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United States Department of Agriculture

Agricultural Research Service

Title: Modeling Denitrification in Coastal Plain Riparian Forests

Authors
item Lowrance, Robert
item Williams, Randall
item Altier, Lee - CALIF.STATE UNIV.-CHICO

Submitted to: Proceedings of the American Society of Agricultural and Biological Engineers International (ASABE)
Publication Type: Proceedings
Publication Acceptance Date: March 15, 2006
Publication Date: N/A

Interpretive Summary: Denitrification, the microbially mediated reduction of nitrate to nitrogen gas in the atmosphere, is the most important process for removing excess N that accumulates from agriculture or other sources. Because of the concern over effects of excess nitrate N on coastal waters and drinking water, denitrification has been proposed as one of the primary means of decreasing the transport of excess nitrate. It has been proposed that large amounts of forested and other wetlands be re-established in major drainage basins, most notably the Mississippi River drainage. The amount of denitrification to be expected in restored wetlands has not been modeled using a transport model that includes important factors controlling denitrification. We used the Riparian Ecosystem Management Model (REMM) to determine the effects of soil carbon, denitrification rate constants, N loading, and forms of N loading on denitrification in modeled hardwood forest wetlands from GA. REMM uses a standard measure of denitrification potential (the amount that occurs under ideal conditions) to estimate actual denitrification rates limited by nitrate, available carbon, and soil moisture. REMM was used to model two typical coastal plain wetland soils, one with higher organic matter and higher denitrification potentials (Kinston series) and one with lower organic matter and lower denitrification potentials (Alapaha series). Vegetation on the two soils was simulated as deciduous hardwoods that lose their leaves in the Fall. Loadings of N were varied within a range of about 5 lb/acre/year to about 200 lb/acre/year and were introduced as either mostly nitrate, mostly ammonium, or a 50:50 mix of nitrate and ammonium. The simulations gave overall denitrification rates similar to measure ones. There were effects of adding different amounts and different types of N as inputs.

Technical Abstract: Denitrification, the microbially mediated reduction of nitrate to di-nitrogen, is the most important process for returning excess fixed N to the atmosphere. Because of the concern over excess fixed N in the environment, denitrification has been proposed as one of the primary means of decreasing the transport of excess nitrate. It has been proposed that large amounts of forested and other wetlands be re-established in major drainage basins, most notably the Mississippi River drainage. Although tested in some major ongoing experiments, the amount of denitrification to be expected in restored wetlands has not been modeled using a transport model that includes important factors controlling denitrification. We used the Riparian Ecosystem Management Model (REMM) to determine the effects of soil carbon, denitrification rate constants, N loading, and forms of N loading on denitrification in modeled hardwood forest wetlands from GA. REMM was used to model two typical coastal plain wetland soils, one with higher organic matter and higher denitrification potentials (Kinston series) and one with lower organic matter and lower denitrification potentials (Alapaha series). Vegetation on the two soils was Fall deciduous hardwoods. Loadings of N were varied within a range of 5 kg N/ha/yr to 200 kg N/ha/yr and were introduced as either mostly nitrate, mostly ammonium, or a 50:50 mix of nitrate and ammonium. Denitrification rate constants for the simulations were based on measured rates of denitrification potential. Results are discussed relative to both measured rates of denitrification in these coastal plain soils and to anticipated rates of denitrification for major watershed water quality improvement projects.

Last Modified: 7/24/2014
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