The methane cycle in ferruginous Lake Matano

Abstract

In Lake Matano, Indonesia, the world's largest known ferruginous basin, more than 50% of authigenic organic matter is degraded through methanogenesis, despite high abundances of Fe (hydr)oxides in the lake sediments. Biogenic CH 4 accumulates to high concentrations (up to 1.4 mmol L ) and SO 4 2) in Lake Matano waters suggests that anaerobic methane oxidation may be coupled to the reduction of Fe (and ⁄ or Mn) (hydr)oxides. Thermodynamic considerations reveal that CH 4 oxidation coupled to Fe(III) or Mn(III ⁄ IV) reduction would yield sufficient free energy to support microbial growth at the substrate levels present in Lake Matano. Flux calculations imply that Fe and Mn must be recycled several times directly within the water column to balance the upward flux of CH 4 . 16S gene cloning identified methanogens in the anoxic water column, and these methanogens belong to groups capable of both acetoclastic and hydrogenotrophic methanogenesis. We find that methane is important in C cycling, even in this very Fe-rich environment. Such Fe-rich environments are rare on Earth today, but they are analogous to conditions in the ferruginous oceans thought to prevail during much of the Archean Eon. By analogy, methanogens and methanotrophs could have formed an important part of the Archean Ocean ecosystem.

Iron formations: A global record of Neoarchaean to Palaeoproterozoic environmental history

“…Li et al, 2013a), the presence of Fe(II)-bearing minerals in IF (e.g., magnetite, siderite, greenalite -recall section 2.3), and the general lack of microfossils preserved in the Fe-rich layers lacking silicification. Moreover, the reduction of ferric iron may also have been coupled to the anaerobic oxidation of methane , an observation supported by the reaction's likely occurrence in modern marine sediments (Riedinger et al, 2014) and lakes (Crowe et al, 2011), as well as in culture experiments (Ettwig et al, 2016;Bray et al, 2017). …”

Emission and oxidation of methane in a meromictic, eutrophic and temperate lake (Dendre, Belgium)

“…Although AOM coupled with Fe-and Mn-reduction (FDMO and MDMO, respectively) has been proposed to occur in various freshwater environments (e.g. ferruginous lakes Matano and Kinneret; Crowe et al, 2011;Sivan et al, 2011;a Norði et al, 2013), to our knowledge no direct rate measurements have been reported in the literature. In this study, we investigated biogeochemistry of the water column of Dendre stone pit lake (Belgium), a relatively deep (maximum depth 30 m) but small (0.032 km 2 ) water body in a former limestone quarry, with a focus on quantifying AOM rates and related electron acceptors.…”

Archaea catalyze iron-dependent anaerobic oxidation of methane

“…Given the 8:1 stoichiometry of Fe 3+ reduced to methane oxidized [3], their contribution to iron cycling, thereby impacting also the geochemistry of phosphorus and sulfur, may be even more important than their impact on the carbon cycle (11,16,18,20). The enrichment of at least one of the microbial players not only now enables a targeted investigation of iron-dependent methane oxidation in physiological and molecular detail, but may also shed light on the long-standing discussion about Fe 2+ -producing processes on early Earth, when AAA-related organisms may have thrived under the methane-rich atmosphere in the ferruginous Archean oceans (12,18,30).…”