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Title: Ecological responses to simulated agricultural runoff in a riverine backwater wetland

item Lizotte, Richard
item Murdock, Justin
item Shields Jr, Fletcher

Submitted to: Society of Environmental Toxicology and Chemistry Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: 7/7/2010
Publication Date: 11/7/2010
Citation: Lizotte Jr, R.E., Murdock, J.N., Shields Jr, F.D. 2010. Ecological responses to simulated agricultural runoff in a riverine backwater wetland. Society of Environmental Toxicology and Chemistry Abstracts. pp. 227.

Interpretive Summary: Abstract Only - Interpretative Summary not required.

Technical Abstract: Riverine backwater wetlands within river floodplains provide valuable ecological functions such as acting as filters for suspended sediment, nutrients and pesticides entering from adjacent agricultural fields, as well as habitat and refugia for aquatic biota. A 500 m long, 20 m wide riverine backwater wetland was hydrologically modified to more efficiently utilize this wetland’s natural filtering capabilities. Our study examined the ecological responses of this wetland amended with a mixture of suspended sediment, two nutrients (nitrogen and phosphorus), and three pesticides (atrazine, metolachlor, and permethrin) during a simulated agricultural runoff event during June 2009. Ecological variables assessed were water column and benthic chlorophyll a, in-situ daily gross primary productivity (GPP), in-situ daily community respiration (CR24), and aqueous 48 h laboratory bioassays using Hyalella azteca. The mixture was injected into the wetland at the upstream site simulating a one hour, 1.27 cm rainfall event from a 16 ha agricultural field. Water samples (1 L) were collected every 30 min within the first 4 h, then every 4 h until 48 h, and again on days 5, 7, 14, 21, and 28 post-amendment at distances of 10 m, 40 m, 300 m and 500 m from the injection point within the wetland for water column chlorophyll a, suspended solids, nutrient, and pesticide analyses. Benthic chlorophyll a was measured at 0 h, 48 h, 7 d, and 14 d. In-situ GPP and CR24 were assessed at 40 m and 300 m using hourly measurements of dissolved oxygen and temperature throughout the 28 d study period. H. azteca 48 h laboratory bioassays were conducted on water samples collected at each site at -9 d, 4 h, 24 h, 48 h, 5 d and 7 d. Peak sediment, nutrient, and pesticide concentrations occurred within 3 h of amendment at 10 m, 40 m, and 300 m downstream. After day 28, all amendments were near or below pre-amendment concentrations. Water samples at 500 m showed no changes in sediments or nutrients; pesticides peaked within 48 h but at <15% of upstream peak concentrations and had dissipated by day 28. Water column chlorophyll a decreased within the first 24 h of amendment up to 40 m and benthic chlorophyll a significantly decreased within 14 d of amendment up to 10 m. Neither in-situ GPP nor CR24 were significantly affected by the amended mixture during the 28 d study period. H. azteca survival significantly decreased within 48 h of amendment up to 300 m. Modified riverine backwater wetlands can rapidly and efficiently trap and process agricultural runoff during moderate rainfall events, mitigating ecological impacts to receiving aquatic systems. However the wetland ecosystem itself undergoes changes in community structure during exposure to the runoff event.