Understanding the sources and fate of nitrate in a highly developed aquifer system

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doi: 10.1016/j.jconhyd.2013.09.004
Authors:Murgulet, Dorina; Tick, Geoffrey R.
Author Affiliations:Primary:
Texas A&M University, Department of Physical and Environmental Sciences, Corpus Christi, TX, United States
University of Alabama, United States
Volume Title:Journal of Contaminant Hydrology
Source:Journal of Contaminant Hydrology, Vol.155, p.69-81. Publisher: Elsevier, Amsterdam, Netherlands. ISSN: 0169-7722
Publication Date:2013
Note:In English. 57 refs.; illus., incl. table, sketch map
Summary:Understanding the processes affecting the transport and fate of nitrate in coastal aquifers has become of great interest in recent years due to concerns of nutrient loading to coastal waters. Novel dual isotopic methods have shown promise for identifying sources and fate of nitrate in shallow groundwater. However, in relatively deep dynamic aquifer systems, the isotopic signatures may be overprinted by mixing of different end-member waters and biogeochemical processes. In this study, δ15N and δ18O of groundwater nitrate are coupled with other forensic geochemistry methods such as Cl/Br, SO4/Cl, and Cl/NO3 mass ratios and land use analysis in order to constrain the isotope correlations and better understand contaminant sources and biogeochemical processes. Most δ15NNO3 values were within ranges expected for nitrate formed by ammonia nitrification in soil. Furthermore, the persistent presence of nitrate in concentrations above background levels (median 2.3 mg/L) and the relatively low δ15NNO3 and δ18ONO3 (median: 4.5±0.2 ppm AIR and 5.2±0.5 ppm VSMOW, respectively) indicate no direct evidence of denitrification. However, denitrification was inferred for a few samples whereby more enriched δ15NNO3 and δ18ONO3 values coupled with an increase in SO4/Cl and Cl/NO3 ratios were observed. Finally, mixing trends were identified for a few of the samples as indicated by δ15NO3 and δ18ONO3 mixing ratios and were consistent with the study area's land-use/land-cover distribution. The combination of methods utilized in this study revealed that in some cases mass ratios were better diagnostics in elucidating the impact of denitrification, mixing processes, and source identification within dynamic aquifer systems than the dual-isotope technique. Abstract Copyright (2013) Elsevier, B.V.
Subjects:Aquifers; Biochemistry; Chromatograms; Coastal aquifers; Denitrification; Environmental analysis; Forensic geology; Ground water; Ion chromatograms; Irrigation; Isotope ratios; Isotopes; Land use; Mixing; N-15/N-14; Nitrates; Nitrogen; Nutrients; O-18/O-16; Organic compounds; Oxygen; Pollutants; Pollution; Stable isotopes; Statistical analysis; Water pollution; Water wells; Alabama; Atlantic Ocean; Baldwin County Alabama; Gulf of Mexico; Mobile Bay; North Atlantic; United States; Lake Shelby; Oyster Bay; Weeks Bay
Coordinates:N301300 N303700 W0873500 W0875600
Record ID:2016054640
Copyright Information:GeoRef, Copyright 2018 American Geosciences Institute. Reference includes data from CAPCAS, Elsevier Scientific Publishers, Amsterdam, Netherlands
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