Biogeochemical processes involving dissolved CO2 and CH4 at Albano, Averno, and Monticchio meromictic volcanic lakes (Central–Southern Italy)
Biogeochemical processes involving dissolved CO2 and CH4 at Albano, Averno, and Monticchio meromictic volcanic lakes (Central–Southern Italy)
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阿尔巴诺、阿韦尔诺和蒙蒂基奥半聚火山湖（意大利中部和南部）涉及溶解 CO2 和 CH4 的生物地球化学过程
DOI：
10.1007/s00445-012-0683-0
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发表时间：
2013
影响因子：
3.5
通讯作者：
Bicocchi
中科院分区：
文献类型：
--
作者：
Cabassi;Vaselli;Fiebig;Nocentini;Capecchiacci;Rouwet;Bicocchi
本文重点研究了意大利中南部火山系统中的四个部分混合湖（Alban Hills）、Averno湖（Phlegrean Fields）、Monticchio Grande湖和Piccolo湖（Mt. Vulture）。在这些湖泊的深层沃茨的特点是存在一个显着的水库大气外溶解的气体，主要由甲烷和二氧化碳。湖泊最深处溶解气的δ 13 C-CH 4和δ D-CH 4值（分别为−66.8 ~ −55.6 ‰ V-PDB和−279 ~ −195 ‰ V-SMOW）表明，CH 4主要由微生物活动产生。格兰德湖、皮科洛湖和阿尔巴诺湖的δ 13 C-CO2值（范围为-5.8至-0.4 ‰ V-PDB）表明，湖底喷口对CO2的贡献很大，其来源于（1）地幔脱气和（2）涉及石灰岩的热变质反应，即，相同的CO2源供给区域性的热的和冷的富含CO2的流体排放。相比之下，阿韦尔诺湖的δ 13 C-CO2值相对较低（从−13.4到−8.2 ‰ V-PDB），表明有机CO2占主导地位。不同深度溶解CO2和CH 4的化学和同位素组成主要取决于（1）外源CO2输入（热液和/或人为）;（2）CO2-CH 4同位素交换;（3）产甲烷和甲烷氧化活动。在上层，垂直水混合，自由氧的可用性，光合作用导致CO2和CH 4浓度急剧下降。在浅水层中，δ 13 C-CO2值随深度增加而增加，而δ 13 C-CH 4值则表现出相反的趋势，利用不同的电子供体物种（如硫酸盐）从CH 4中产生生物CO2，往往会抵消甲烷生成过程，而甲烷生成过程的效率在水-底质界面处达到最大值。根据δ 13 C-CO2值计算的理论值和测量的δ 13 CTDIC值并不一致，表明CO2和主要的含碳离子（HCO 3 −）并不处于同位素平衡状态，这可能是由于涉及CO2和CH 4的生物化学过程的快速动力学。本研究表明，垂直模式的CO2/CH 4比和δ 13 C-CO2和δ 13 C-CH 4被视为有前途的工具，以检测扰动，有关不同的原因，如CO2输入的变化，从湖底泉，可能会影响好氧和厌氧层的部分分解火山湖。
This paper focuses on the chemical and isotopic features of dissolved gases (CH4and CO2) from four meromictic lakes hosted in volcanic systems of Central–Southern Italy: Lake Albano (Alban Hills), Lake Averno (Phlegrean Fields), and Monticchio Grande and Piccolo lakes (Mt. Vulture). Deep waters in these lakes are characterized by the presence of a significant reservoir of extra-atmospheric dissolved gases mainly consisting of CH4and CO2. The δ13C-CH4and δD-CH4values of dissolved gas samples from the maximum depths of the investigated lakes (from −66.8 to −55.6 ‰ V-PDB and from −279 to −195 ‰ V-SMOW, respectively) suggest that CH4is mainly produced by microbial activity. The δ13C-CO2values of Lake Grande, Lake Piccolo, and Lake Albano (ranging from −5.8 to −0.4 ‰ V-PDB) indicate a significant CO2contribution from sublacustrine vents originating from (1) mantle degassing and (2) thermometamorphic reactions involving limestone, i.e., the same CO2source feeding the regional thermal and cold CO2-rich fluid emissions. In contrast, the relatively low δ13C-CO2values (from −13.4 to −8.2 ‰ V-PDB) of Lake Averno indicate a prevalent organic CO2. Chemical and isotopic compositions of dissolved CO2and CH4at different depths are mainly depending on (1) CO2inputs from external sources (hydrothermal and/or anthropogenic); (2) CO2–CH4isotopic exchange; and (3) methanogenic and methanotrophic activity. In the epilimnion, vertical water mixing, free oxygen availability, and photosynthesis cause the dramatic decrease of both CO2and CH4concentrations. In the hypolimnion, where the δ13C-CO2values progressively increase with depth and the δ13C-CH4values show an opposite trend, biogenic CO2production from CH4using different electron donor species, such as sulfate, tend to counteract the methanogenesis process whose efficiency achieves its climax at the water–bottom sediment interface. Theoretical values, calculated on the basis of δ13C-CO2values, and measured δ13CTDICvalues are not consistent, indicating that CO2and the main carbon-bearing ion species (HCO3−) are not in isotopic equilibrium, likely due to the fast kinetics of biochemical processes involving both CO2and CH4. This study demonstrates that the vertical patterns of the CO2/CH4ratio and of δ13C-CO2and δ13C-CH4are to be regarded as promising tools to detect perturbations, related to different causes, such as changes in the CO2input from sublacustrine springs, that may affect aerobic and anaerobic layers of meromictic volcanic lakes.
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