Effects of dredging an agricultural drainage ditch on water column herbicide concentration, as predicted by fluvarium techniques

Abstract:

In artificially drained agricultural areas, dredging of drainage ditches is often necessary to ensure adequate field drainage. Stream-simulator (fluvarium) experiments were performed to evaluate the potential of associated bed material changes to impact water column concentrations of atrazine, metolachlor, and glyphosate. In the first experiments, water having high herbicide concentrations flowed across bed sediment collected from a ditch immediately before or after dredging. Afterward, water having initially zero herbicide concentrations flowed across these sediments. Results indicate that the bed sediments remaining after dredging, which had coarser texture and lower organic matter, may contribute to overall higher water herbicide levels in the short term by removing significantly less glyphosate from contaminated water and contributing marginally higher sustained levels of herbicide to uncontaminated water, applicable where sediments exhibit similar dredging characteristic effects. In this case, dredging when herbicide levels are expected to be lowest can help minimize increased transport of some herbicides.