Department of Earth Sciences, University of Florence, Via G. La Pira 4, Florence, Italy.
IGG-CNR Institute of Geosciences and Earth Resources, National Research Council of Italy, Via La Pira 4, Florence, Italy.
PLoS One. 2018 Mar 6;13(3):e0193914. doi: 10.1371/journal.pone.0193914. eCollection 2018.
Volcanic lakes are characterized by physicochemical favorable conditions for the development of reservoirs of C-bearing greenhouse gases that can be dispersed to air during occasional rollover events. By combining a microbiological and geochemical approach, we showed that the chemistry of the CO2- and CH4-rich gas reservoir hosted within the meromictic Lake Averno (Campi Flegrei, southern Italy) are related to the microbial niche differentiation along the vertical water column. The simultaneous occurrence of diverse functional groups of microbes operating under different conditions suggests that these habitats harbor complex microbial consortia that impact on the production and consumption of greenhouse gases. In the epilimnion, the activity of aerobic methanotrophic bacteria and photosynthetic biota, together with CO2 dissolution at relatively high pH, enhanced CO2- and CH4 consumption, which also occurred in the hypolimnion. Moreover, results from computations carried out to evaluate the dependence of the lake stability on the CO2/CH4 ratios, suggested that the water density vertical gradient was mainly controlled by salinity and temperature, whereas the effect of dissolved gases was minor, excepting if extremely high increases of CH4 are admitted. Therefore, biological processes, controlling the composition of CO2 and CH4, contributed to stabilize the lake stratification of the lake. Overall, Lake Averno, and supposedly the numerous worldwide distributed volcanic lakes having similar features (namely bio-activity lakes), acts as a sink for the CO2 supplied from the hydrothermal/magmatic system, displaying a significant influence on the local carbon budget.
火山湖具有有利于形成含碳温室气体储层的物理化学条件，这些气体在偶尔的翻转事件中会扩散到大气中。通过结合微生物学和地球化学方法，我们表明，位于意大利南部坎皮弗莱格雷（Campi Flegrei）的分层湖阿韦尔诺（Averno Lake）中富含有二氧化碳和甲烷的气体储层的化学性质与沿垂直水柱的微生物生态位分化有关。不同功能群的微生物同时存在，它们在不同的条件下运作，这表明这些栖息地中存在着复杂的微生物群落，它们对温室气体的产生和消耗有影响。在上层水中，好氧甲烷营养细菌和光合作用生物的活性，以及在相对较高 pH 值下 CO2 的溶解，增强了 CO2 和 CH4 的消耗，这种消耗也发生在下层水中。此外，为评估湖水稳定性对 CO2/CH4 比值的依赖性而进行的计算结果表明，湖水密度的垂直梯度主要受盐度和温度控制，而溶解气体的影响较小，但如果甲烷的浓度极高，则除外。因此，控制 CO2 和 CH4 组成的生物过程有助于稳定湖水的分层。总的来说，阿韦尔诺湖，以及可能还有许多具有类似特征（即生物活性湖）的分布在世界各地的火山湖，作为来自热液/岩浆系统供应的 CO2 的汇，对当地的碳预算有显著的影响。
