Nitrate Reduction In Streambed Sediments: Effects Of Flow And Biogeochemical Kinetics

ASU Author/Contributor (non-ASU co-authors, if there are any, appear on document)
Chuanhui Gu Ph.D., Assistant Professor (Creator)
Appalachian State University (ASU )
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Abstract: The effect of retention time on redox sequences along the hydrological flow path of groundwater discharging through low-relief coastal stream sediments and the subsequent impact on the fate of NO3  carried in the groundwater was examined in two intact cores. Rates of denitrification were determined for the organic-rich streambedsediments, and a macroscopic, multispecies, reactive transport model based on multiple Monod kinetics was developed to interpret and extend the experimental results. Regionalized sensitivity analysis and parameter estimation were used to determine a set of parameters that best describe the experimental data for one column. The calibrated model successfully replicated the spatial profiles of nitrate under both steady and transient conditions in the second column operated under different conditions. A dimensionless form of the model was used to examine how coupled biogeochemical reactions and hydrological transport processes operate within the stream sediments could be understood in terms of Peclet (ratio of advection to dispersion) and Damkohler numbers (the ratio ofthe characteristic time of transport to the characteristic time for reaction). At the study site, the Peclet number and the Damkohler numbers for both oxygen and nitrate are high (Pe = 25, DaN = 47.5, and DaO = 40). When Pe > 5, Damkohler numbers explain observed variations in nitrate removal rates; as the flow rate increases, the solute residence time in the reactive zone is shortened resulting in a lesser extent of reaction, such that more NO3  is delivered to the stream water.

Additional Information

Gu, Chuanhui, A.L. Mills, G.M.Hornberger, and J.S.Herman (2007). "Nitrate Reduction in Streambed Sediments: Effects of Flow and Biogeochemical Kinetics," Water Resources Research. Version of Record available from Wiley: [DOI:10.1029/2007WR006027], [ISSN: 0043-1397]
Language: English
Date: 2007
streambed sediments, groundwater, denitrification, hydrological processes

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