Big Soda Lake Research Articles

Microbiology of Big Soda Lake, a multi-extreme meromictic volcanic crater lake in the Nevada desert.

Big Soda Lake, Nevada, is a multi-extreme meromictic lake, whose hypersaline hyperalkaline bottom waters feature permanent anoxia and high concentrations of arsenic, sulphide and ammonia. These properties make Big Soda Lake-and the adjacent Little Soda Lake-a fascinating system for exploring life's boundaries, discovering novel microbial taxa and identifying biotechnologically useful strains. To date, the taxonomic diversity and metabolic capabilities of microorganisms in this system remain largely unknown. Here, we fill this gap using microbiome surveys across the Big and Little Soda Lake water columns, including 16S rRNA sequencing, fungal ITS2 sequencing and gene- and genome-resolved metagenomics. We accompany these surveys with measurements of salinity, pH, temperature, oxygen, ammonium and ammonia concentrations. Our analyses reveal rich bacterial communities, taxonomically and functionally differentiated along Big Soda Lake's oxycline and, to lesser extent, between lakes. Fungal communities were dominated by a small number of families, while nearly no archaea were detected. Pathways related to perchlorate reduction, anoxygenic phototrophy, fermentation, dissimilatory metabolism of arsenite/arsenate, sulphur compounds, nitrogen compounds and hydrogen, were particularly prevalent. A total of 129 high-quality bacterial and archaeal metagenome-assembled genomes (completeness ≥ 80%, contamination ≤ 5%) were recovered, yielding insight into the taxonomic distribution of microbial metabolic pathways.

Potential role for microbial ureolysis in the rapid formation of carbonate tufa mounds.

Modern carbonate tufa towers in the alkaline (~pH 9.5) Big Soda Lake (BSL), Nevada, exhibit rapid precipitation rates (exceeding 3cm/year) and host diverse microbial communities. Geochemical indicators reveal that carbonate precipitation is, in part, promoted by the mixing of calcium-rich groundwater and carbonate-rich lake water, such that a microbial role for carbonate precipitation is unknown. Here, we characterize the BSL microbial communities and evaluate their potential effects on carbonate precipitation that may influence fast carbonate precipitation rates of the active tufa mounds of BSL. Small subunit rRNA gene surveys indicate a diverse microbial community living endolithically, in interior voids, and on tufa surfaces. Metagenomic DNA sequencing shows that genes associated with metabolisms that are capable of increasing carbonate saturation (e.g., photosynthesis, ureolysis, and bicarbonate transport) are abundant. Enzyme activity assays revealed that urease and carbonic anhydrase, two microbial enzymes that promote carbonate precipitation, are active in situ in BSL tufa biofilms, and urease also increased calcium carbonate precipitation rates in laboratory incubation analyses. We propose that, although BSL tufas form partially as a result of water mixing, tufa-inhabiting microbiota promote rapid carbonate authigenesis via ureolysis, and potentially via bicarbonate dehydration and CO2 outgassing by carbonic anhydrase. Microbially induced calcium carbonate precipitation in BSL tufas may generate signatures preserved in the carbonate microfabric, such as stromatolitic layers, which could serve as models for developing potential biosignatures on Earth and elsewhere.

Phylogenetic characterization and screening of halophilic bacteria from Algerian salt lake for the production of biosurfactant and enzymes

Environments containing significant concentration of NaCl such as salt lakes harbor extremophiles microorganisms which have a great biotechnology interest. To explore the diversity of Bacteria in Chott Tinsilt (Algeria), an isolation program was performed. Water samples were collected from the saltern during the pre-salt harvesting phase. This Chott is high in salt (22.47% (w/v). Seven halophiles Bacteria were selected for further characterization. The isolated strains were able to grow optimally in media with 10–25% (w/v) total salts. Molecular identification of the isolates was performed by sequencing the 16S rRNA gene. It showed that these cultured isolates included members belonging to the Halomonas, Staphylococcus, Salinivibrio, Planococcus and Halobacillus genera with less than 98% of similarity with their closest phylogenetic relative. The halophilic bacterial isolates were also characterized for the production of biosurfactant and industrially important enzymes. Most isolates produced hydrolases and biosurfactants at high salt concentration. In fact, this is the first report on bacterial strains (A4 and B4) which were a good biosurfactant and coagulase producer at 20% and 25% ((w/v)) NaCl. In addition, the biosurfactant produced by the strain B4 at high salinity (25%) was also stable at high temperature (30-100°C) and high alkalinity (pH 11).

“Assessment of Spatiotemporal Water Quality Variations, Impact Analysis and Trophic Status of Big Soda Lake Van, Turkey

The study was conducted in order to assess the spatiotemporal variations of selected water quality parameters, impact analysis, and trophic status on the Edremit shores of Lake Van. Water samples were collected from 10 representative sampling stations taken from the influent, effluent, and from Lake Van itself in order to analyze the physicochemical parameters in both dry and wet seasons. The trophic status of the lake was determined using Carlson trophic state index. Impact analysis was conducted based on the method most commonly used in management strategies related to surface waters in Turkey. The results of the study show that five factors obtained from principal component indicated that the parameters responsible for water quality changes were mostly related to salts and soda, physicochemical parameters, point and diffuse pollutions discharge, and other organic pollutants. In the impact analysis pH, COD (chemical oxygen demand), BOD (biological oxygen demand), and TP (total phosphorus) (except for EC (electrical conductivity)) parameters were found to have medium impact, while DO (dissolved oxygen) and TN (total nitrogen) parameters had no impact. The pH, EC, SO4−2, Cl−, TP, COD, and BOD values measured at 10 sampling stations were considered to be Class IV according to national regulations. The final trophic status of lake, according to the Carlson trophic index, was assessed to be eutrophic. Understanding this variation is important so as to develop new ways to resolve issues of sustainable water management. In addition, it is considered essential to prepare guidelines for the trophic status of Lake Van.

Arsenite as an Electron Donor for Anoxygenic Photosynthesis: Description of Three Strains of Ectothiorhodospira from Mono Lake, California and Big Soda Lake, Nevada.

Three novel strains of photosynthetic bacteria from the family Ectothiorhodospiraceae were isolated from soda lakes of the Great Basin Desert, USA by employing arsenite (As(III)) as the sole electron donor in the enrichment/isolation process. Strain PHS-1 was previously isolated from a hot spring in Mono Lake, while strain MLW-1 was obtained from Mono Lake sediment, and strain BSL-9 was isolated from Big Soda Lake. Strains PHS-1, MLW-1, and BSL-9 were all capable of As(III)-dependent growth via anoxygenic photosynthesis and contained homologs of arxA, but displayed different phenotypes. Comparisons were made with three related species: Ectothiorhodospira shaposhnikovii DSM 2111, Ectothiorhodospira shaposhnikovii DSM 243T, and Halorhodospira halophila DSM 244. All three type cultures oxidized arsenite to arsenate but did not grow with As(III) as the sole electron donor. DNA–DNA hybridization indicated that strain PHS-1 belongs to the same species as Ect. shaposhnikovii DSM 2111 (81.1% sequence similarity), distinct from Ect. shaposhnikovii DSM 243T (58.1% sequence similarity). These results suggest that the capacity for light-driven As(III) oxidation is a common phenomenon among purple photosynthetic bacteria in soda lakes. However, the use of As(III) as a sole electron donor to sustain growth via anoxygenic photosynthesis is confined to novel isolates that were screened for by this selective cultivation criterion.

Earth analogues for past and future life on Mars: isolation of perchlorate resistant halophiles from Big Soda Lake

AbstractThe Martian regolith is known to contain a maximum of 0.5% (w/v) perchlorate (ClO4−) that is toxic for most living organisms. With such high concentrations of perchlorates on Mars, is there any possibility of life? Here, in order to search and identify potential organisms on Earth, which could survive the perchlorate levels on Mars, we have isolated four perchlorate resistant, halophilic/halotolerant bacterial species from Big Soda Lake (BSL) in Nevada, USA. The 16S ribosomal RNA sequences revealed that these halophiles belong to the genera Bacillus, Alkalibacillus and Halomonas. Growth curves were obtained using a saline medium with different concentrations of magnesium, sodium and/or calcium perchlorate salt to simulate the Martian eutectic brine water. All four species, BSL1-4, grew in high saline media in the presence of perchlorates. This is the first growth experiment using multiple perchlorate salts. BSL3 relative to Halomonas salifodinae showed high maximum growth (Optical Density) comparing with other isolates in the presence of 1% perchlorate salts. Also, BSL1 relative to Bacillus licheniformis survived in the presence of 5% Na-perchlorate, but growth was slower in the absence of Na-perchlorate. The results revealed that these new model microbes are capable of tolerating the hypothesized hypersaline and perchlorate-rich Martian subsurface water environment. Perchlorate-resistant halophile would serve as a new model to understand the biochemistry that may occur on Mars.

A 1500 year record of hydrologic variability in the northwestern Great Basin from sediments in Big Soda Lake, Churchill County, Nevada

A 1500 year record of hydrologic variability in the northwestern Great Basin from sediments in Big Soda Lake, Churchill County, Nevada

Middle Holocene changes in Big Soda Lake, Nevada: Climatically or hydrologically induced changes?

Middle Holocene changes in Big Soda Lake, Nevada: Climatically or hydrologically induced changes?

Transformation of monothioarsenate by haloalkaliphilic, anoxygenic photosynthetic purple sulfur bacteria.

Thioarsenates are the dominant arsenic species in arsenic-rich, alkaline, and sulfidic waters, but bacterial interactions with these compounds have only recently been examined. Previous studies have shown that microorganisms play a role in the transformation of monothioarsenate to arsenate, including use of monothioarsenate as a chemolithotrophic electron donor coupled with oxygen as an electron acceptor. We obtained enrichment cultures from two saline, alkaline lakes (Mono Lake, CA and Big Soda Lake, NV) that are able to use monothioarsenate as the sole electron donor for anoxygenic photosynthesis. These anoxic cultures were able to convert a 1 mM mixture of thioarsenates completely to arsenate in c. 13 days and 4 mM monothioarsenate to arsenate in c. 17 days. This conversion was light dependent; thus, monothioarsenate can be used as the sole electron donor for anoxygenic photosynthesis. Both of the Mono Lake and Big Soda Lake enrichment cultures were dominated by an organism closely related to Ectothiorhodospira species. We tested additional strains of purple sulfur bacteria and found widespread ability to use monothioarsenate as an electron donor. The ability of bacteria to transform thioarsenates directly via anoxygenic photosynthesis adds a new perspective to the well-studied arsenic and sulfur cycles.

Evidence for late Holocene hydrologic change at Big Soda Lake, a MAAR lake in northwest Nevada

Evidence for late Holocene hydrologic change at Big Soda Lake, a MAAR lake in northwest Nevada

Thermodynamic limits to microbial life at high salt concentrations

Life at high salt concentrations is energetically expensive. The upper salt concentration limit at which different dissimilatory processes occur in nature appears to be determined to a large extent by bioenergetic constraints. The main factors that determine whether a certain type of microorganism can make a living at high salt are the amount of energy generated during its dissimilatory metabolism and the mode of osmotic adaptation used. I here review new data, both from field observations and from the characterization of cultures of new types of prokaryotes growing at high salt concentrations, to evaluate to what extent the theories formulated 12 years ago are still valid, need to be refined, or should be refuted on the basis of the novel information collected. Most data agree well with the earlier theories. Some new observations, however, are not easily explained: the properties of Natranaerobius and other haloalkaliphilic thermophilic fermentative anaerobes, growth of the sulfate-reducing Desulfosalsimonas propionicica with complete oxidation of propionate and Desulfovermiculus halophilus with complete oxidation of butyrate, growth of lactate-oxidizing sulfate reducers related to Desulfonatronovibrio at 346 g l(-1) salts at pH 9.8, and occurrence of methane oxidation in the anaerobic layers of Big Soda Lake and Mono Lake.

Exceptionally fast growth rate of <100-yr-old tufa, Big Soda Lake, Nevada: Implications for using tufa as a paleoclimate proxy

Large tufa mounds (>3 m tall, with a basal circumference of 5 m) have been discovered on the margin of Big Soda Lake, Nevada, USA. These tufa mounds are rooted at a maximum of 4 m below the current lake surface and are actively forming from groundwater seepage, which can be seen emanating from the top of the tufa mounds. Big Soda Lake is a volcanic crater lake whose water level is maintained exclusively by groundwater. The age of the tufa mounds is well constrained because prior to the development of the Newlands Irrigation Project in 1907, the water level was ∼18 m lower than the current lake level. The vertical columnar nature of the tufa mounds indicates that they formed under the lake and not subaerially. Thus, the tufa mounds are <100 yr old and have grown at a rate ≥30 mm/yr. Stable oxygen and carbon isotope analyses of tufa carbonate compared to isotopic analyses of groundwater and lake water and hydrochemical data indicate that the fluids responsible for their precipitation are a simple mixture of modern groundwater and lake water and do not reflect a recent climate signature. The exceptionally fast growth of the tufa mounds indicates that large tufa deposits may form almost instantaneously in geologic time. Given this potential for rapid growth and the fact that variations in isotopic compositions of tufa deposits have been interpreted in terms of changes in paleoclimate and changes in the composition of recharge water over thousands of years, care should be taken when trying to determine the significance of variations in isotopic or chemical compositions of tufas that may have been caused by mixing with groundwater.

Deuterium NMR characterization of noncovalent interactions between monoaromatic compounds and fulvic acids

Deuterium nuclear magnetic resonance spectroscopy ( 2H-NMR) spin–lattice relaxation ( T 1) experiments were used to measure noncovalent interactions between deuterated monoaromatic compounds (phenol- d 5, pyridine- d 5, benzene- d 6) and fulvic acids isolated from the Suwannee River and Big Soda Lake. Noncovalent interactions, in aqueous solution, were examined as a function of monoaromatic hydrocarbon functional groups, fulvic acid concentration and identity, and solution pH. Phenol did not exhibit noncovalent interactions with either fulvic acid at any pH. Pyridine, in a pH range from 3 to 8, interacted with Suwannee River fulvic acid, forming a bond involving the lone pair of electrons on nitrogen. Conversely, no interactions were observed between pyridine and Big Soda Lake fulvic acid; the difference in noncovalent interactions is attributed to the structural and chemical differences of the two fulvic acids. The translational and rotational molecular motion of benzene increased in the presence of both fulvic acids, indicating that in aqueous solution, fulvic acids solubilize benzene rather than forming discrete bonds as with pyridine. The results of this study demonstrate that monoaromatic functional groups, solution pH, and identity and concentration of fulvic acid can influence the type and degree of noncovalent interactions with dissolved organic matter.

Measurement of in situ rates of selenate removal by dissimilatory bacterial reduction in sediments

vertical distribution in sediments relative to other forms • A radioisotope method for measurement of bacterial of anaerobic bacterial respiration. An understanding of respiratory reduction of selenate to elemental selenium in how the process of dissimilatory selenate reduction oper­ aquatic sediments was devised. Sediments were labeled ates in these respects should ultimately aid the design of with [75Se]selenate, incubated, and washed, and 75SeO(S) treatment schemes and the rehabilitation of selenium­ was determined as counts remaining in the sediment. Core contaminated regions. In order to answer these questions profiles of selenate reduction, sulfate reduction, and den­ and to achieve these long-term goals, it was f1I'St necessary itrification were made simultaneously in the sediments of to devise a method for measuring in situ selenate reduction. an agricultural wastewater evaporation pond. Most of the In situ measures of bacterial activities have been a focus in situ selenate reduction (850/0) and all the denitrification of microbial ecology for the past 25 years. A variety of activities were confined to the upper 4-8 em of the profile, whereas sulfate reduction was greatest below 8 em (890/0 techniques employing radioisotopes, gas chromatography, of total). The integrated areal rate of selenate reduction and/or enzyme inhibitors or analogues have been exploited was 301 J,tmol m-2 day, which results in a turnover of to assess environmental rates of methanogenesis (8), den­ water column selenate in 82.4 days. itrification (9, 10), nitrogen fixation (11), and sulfate re­ duction (12). This latter process is analogous to the methods we report herein to measure selenate reduction. Introduction However, in the case of selenate reduction, our task was Oxyanions of selenium have been identified as toxic simplified because 75Se is a 'Y-emitting radioisotope (t l / 2 constituents in drainage waters from irrigated, seleniferous =120 days), which circumvents the quenching/efficiency agricultural soils (1). This environmental problem is ap­ problem associated with liquid scintillation counting of parently quite common in many regions of the western weak ~-emitters like 35S. Thus, there was no need to United States (2). Therefore, methods that address the volatilize and trap the product 75SeO(S) as there is for question of removal of selenium oxyanions from soils [35S]sulfide, but merely to wash away the added [75Se]­ and/or drainage waters by various means have received selenate. Our results with core profiles from a selenium­ considerable attention because they offer the prospect of rich agricultural wastewater evaporation pond represent restoring water or soil quality while allowing for the con­ quasi in situ assays because they were incubated in the tinuation of irrigated farming. With regard to possible laboratory under conditions approximating the field. microbiological methods, volatilization of selenium by However, our results indicate that selenate reduction oc­ formation of alkylated gases (e.g., dimethyl selenide) has curs in the surficial layers of these sediments, in proximity been suggested for treatment of soils (3) or impacted marsh to the region of active denitrification, yet spatially sepa­ waters, such as those of the Kesterson Wildlife Refuge (4, rated from sulfate reduction occurring deeper in the core. 5). Areal rates of selenate removal obtained from this core J Recently, we reported on a novel process by which indicate its rapid removal by reduction to SeO(s), and a anaerobic bacteria respire selenate, which in turn bio­ quick turnover of water column selenate. When combined chemically reduces this oxyanion to selenite and ultimately with previous observations with regard to inhibitors and to elemental selenium (6). This dissimilatory reduction stimulators of selenium reduction, the conceptual design was demonstrated to occur in sediments, was independent of an efficient anaerobic selenate digester can be dis­ of sulfate, and was inhibited by nitrate and chromate. cerned. Bacterial cultures capable of selenate respiratory growth have been isolated (6, 7). Although we were able to show Experimental Section that this process holds the potential to rapidly remove and Sites and Sampling. Surficial (upper ro.J20 em) sedi­ sequester considerable quantities (millimolar) of added ments were collected from Hunter Drain, an agricultural selenate from sediment slurries, the questions remained drain located in Stillwater, NV, where selenium contam­ as to how rapidly it proceeds in nature, and what was its ination is documented (2), as well as from the littoral zone of Big Soda Lake, an alkaline/saline environment (13)

Isolation of strictly anaerobic halophiles from the aerobic surface sediments of hypersaline environments in California and Nevada

Four strictly anaerobic, chemoorganotrophic halophiles were isolated from the hypersaline surface sediments of the evaporating closed lagoon at the rim of Salton Sea, California, and of Big Soda Lake, Nevada, whose condition was not strictly anaerobic. All of the isolates were Gram-negative, motile, non-spore-forming, moderately halophilic eubacteria and required a minimum concentration of 3–10% NaCl in the growth medium. Among the four isolates, strain SS-21 could grow at more than 30% NaCl concentration, and strain M-20 was an alkalophine. Isolation of these bacteria suggests that a variety of anaerobic halophiles is widely distributed in hypersaline environments.

Microbial and biogeochemical processes in Big Soda Lake, Nevada

Summary Meromictic, alkaline lakes represent modern-day analogues of lacustrine source rock depositional environments. In order to further our understanding of how these lakes function in terms of limnological and biogeochemical processes, we have conducted an interdisciplinary study of Big Soda Lake. Annual mixolimnion productivity (ca. 500 g m −2 ) is dominated by a winter diatom bloom (600f annual) caused by upward transport of ammonia to the epilimnion. The remainder of productivity is attributable to chemoautotrophs (30%) and photosynthetic bacteria (10%) present at the oxic-anoxic interface from May to November. Studies of bacterial heterotrophy and particulate fluxes in the water column indicate that about 900f annual productivity is remineralized in the mixolimnion, primarily by fermentative bacteria. However, high rates of sulphate reduction (9–29 mmol m −2 yr −1 ) occur in the monimolimnion waters, which could remineralize most (if not all) of the primary productivity. This discrepancy has not as yet been fully explained. Low rates of methanogenesis also occur in the monimolimnion waters and sediments. Most of the methane is consumed by anaerobic methane oxidation occurring in the monimolimnion water column. Other bacterial processes occurring in the lake are also discussed. Preliminary studies have been made on the organic geochemistry of the monimolimnion sediments. Carbon-14-dating indicates a lower depositional rate prior to meromixis and a downcore enrichment in 13 C of organic carbon and chlorophyll derivatives. Hydrous pyrolysis experiments indicate that the sediment organic matter is almost entirely derived from the water column with little or no contribution from terrestrial sources. The significance of the organics released by hydrous pyrolysis is discussed.

Big Soda Lake (Nevada). 2. Pelagic sulfate reduction

The epilimnion of hypersaline, alkaline, meromictic Big Soda Lake contains an average 58 mmol sulfate liter−1 and 0.4 µmol dissolved iron liter−1. The monimolimnion, which is permanently anoxic, has a sulfide concentration ranging seasonally from 4 to 7 mmol liter−1. Depth profiles of sulfate reduction in the monimolimnion, assayed with a 35S tracer technique and in situ incubations, demonstrated that sulfate reduction occurs within the water column of this extreme environment. The average rate of reduction in the monimolimnion was 3 µmol sulfate liter−1 d−1 in May compared to 0.9 in October. These values are comparable to rates of sulfate reduction reported for anoxic waters of more moderate environments. Sulfate reduction also occurred in the anoxic zone of the mixolimnion, though at significantly lower rates (0.025–0.090 µmol liter−1 d−1 at 25 m). Additions of FeS (1.0 mmol liter−1) doubled the endogenous rate of sulfate reduction in the monimolimnion, while MnS and kaolinite had no effect. These results suggest that sulfate reduction in Big Soda Lake is iron limited and controlled by seasonal variables other than temperature. Estimates of the organic carbon mineralized by sulfate reduction exceed measured fluxes of particulate organic carbon sinking from the mixolimnion. Thus, additional sources of electron donors (other than those derived from the sinking of pelagic autotrophs) may also fuel monimolimnetic sulfate reduction in the lake.

Big Soda Lake (Nevada). 4. Vertical fluxes of particulate matter: Seasonality and variations across the chemocline

Vertical fluxes of particulate organic matter were measured with sediment traps above and below the chemocline of Big Soda Lake to define the seasonality of sinking losses from the mixolimnion and determine the effectiveness of the chemocline (pycnocline) as a barrier to the sinking of biogenic particles. Seasonality of sedimentation rates reflected seasonal changes in the community of autotrophs. During summer‐autumn, when production is dominated by autotrophic bacteria, vertical fluxes were small: 100 mg C m−2 d−1 and ≅0.5 mg Chl a m−2 d−1. Following the winter diatom bloom, vertical fluxes increased markedly: ≅570 mg C m−2 d−1 and 23 mg Chl a m−2 d−1. The bulk of the seston (&gt; 80%) and particulate carbon (≅ 65%) sinking to the chemocline passed through it, showing that this very sharp density discontinuity does not effectively retard the sinking of particulate matter. However sinking losses of particulate carbon were generally small (≅10%) relative to previous measures of primary productivity, indicating that the mixolimnion is a zone of efficient carbon cycling. Exceptions occurred following the winter bloom when sinking losses were a larger fraction (≅40%) of productivity.

Big Soda Lake (Nevada). 1. Pelagic bacterial heterotrophy and biomass1

Bacterial activities and abundance were measured seasonally in the water column of meromictic Big Soda Lake which is divided into three chemically distinct zones: aerobic mixolimnion, anaerobic mixolimnion, and anaerobic monimolimnion. Bacterial abundance ranged between 5 and 52 x 106 cells ml−1, with highest biomass at the interfaces between these zones: 2–4 mg C liter−1 in the photosynthetic bacterial layer (oxycline) and 0.8–2.0 mg C liter−1 in the chemocline. Bacterial cell size and morphology also varied with depth: small coccoid cells were dominant in the aerobic mixolimnion, whereas the monimolimnion had a more diverse population that included cocci, rods, and large filaments. Heterotrophic activity was measured by [methyl‐3H]thymidine incorporation and [14C]glutamate uptake. Highest uptake rates were at or just below the photosynthetic bacterial layer and were attributable to small (&lt;1 µm) heterotrophs rather than the larger photosynthetic bacteria. These high rates of heterotrophic uptake were apparently linked with fermentation; rates of other mineralization processes (e.g. sulfate reduction, methanogenesis, denitrification) in the anoxic mixolimnion were insignificant. Heterotrophic activity in the highly reduced monimolimnion was generally much lower than elsewhere in the water column. Therefore, although the monimolimnion contained most of the bacterial abundance and biomass (∼60%), most of the cells there were inactive.

Big Soda Lake (Nevada). 3. Pelagic methanogenesis and anaerobic methane oxidation1

In situ rates of methanogenesis and methane oxidation were measured in meromictic Big Soda Lake. Methane production was measured by the accumulation of methane in the headspaces of anaerobically sealed water samples; radiotracer was used to follow methane oxidation. Nearly all the methane oxidation occurred in the anoxic zones of the lake. Rates of anaerobic oxidation exceeded production at all depths studied in both the mixolimnion (2–6 vs. 0.1–1 nmol liter−1 d−1) and monimolimnion (49–85 vs. 1.6–12 nmol liter−1 d−1) of the lake. Thus, a net consumption of methane equivalent to 1.36 mmol m−2 d−1 occurred in the anoxic water column. Anaerobic methane oxidation had a first‐order rate constant of 8.1±0.5 × 10−4 d−1, and activity was eliminated by filter sterilization. However, in situ methane oxidation was of insufficient magnitude to cause a noticeable decrease of ambient dissolved methane levels over an incubation period of 97 h.