Airborne quantification of net methane and carbon dioxide fluxes from European Arctic wetlands in Summer 2019

Arctic wetlands and surrounding ecosystems are both a significant source of methane (CH 4 ) and a sink of carbon dioxide (CO 2 ) during summer months. However, precise quantification of this regional CH 4 source and CO 2 sink remains poorly characterized. A research flight using the UK Facility for Airborne Atmospheric Measurement was conducted in July 2019 over an area (approx. 78 000 km 2 ) of mixed peatland and forest in northern Sweden and Finland. Area-averaged fluxes of CH 4 and carbon dioxide were calculated using an aircraft mass balance approach. Net CH 4 fluxes normalized to wetland area ranged between 5.93 ± 1.87 mg m −2 h −1 and 4.44 ± 0.64 mg m −2 h −1 (largest to smallest) over the region with a meridional gradient across three discrete areas enclosed by the flight survey. From largest to smallest, net CO 2 sinks ranged between −513 ± 74 mg m −2 h −1 and −284 ± 89 mg m −2 h −1 and result from net uptake of CO 2 by vegetation and soils in the biosphere. A clear gradient of decreasing bulk and area-averaged CH 4 flux was identified from north to south across the study region, correlated with decreasing peat bog land area from north to south identified from CORINE land cover classifications. While N 2 O mole fraction was measured, no discernible gradient was measured over the flight track, but a minimum flux threshold using this mass balance method was calculated. Bulk (total area) CH 4 fluxes determined via mass balance were compared with area-weighted upscaled chamber fluxes from the same study area and were found to agree well within measurement uncertainty. The mass balance CH 4 fluxes were found to be significantly higher than the CH 4 fluxes reported by many land-surface process models compiled as part of the Global Carbon Project. There was high variability in both flux distribution and magnitude between the individual models. This further supports previous studies that suggest that land-surface models are currently ill-equipped to accurately capture carbon fluxes inthe region. This article is part of a discussion meeting issue 'Rising methane: is warming feeding warming? (part 2)'.

Spatial and temporal patterns of biophysical variables and their influence on CO2 flux in a high arctic wetland

Arctic wetlands have been globally important carbon reservoirs throughout the past but climate change is threatening to shift their status to carbon sources. Increasing Arctic temperatures are depleting perennial snowpacks these wetlands depend upon as their hydrological inputs which is altering their environmental conditions and carbon cycles. The objective of this study is to investigate how the physical conditions of Arctic wetlands will be altered by climate change and what influence these changes will have on CO2 exchange. High spatial and temporal resolution biophysical data from a high Arctic wetland, collected over the growing season of 2015, was used for this analysis. The results from this study indicate that the wetland is at risk of thawing and drying out under a warmer climate regime. CO2 emissions were found to increase most significantly with increased air temperatures, while CO2 uptake increased with increases in solar radiation and soil moisture. Combined, these results suggest that CO2 production in the soil will increase while CO2 uptake will decrease in Arctic wetlands as climate change continues.

Spatial and temporal patterns of biophysical variables and their influence on CO2 flux in a high arctic wetland

Arctic wetlands have been globally important carbon reservoirs throughout the past but climate change is threatening to shift their status to carbon sources. Increasing Arctic temperatures are depleting perennial snowpacks these wetlands depend upon as their hydrological inputs which is altering their environmental conditions and carbon cycles. The objective of this study is to investigate how the physical conditions of Arctic wetlands will be altered by climate change and what influence these changes will have on CO2 exchange. High spatial and temporal resolution biophysical data from a high Arctic wetland, collected over the growing season of 2015, was used for this analysis. The results from this study indicate that the wetland is at risk of thawing and drying out under a warmer climate regime. CO2 emissions were found to increase most significantly with increased air temperatures, while CO2 uptake increased with increases in solar radiation and soil moisture. Combined, these results suggest that CO2 production in the soil will increase while CO2 uptake will decrease in Arctic wetlands as climate change continues.

Characterizing Wetland Inundation and Vegetation Dynamics in the Arctic Coastal Plain Using Recent Satellite Data and Field Photos

Arctic wetlands play a critical role in the global carbon cycle and are experiencing disproportionate impacts from climate change. Even though Alaska hosts 65% of U.S. wetlands, less than half of the wetlands in Alaska have been mapped by the U.S. Fish and Wildlife Service National Wetlands Inventory (NWI) or other high-resolution wetlands protocols. The availability of time series satellite data and the development of machine learning algorithms have enabled the characterization of Arctic wetland inundation dynamics and vegetation types with limited ground data input. In this study, we built a semi-automatic process to generate sub-pixel water fraction (SWF) maps across the Coastal Plain of the Arctic National Wildlife Refuge (ANWR) in Alaska using random forest regression and 139 Sentinel-2 images taken in ice-free seasons from 2016 to 2019. With this, we characterized the seasonal dynamics of wetland inundation and explored their potential usage in determining NWI water regimes. The highest levels of surface water expression were detected in June, resulting from seasonal active layer thaw and snowmelt. Inundation was most variable in riverbeds, lake and pond margins, and depressional wetlands, where water levels fluctuate substantially between dry and wet seasons. NWI water regimes that indicate frequent inundation, such as permanently flooded wetlands, had high SWF values (SWF ≥ 90%), while those with infrequent inundation, such as temporarily flooded wetlands, had low SWF values (SWF < 10%). Vegetation types were also classified through the synergistic use of a vegetation index, water regimes, synthetic-aperture radar (SAR) data, topographic data, and a random forest classifier. The random forest classification algorithms demonstrated good performance in classifying Arctic wetland vegetation types, with an overall accuracy of 0.87. Compared with NWI data produced in the 1980s, scrub-shrub wetlands appear to have increased from 91 to 258 km2 over the last three decades, which is the largest percentage change (182%) among all vegetation types. However, additional field data are needed to confirm this shift in vegetation type. This study demonstrates the potential of using time series satellite data and machine learning algorithms in characterizing inundation dynamics and vegetation types of Arctic wetlands. This approach could aid in the creation and maintenance of wetland inventories, including the NWI, in Arctic regions and enable an improved understanding of long-term wetland dynamics.

Effects of labile carbon on anaerobic decomposition processes in permafrost wetlands

&lt;p&gt;Climate warming and permafrost thaw are exposing the large carbon (C) pools of northern wetlands to enhanced decomposition, potentially increasing the release of the greenhouse gases carbon dioxide (CO&lt;sub&gt;2&lt;/sub&gt;) and methane (CH&lt;sub&gt;4&lt;/sub&gt;). Permafrost thaw is usually associated with changes in hydrology and vegetation: Ground collapse leads to the formation of new, productive thermokarst wetlands, and active layer deepening allows plant roots to penetrate to deeper soil layers. These processes promote interaction between old permafrost carbon and recent plant-derived carbon, but the effect of this interaction on anaerobic decomposition processes is poorly known.&lt;/p&gt;&lt;p&gt;Here, we report the preliminary results of a 1+-year-long soil incubation experiment where we investigated the role of fresh organics on anaerobic decomposition in arctic wetlands. We sampled mineral subsoil of Greenlandic wetland sites and the active layer and permafrost peat in a Swedish palsa mire, and incubated them with and without repeated amendments of &lt;sup&gt;13&lt;/sup&gt;C enriched glucose and cellulose. We determined the rate and isotopic composition of CO&lt;sub&gt;2&lt;/sub&gt; and CH&lt;sub&gt;4&lt;/sub&gt; with an isotopic laser, and estimated the contribution of soil organic matter decomposition vs. added carbon to the total C gas release. These results represent new understanding on how plant-derived organics change the magnitude and composition of C gas, thus affecting the climatic feedbacks from permafrost wetland C pool.&lt;/p&gt;

Vulnerability and Importance of Arctic Wetlands as large-scale nature-based solutions for Sustainability in a Changing Climate

&lt;p&gt;Wetlands as large-scale nature-based solutions (NBS) provide multiple ecosystem services of local, regional, and global importance. Knowledge concerning location and vulnerability of wetlands, specifically in the Arctic, is vital to understand and assess the current status and future potential changes in the Arctic. Using available high-resolution wetland databases together with datasets on soil wetness and soil types, we created the first high-resolution map with full coverage of Arctic wetlands. Arctic wetlands' vulnerability is assessed for the years 2050, 2075, and 2100 by utilizing datasets of permafrost extent and projected mean annual average temperature from HadGEM2-ES climate model outputs for three change scenarios (RCP2.6, 4.5, and 8.5). With approximately 25% of Arctic landmass covered with wetlands and 99% being in permafrost areas, Arctic wetlands are highly vulnerable to changes in all scenarios, apart from RCP2.6 where wetlands remain largely stable. Climate change threatens Arctic wetlands and can impact wetland functions and services. These changes can adversely affect the multiple services this sort of NBS can provide in terms of great social, economic, and environmental benefits to human beings. Consequently, negative changes in Arctic wetland ecosystems can escalate land-use conflicts resulting from natural capital exploitation when new areas become more accessible for use. Limiting changes to Arctic wetlands can help maintain their ecosystem services and limit societal challenges arising from thawing permafrost wetlands, especially for indigenous populations dependent on their ecosystem services. This study highlights areas subject to changes and provides useful information to better plan for a sustainable and social-ecological resilient Arctic.&lt;/p&gt;&lt;p&gt;Keywords: Arctic wetlands, permafrost thaw, regime shift vulnerability, climate projection&lt;/p&gt;

Mapping of Arctic Wetlands with Threats of Future Permafrost Thaw

&lt;p&gt;The Arctic is warming twice as fast as the rest of the globe, causing changes to Arctic ecosystems. While wetlands in the Arctic provide many ecosystem services with both local and global importance, still more knowledge is needed on the location and state of Arctic wetlands to successfully focus adaptation and mitigation efforts. To understand the links between temperature changes and changes to Arctic wetlands, this study includes the use of spatial tools to map existing wetlands and model permafrost response to temperature changes, highlighting wetland areas with risks of future changes. Using available high-resolution wetland databases together with soil wetness and soil type data, a wetland map covering the Arctic was created. Based on existing relationships between climate and observed permafrost, future changes in permafrost were modeled using projected mean annual temperature from the HadGEM2-ES climate model outputs for the RCP2.6, 4.5 and 8.5 scenarios and for years 2050, 2075 and 2100. We found that the Arctic contains a large number of wetlands and a very significant number of these exist on permafrost. As substantial permafrost thaw is projected, the extent and properties of wetlands will shift, and local/regional increases or decreases in wetland extent will depend on variables such as soil type. These changes could lead to serious local consequences, such as threats to food and water security, changes in distribution and demographics of animal and plant species, and losses and disruptions of infrastructure. The findings of this study highlight vulnerable areas that need extra attention in terms of adaptation and mitigation efforts to limit the likely impacts of projected changes, given the current trends.&lt;/p&gt;&lt;p&gt;Keywords: Arctic wetland, spatial modeling, permafrost, climate change&lt;/p&gt;