Vegetated drainage ditches help reduce downstream pollution

01/31/2013 01:03:00 PM
Vicky Boyd

Vegetation in ditches can be a dicey matter.

Many growers trim or dredge them to reduce impediments to water flow, according to a news release.

But Matt Moore, an ecologist with the Agricultural Research Service in Oxford, Miss., has found that drainage ditches with plants help prevent agricultural pollutants in field runoff from reaching nearby surface waters.

Moore has conducted several studies during the past 10 years looking at how vegetated agricultural drainage ditches reduce the amount of pesticides and sediments making their way downstream.

In one study, he spent 28 days evaluating the movement of the herbicide atrazine and the insecticide lambda-cyhalothrin in a 160-foot section of vegetated agricultural drainage ditch in Mississippi.

Within an hour of a simulated runoff event, 61 percent of the atrazine and 87 percent of the lambda-cyhalothrin had transferred from the water to the ditch vegetation.

Yet at the end of the 160-long section, runoff of both pesticides had been reduced to levels considered nontoxic for most aquatic life.

Moore obtained similar results looking at lambda-cyhalotrin and the insecticide bifenthrin.

Just three hours from the start of a simulated runoff event, ditchbank vegetation had already captured 96 percent of the lambda-cyhalothrin and 99 percent of the bifenthrin.

He also has conducted similar tests on vegetated drainage ditches in Yolo County, Calif.

In that trial, he compared a U-shaped vegetated ditch, a V-shaped vegetated ditch and a V-shaped non-vegetated ditch.

Each 545-foot-long ditch was amended for eight hours with a mix of the insecticides diazinon and permethrin and suspended sediment.

A water analysis afterward found it took only 69 feet of the V-shaped vegetated ditch to reduce pesticide concentrations by 50 percent whereas it took 485 feet of the non-vegetated ditch to cut in half the concentrations.

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