Role of Pond Sediments for Trapping Pesticides in an Agricultural Catchment (Auradé, SW France): Distribution and Controlling Factors

Abstract

In agricultural areas, ponds are suitable wetland environments to dissipate and reduce the occurrence of pesticides in aquatic environments. However, their impact at a catchment scale is still poorly understood. This study aims to determine how these organic contaminants were trapped in a pond located in an agricultural critical zone from SW France (Auradé catchment). The spatial distribution of pesticide concentrations and their different controlling factors were investigated in waters and sediments collected during two distinct seasons. The results highlighted (i) the link between the presence of the molecules and the agricultural practices upstream, (ii) the influence of hydrological/seasonal conditions, especially on hydrophobic molecule accumulation such as tebuconazole, (iii) the key role of clay content in sediments on the control of moderately hydrophilic pesticides (metolachlor and boscalid), but also the unexpected role of coarse particles for boscalid; and (iv) the influence of sediment depth on pesticide storage. Nevertheless, other physico-chemical parameters, such as mineralogical composition of sediment, needed to be considered to explain the pesticide patterns. This study brings a new hypothesis to be investigated in the future about pesticide behaviour in such pond environments.

Pond mitigation in dissolved and particulate pesticide transfers: Influence of storm events and seasonality (Auradé agricultural catchment, SW-France)

“…20 Highly hydrophobic molecules such as pendimethalin (logK OW = 5.2) sorbed to the TSS and at the same time, the pond released 5.6 tons per km² of TSS. Moreover, a previous study highlighted that the amount of pesticides stored in the sediment (both at the surface and in deeper layers) was not negligible (Chaumet et al 2021), especially considering the significant height of the entire sediment layer (about 1.5 m on average). Therefore, even though the pond retains pesticides, a significant proportion of these molecules may be transported downstream by resuspension during flood events from the sediments where they were previously stored.…”

“…The retention of molecules in soils over the years is favoured by the carbonate context of the molasse. The process of sorption of pesticides as well as of metals onto pond sediment particles has been demonstrated by Chaumet et al (2021) and by , respectively.…”

“…In addition, pesticides can be biodegraded, photolyzed or volatised in the water column (Droz et al 2021;Papaevangelou et al 2017). Pesticides in the particulate phase may also be stored in the bottom sediments by settling, as in the Bassioué pond, where the sediment compartment is rather thick (Chaumet et al 2021). Due to the high intensity of flood events, however, this process can be considered non-permanent due to the resuspension phenomenon (Chaumet et al 2021;.…”

“…Pesticides in the particulate phase may also be stored in the bottom sediments by settling, as in the Bassioué pond, where the sediment compartment is rather thick (Chaumet et al 2021). Due to the high intensity of flood events, however, this process can be considered non-permanent due to the resuspension phenomenon (Chaumet et al 2021;. -Pond mitigation in dissolved and particulate pesticide transfers: influence of storm events and seasonality (Auradé agricultural catchment, SW-France).…”

“…This highlights the influence of the pond in terms of retention, especially on hydrophobic molecules sorbed to particles such as aclonifen and pendimethalin. These molecules have more time to settle and be stored in the sediments (Chaumet et al 2021). The pond has a limited water head and the intensity of the rainfall events falling on very steeply sloping lands leads to very rapid transport across the pond during the flood events.…”