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Hydrogeology and redox geochemistry of CH 4 in a Late Wisconsinan Till and Loess Sequence in central Iowa
Author(s) -
Simpkins W. W.,
Parkin T. B.
Publication year - 1993
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 - 10.1029/93wr01687
Subject(s) - dissolved organic carbon , geology , loess , hydrogeology , groundwater recharge , groundwater , redox , environmental chemistry , geochemistry , hydrology (agriculture) , aquifer , chemistry , geomorphology , oceanography , inorganic chemistry , geotechnical engineering
The hydrogeology and redox geochemistry of CH 4 in two hydrogeological settings within a late Wisconsinan till and loess sequence in central Iowa were investigated using CH 4 , Eh, dissolved O 2 , NO 3 ‐N, NH 4 ‐N, dissolved Fe, SO 4 , H 2 S, dissolved organic carbon (DOC), particulate organic carbon (POC), δ 13 C‐CH 4 , δ 2 H‐CH 4 , δ 13 C of dissolved inorganic carbon (DIC), and 14 C−CH 4 . Depleted δ 13 C‐CH 4 and δ 2 H‐CH 4 values, enriched δ 13 C‐DIC values, and the lack of higher hydrocarbons suggest that the CH 4 is microbial and is formed by CO 2 reduction. Carbon 14 dates of CH 4 indicate that 14,000‐ to 17,000‐year‐old POC and DOC in the 1oess and till compose the substrate for methanogenesis. Production of CH 4 probably began after deglaciation at about 12,000 years B.P. and has continued to the present. Groundwater recharge, particularly in the upland topographic position at the site, has decreased CH 4 concentrations in the upper part of the till.