Vegetated Ditches for Mitigation of Contaminants in Agricultural Runoff

The global population is expected to climb to 8.5 billion by the year 2030, and by 2050, it is projected to reach 9.7 billion individuals. Meeting the food and fiber requirements for humanity with finite land resources will require agriculture to continue to increase production while also decreasing potential impacts to natural resources. In addition to in-field conservation practices that focus on tillage reduction and planting of cover crops to prevent soil erosion, edge-of-field conservation practices that mitigate impacts of agricultural runoff are also critical to protect downstream aquatic resources. To develop edge-of-field practices that limit loss of acreage, research was initiated in the 1990s to evaluate the possibility of using vegetated agricultural drainage ditches (VADDs) to mitigate the transport of contaminants (primarily pesticides and nutrients) in runoff. This chapter includes an overview of early vegetated ditch mitigation studies conducted in the USA and the expansion of VADDs research in other countries. In this chapter, we highlight: (1) important concepts behind the use of VADDs; (2) case studies of contaminant mitigation by vegetated ditches; (3) new technologies incorporated within VADDs to further promote contaminant mitigation; and (4) challenges and future research directions. Overall, VADDs show promise for the removal of a range of pesticides and for removals of nitrogen species from agricultural runoff. Studies of phosphorus removals by VADDs show variable results, but advanced ditch designs, additional treatment technologies and harvesting of plants during senescence may improve mitigation results. Key parameters for removal efficiencies include plant densities, the length, and the hydraulic retention times of the VADD systems.