Effect of ditch dredging on the fate of nutrients in deep drainage ditches of the Midwestern United States

Abstract:

Dredging of drainage ditches is necessary to ensure that agricultural fields are drained adequately. This study compared the potential impacts of dredging on water quality. Using a fluvarium (stream simulator), bed material collected from drainage ditches prior to dredging was better able to remove NO₃-N, NH₄-N, and soluble P from water than material collected from the bed of the ditches after dredging. Water column NH₄-N concentrations were reduced to 0 mg L⁻¹ (0 ppm) earlier in pre-dredged bed material. Nutrient uptake rates were greater for the ditch bed materials collected prior to dredging. Dredging decreased the specific surface area of ditch bed sediments and removed some of the biota responsible for nutrient uptake by the bed sediments in these ditches. Resource managers should perform maintenance tasks, including ditch dredging, when nutrient loads are expected to be low, thus minimizing the potential water quality impacts.