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Responses of Hyalella azteca and phytoplankton to a simulated agricultural runoff event in a managed backwater wetland

Lizotte, Richard E., Jr., Douglas Shields, F., Jr., Murdock, Justin N., Knight, Scott S.
Chemosphere 2012 v.87 no.7 pp. 684
Algae, Hyalella azteca, agricultural runoff, aquatic invertebrates, atrazine, chlorophyll, environmental fate, floodplains, land management, metolachlor, nitrogen, nutrients, permethrin, phosphorus, phytoplankton, pigments, rain, risk reduction, sediments, toxicity, wetlands
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 1h, 1.27cm rainfall event from a 16ha agricultural field. Water (1L) was collected every 30min within the first 4h, every 4h until 48h, and on days 5, 7, 14, 21, and 28 post-amendment at distances of 0, 10, 40, 300 and 500m 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, 4, 24, 48h, 5d and 7d. Greatest sediment, nutrient, and pesticide concentrations occurred within 3h of amendment at 0m, 10m, 40m, and 300m downstream. Sediments and nutrients showed little variation at 500m whereas pesticides peaked within 48h but at <15% of upstream peak concentrations. After 28d, all mixture components were near or below pre-amendment concentrations. H. azteca survival significantly decreased within 48h of amendment up to 300m in association with permethrin concentrations. Chlorophyll a decreased within the first 24h of amendment up to 40m primarily in conjunction with herbicide concentrations. Variations in chlorophyll a at 300 and 500m 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.