Concentrations and Isotope Ratios of Dissolved Inorganic Carbon in Denitrifying Environments

Author

C. Nascimento
Eliot A. Atekwana, Missouri University of Science and Technology
R. V. Krishnamurthy

Abstract

We measured the concentration and isotope ratio of dissolved inorganic carbon (DIC) in groundwater associated with denitrification (C_org + NO₃^- = CO₂ + N₂) in an agriculturally impacted site in southwestern Michigan. Samples with the lowest nitrate levels also had low dissolved oxygen content and were more depleted in δ¹³C than background groundwater. All the samples had DIC concentrations in excess of titratable alkalinity. The magnitude of this DIC in excess of alkalinity correlated with a decreasing δ¹³C attesting to the presence of CO₂ derived from organic carbon. Carbon dioxide is one of the by-products of denitrification. Since the carbon isotope ratio of carbon dioxide produced during denitrification can be expected to be similar to that of the substrate consumed in the process, this can serve as a useful tool in monitoring denitrification. The estimated carbon isotope ratio of source carbon added to the DIC pool via denitrification was close to the value obtained for the organic carbon in the aquifer solids, suggesting that the carbon substrate used in denitrification came from soil organic matter. The results provide support for the hypothesis that the concentration and carbon isotope ratios (δ¹³C) of dissolved inorganic carbon (DIC) in groundwater might be useful to monitor denitrification.

Recommended Citation

C. Nascimento et al., "Concentrations and Isotope Ratios of Dissolved Inorganic Carbon in Denitrifying Environments," Geophysical Research Letters, vol. 24, no. 12, pp. 1511 - 1514, American Geophysical Union (AGU), Jun 1997.

The definitive version is available at https://doi.org/10.1029/97GL01404

Department(s)

Geosciences and Geological and Petroleum Engineering

Keywords and Phrases

Carbon; Carbon Dioxide; Groundwater; Isotopes; Nitrogen; Aquifers; Byproducts; Denitrification; Dissolution; Dissolved Oxygen; Groundwater; Groundwater Resources; Isotopes; pH; Concentration Measurement; Organic Carbon; Agricultural Pollution; Dissolved Inorganic Carbon; Groundwater Quality; Isotopic Composition; Nitrate; Carbon Isotope Ratio; Carbon Substrates; Isotope Ratio; Low Dissolved Oxygen; Michigan; Nitrate Levels; Soil Organic Matters

International Standard Serial Number (ISSN)

0094-8276

Document Type

Article - Journal

Document Version

Final Version

File Type

text

Language(s)

English

Rights

© 1997 American Geophysical Union (AGU), All rights reserved.

Publication Date

01 Jun 1997