Emission of Greenhouse Gases From Water Tracks Draining Arctic Hillslopes

Abstract

Experimental and ambient warming of Arctic tundra results in emissions of greenhouse gases to the atmosphere, contributing to a positive feedback to climate warming. Estimates of gas emissions from lakes and terrestrial tundra confirm the significance of aquatic fluxes in greenhouse gas budgets, whereas few estimates describe emissions from fluvial networks. We measured dissolved gas concentrations and estimated emissions of carbon dioxide (CO 2), methane (CH 4), and nitrous oxide (N 2 O) from water tracks, vegetated depressions that hydrologically connect hillslope soils to lakes and streams. Concentrations of trace gases generally increased as ground thaw deepened through the growing season, indicating active production of greenhouse gases in thawed soils. Wet antecedent conditions were correlated with a decline in CO 2 and CH 4 concentrations. Dissolved N 2 O in excess of atmospheric equilibrium occurred in drier water tracks, but on average water tracks took up N 2 O from the atmosphere at low rates. Estimated CO 2 emission rates for water tracks were among the highest observed for Arctic aquatic ecosystems, whereas CH 4 emissions were of similar magnitude to streams. Despite occupying less than 1% of total catchment area, surface waters within water tracks were an estimated source of up to 53-85% of total CH 4 emissions from their catchments and offset the terrestrial C sink by 5-9% during the growing season. Water tracks are abundant features of tundra landscapes that contain warmer soils and incur deeper thaw than adjacent terrestrial ecosystems and as such might contribute to ongoing and accelerating release of greenhouse gases from permafrost soils to the atmosphere. Plain Language Summary The Arctic is warming at least twice as rapidly as the rest of the Earth. Warming thaws permafrost, defined as ground that remains frozen for more than 2 years, and results in increased production and release of greenhouse gases by microbes. These gases, including carbon dioxide, methane, and nitrous oxide, trap heat in the atmosphere and contribute to further warming. Emissions of these gases have been extensively observed from soils and lakes in the Arctic, but fewer observations describe greenhouse gas emissions from stream networks. We estimated emissions of greenhouse gases from water flowing in vegetated depressions on Arctic hillslopes, called water tracks, which are tributaries of lakes and rivers. Water tracks may be conduits for gases from soils to the atmosphere. Compared to terrestrial tundra, water tracks emitted more carbon dioxide and methane than expected from their small areal coverage. Water tracks typically withdrew nitrous oxide from the atmosphere, though smaller water tracks supported higher concentrations and net emission of nitrous oxide. The abundance of water tracks combined with high rates of carbon dioxide and methane emission relative to adjacent ecosystems suggests that these features might contribute to increased release of greenhouse gases from Arctic landscapes as permafrost thaws.

Subarctic catchment water storage and carbon cycling – Leading the way for future studies using integrated datasets at Pallas, Finland

“…Our observations suggest that limited catchment dynamic storage in subarctic regions that are geologically similar to Pallas may have critical ecohydrological implications given future uncertainties in snowfall inputs (Bailey et al, 2021), and especially the timing of snowmelt processes. Simultaneously, ecohydrological connectivity strongly influences local and landscape processes in terms of carbon (DOC and DIC) export and GHG emissions (Harms et al, 2020). The latest sensor technologies and high‐frequency measurements can reveal highly‐detailed processes as shown by our snap‐shot analysis.…”

Bacterioplankton dispersal and biogeochemical function across Alaskan Arctic catchments

“…Simultaneously, environmental selection affects the composition (i.e. absolute makeup and relative diversity of taxonomy) of a bacterioplankton community and its functional ability to affect the local biogeochemistry, such as the decomposition of biological material, delivery of nutrients and DOC to surface waters, and generation of greenhouse gases (Harms et al, 2020; Malard & Pearce, 2018; Monteaux et al, 2020).…”

The highest methane concentrations in an Arctic river are linked to local terrestrial inputs

“…During the Arctic melt season (May to June), the surface hydrologic connectivity between the land and rivers is enhanced. As the seasonal progression takes place, deeper water-saturated soil layers are thawed, and substances, microorganisms, and gases, like CH4, are mobilized through the lateral transfer from groundwater discharge into Arctic inland waters, particularly to the 635 fluvial network (Connolly et al, 2020;Harms et al, 2020;Saunois et al, 2020). It has been demonstrated that the majority of the CH4 emitted to the atmosphere from subarctic ponds is sustained by the discharge of CH4 from groundwaters upon the active layer thaw (Olid et al, 2021).…”

“…The Arctic Ocean is one of the most river-influenced and land-locked of all the world oceans (Charkin et al, 2017;Shakirov et al, 2020), receiving annually about 10 % of the global runoff (Lammers et al, 2001), through the input from the main six Arctic rivers: Yenisey, Lena, Ob, Mackenzie, Yukon, and Kolyma. These rivers connect the ocean with the land, by mediating the transport of CH4 stored in terrestrial surface waters or groundwaters, or through 65 soil-water interactions in thawed water tracks (Connolly et al, 2020;Dabrowski et al, 2020;Harms et al, 2020;Saunois et al, 2020). Thus, the riverine transport of soil-derived CH4 from permafrost may influence the CH4 concentrations in the Arctic shelf system.…”

“…Trapped or newly formed CH4 can be emitted directly to the atmosphere after the abrupt or gradual permafrost thaw (Olefeldt et al, 2013;Saunois et al, 2020;Turetsky et al, 2020), or be laterally transported into neighboring inland waters via surface hydraulic connectivity or underground drainage (e.g., Dabrowski et al, 2020). Current and projected changes in the Arctic land surface hydrology, vegetation, landscape, and temperature due to permafrost thaw, will modulate CH4 concentrations in Arctic fluvial ecosystems (Harms et al, 2020;Olid et al, 2021).…”