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The carbon isotope geochemistry of a small groundwater system in northeastern Ontario
Author(s) -
Fritz P.,
Reardon E. J.,
Barker J.,
Brown R. M.,
Cherry J. A.,
Killey R. W. D.,
McNaughton D.
Publication year - 1978
Publication title -
water resources research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.863
H-Index - 217
eISSN - 1944-7973
pISSN - 0043-1397
DOI - 10.1029/wr014i006p01059
Subject(s) - isotopes of carbon , dissolved organic carbon , carbonate , aquifer , groundwater , environmental chemistry , geology , isotope fractionation , fractionation , carbon fibers , geochemistry , total inorganic carbon , methane , total organic carbon , mineralogy , carbon dioxide , chemistry , materials science , geotechnical engineering , composite number , composite material , organic chemistry
The carbon isotopic composition ( 13 C and 14 C) of the inorganic carbon dissolved in the waters of a small, largely unconfined aquifer in unconsolidated sediments on the Canadian Shield has been investigated. Three principal carbon sources are recognized: soil CO 2 , rock carbonate, and biogenic CO 2 . The average δ 13 C value of the soil CO 2 is close to −21.0 ± 1.5%, and present‐day 14 C activities of the soil CO 2 vary between 130 and 162% modern 14 C. Very minor amounts (< 1.0%) of carbonate minerals (δ 13 C = −0.6‰) are present within the aquifer and react with this soil CO 2 to produce a dissolved inorganic carbon (DIC) with 14 C activities which are as much as 50% below the initial activities of the soil CO 2 . The third carbon source, a biogenic CO 2 , could be detected only indirectly, and its presence is primarily deduced from the occurrence of methane in the deeper parts of these aquifers. The large isotope fractionation which occurs during bacterial coproduction of CO 2 with this methane results, however, in a 13 C‐rich CO 2 and thus a DIC with high δ 13 C values. Values of δ 13 C as high as +11‰ have been measured in groundwaters on the Canadian Shield. Since the origin of the destroyed organic matter is not yet known, no assessment of the importance of this CO 2 for the 14 C contents of the DIC is possible.