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Title: USE OF TRACER INJECTION EXPERIMENTS TO QUANTIFY NITRATE LOSS IN TWO ADJACENT WETLAND STREAMS DRAINING AN AGRICULTURAL FIELD IN THE GEORGIA PIEDMONT

Author
item Schroer, K
item Thomas, R
item Endale, Dinku
item Washington, J
item Nzengung, V

Submitted to: USDA-CSREES National Water Quality Conference
Publication Type: Abstract Only
Publication Acceptance Date: 11/3/2005
Publication Date: 2/5/2006
Citation: Schroer, K.L., Thomas, R.C., Endale, D.M., Washington, J.W., Nzengung, V. 2006. Use of tracer injection experiments to quantify nitrate loss in two adjacent wetland streams draining an agricultural field in the Georgia Piedmont [abstract]. In: Proceedings on the 2006 USDA-CSREES National Water Quality Conference, February 5-6, 2006, San Antonio, Texas. Available: http://wwww.extension,iastate.edu/WaterConf2006/ShowAbstract.aspx?

Interpretive Summary:

Technical Abstract: This study investigated the extent to which nitrate was removed from and/or stored in a small wetland depression down-gradient of a 10-ha cattle rotational grazing pasture and a 2.5-ha cropped catchment at the USDA-ARS J. Phil Campbell Sr. Natural Resource Conservation Center in Watkinsville, GA. A stream originates at a perennial spring at the base of the pasture and is protected from surface runoff by a berm. An adjacent stream is open to surface runoff from part of the pasture and receives shallow groundwater from the cropped catchment and part of the pasture but does not have a discrete perennial spring. The two streams join approximately 60m downstream. We performed four seasonal stream tracer injection experiments in the spring-fed channel. During the summer experiment, we conducted the experiment simultaneously in the spring-fed and runoff stream. We injected nitrate and bromide at constant rates for 30 minutes and sampled intensively at several sampling locations throughout the day until field measurements of [NO3-] reached pre-injection background levels. In addition, at one control station in each stream, we sampled several times throughout the rising and falling NO3- limb for T, pH, DO, SpC, dissolved organic C, Fe (II, III and total), NH4+, and the dissolved gases N2O, CH4, CO2 and H2. Background NO3--N concentrations in the two stream channels generally decrease from 6-12mg/L at the source to 0.2-5mg/L at their confluence, with more loss observed along the runoff stream. Daily load calculations, natural chloride concentrations, and the tracer test results indicate that dilution by ground water flux does not fully account for nitrate loss. Preliminary results indicate percent recoveries for nitrate vary with sampling location and with season. This research will help quantify the extent to which the apparent nitrate loss is due to dilution versus storage and/or denitrification in the wetland.