Nutrient and Pesticide Mitigation by Common Aquatic Plants

Author(s): Moore, M.; Locke, M.

While some debate the severity, all agree that agriculture contributes to non-point source pollution issues. The challenge of feeding and providing fiber for a rapidly growing national and global population results in more marginal land being utilized for production acreage. As a result, conservation planners must look for innovative, cost-efficient practices to minimize impacts of agricultural runoff containing pesticides and nutrients. To that end, twelve experimental mesocosms (1.3 x 0.7 x 0.6 m) were established with a 16 cm of Lexington silt loam atop a base of sand (22 cm). Mesocosms were planted in monocultures of either Myriophyllum aquaticum (parrot feather), Polygonum amphibium (water knotweed), or Typha latifolia (common cattail). Three mesocosms were also 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 amendment of simulated agricultural runoff, 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 hydraulic time retention time. Most significant differences between vegetated mesocosms and controls occurred when comparing mean contaminant breakdown rates post-amendment. Typha indicated significantly greater PO4, NH4+, TOC, TKN, TP, clomazone, propanil, and cyfluthrin breakdown percentages than controls during post-amendment (8–48 h). Likewise, Myriophyllum demonstrated significantly greater breakdown post-amendment for PO4, TOC, TKN, TP, clomazone, and propanil when compared to controls. Polygonum had greater NH4+, NO3-, TOC, TKN, TP, clomazone, propanil, and cyfluthrin breakdown percentages than controls during post-amendment. All three plant species had significantly greater percent propanil and cyfluthrin retention after the 6 h "clean" flush when compared to controls. These variable results indicate the importance of not only examining a variety of aquatic plants and their contaminant mitigation efficiency, but also determining potential downstream wash-off effects from multiple runoff events. Using natural systems, such as ditch vegetation, in the mitigation of agricultural runoff is a critical research area which must be further explored.

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