Experimental evidence for using vegetated ditches for mitigation of complex contaminant mixtures in agricultural runoff

Authors: Moore, Matthew; Locke, Martin

Submitted to: Journal of Water Air and Soil Pollution
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/20/2020
Publication Date: 3/18/2020
Citation: Moore, M.T., Locke, M.A. 2020. Experimental evidence for using vegetated ditches for mitigation of complex contaminant mixtures in agricultural runoff. Journal of Water Air and Soil Pollution. 231:140. https://doi.org/10.1007/s11270-020-04489-y.
DOI: https://doi.org/10.1007/s11270-020-04489-y

Interpretive Summary: Agricultural runoff following storm or irrigation events can transport unwanted nutrients and pesticides into rivers, lakes, and streams. This in turn can harm the aquatic insects, fish, and overall water quality of the water bodies. Management practices have been proposed to help clean runoff water as it exits the field before entering water bodies. Common aquatic plants found in drainage ditches can clean the nutrients and pesticides through retention and sorption before they enter water bodies. Continued research is needed to optimize the type and quantity of vegetation needed to reduce negative impacts of agricultural runoff. This research is important to conservation planners and natural resource managers when designing and providing cost-share for implementation of management practices.

Technical Abstract: Feeding and providing fiber for a growing global population requires striking a balance between increasing production and decreasing environmental impacts in agricultural settings. We established twelve experimental mesocosms (1.3 x 0.7 x 0.6 m) with 16 cm of Lexington silt loam atop a base of sand (22 cm) and examined the ability of three emergent wetland aquatic plants common to the United States to remediate pesticides and nutrients in runoff. Mesocosms were planted in monocultures of Myriophyllum aquaticum (parrot feather), Polygonum amphibium (water knotweed), and Typha latifolia (common cattail), or left unvegetated to serve as controls. All mesocosms were amended with target concentrations of 10 mg L-1 (each) nitrate, ammonium, and orthophosphate; 20 µg L-1 (each) of the pesticides propanil and clomazone; and 10 µg L-1 of the pesticide cyfluthrin. After a 6 h simulated agricultural runoff with amended water, mesocosms sat idle for 48 h before flushing with unamended municipal water for another 6 h. Outflow water samples were routinely collected and analyzed for contaminant concentrations. No significant differences were noted between the control and any of the three different vegetation types regarding the percent contaminant retained within the 6 h simulated runoff event. Most significant differences between vegetated mesocosms and controls occurred when comparing mean contaminant transfer / transformation rates post-amendment. All three plant species retained more total Kjeldahl nitrogen and total phosphorus than the control, but differences among plant species occurred regarding retention of dissolved nutrients orthophosphate, ammonium, and nitrate. Similarly, all three plant species retained more propanil than controls during post amendment (8-48 h), but individual plant differences occurred with regard to clomazone and cyfluthrin retention. While variation in mitigation of specific dissolved components of nutrients suggests different mechanisms involved in nutrient cycling within our mesocosms, consistent overall total nutrient and pesticide reduction during the post amendment period indicate that holding runoff in vegetated ditches may reduce transport of agricultural contaminants to downstream aquatic ecosystems.