UNDERSTANDING AND PREDICTING THE IMPACT OF AGRICULTURE ON THE ENVIRONMENTAL INTEGRITY OF MANAGED WATERSHEDS
Location: Water Quality and Ecology Research
Title: Role of vegetation in a constructed wetland on nutrient-pesticide mixture toxicity of Hyalella azteca
Submitted to: Archives of Environmental Contamination and Toxicology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 16, 2010
Publication Date: January 24, 2011
Citation: Lizotte Jr, R.E., Moore, M.T., Locke, M.A., Kroger, R. 2011. Role of vegetation in a constructed wetland on nutrient-pesticide mixture toxicity of Hyalella azteca. Archives of Environmental Contamination and Toxicology. 60(2):261-271. DOI:10.1007/s00244-010-9596-0.
Interpretive Summary: We examined nutrient and pesticide effects on an aquatic invertebrate animal, Hyalella azteca, in a divided constructed wetland, one half with plants and one half without any plants. We looked at how well this wetland with or without plants could decrease the effects of two pesticides, diazinon and permethrin, and two nutrients, nitrogen and phosphorus, on aquatic animals. The study showed that plants were better at decreasing the effects of nutrients and pesticides within the first 5 hours. Also, we showed that holding the nutrient and pesticide contaminated water in the constructed wetland for 21 days was needed to remove toxicity. Our results are of interest to regulatory and other agencies and the pesticide industry by providing additional information to improve and sustain river, stream and lake water quality and overall environmental quality using constructed wetlands as an effective conservation practice.
The toxicity of a nutrient-pesticide mixture in non-vegetated and vegetated sections of a constructed wetland (60 X 30 X 0.3 m) was assessed using Hyalella azteca 48 h aqueous whole effluent toxicity bioassays. Both sections were amended with a mixture of sodium nitrate, triple super phosphate, diazinon, and permethrin simulating storm-event agricultural runoff. Aqueous samples were collected at inflow, middle, and outflow points within each section 5 h, 24 h, 72 h, 7 d, 14 d, and 21 d post-amendment. Nutrients and pesticides were detected throughout both wetland sections with concentrations longitudinally decreasing more in vegetated than non-vegetated section within 24 h. Survival effluent dilution point estimates, NOECs, LOECs and LC50s, indicated greatest differences in toxicity between non-vegetated and vegetated sections at 5 h. Associations of nutrient and pesticide concentrations with NOECs indicated earlier toxicity (5-72 h) was from permethrin and diazinon whereas later toxicity (7-21 d) was from primarily diazinon. Nutrient-pesticide mixture concentration-response assessment using toxicity quotient (TQ) and toxicity index (TI) models indicated H. azteca toxicity was due primarily to pesticides diazinon and permethrin. Results show that the effects of vegetation versus no vegetation on nutrient-pesticide mixture toxicity are not evident after 5 h and a 21 d retention time is necessary to improve H. azteca survival to =90% in constructed wetlands of this size.