SOURCES AND FLUX OF NATURAL GASES FROM MONO LAKE, CALIFORNIA
SOURCES AND FLUX OF NATURAL GASES FROM MONO LAKE, CALIFORNIA
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DOI：
10.1016/0016-7037(87)90367-x
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发表时间：
1987-11-01
影响因子：
5
通讯作者：
WHITICAR, MJ
中科院分区：
文献类型：
--
作者：
OREMLAND, RS;MILLER, LG;WHITICAR, MJ
当存在多种来源时，识别特定环境中天然气的形成机制的能力需要考虑几个地球化学因素。在莫诺湖已经确定了四个主要的甲烷来源。其中两个气源与大量天然气渗漏有关，这些气源发生在湖中的不同位置，并延伸到目前的边界之外；另外两个气源是当前微生物过程的结果。在天然气渗漏中，我们观测到的流量高达160摩尔CH4day-1，并估计全湖年渗漏通量为2.1倍。106摩尔甲烷。地化参数(β13CH4；，ΔDCH4，CH4/[C2H6+C2H8])和Δ14CH4测量结果表明，大多数渗漏来自古生物成因(约-70‰)。更新世天然气矿床，是目前和以前所标明的。温泉附近的天然气渗漏与生物成因气相结合，是埋藏有机质热液蚀变形成的重要热成气成分。目前对该湖天然气来源负责的微生物过程包括沿海地区的中上层产甲烷作用和陆生草类的分解。中上层沉积物中的甲烷生成导致甲烷饱和(在50厘米处为2-3毫米；增量13CH4=约-85个/磨坊)。间隙硫酸盐从表层的133 mm减少到110 cm以下的35 mm，表明硫酸盐还原和产甲烷作用是同时进行的。甲烷从沉积物中扩散出来，导致缺氧底水中的浓度约为50µm。氧气/缺氧界面的甲烷氧化使浓度降低了98%，但地表水(0.1-1.3µm)的浓度相对于大气是过饱和的。13CH4(范围=-21.8到-71.8)其中，相对于底水和沉积物中的甲烷，未氧化的残留甲烷以13C的形式富集。甲烷的平均向外通量为2.77倍。107摩尔/年。甲烷的第四个，但也是次要的来源(13CH4=-55.2)与湖中陆生牧草的分解有关。S最近扩大了滨海带。
The ability to identify a formation mechanism for natural gas in a particular environment requires consideration of several geochemical factors when there are multiple sources present. Four primary sources of methane have been identified in Mono Lake. Two of these sources were associated with numerous natural gas seeps which occur at various locations in the lake and extend beyond its present boundary; the two other gas sources result from current microbiological processes. In the natural gas seeps, we observed flow rates as high as 160 moles CH4 day-1, and estimate total lakewide annual seep flux to be 2.1 .times. 106 moles CH4. Geochemical parameters (.delta.13CH4;, .delta.DCH4, CH4/[C2H6 + C2H8]) and .DELTA.14CH4 measurements revealed that most of the seeps originate from a paleo-biogenic (.delta.13CH4 = about -70.permill.) natural gas deposit of Pleistocene age which underlies the current and former labeled. Gas seeps in the vicinity of hot springs had, in combination with the biogenic gas, a prominent thermogenic gas component resulting from hydrothermal alteration of buried organic matter. Current microbiological processes responsible for sources of natural gas in the lake included pelagic methanogenesis and decomposition of terrestrial grasses in the littoral zone. Methanogenesis in the pelagic sediments resulted in methane saturation (2-3 mM at 50 cm; .delta.13CH4 = about -85.permill.). Interstitial sulfate decreased from 133 mM at the surface to 35 mM by 110cm depth, indicating that sulfate-reduction and methanogenesis operated concurrently. Methane diffused out of the sediments resulting in concentrations of about 50 .mu.M in the anoxic bottom waters. Methane oxidation in the oxic/anoxic boundary lowered the concentration by >98%, but values in surface waters (0.1-1.3 .mu.M) were supersaturated with respect to the atmosphere. The .delta.13CH4 (range = -21.8 to -71.8.permill.) of this unoxidized residual methane was enriched in 13C relative to methane in the bottom water and sediments. Average outward flux of this methane was 2.77 .times. 107 moles yr-1. A fourth, but minor source of methane (.delta.13CH4 = -55.2.permill.) was associated with the decomposition of terrestrial grasses taking place in the lake''s recently expanded littoral zone.