Wassenaar L I, Hendry M J
Environment Canada, 11 Innovation Boulevard, Saskatoon, Saskatchewan, Canada.
Ground Water. 2007 Jul-Aug;45(4):447-60. doi: 10.1111/j.1745-6584.2007.00328.x.
The vadose zone and ground water environments are a sink for atmospheric O(2). The pathways and rates of O(2) consumption are primarily related to the availability and rate of oxidation of key reductants (e.g., organics, sulfides), through a combination of biological or abiotic reactions. The range in delta(18)O of O(2) in the subsurface is large, from +20 per thousand to +39 per thousand (Vienna Standard Mean Ocean Water) in the vadose zone and from +12 per thousand to +46 per thousand in ground water. The aggregated O(2) isotope fractionation by consumption (alpha(k)) was found to range from 0.970 to 1.300 and 0.980 to 1.030 in vadose zones and aquifers, respectively. These data suggest the delta(18)O patterns in both unsaturated zones and aquifers can be attributed to microbially mediated reactions (alpha(k)= range from 0.975 to 1.000), but there are apparently other inverse isotope fractionating processes (alpha(k) > 1.000). Circumstantial evidence suggested O(2) processed during the sulfide oxidation and precipitation of Fe-oxyhydroxides process (or other unidentified processes) could be the cause of the significant (18)O depletions. Overall, delta(18)O data from vadose zones and ground water revealed that isotope fractionation by consumption of gaseous and dissolved O(2) in the subsurface and ground water environments is more complicated than what has classically been attributed solely to geomicrobial respiration. Given the questions and inexplicable data arising from this study, further detailed research on O(2) consuming processes in the Earth's subsurface and ground water is warranted.
包气带和地下水环境是大气中氧气的汇。氧气消耗的途径和速率主要与关键还原剂（如有机物、硫化物）的可用性和氧化速率有关，这是通过生物或非生物反应的组合实现的。地下水中氧气的δ(18)O范围很大，包气带中为千分之20至千分之39（维也纳标准平均海水），地下水中为千分之12至千分之46。发现包气带和含水层中因消耗导致的总氧气同位素分馏（α(k)）分别为0.970至1.300和0.980至1.030。这些数据表明，不饱和带和含水层中的δ(18)O模式可归因于微生物介导的反应（α(k)范围为0.975至1.000），但显然存在其他逆同位素分馏过程（α(k)>1.000）。间接证据表明，在硫化物氧化和铁羟基氧化物沉淀过程（或其他未确定过程）中处理的氧气可能是导致显著的(18)O亏损的原因。总体而言，包气带和地下水的δ(18)O数据表明，地下和地下水环境中气态和溶解态氧气消耗导致的同位素分馏比传统上仅归因于地质微生物呼吸的情况更为复杂。鉴于本研究中出现的问题和无法解释的数据，有必要对地球地下和地下水中的氧气消耗过程进行进一步详细研究。
