Search

Methane-cycling is becoming more important in high-latitude ecosystems as global warming makes permafrost organic carbon increasingly available. We explored 387 samples from three high-latitudes regions (Siberia, Alaska and Patagonia) focusing on mineral/organic soils (wetlands, peatlands, forest), lake/pond sediment and water. Physicochemical, climatic and geographic variables were integrated with 16S rDNA amplicon sequences to determine the structure of the overall microbial communities and of specific methanogenic and methanotrophic guilds. Physicochemistry (especially pH) explained the largest proportion of variation in guild composition, confirming species sorting (i.e., environmental filtering) as a key mechanism in microbial assembly. Geographic distance impacted more strongly beta diversity for (i) methanogens and methanotrophs than the overall prokaryotes and, (ii) the sediment habitat, suggesting that dispersal limitation contributed to shape the communities of methane-cycling microorganisms. Bioindicator taxa characterising different ecological niches (i.e., specific combinations of geographic, climatic and physicochemical variables) were identified, highlighting the importance of Methanoregula as generalist methanogens. Methylocystis and Methylocapsa were key methanotrophs in low pH niches while Methylobacter and Methylomonadaceae in neutral environments. This work gives insight into the present and projected distribution of methane-cycling microbes at high latitudes under climate change predictions, which is crucial for constraining their impact on greenhouse gas budgets., (© 2023 The Authors. Environmental Microbiology published by Applied Microbiology International and John Wiley & Sons Ltd.)

High latitudes are experiencing intense ecosystem changes with climate warming. The underlying methane (CH 4 ) cycling dynamics remain unresolved, despite its crucial climatic feedback. Atmospheric CH 4 emissions are heterogeneous, resulting from local geochemical drivers, global climatic factors, and microbial production/consumption balance. Holistic studies are mandatory to capture CH 4 cycling complexity. Here, we report a large set of integrated microbial and biogeochemical data from 387 samples, using a concerted sampling strategy and experimental protocols. The study followed international standards to ensure inter-comparisons of data amongst three high-latitude regions: Alaska, Siberia, and Patagonia. The dataset encompasses different representative environmental features (e.g. lake, wetland, tundra, forest soil) of these high-latitude sites and their respective heterogeneity (e.g. characteristic microtopographic patterns). The data included physicochemical parameters, greenhouse gas concentrations and emissions, organic matter characterization, trace elements and nutrients, isotopes, microbial quantification and composition. This dataset addresses the need for a robust physicochemical framework to conduct and contextualize future research on the interactions between climate change, biogeochemical cycles and microbial communities at high-latitudes., (© 2022. The Author(s).)

It is commonly assumed that methane (CH 4 ) released by lakes into the atmosphere is mainly produced in anoxic sediment and transported by diffusion or ebullition through the water column to the surface of the lake. In contrast to that prevailing idea, it has been gradually established that the epilimnetic CH 4 does not originate exclusively from sediments but is also locally produced or laterally transported from the littoral zone. Therefore, CH 4 cycling in the epilimnion and the hypolimnion might not be as closely linked as previously thought. We utilized a high-resolution method used to determine dissolved CH 4 concentration to analyze a Siberian lake in which epilimnetic and hypolimnetic CH 4 cycles were fully segregated by a section of the water column where CH 4 was not detected. This layer, with no detected CH 4 , was well below the oxycline and the photic zone and thus assumed to be anaerobic. However, on the basis of a diffusion-reaction model, molecular biology, and stable isotope analyses, we determined that this layer takes up all the CH 4 produced in the sediments and the deepest section of the hypolimnion. We concluded that there was no CH 4 exchange between the hypolimnion (dominated by methanotrophy and methanogenesis) and the epilimnion (dominated by methane lateral transport and/or oxic production), resulting in a vertically segregated lake internal CH 4 cycle.

The Cuatro Cienegas Basin (CCB) in the Chihuahuan desert is characterized by the presence of over 500 ponds located in an endorheic basin. These ponds are subsaline ecosystems characterized by a low productivity and a particularly high sulfate concentration, comparable to marine environments. This study focused on assessing the main physicochemical parameters in these ponds along with the characterization of the CH 4 dynamics through the determination of fluxes, dissolved CH 4 concentrations, and net methanotrophic and methanogenic activity. Despite a sulfate concentration ranging from 1.06 to 4.73 g L -1 , the studied ponds showed moderate but clear CH 4 production and emission, which suggests that methanogenesis is not completely outcompeted by sulfate reduction. CH 4 fluxes ranged from 0.12 to 0.98 mg m -2 d -1 , which falls within the higher range of marine emissions and within the lower range reported for coastal saline lagoons and saline ponds. During summer, significant CH 4 production in the oxic water column was observed. In addition to CH 4 , CO 2 fluxes were determined at levels from 0.2 to 53 g m -2 d -1 , which is within the range recorded for saline lakes in other parts of the world. Our results provide additional evidence that subsaline/saline aquatic ecosystems play an important role in the emission of greenhouse gases to the atmosphere., (Copyright © 2019 Elsevier B.V. All rights reserved.)

An open dynamic chamber for the continuous monitoring of diffusive and ebullitive fluxes of methane (CH 4 ) in aquatic ecosystems was designed and developed. This method is based on a standard floating chamber in which a well-defined carrier gas flows. The concentration of CH 4 is measured continuously at the outlet of the chamber, and the flux is determined from a mass balance equation. The method was carefully tested in a laboratory and was subsequently applied to two lakes, in Mexico, with contrasting trophic states. We show here that the method allows for the continuous quantification of CH 4 diffusive flux higher than 25 × 10 -6 g m -2 h -1 , the determination of ebullitive flux, and the individual characterization of bubbles larger than 1.50-1.72 mm in diameter. The method was also applied to determine carbon dioxide emissions (CO 2 ). In that case, the method was less sensitive but allowed for the characterization of diffusive fluxes higher than 10 mg CO 2 m -2 h -1 and of bubbles larger than 5.3-8.4 mm in diameter. This high-throughput method can be adapted to any gas detector at low cost, making it a convenient tool to better constrain greenhouse gas emission from freshwater ecosystems.

The sub-Antarctic Magellanic ecoregion is a part of the world where ecosystems have been understudied and where the CH 4 cycling and emissions in lakes has not ever been reported. To fill that knowledge gap, a lake and a reservoir located at 53°S were selected and studied during three campaigns equally distributed over one year. Among the parameters measured were CH 4 and CO 2 emissions, as well their dissolved concentrations in the water column, which were determined with high spatial resolution. No ebullition was observed and the CH 4 flux ranged from 0.0094 to 4.47mmolm -2 d -1 while the CO 2 flux ranged from -22.95 to 35.68mmolm -2 d -1 . Dissolved CH 4 concentrations varied over more than four orders of magnitude (0.025-128.75μmolL -1 ), and the dissolved carbon dioxide ranged from below the detection limit of our method (i.e., 0.15μmolL -1 ) to 379.09μmolL -1 . The high spatial resolution of the methods used enabled the construction of bathymetric maps, surface contour maps of CH 4 and CO 2 fluxes, and transect contour maps of dissolved oxygen, temperature, and dissolved greenhouse gases. Overall, both lakes were net greenhouse gas producers and were not significantly different from temperate lakes located at a similar northern latitudes (53°N), except that ebullition was never observed in the studied sub-Antarctic lakes., (Copyright © 2017 Elsevier B.V. All rights reserved.)

A novel low-cost method for the combined, real-time, and in situ determination of dissolved methane and carbon dioxide concentrations in freshwater ecosystems was designed and developed. This method is based on the continuous sampling of water from a freshwater ecosystem to a gas/liquid exchange membrane. Dissolved gas is transferred through the membrane to a continuous flow of high purity nitrogen, which is then measured by an off-axis integrated cavity output spectrometer (OA-ICOS). This method, called M-ICOS, was carefully tested in a laboratory and was subsequently applied to four lakes in Mexico and Alaska with contrasting climates, ecologies, and morphologies. The M-ICOS method allowed for the determination of dissolved methane and carbon dioxide concentrations with a frequency of 1 Hz and with a method detection limit of 2.76 × 10(-10) mol L(-1) for methane and 1.5 × 10(-7) mol L(-1) for carbon dioxide. These detection limits are below saturated concentrations with respect to the atmosphere and significantly lower than the minimum concentrations previously reported in lakes. The method is easily operable by a single person from a small boat, and the small size of the suction probe allows the determination of dissolved gases with a minimized impact on shallow freshwater ecosystems.