Smith R L, Howes B L, Garabedian S P
Water Resources Division, U.S. Geological Survey, Lakewood, Colorado 80225.
Appl Environ Microbiol. 1991 Jul;57(7):1997-2004. doi: 10.1128/aem.57.7.1997-2004.1991.
Methane oxidation was measured in an unconfined sand and gravel aquifer (Cape Cod, Mass.) by using in situ natural-gradient tracer tests at both a pristine, oxygenated site and an anoxic, sewage-contaminated site. The tracer sites were equipped with multilevel sampling devices to create target grids of sampling points; the injectate was prepared with groundwater from the tracer site to maintain the same geochemical conditions. Methane oxidation was calculated from breakthrough curves of methane relative to halide and inert gas (hexafluroethane) tracers and was confirmed by the appearance of 13C-enriched carbon dioxide in experiments in which 13C-enriched methane was used as the tracer. A Vmax for methane oxidation could be calculated when the methane concentration was sufficiently high to result in zero-order kinetics throughout the entire transport interval. Methane breakthrough curves could be simulated by modifying a one-dimensional adevection-dispersion transport model to include a Michaelis-Menten-based consumption term for methane oxidation. The Km values for methane oxidation that gave the best match for the breakthrough curve peaks were 6.0 and 9.0 microM for the uncontaminated and contaminated sites, respectively. Natural-gradient tracer tests are a promising approach for assessing microbial processes and for testing in situ bioremediation potential in groundwater systems.
通过在马萨诸塞州科德角一个无压砂石含水层中，对一个原始充氧场地和一个缺氧、受污水污染场地进行原位自然梯度示踪试验，测定了甲烷氧化情况。示踪场地配备了多级采样装置，以创建采样点的目标网格；注入液采用示踪场地的地下水配制，以保持相同的地球化学条件。甲烷氧化是根据甲烷相对于卤化物和惰性气体（六氟乙烷）示踪剂的穿透曲线计算得出的，并在以13C富集甲烷作为示踪剂的实验中，通过13C富集二氧化碳的出现得到证实。当甲烷浓度足够高，以至于在整个运移区间内导致零级动力学时，就可以计算出甲烷氧化的最大反应速率（Vmax）。通过修改一维平流-弥散输运模型，纳入基于米氏方程的甲烷氧化消耗项，可以模拟甲烷穿透曲线。对于未受污染和受污染场地，使穿透曲线峰值匹配最佳的甲烷氧化米氏常数（Km）值分别为6.0和9.0微摩尔。自然梯度示踪试验是评估微生物过程和测试地下水系统原位生物修复潜力的一种很有前景的方法。
