Premium
Hydrogeochemistry of a Clayey Till: 2. Sources of CO 2
Author(s) -
Keller C. Kent
Publication year - 1991
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 - 10.1029/91wr01587
Subject(s) - vadose zone , aquifer , water table , geology , groundwater , total organic carbon , soil gas , dissolved organic carbon , organic matter , isotopes of carbon , soil water , calcareous , mineralogy , environmental chemistry , hydrology (agriculture) , soil science , chemistry , paleontology , geotechnical engineering , organic chemistry
The spatial distributions of inorganic and organic carbon in gas, aqueous, and solid phases were studied in an 18‐m‐thick surficial deposit of fractured clayey calcareous till. Large PCO 2 increases were observed with increasing depth at the bottoms of vadose zones from which solid organic carbon had been depleted. Hydrochemical reaction simulations indentified a reaction path consistent with PCO 2 , O 2 , major element chemistry, 13 C, and 14 C isotope observations; this path is “open” to a biogenic CO 2 reservoir with PCO 2 higher than, and 14 C composition considerably different from, that of the soil zone. Such CO 2 reservoirs, occurring in deep‐vadose/shallow saturated zones and thus isolated by overlying sediments from temperature fluctuations which limit soil‐zone respiration, may be common in the Western Glaciated Plains as evidenced by prevalence of hard, high‐PCO 2 waters in the region's intertill aquifers. Carbon 14 data suggest that in the till, both dissolved organic C and dissolved inorganic C have two sources: soil organic matter and kerogen in the till matrix. Regardless of source(s), initial 14 C activities of both aqueous C pools at the water table are “diluted” substantially relative to the actual residence time of the water; unappreciated, this could cause large relative errors in the calculation of radiocarbon‐based groundwater age dates.