The role of storm flows in concentration of pesticides associated with particulate and dissolved fractions as a threat to aquatic ecosystems - Case study: the agricultural watershed of Save river (Southwest of France)

Abstract

Key-words: pesticide, TSM, DOC, hysteresis patterns, flood flowMeasurement of the fluxes of pesticides was carried out for a year, ending in March 2009, in the Save catchment, in the vicinity of Toulouse. The hydrograph separation technique was used to evaluate the respective contribution of stormflow and baseflow in transport of 12 pesticide molecules. Transport of over 59% of pesticides and their controlling factors such as total suspended matter (TSM), particulate organic carbon (POC) and dissolved organic carbon (DOC) occurred during storm periods. Hysteresis patterns could be observed in the concentration-discharge relationships only for some molecules between rising and falling periods of the storm hydrograph. Clockwise hysteresis was noticed for low to moderately soluble pesticide molecules and for particulate fractions, which explains the role of surface runoff in pesticide displacement. In contrast, anticlockwise hysteresis was registered for soluble molecules and dissolved fractions, explaining the role of subsurface flows and soil leaching processes. The important role of TSM, POC and DOC in pesticide transport was clearly established. We also came to the conclusion that the role of stormy periods in pesticide movement and their controlling factors worked as a threat to aquatic ecosystems. And there was a positive relation between riverine TSM, POC, DOC and pesticides according to pesticide properties. RÉSUMÉLe rôle des crues sur la concentration en pesticides associés aux fractions particulaires et dissoutes, une menace pour les écosystèmes aquatiques Cas d'étude : le bassin versant agricole de la rivière Save (sud-ouest de la France) Mots-clés :pesticide, MES, COD, hystérésis, crue transportés durant les périodes de crue. Des hystérésis peuvent être observées sur les relations concentrations-débits, uniquement pour quelques molécules, entre la montée et la descente de crue. Des hystérésis dextres (sens des aiguilles d'une montre) sont observées pour les molécules peu ou modérément solubles et pour les fractions particulaires montrant le rôle du ruissellement de surface dans le transfert des pesticides. Au contraire, des hystérésis senestres (sens inverse) sont observées pour les molécules solubles et les fractions dissoutes montrant le rôle des écoulements hypodermiques et du lessivage des sols. On a pu établir clairement le rôle important des MES, du COP et du COD dans le transport des pesticides. Les résultats obtenus nous montrent aussi le rôle joué par les épisodes de crue sur les transferts de pesticides et de leurs facteurs de contrôle, représen-tant un risque potentiel important de contamination des eaux et une menace pour les écosystèmes aquatiques. Des relations positives sont mises en évidence entre les teneurs en MES, COD ou COP et les concentrations en pesticides selon les propriétés physico-chimiques des différents pesticides.

Significance of floods in metal dynamics and export in a small agricultural catchment

“…2). The same pattern was already observed in the same area for hydrophobic molecules of pesticides (Taghavi et al, 2010(Taghavi et al, , 2011.…”

Hydrological hysteresis and its value for assessing process consistency in catchment conceptual models

“…Hysteresis patterns between concentration and discharge have been largely documented for storm event characterization (Evans and Davies, 1998;Evans et al, 1999;Taghavi et al, 2011). Some studies also report similar patterns on the annual scale (e.g.…”

High-frequency monitoring of surface water quality at the outlet of the Ibrahim River (Lebanon): A multivariate assessment

“…Water samples were collected at the outlet of the Ibrahim River with higher density during flood events. In fact, high fluxes of materials are exported to the outlet of rivers during these hydrological events (El Azzi et al, 2013;El Azzi et al, 2016;Taghavi et al, 2011). Both physicochemical and microbiological parameters were then tested, and a multivariate study formed the basis for the development of an Ibrahim WQI ( IWQI) which would reliably describe and rate the quality of the water in the future.…”