Microbial processes of the carbon and sulfur cycles in an ice‐covered, iron‐rich meromictic lake Svetloe (Arkhangelsk region, Russia)

Abstract

Biogeochemical, isotope geochemical and microbiological investigation of Lake Svetloe (White Sea basin), a meromictic freshwater was carried out in April 2014, when ice thickness was ∼0.5 m, and the ice-covered water column contained oxygen to 23 m depth. Below, the anoxic water column contained ferrous iron (up to 240 μμM), manganese (60 μM), sulfide (up to 2 μM) and dissolved methane (960 μM). The highest abundance of microbial cells revealed by epifluorescence microscopy was found in the chemocline (redox zone) at 23-24.5 m. Oxygenic photosynthesis exhibited two peaks: the major one (0.43 μmol C L day ) below the ice and the minor one in the chemocline zone, where cyanobacteria related to Synechococcus rubescens were detected. The maximum of anoxygenic photosynthesis (0.69 μmol C L day ) at the oxic/anoxic interface, for which green sulfur bacteria Chlorobium phaeoclathratiforme were probably responsible, exceeded the value for oxygenic photosynthesis. Bacterial sulfate reduction peaked (1.5 μmol S L day ) below the chemocline zone. The rates of methane oxidation were as high as 1.8 μmol CH L day at the oxi/anoxic interface and much lower in the oxic zone. Small phycoerythrin-containing Synechococcus-related cyanobacteria were probably involved in accumulation of metal oxides in the redox zone.

Geochemical Characterization of Two Ferruginous Meromictic Lakes in the Upper Midwest, USA

“…These lakes include Lake Matano (Indonesia; Crowe et al, ), Lake La Cruz (Spain; Walter et al, ), Lake Pavin (France; Viollier et al, ; Lehours et al, ), and the ferruginous Kabuno Bay within Lake Kivu (Democratic Republic of Congo; Llirós et al, ). The analog utility of these lakes seems to be spurring discovery or recognition of additional geographically diverse lakes as ferruginous (e.g., Savvichev et al, ). The presence of anoxic and ferruginous conditions in the bottom waters of lakes, which either do not turn over at all, or turn over regularly or occasionally, may not be that rare.…”

Biogeochemical and physical controls on methane fluxes from two ferruginous meromictic lakes

“…While relative abundance of organisms does not necessarily correspond to biogeochemical activity, these observations provide circumstantial evidence for further studies to investigate the relationship between methanogens and pelagic CH 4 production. Furthermore, water column methanogenesis has been noted at Lake Matano (Crowe et al, ) and Lake Svetloe, although rates were two orders of magnitude less than rates measured in the sediment (Savvichev et al, ).…”

“…Crowe et al () suggested that Fe(III)‐bearing minerals may be resistant to microbial reduction in ferruginous systems, and our data support this. A precedent for the dominant role of methanogenesis in organic carbon degradation has also been put forward by the activity measurements of different anaerobic pathways in ferruginous Lake Matano and Lake Svetloe (Crowe et al, ; Savvichev et al, ), and similar work would be useful in Brownie and Canyon Lakes.…”

“…The microbiological processes and biogeochemical cycling occurring in ferruginous meromictic lakes are often invoked as having analogy to redox‐stratified, ferruginous oceans of the Archean and Proterozoic eons (Poulton & Canfield, ). For instance, processes of microbial Fe(II) oxidation and Fe(III) reduction have been observed to impact the carbon cycle across the O 2 and Fe(II) redoxcline in lakes (e.g., Berg et al, ; Berg et al, ; Camacho, Walter, et al, ; Gorlenko, Vainstein, & Chebotarev, ; Savvichev et al, ; Walter et al, ). These processes are also envisioned to have impacted the carbon cycle in ferruginous oceans (Posth, Konhauser, & Kappler, ).…”

“…These processes are also envisioned to have impacted the carbon cycle in ferruginous oceans (Posth, Konhauser, & Kappler, ). Recent work in these lakes has highlighted the utility of such lakes to investigate microbiological and geochemical aspects of CH 4 cycling (e.g., Crowe et al, ; Dupuis et al, ; Lopes et al, ; Oswald, Jegge, et al, ; Savvichev et al, ). The CH 4 cycle in ferruginous lakes has been most thoroughly discussed in the context of Indonesian Lake Matano and has given rise to active debate surrounding organic matter preservation in ferruginous oceans (Crowe et al, ; Kuntz, Laakso, Schrag, & Crowe, ; Laakso & Schrag, ).…”