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NITROGEN RETENTION OF THE LARGEST RIVER SWAMP IN NORTH AMERICA

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan www.asabe.org

Citation:  Watershed Management to Meet Water Quality Standards and Emerging TMDL (Total Maximum Daily Load) Proceedings of the Third Conference 5-9 March 2005 (Atlanta, Georgia USA) Publication Date 5 March 2005  701P0105.(doi:10.13031/2013.18042)
Authors:   Y. Jun Xu
Keywords:   Hypoxia, Eutrophication, Nitrogen removal, Wetlands, Mississippi-Atchafalaya, Gulf of Mexico

Freshwater diversion from the lower Mississippi River into the region’s wetlands has been considered an alternative means for reducing nitrogen loading. However, it is largely unknown how much nitrogen actually can be retained from the overflowing waters in those natural wetlands. This study is to determine nitrogen retention capacity of the Atchafalaya River Swamp that conveys 30% of the Mississippi’s water into the Gulf of Mexico. By utilizing river’s longterm discharge and water quality data (1978-2002), nitrogen fluxes were quantified and their relationships with the basin’s hydrologic conditions were investigated. A total Kjeldahl nitrogen (TKN) mass input-output balance between the upstream and downstream locations was established to examine the organic nitrogen removal potential for this large swamp basin. The results showed that on average, TKN input into the Atchafalaya was 200,323 tons yr-1 and TKN output was 145,917 tons yr-1, resulting in a 27% removal rate. Monthly nitrogen input and output in the basin were highest from March to June (input vs. output: 25,000 vs. 18,000 tons mon-1) and lowest from August to November (8,000 vs. 6,000 tons mon-1). There was a large variation in both annual and inter-annual nitrogen removals. The variability was positively correlated with the amount of inflow at Simmesport, suggesting that regulating the river’s inflow at the Old River flood control structures will help reduce nitrogen loading of the Mississippi River to the Gulf of Mexico. Furthermore, the in-stream loss of nitrogen indicates that previous studies may have overestimated nitrogen discharge from the Mississippi-Atchafalaya River system.

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