Is tile drainage water representative of root zone leaching of pesticides?

Abstract

Given the methods presently available, determination of flux-averaged concentrations of pesticides in structured soils is always a compromise. Most of the available methods entail major uncertainties and limitations. Tile drainage monitoring has several advantages, but the extent to which it is representative of overall leaching has been questioned because it comprises a mixture of water of different origins. This literature review evaluates whether drainage water pesticide concentrations are representative of root zone leaching of pesticides. As there are no reports quantifying the extent to which the flux-averaged concentration of pesticides in drainage water differs from that found between the drains, evidence-based conclusions cannot be drawn. Nevertheless, the existing literature does suggest that the concentration in drainage water does not always correspond to the concentration at drain depth between the drains; depending on the conditions pertaining, the concentrations may be higher or lower. As to whether the flux-averaged concentration of pesticides in drainage water is representative of the interdrain concentration at drain depth it is concluded that (1) the representativeness of drainage water concentrations can be questioned on very well-drained soils and on poorly drained soils with little capacity for lateral transport beneath the plough layer, (2) the conditions provided by relatively porous soils and moderate climatic conditions are conducive to the drainage water concentration being representative and (3) drainage water will be more representative in the case of weakly sorbed pesticides than for strongly sorbed pesticides. Used critically, it is thus believed that drainage water concentrations can serve to characterize the flux-averaged concentration of pesticides at drain depth. However, the use of drainage water for determining average concentrations necessitates thorough investigation and interpretation of precipitation, percolation, drain outflow and concentration dynamics.

When does the fluazifop-P-butyl degradate, TFMP, leach through an agricultural loamy soil to groundwater?

“…Drainage was initiated two days later, even though the groundwater table had not risen to tile drain level before day 7 after application. This early drainage during unsaturated periods has also been reported by Villholth et al (1998) and Jacobsen and Kjaer (2007). With the groundwater table being nearly as low as that in the first application, this indicated a drier soil than at the time of the second and third applications.…”

“…6). This early drainage under unsaturated soil conditions may have occurred via discontinuities directly connected to the tile drains (Jacobsen and Kjaer, 2007) and has also been reported by Villholth et al (1998). However these two drainage events were not large enough for a sample to be taken by the auto-sampler system and the drainage was therefore not analysed for TFMP.…”

Pesticide leaching through sandy and loamy fields – Long-term lessons learnt from the Danish Pesticide Leaching Assessment Programme

“…Applying pesticides under these conditions allows their drain-facilitated direct transfer from the uppermost groundwater to the surface water. In such periods, the horizontal transport of pesticides and degradation products to the drains will be controlled by the hydraulic ability of the connected three-dimensional fracture system, together with the potential occurrence of sand inclusions (Jacobsen and Kjaer, 2006;Kessler et al, 2012). The vertical hydraulic component of the fracture system seems to be dominant in the Silstrup and Faardrup fields, whereas it appears minimal in the Estrup field, causing long periods of drainage flow and transport (Jorgensen et al, 2012).…”

Predicting rapid herbicide leaching to surface waters from an artificially drained headwater catchment using a one dimensional two-domain model coupled with a simple groundwater model

“…Further examples of detailed field investigations are presented by Richard and Steerhuis (1988), Haria et al (1994), McVoy et al (1995), Harris and Catt (1999), Villholth et al (2000), Gerke and Köhne (2004), Gärdenäs et al (2006) and Stone and Wilson (2006); apart from the investigation of Gärdenäs et al (2006), the studies relate to areas of less than 1 ha with ground slopes less than 3%. Reviews of field studies are presented by Kladivko et al, 2001 andKjaer (2007).…”