UNDERSTANDING AND PREDICTING THE IMPACT OF AGRICULTURE ON THE ENVIRONMENTAL INTEGRITY OF MANAGED WATERSHEDS
Location: Water Quality and Ecology Research
Title: Responses of Hyalella azteca and phytoplankton to a simulated agricultural runoff event in a managed backwater wetland
Submitted to: Chemosphere
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 21, 2011
Publication Date: January 13, 2012
Citation: Lizotte Jr, R.E., Shields Jr, F.D., Murdock, J.N., Knight, S.S. 2012. Responses of Hyalella azteca and phytoplankton to a simulated agricultural runoff event in a managed backwater wetland. Chemosphere. 87(7):684-691. DOI:10.1016/j.chemosphere.2011.12.058.
Interpretive Summary: We examined nutrient and pesticide effects on an aquatic invertebrate animal, Hyalella azteca, and algae in a managed wetland after an artificially produced runoff event. We looked at how well this managed wetland could decrease the effects of three pesticides, atrazine, S-metolachlor, and permethrin, and two nutrients, nitrogen and phosphorus, on aquatic animals and algae. The study showed that the managed wetland was effective at decreasing the effects of nutrients and pesticides in agricultural runoff on aquatic animals and algae during average rainfall events. 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.
We assessed the aqueous toxicity mitigation capacity of a hydrologically managed floodplain wetland following a synthetic runoff event amended with a mixture of sediments, nutrients (nitrogen and phosphorus), and pesticides (atrazine, S-metolachlor, and permethrin) using 48-h Hyalella azteca survival and phytoplankton pigment, chlorophyll a. The runoff event simulated a one hour, 1.27 cm rainfall event from a 16 ha agricultural field. Water (1 L) was collected every 30 min within the first 4 h, every 4 h until 48 h, and on days 5, 7, 14, 21, and 28 post-amendment at distances of 0, 10, 40, 300 and 500 m from the amendment point for chlorophyll a, suspended sediment, nutrient, and pesticide analyses. H. azteca 48-h laboratory survival was assessed in water collected at each site at 0 h, 4 h, 24 h, 48 h, 5 d and 7 d. Greatest sediment, nutrient, and pesticide concentrations occurred within 3 h of amendment at 0 m, 10 m, 40 m, and 300 m downstream. Sediments and nutrients showed little variation at 500 m whereas pesticides peaked within 48 h but at <15% of upstream peak concentrations. After 28 days, all mixture components were near or below pre-amendment concentrations. H. azteca survival significantly decreased within 48 h of amendment up to 300 m in association with permethrin concentrations. Chlorophyll a decreased within the first 24 h of amendment up to 40 m primarily in conjunction with herbicide concentrations. Variations in chlorophyll a at 300 and 500 m were associated with nutrients. Managed floodplain wetlands can rapidly and effectively trap and process agricultural runoff during moderate rainfall events, mitigating impacts to aquatic invertebrates and algae in receiving aquatic systems.