Open AccessCharacterizing Vadose Zone Hydrocarbon Biodegradation Using Carbon Dioxide Effluxes, Isotopes, and Reactive Transport Modeling
Author(s) -
Sihota Natasha J.,
Mayer K. Ulrich
Publication year - 2012
Publication title -
vadose zone journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.036
H-Index - 81
ISSN - 1539-1663
DOI - 10.2136/vzj2011.0204
Subject(s) - vadose zone , environmental chemistry , biodegradation , hydrocarbon , environmental science , degradation (telecommunications) , carbon dioxide , soil gas , contamination , carbon cycle , isotopes of carbon , soil science , chemistry , soil water , total organic carbon , ecosystem , ecology , telecommunications , organic chemistry , biology , computer science
Naturally occurring biodegradation of hydrocarbon compounds may offer a sustainable management option at contaminated sites. However, a sound understanding of contaminant mass loss rates is required to enable estimation of source zone longevity, serving to alleviate public concerns and inform decision makers. Under some conditions, surficial CO 2 efflux measurements can be useful to delineate petroleum hydrocarbon containing source zones, and to provide estimates of depth‐integrated vadose zone hydrocarbon degradation rates. However, the accuracy of degradation rate estimates is limited by our ability to separate CO 2 effluxes associated with contaminant decomposition from those attributable to naturally occurring soil respiration. To understand CO 2 sources and transport processes within the vadose zone, this work combines measurement of surficial CO 2 effluxes with detailed analysis of soil gas composition– including the radiocarbon and stable isotopic composition of CO 2 . Quantitative reactive transport modeling allows further evaluation of controls on CO 2 generation and fate, and CH 4 generation and oxidation. Results confirm that, in the source zone at the Bemidji site, the majority of CO 2 originates from degradation of the oil body. In addition, radiocarbon in CO 2 proves particularly useful in determining the contribution of contaminant degradation to the measured CO 2 efflux.