watersheds, and that lower yields lead to an increased contamination of water by NO3 in Mélarchez, attributed to a bigger export by of available Nitrate in soil by drainage possibly because of a lower Nuptake by plants following a lower crop development. Even if we did not observe such relation between agricultural yields and Nitrate concentration at the outlet of the 37 selected watersheds, our exploratory study tends to reveal that small watersheds with intensively drained agriculture are exposed to bigger Nitrate exports to surface watercourses after climatic anomalies that affected crop growth and development. This emphasized the need for better agricultural practices managing N inputs to the soil and curative measures aiming at enhancing nitrate retention or elimination through natural processes occurring in the drainage network.
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Dates and versions

hal-04208862 , version 1 (15-09-2023)

Identifiers

  • HAL Id : hal-04208862 , version 1

Cite

Matthieu Descout. Exporatory Study to assess the impact of climatic anomalies and agricultural yields on water quality from agricultural drainage. Environmental Sciences. 2019. ⟨hal-04208862⟩
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