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The Determination of In-Stream Denitrification Using Five Methods in the North Carolina Coastal Plain

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

Citation:  Paper number  032280,  2003 ASAE Annual Meeting . (doi: 10.13031/2013.13825) @2003
Authors:   T. W. Appelboom, G.M. Chescheir, R.W. Skaggs, J. W. Gilliam
Keywords:   In-Stream process, denitrification, mass transfer coefficient, nitrate removal, N15, O18

Denitrification within the stream bed sediments is the most important in-stream process for the removal of nitrogen from flowing waters. Five methods were used to determine a mass transfer coefficient ( ) to describe the denitrification potential of sediments in a drainage canal system in a forested watershed in the North Carolina coastal plain. The methods were: 1.) nitrate depletion from overlaying water measured in the field using in-situ tanks, 2.) nitrate depletion from overlaying water measured in the lab using undisturbed cores, 3.) naturally occurring background N15 and O18 abundance in the canal waters, 4.) N15-nitrate enrichment of in-situ tanks, and 5.) calculations based on diffusion rates. Results showed denitrification occurs within the canals of the forested watershed studied. Methods 1 and 2 resulted in nitrate mass transfer coefficients of the same magnitude (0.0161 m/day and 0.0119 m/day respectively) though the difference is statistically significant. Method 3 resulted in positive indications of denitrification. Method 4 resulted in unusable data due to problems encountered with the design of the study. Method 5 resulted in lower estimates of the nitrate mass transfer coefficient (0.0029 m/day) due to the simplicity of the method (Method 5 was statistically different from both Methods 1 and 2). Each method allows the investigation of different aspects of in-stream denitrification. Method 1 allows for the most accurate estimates of the mass transfer coefficient at a point in time due to naturally occurring environmental conditions. Method 2 allows for the effects of factors such as depth, temperature, initial concentration, pH, etc. to be studied in detail. Method 3 allows for a quick determination of the presence of denitrification in both large and small watersheds. Method 4 can be used in modified form to determine mass transfer coefficients for in stream denitrification, but is very expensive and difficult, and is thus not recommended. Method 5, as presented here, is far too simplistic to be of use in determining mass transfer coefficients.

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