Direct Experimental Evidence of Non-first Order Degradation Kinetics and Sorption-Induced Isotopic Fractionation in a Mesoscale Aquifer: 13C/12C Analysis of a Transient Toluene P

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• 作者：Shiran Qiu ; Dominik Eckert ; Olaf A. Cirpka ; Marko Huenniger ; Peter Knappett ; Piotr Maloszewski ; Rainer U. Meckenstock ; Christian Griebler ; Martin Elsner
• 刊名：Environmental Science & Technology (ES&T)
• 出版年：2013
• 出版时间：July 2, 2013
• 年：2013
• 卷：47
• 期：13
• 页码：6892-6899
• 全文大小：378K
• 年卷期：v.47,no.13(July 2, 2013)
• ISSN：1520-5851

文摘

The injection of a mixed toluene and Dub>2ub>O (conservative tracer) pulse into a pristine mesoscale aquifer enabled a first direct experimental comparison of contaminant-specific isotopic fractionation from sorption versus biodegradation and transverse dispersion on a relevant scale. Water samples were taken from two vertically resolved sampling ports at 4.2 m distance. Analysis of deuterium and toluene concentrations allowed quantifying the extent of sorption (R = 1.25) and biodegradation (37% and 44% of initial toluene at the two sampling ports). Sorption and biodegradation were found to directly affect toluene up>13up>C/up>12up>C breakthrough curves. In particular, isotope trends demonstrated that biodegradation underwent Michaelis鈥揗enten kinetics rather than first-order kinetics. Carbon isotope enrichment factors obtained from an optimized reactive transport model (Eckert et al., this issue) including a possible isotope fractionation of transverse dispersion were 蔚up>equup>ub>sorptionub> = 鈭?.31 鈥? 蔚up>kinup>ub>transverse-dispersionub> = 鈭?.82 鈥? and 蔚up>kinup>ub>biodegradationub> = 鈭?.15 鈥? Extrapolation of our results to the scenario of a continuous injection predicted that (i) the bias in isotope fractionation from sorption, but not transverse dispersion, may be avoided when the plume reaches steady-state; and (ii) the relevance from both processes is expected to decrease at longer flow distances when isotope fractionation of degradation increasingly dominates.