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Abstract The conservation of forest landscapes is crucial for global climate strategies, and the forest in Tierra del Fuego, located in Patagonia, represents the southernmost example on Earth. These ecosystems are critical for Chile’s roadmap toward carbon neutrality. Unfortunately, these ecosystems have been impacted by logging and beaver activities. Currently, the precise contribution of each driver to forest cover and carbon stock loss remains insufficiently quantified, impeding effective policymaking and the implementation of strategies to safeguard and enhance carbon stocks in these ecosystems. In this study, we conducted an assessment of forest carbon stock loss resulting from both logging and beaver activities in Chilean Tierra del Fuego from 1986 to 2019. While beavers have received significant attention for their substantial contribution to forest cover loss (56.1% forest cover, ≈ 1.4 MtC), our findings suggest that logging has nearly equally contributed to carbon stock depletion (43.8% forest cover, ≈ 1.2 MtC). Consequently, the prevailing focus on beavers has obscured the ongoing logging-induced carbon stock loss. The implications of our study highlight the urgency for comprehensive consideration of both drivers in Chile’s climate strategy to fulfill the country’s mitigation commitments.

We present a reliable and robust open dynamic chamber for measuring greenhouse gas exchange in peatlands with minimal disturbance of the ground. This chamber, called the “skirt chamber”, is based on a transparent plastic film placed above an open frame made of sparse interwoven wires and expanded around the base of the chamber below a steel chain that ensures contact to the ground, avoiding damage, trenching, and cutting vegetation. Gas exchange is determined using a portable gas analyzer from a mass balance in which the imperfect sealing of the chamber to the ground is quantified through the injection of a methane pulse. The method was tested on a pristine peatland dominated by Sphagnum magellanicum located on Navarino Island in the subantarctic Magellanic ecoregion in Chile. Our results indicate that the skirt chamber allowed the determination of methane fluxes and ecosystem respiration in about 20 min, with a limit of detection of 0.185 mg CH4 m−2 h−1 and 173 mg CO2 m−2 h−1, respectively. We conclude that the skirt chamber is a minimally intrusive, fast, portable, and inexpensive method that allows the quantification of greenhouse gas emissions with high spatial resolution in remote locations and without delay.

Measurement(s) microbial diversity • microbial abundances • cations and anions • trace elements Technology Type(s) MiSeq sequencing 16S rRNA gene • Real Time PCR • HPLC • ICP-MS Sample Characteristic - Organism bacteria • archaea Sample Characteristic - Environment lake water • lake sediment • wetland • peatland • soil • pond Sample Characteristic - Location Western Siberia • Alaska • Patagonia • Cape Horn province • Magellanic subantarctic ecoregion

Mosses of the genus Sphagnum are the dominant vegetation in most pristine peatlands in temperate and high‐latitude regions. They play a crucial role in carbon sequestration, being responsible for ca. 50% of carbon accumulation through their active participation in peat formation. They have a significant influence on the dynamics of CO2 emissions due to an efficient maximum potential photosynthetic rate, lower respiration rates, and the production of a recalcitrant litter whose decomposition is gradual. However, various anthropogenic disturbances and land use management actions that favor its reestablishment have the potential to modify the dynamics of these CO2 emissions. Therefore, the objective of this review is to discuss the role of Sphagnum in CO2 emissions generated in peatland ecosystems, and to understand the impacts of anthropogenic practices favorable and detrimental to Sphagnum on these emissions. Based on our review, increased Sphagnum cover reduces CO2 emissions and fosters C sequestration, but drainage transforms peatlands dominated by Sphagnum into a persistent source of CO2 due to lower gross primary productivity of the moss and increased respiration rates. Sites with moss removal used as donor material for peatland restoration emit twice as much CO2 as adjacent undisturbed natural sites, and those with commercial Sphagnum extraction generate almost neutral CO2 emissions, yet both can recover their sink status in the short term. The reintroduction of fragments and natural recolonization of Sphagnum in transitional peatlands, can reduce emissions, recover, or increase the CO2 sink function in the short and medium term. Furthermore, Sphagnum paludiculture is seen as a sustainable alternative for the use of transitional peatlands, allowing moss production strips to become CO2 sink, however, it is necessary to quantify the emissions of all the components of the field of production (ditches, causeway), and the biomass harvested from the moss to establish a final closing balance of C. [ABSTRACT FROM AUTHOR]

Methanotrophic bacteria play an important role oxidizing a significant fraction of methane (CH4) produced in lakes. Aerobic CH4 oxidation depends mainly on lake CH4 and oxygen (O2) concentrations, in such a manner that higher MO rates are usually found at the oxic/anoxic interface, where both molecules are present. MO also depends on temperature, and via methanogenesis, on organic carbon input to lakes, including from thawing permafrost in thermokarst (thaw)-affected lakes. Given the large variability in these environmental factors, CH4 oxidation is expected to be subject to large seasonal and geographic variations, which have been scarcely reported in the literature. In the present study, we measured CH4 oxidation rates in 30 Alaskan lakes along a north-south latitudinal transect during winter and summer with a new field laser spectroscopy method. Additionally, we measured dissolved CH4 and O2 concentrations. We found that in the winter, aerobic CH4 oxidation was mainly controlled by the dissolved O2 concentration, while in the summer it was controlled primarily by the CH4 concentration, which was scarce compared to dissolved O2. The permafrost environment of the lakes was identified as another key factor. Thermokarst (thaw) lakes formed in yedoma-type permafrost had significantly higher CH4 oxidation rates compared to other thermokarst and non-thermokarst lakes formed in non-yedoma permafrost environments. As thermokarst lakes formed in yedoma-type permafrost have been identified to receive large quantities of terrestrial organic carbon from thaw and subsidence of the surrounding landscape into the lake, confirming the strong coupling between terrestrial and aquatic habitats and its influence on CH4 cycling.

Thermokarst (thaw) lakes emit methane (CH4) to the atmosphere formed from thawed permafrost organic matter (OM), but the relative magnitude of CH4 production in surface lake sediments vs. deeper thawed permafrost horizons is not well understood. We assessed anaerobic CH4 production potentials from various depths along a 590 cm long lake sediment core that captured the entire sediment package of the talik (thaw bulb) beneath the center of an interior Alaska thermokarst lake, Vault Lake, and the top 40 cm of thawing permafrost beneath the talik. We also studied the adjacent Vault Creek permafrost tunnel that extends through ice-rich yedoma permafrost soils surrounding the lake and into underlying gravel. Our results showed CH4 production potentials were highest in the organic-rich surface lake sediments, which were 151 cm thick (mean ± SD: 5.95 ± 1.67 μg C–CH4 g dw−1 d−1; 125.9 ± 36.2 μg C–CH4 g C−1org d−1). High CH4 production potentials were also observed in recently thawed permafrost (1.18 ± 0.61 μg C–CH4g dw−1 d−1; 59.60± 51.5 μg C–CH4 g C−1org d−1) at the bottom of the talik, but the narrow thicknesses (43 cm) of this horizon limited its overall contribution to total sediment column CH4 production in the core. Lower rates of CH4 production were observed in sediment horizons representing permafrost that has been thawing in the talik for a longer period of time. No CH4 production was observed in samples obtained from the permafrost tunnel, a non-lake environment. Our findings imply that CH4 production is highly variable in thermokarst lake systems and that both modern OM supplied to surface sediments and ancient OM supplied to both surface and deep lake sediments by in situ thaw and shore erosion of yedoma permafrost are important to lake CH4 production.

Uncertainties in the magnitude and seasonality of various gas emission modes, particularly among different lake types, limit our ability to estimate methane (CH4) and carbon dioxide (CO2) emissions from northern lakes. Here we assessed the relationship between CH4 and CO2 emission modes in 40 lakes along a latitudinal transect in Alaska to lakes' physicochemical properties and geographic characteristics, including permafrost soil type surrounding lakes. Emission modes included direct ebullition, diffusion, storage flux, and a newly identified ice-bubble storage (IBS) flux. We found that all lakes were net sources of atmospheric CH4 and CO2, but the climate warming impact of lake CH4 emissions was 2 times higher than that of CO2. Ebullition and diffusion were the dominant modes of CH4 and CO2 emissions, respectively. IBS, ~10% of total annual CH4 emissions, is the release to the atmosphere of seasonally ice-trapped bubbles when lake ice confining bubbles begins to melt in spring. IBS, which has not been explicitly accounted for in regional studies, increased the estimate of springtime emissions from our study lakes by 320%. Geographically, CH4 emissions from stratified, mixotrophic interior Alaska thermokarst (thaw) lakes formed in icy, organic-rich yedoma permafrost soils were 6-fold higher than from non-yedoma lakes throughout the rest of Alaska. The relationship between CO2 emissions and geographic parameters was weak, suggesting high variability among sources and sinks that regulate CO2 emissions (e.g., catchment waters, pH equilibrium). Total CH4 emission was correlated with concentrations of soluble reactive phosphorus and total nitrogen in lake water, Secchi depth, and lake area, with yedoma lakes having higher nutrient concentrations, shallower Secchi depth, and smaller lake areas. Our findings suggest that permafrost type plays important roles in determining CH4 emissions from lakes by both supplying organic matter to methanogenesis directly from thawing permafrost and by enhancing nutrient availability to primary production, which can also fuel decomposition and methanogenesis.

The conservation of forest landscapes is crucial for global climate strategies, and the forest in Tierra del Fuego, located in Patagonia, represents the southernmost example on Earth. These ecosystems are critical for Chile's roadmap toward carbon neutrality. Unfortunately, these ecosystems have been impacted by logging and beaver activities. Currently, the precise contribution of each driver to forest cover and carbon stock loss remains insufficiently quantified, impeding effective policymaking and the implementation of strategies to safeguard and enhance carbon stocks in these ecosystems. In this study, we conducted an assessment of forest carbon stock loss resulting from both logging and beaver activities in Chilean Tierra del Fuego from 1986 to 2019. While beavers have received significant attention for their substantial contribution to forest cover loss (56.1% forest cover, ≈ 1.4 MtC), our findings suggest that logging has nearly equally contributed to carbon stock depletion (43.8% forest cover, ≈ 1.2 MtC). Consequently, the prevailing focus on beavers has obscured the ongoing logging-induced carbon stock loss. The implications of our study highlight the urgency for comprehensive consideration of both drivers in Chile's climate strategy to fulfill the country's mitigation commitments. [ABSTRACT FROM AUTHOR]

We present a reliable and robust open dynamic chamber for measuring greenhouse gas exchange in peatlands with minimal disturbance of the ground. This chamber, called the "skirt chamber", is based on a transparent plastic film placed above an open frame made of sparse interwoven wires and expanded around the base of the chamber below a steel chain that ensures contact to the ground, avoiding damage, trenching, and cutting vegetation. Gas exchange is determined using a portable gas analyzer from a mass balance in which the imperfect sealing of the chamber to the ground is quantified through the injection of a methane pulse. The method was tested on a pristine peatland dominated by Sphagnum magellanicum located on Navarino Island in the subantarctic Magellanic ecoregion in Chile. Our results indicate that the skirt chamber allowed the determination of methane fluxes and ecosystem respiration in about 20 min, with a limit of detection of 0.185 mg CH 4 m -2 h -1 and 173 mg CO 2 m -2 h -1 , respectively. We conclude that the skirt chamber is a minimally intrusive, fast, portable, and inexpensive method that allows the quantification of greenhouse gas emissions with high spatial resolution in remote locations and without delay. [ABSTRACT FROM AUTHOR]

Microbial methane (CH4) ebullition (bubbling) from anoxic lake sediments comprises a globally significant flux to the atmosphere, but ebullition bubbles in temperate and polar lakes can be trapped by winter ice cover and later released during spring thaw. This "ice-bubble storage" (IBS) constitutes a novel mode of CH4 emission. Before bubbles are encapsulated by downward-growing ice, some of their CH4 dissolves into the lake water, where it may be subject to oxidation. We present field characterization and a model of the annual CH4 cycle in Goldstream Lake, a thermokarst (thaw) lake in interior Alaska. We find that summertime ebullition dominates annual CH4 emissions to the atmosphere. Eighty percent of CH4 in bubbles trapped by ice dissolves into the lake water column in winter, and about half of that is oxidized. The ice growth rate and the magnitude of the CH4 ebullition flux are important controlling factors of bubble dissolution. Seven percent of annual ebullition CH4 is trapped as IBS and later emitted as ice melts. In a future warmer climate, there will likely be less seasonal ice cover, less IBS, less CH4 dissolution from trapped bubbles, and greater CH4 emissions from northern lakes.

Peatland open‐water pools can be net carbon (C) emitters within heterogeneous peatland ecosystems that are generally net C sinks. However, the intra‐ and inter‐regional patterns and drivers of CO2 and CH4 production, as well as their link with dissolved organic matter (DOM) quality and quantity, remain poorly understood. We analyzed a range of optical characteristics and chemical variables controlling DOM and CO2 and CH4 concentrations in peatland pools across two regions with contrasting geographical properties (i.e., climate, topography, morphometry, and vegetation cover) of eastern Canada and Chilean Patagonia. We found inter‐regional patterns in CO2, CH4 and DOM concentrations and composition that were coherent with patterns in mean annual temperature and precipitation, and vegetation cover. Cross‐regional patterns of CO2 and CH4 were driven by morphometry, vegetation cover, and protein‐like DOM composition, a proxy of high biological activity, whereas temporal variations of CO2 and CH4 concentrations were further influenced by seasonal changes in humic‐like DOM composition, dissolved organic carbon and nutrients (i.e., total phosphorus and total nitrogen) concentrations, as well as pH and oxygen levels. Our results suggest that geophysical constraints associated with local peat and pool characteristics as well as climate patterns are major drivers of DOM and greenhouse gases concentrations and the links between them in broadly distributed peatland pools. Key Points: Broad‐scale patterns in peatland pools dissolved organic matter (DOM) and CO2 were driven by vegetation cover and pool morphometryBroad‐scale patterns in CH4 were the most responsive among C‐species to long‐term climate averages across regionsProtein‐like DOM controls within‐pool greenhouse gases (GHG) concentrations across regions, while humic‐like DOM drives within‐site temporal GHG concentrations [ABSTRACT FROM AUTHOR]

“Lago de Guadalupe” is an important freshwater ecosystem located in the northern part of the metropolitan area surrounding Mexico City, under high demographic pressure. It receives approximately 15 hm3·y-1 of untreated municipal wastewater from the surrounding municipalities. In order to develop a comparative assessment of the pollution effect over the limnological characteristics of Lago de Guadalupe, this lake was characterised from February 2006 to July 2009, and the results were compared with those obtained from a non-polluted lake “Lago el Llano” located in the same drainage area. Lago de Guadalupe was hypereutrophic with anoxic conditions throughout most of the water column. In contrast, Lago el Llano was mesotrophic with high dissolved oxygen concentrations throughout the entire water column with a clinograde profile. Both reservoirs had a monomictic mixing regime. The longitudinal zonation of physicochemical and biological variables were investigated in order to better understand the processes controlling the water quality across the reservoir during its residence time. This study shows the impact of anthropogenic pollution on the limnological characteristics of a subtropical reservoir and confirms that under adequate management schemes, namely avoiding pollution and wastewater discharges, subtropical reservoirs can be prevented from developing eutrophic conditions.