Premium
Microbial H2 Cycling Does Not Affect δ2H Values of Ground Water.
Author(s) -
Landmeyer James E.,
Chapelle Francis H.,
Bradley Paul M.
Publication year - 2000
Publication title -
groundwater
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.84
H-Index - 94
eISSN - 1745-6584
pISSN - 0017-467X
DOI - 10.1111/j.1745-6584.2000.tb00223.x
Subject(s) - environmental chemistry , groundwater , cycling , groundwater recharge , chemistry , biodegradation , hydrocarbon , anaerobic exercise , fractionation , environmental science , aquifer , geology , biology , history , geotechnical engineering , archaeology , physiology , organic chemistry
Stable hydrogen‐isotope values of ground water (δ 2 H) and dissolved hydrogen concentrations (H 2(aq) ) were quantified in a petroleum‐hydrocarbon contaminated aquifer to determine whether the production/consumption of H 2 by subsurface microorganisms affects ground water δ 2 H values. The range of δ 2 H observed in monitoring wells sampled (−27.8 % c to −15.5 % c ) was best explained, however, by seasonal differences in recharge temperature as indicated using ground water δ 18 O values, rather than iso‐topic exchange reactions involving the microbial cycling of H 2 during anaerobic petroleum‐hydrocarbon biodegradation. The absence of a measurable hydrogen‐isotope exchange between microbialy cycled H 2 and ground water reflects the fact that the amount of H 2 available from the anaerobic decomposition of petroleum hydrocarbons is small relative to the amount of hydrogen present in water, even though milligram per liter concentrations of readily biodegradable contaminants are present at the study site. Additionally, isotopic fractionation calculations indicate that in order for H 2 cycling processes to affect δ 2 H values of ground water, relatively high concentrations of H 2 (>0.080 M) would have to be maintained, considerably higher than the 0.2 to 26 nM present at this site and characteristic of anaerobic conditions in general. These observations suggest that the conventional approach of using δ 2 H and δ 18 O values to determine recharge history is appropriate even for those ground water systems characterized by anaerobic conditions and extensive microbial H 2 cycling.