Biogeochemical and physical controls on methane fluxes from two ferruginous meromictic lakes
Biogeochemical and physical controls on methane fluxes from two ferruginous meromictic lakes
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DOI：
10.1111/gbi.12365
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发表时间：
2019-10
期刊：
影响因子：
3.7
通讯作者：
N. Lambrecht;S. Katsev;C. Wittkop;S. Hall;C. Sheik;A. Picard;M. Fakhraee;E. Swanner
中科院分区：
文献类型：
--
作者：
N. Lambrecht;S. Katsev;C. Wittkop;S. Hall;C. Sheik;A. Picard;M. Fakhraee;E. Swanner
底水缺氧的分生湖泊通常有活跃的甲烷循环，甲烷通常在缺氧条件下由生物产生，并在到达大气之前在含氧的地表水中氧化。在深海中含有溶解的亚铁（即含铁）的湖泊是罕见的，但却很有价值，因为在地球化学上，它们类似于前寒武纪时期主导地球海洋的条件，当时铁和甲烷循环之间的相互作用可能形成了地球气候的温室调节。在这里，我们探索了布朗尼湖和峡谷湖的甲烷通量控制，这两个含铁的分生湖泊含有相似的浓度(最大。在它们的底部水中溶解的甲烷。甲烷菌目是两个湖泊中检测到的优势产甲烷菌。在布朗尼湖，甲烷菌丰度、甲烷浓度随沉积物深度的增加而增加，以及同位素数据表明，甲烷生成在缺氧水体中是一个活跃的过程。在峡谷湖，甲烷生成主要发生在沉积物中。两个水柱中存在的最丰富的好氧甲烷氧化细菌与γ变形菌有关，几乎没有证据表明厌氧甲烷氧化生物存在或活跃。在地表的直接测量显示，来自布朗尼湖的甲烷通量比来自峡谷湖的通量大两个数量级。实测和计算的湍流扩散通量的比较表明，布朗尼湖的甲烷通量大部分是非扩散的。虽然甲烷氧化菌的作用减弱了峡谷湖的湍流扩散甲烷通量，但在湖底仍检测到溶解甲烷，提示甲烷来自沿岸沉积物的横向输送。这些结果强调了直接测量在估算水柱甲烷总通量中的重要性，并且甲烷的非扩散输送可能是考虑其他含铁系统的重要因素。
Meromictic lakes with anoxic bottom waters often have active methane cycles whereby methane is generally produced biogenically under anoxic conditions and oxidized in oxic surface waters prior to reaching the atmosphere. Lakes that contain dissolved ferrous iron in their deep waters (i.e., ferruginous) are rare, but valuable, as geochemical analogues of the conditions that dominated the Earth's oceans during the Precambrian when interactions between the iron and methane cycles could have shaped the greenhouse regulation of the planet's climate. Here, we explored controls on the methane fluxes from Brownie Lake and Canyon Lake, two ferruginous meromictic lakes that contain similar concentrations (max. >1 mM) of dissolved methane in their bottom waters. The order Methanobacteriales was the dominant methanogen detected in both lakes. At Brownie Lake, methanogen abundance, an increase in methane concentration with respect to depths closer to the sediment, and isotopic data suggest methanogenesis is an active process in the anoxic water column. At Canyon Lake, methanogenesis occurred primarily in the sediment. The most abundant aerobic methane‐oxidizing bacteria present in both water columns were associated with the Gammaproteobacteria, with little evidence of anaerobic methane oxidizing organisms being present or active. Direct measurements at the surface revealed a methane flux from Brownie Lake that was two orders of magnitude greater than the flux from Canyon Lake. Comparison of measured versus calculated turbulent diffusive fluxes indicates that most of the methane flux at Brownie Lake was non‐diffusive. Although the turbulent diffusive methane flux at Canyon Lake was attenuated by methane oxidizing bacteria, dissolved methane was detected in the epilimnion, suggestive of lateral transport of methane from littoral sediments. These results highlight the importance of direct measurements in estimating the total methane flux from water columns, and that non‐diffusive transport of methane may be important to consider from other ferruginous systems.