Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/5/2007
Publication Date: 3/5/2008
Citation: Moore, M.T., Denton, D.L., Cooper, C.M., Wrysinski, J., Miller, J.L., Reece, K., Crane, D., Robins, P. 2008. Mitigation assessment of vegetated drainage ditches for collecting irrigation runoff in California. Journal of Environmental Quality. 37:486-493. Interpretive Summary: Irrigation runoff from California tomato fields carries pesticides, such as diazinon and permethrin, to aquatic receiving systems. To help reduce the amount of pesticide transport, vegetated agricultural drainage ditches have been suggested as a best management practice for the edges of fields. Three ditches were constructed along the edge of a tomato field in Yolo County, California. A simulated irrigation event containing water, sediment, and pesticides was conducted on each of the three ditches. Pesticide fate and transport was evaluated temporally and spatially in each ditch. Vegetated ditches were able to reduce initial pesticide concentrations by 50% in 21-55 m, while unvegetated ditches required 239-408 m to accomplish the same task. This study demonstrated including plants in agricultural drainage ditches is an important component for improvement and design of economical and environmentally sound best management practices for agriculture.
Technical Abstract: Widespread contamination of California water bodies by the organophosphate insecticides diazinon and chlorpyrifos is well documented. While their usage has decreased over the last few years, a concomitant increase in pyrethroid usage (e.g permethrin) (replacement insecticides) has occurred. Vegetated agricultural drainage ditches (VADD) have been proposed as a potential economical and environmentally efficient management practice to mitigate the effects of pesticides in irrigation and storm runoff. Three ditches were constructed in Yolo County, California for a field trial. A U-shaped vegetated ditch, a V-shaped vegetated ditch, and a V-shaped unvegetated ditch were each amended for 8 h with a mixture of diazinon, permethrin, and suspended sediment simulating an irrigation runoff event. Water, sediment, and plant samples were collected spatially and temporally and analyzed for diazinon and permethrin concentrations. Pesticide half-lives were similar between ditches and pesticides, ranging from 2.4-6.4 h. Differences in half-distances (distance required to reduce initial pesticide concentration by 50%) among pesticides and ditches were substantial, indicating importance of vegetation in mitigation. Cis-permethrin half-distances ranged from 22 m (V-vegetated) to 347 m (V-unvegetated). Half-distances for trans-permethrin were similar, ranging from 21 m (V-vegetated) to 239 m (V-unvegetated). Diazinon half-distances demonstrated the greatest differences (55 m for V-vegetated and 1155 m for V-unvegetated). Such economical and environmentally successful management practices will offer farmers, ranchers, and landowners a viable alternative to more conventional (and sometimes expensive) practices currently suggested by conservation organizations.