Vegetation in Runoff Ditches Reduce Contaminates
In an article by the Agriculture Research Service from the USDA, entitled "Drainage Ditch Research Reveals Opportunities for Cleaning Up Runoff" (published in the January 2013 issue of Agricultural Research magazine), research was conducted by Matt Moore on contaminates of atrazine, lambda-cyhalothrin and their movement in irrigation ditches. In one study he found that after one hour, ditch vegetation in a 160 foot section of ditch had removed 61% of the atrazine and 87% of the lambda-cyhalothrin to non-toxic levels at the end of the ditch. In another study of lambda-cyhalothrin and bifenthrin, (both pyrethroid pesticides). In only 3 hours 96 percent of the lambda-cyhalothrin and 99 percent of the bifenthrin were captured by the ditch vegetation.
This has also been proven for nutrients such as phosphorous and nitrogen. Ditch shape and the vegetation that grows there will make a difference in what gets absorbed. The amount of time in the ditch and the length of the ditch will be factors to consider as well.
To read more about some of the findings on this and other studies about pesticides and nutrients moving from fields into ditches you can click on the full article here. http://www.ars.usda.gov/is/AR/archive/jan13/ditch0113.htm