Methane transport from the active layer to lakes in the Arctic using Toolik Lake, Alaska, as a case study (original) (raw)
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Arctic lakes are continuous methane sources to the atmosphere under warming conditions
Environmental Research Letters
Methane is the second most powerful carbon-based greenhouse gas in the atmosphere and its production in the natural environment through methanogenesis is positively correlated with temperature. Recent field studies showed that methane emissions from Arctic thermokarst lakes are significant and could increase by two-to four-fold due to global warming. But the estimates of this source are still poorly constrained. By using a process-based climate-sensitive lake biogeochemical model, we estimated that the total amount of methane emissions from Arctic lakes is 11.86 Tg yr −1 , which is in the range of recent estimates of 7.1-17.3 Tg yr −1 and is on the same order of methane emissions from northern high-latitude wetlands. The methane emission rate varies spatially over high latitudes from 110.8 mg CH 4 m −2 day −1 in Alaska to 12.7 mg CH 4 m −2 day −1 in northern Europe. Under Representative Concentration Pathways (RCP) 2.6 and 8.5 future climate scenarios, methane emissions from Arctic lakes will increase by 10.3 and 16.2 Tg CH 4 yr −1 , respectively, by the end of the 21st century.
Journal of Advances in Modeling Earth Systems
To date, methane emissions from lakes in the pan-arctic region are poorly quantified. In order to investigate the response of methane emissions from this region to global warming, a process-based climate-sensitive lake biogeochemical model was developed. The processes of methane production, oxidation, and transport were modeled within a one-dimensional sediment and water column. The sizes of 14 C-enriched and 14 C-depleted carbon pools were explicitly parameterized. The model was validated using observational data from five lakes located in Siberia and Alaska, representing a large variety of environmental conditions in the arctic. The model simulations agreed well with the measured water temperature and dissolved CH 4 concentration (mean error less than 1 C and 0.2 lM, respectively). The modeled CH 4 fluxes were consistent with observations in these lakes. We found that bubbling-rate-controlling nitrogen (N 2 ) stripping was the most important factor in determining CH 4 fraction in bubbles. Lake depth and ice cover thickness in shallow waters were also controlling factors. This study demonstrated that the thawing of Pleistocene-aged organic-rich yedoma can fuel sediment methanogenesis by supplying a large quantity of labile organic carbon. Observations and modeling results both confirmed that methane emission rate at thermokarst margins of yedoma lakes was much larger (up to 538 mg CH 4 m 22 d 21 ) than that at nonthermokarst zones in the same lakes and a nonyedoma, nonthermokarst lake (less than 42 mg CH 4 m 22 d 21 ). The seasonal variability of methane emissions can be explained primarily by energy input and organic carbon availability. Key Points: CH4 emissions from lakes can be modeled by using a process-based model Bubbling rate controlling N2 strippig predominantly determines CH4 concentration The thawing of organic-rich yedoma permafrost can fuel sediment methanogenesis Supporting Information: Supporting Information S1 Correspondence to: Q. Zhuang, qzhuang@purdue.edu Citation: Tan, Z., Q. Zhuang, and K. W. Anthony (2015), Modeling methane emissions from arctic lakes: Model development and site-level study, J. Adv. Model. Earth Syst., 07,
Wetlands and freshwater bodies (mainly lakes) are the largest natural sources of the greenhouse gas CH 4 to the atmosphere. Great efforts have been made to quantify these source emissions and their uncertainties. Previous research suggests that there might be significant uncertainties coming from "double accounting" emissions from freshwater bodies and wetlands. Here we quantify the methane emissions from both land and freshwater bodies in the pan-Arctic with two process-based biogeochemistry models by minimizing the double accounting at the landscape scale. Two non-overlapping dynamic areal change datasets are used to drive the models. We estimate that the total methane emissions from the pan-Arctic are 36.46 ± 1.02 Tg CH 4 yr −1 during 2000-2015, of which wetlands and freshwater bodies are 21.69 ± 0.59 Tg CH 4 yr −1 and 14.76 ± 0.44 Tg CH 4 yr −1 , respectively. Our estimation narrows the difference between previous bottom-up (53.9 Tg CH 4 yr −1) and top-down (29 Tg CH 4 yr −1) estimates. Our correlation analysis shows that air temperature is the most important driver for methane emissions of inland water systems. Wetland emissions are also significantly affected by vapor pressure, while lake emissions are more influenced by precipitation and landscape areal changes. Sensitivity tests indicate that pan-Arctic lake CH 4 emissions were highly influenced by air temperature but less by lake sediment carbon increase.
Modeling methane emissions from arctic lakes: Model development and site-level study
Journal of Advances in Modeling Earth Systems, 2015
To date, methane emissions from lakes in the pan-arctic region are poorly quantified. In order to investigate the response of methane emissions from this region to global warming, a process-based climate-sensitive lake biogeochemical model was developed. The processes of methane production, oxidation, and transport were modeled within a one-dimensional sediment and water column. The sizes of 14 C-enriched and 14 C-depleted carbon pools were explicitly parameterized. The model was validated using observational data from five lakes located in Siberia and Alaska, representing a large variety of environmental conditions in the arctic. The model simulations agreed well with the measured water temperature and dissolved CH 4 concentration (mean error less than 1 C and 0.2 lM, respectively). The modeled CH 4 fluxes were consistent with observations in these lakes. We found that bubbling-rate-controlling nitrogen (N 2 ) stripping was the most important factor in determining CH 4 fraction in bubbles. Lake depth and ice cover thickness in shallow waters were also controlling factors. This study demonstrated that the thawing of Pleistocene-aged organic-rich yedoma can fuel sediment methanogenesis by supplying a large quantity of labile organic carbon. Observations and modeling results both confirmed that methane emission rate at thermokarst margins of yedoma lakes was much larger (up to 538 mg CH 4 m 22 d 21 ) than that at nonthermokarst zones in the same lakes and a nonyedoma, nonthermokarst lake (less than 42 mg CH 4 m 22 d 21 ). The seasonal variability of methane emissions can be explained primarily by energy input and organic carbon availability. Key Points: CH4 emissions from lakes can be modeled by using a process-based model Bubbling rate controlling N2 strippig predominantly determines CH4 concentration The thawing of organic-rich yedoma permafrost can fuel sediment methanogenesis Supporting Information: Supporting Information S1 Correspondence to: Q. Zhuang, qzhuang@purdue.edu Citation: Tan, Z., Q. Zhuang, and K. W. Anthony (2015), Modeling methane emissions from arctic lakes: Model development and site-level study, J. Adv. Model. Earth Syst., 07,
Earth and Planetary Science Letters, 2016
Here we use a portable method to obtain high spatial resolution measurements of concentrations and calculate diffusive water-to-air fluxes of CH 4 and CO 2 from two subarctic coastal regions (Kasitsna and Jakolof Bays) and an Arctic lake (Toolik Lake). The goals of this study are to determine distributions of these concentrations and fluxes to (1) critically evaluate the established protocols of collecting discrete water samples for these determinations, and to (2) provide a first-order extrapolation of the regional impacts of these diffusive atmospheric fluxes. Our measurements show that these environments are highly heterogeneous. Areas with the highest dissolved CH 4 and CO 2 concentrations were isolated, covering less than 21% of the total lake and bay areas, and significant errors can be introduced if the collection of discrete water samples does not adequately characterize these spatial distributions. A first order extrapolation of diffusive fluxes to all arctic regions with similar characteristics as Toolik Lake suggests that these lakes are likely supplying 0.21 and 15.77 Tg of CH 4 and CO 2 to the atmosphere annually, respectively. Similarly, we found that the Subarctic Coastal Ocean is likely supplying 0.027 Tg of CH 4 annually and is taking up roughly 524 Tg of CO 2 per year. Although diffusive fluxes at
Methane bubbling from northern lakes: present and future contributions to the global methane budget
Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 2007
Large uncertainties in the budget of atmospheric methane (CH 4 ) limit the accuracy of climate change projections. Here we describe and quantify an important source of CH 4point-source ebullition (bubbling) from northern lakes-that has not been incorporated in previous regional or global methane budgets. Employing a method recently introduced to measure ebullition more accurately by taking into account its spatial patchiness in lakes, we estimate point-source ebullition for 16 lakes in Alaska and Siberia that represent several common northern lake types: glacial, alluvial floodplain, peatland and thermokarst (thaw) lakes. Extrapolation of measured fluxes from these 16 sites to all lakes north of 458 N using circumpolar databases of lake and permafrost distributions suggests that northern lakes are a globally significant source of atmospheric CH 4 , emitting approximately 24.2G10.5 Tg CH 4 yr K1 . Thermokarst lakes have particularly high emissions because they release CH 4 produced from organic matter previously sequestered in permafrost. A carbon mass balance calculation of CH 4 release from thermokarst lakes on the Siberian yedoma ice complex suggests that these lakes alone would emit as much as approximately 49 000 Tg CH 4 if this ice complex was to thaw completely. Using a space-for-time substitution based on the current lake distributions in permafrost-dominated and permafrost-free terrains, we estimate that lake emissions would be reduced by approximately 12% in a more probable transitional permafrost scenario and by approximately 53% in a 'permafrost-free' Northern Hemisphere. Long-term decline in CH 4 ebullition from lakes due to lake area loss and permafrost thaw would occur only after the large release of CH 4 associated thermokarst lake development in the zone of continuous permafrost.
Biogeosciences Discussions, 2014
Uncertainties in the magnitude and seasonality of various gas emission modes, particularly among different lake types, limit our ability to estimate methane (CH 4) and carbon dioxide (CO 2) emissions from northern lakes. Here we assessed the relationship between CH 4 and CO 2 emission modes in 40 lakes along a latitudinal transect in Alaska to physicochemical limnology 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 CH 4 and CO 2 , but the climate warming impact of lake CH 4 emissions was two times higher than that of CO 2. Ebullition and Diffusion were the dominant modes of CH 4 and CO 2 emissions respectively. IBS, ∼ 10 % of total annual CH 4 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, CH 4 emissions from stratified, dystrophic 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. Total CH 4 emission was correlated with concentrations of phosphate 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 CH 4 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.
MASTER'S THESES AND CAPSTONES, 2019
Across the Arctic, postglacial lakes contribute a substantial amount of the total atmospheric methane (CH4), and their emissions are predicted to increase. However, there is still much uncertainty as to the contribution of northern water bodies to atmospheric CH4 emissions. This is mainly due to the spatiotemporal variability of the predominant pathway of emission from high latitude lakes: ebullition (bubbling). There are a myriad of factors that affect ebullition fluxes, including solar radiation input and atmospheric pressure, which make it difficult to model the impact on regional emissions. Very few studies have correlated sediment characteristics and submerged vegetation density with ebullition, to see what drives the variation across space and time. This study investigated the effect of submerged aquatic macrophyte (SAM) species distribution and abundance on CH4 dynamics in three postglacial lakes in Stordalen Mire, near Abisko, Sweden (68°21'N, 18°49'E). Submerged vegetation density maps developed from vegetation transects and sediment geochemistry derived from sediment cores were compared to ebullitive flux measured with bubble traps,. The source contribution of terrestrial and aquatic vegetation to the lake sediment carbon (C), the substrate for methanogens, was investigated using δ13C stable isotope analysis and organic carbon-to-nitrogen (C:N) elemental analyses. These data suggest that the organic C in postglacial subarctic lakes are a mixture of allochthonous and autochthonous inputs, with significant C being added by the in-situ decay of submerged vegetation, providing annual organic matter to the sediment. It was found that submerged vegetation density does not influence sediment CH4 concentrations, but rather, among shallow zone cores, the physical structure of the sediments drives most of the variation in ebullitive flux. Among shallow zones, the best predictor of overlying CH4 ebullitive efflux is the sediment porosity. It was also found that total sediment CH4 concentration has a strong negative relationship with ebullitive efflux, meaning that high sediment CH4 concentration is not an indication of high ebullition potential. Increased macrophyte density was not observed to ‘fertilize’ the sediment with organic C, nor did submerged vegetation density have any observed effect on sediment CH4 concentrations, downcore geochemistry, or ebullitive flux. Findings suggest that in a system that is not C-limited, it is perhaps the C quality and not the C quantity that drives the variability in methanogenesis. An investigation into which microbial communities exist in these sediments and in what abundance is required. These data also suggest that anaerobic oxidation of methane (AOM) might also be occurring even in freshwater lake environments, a finding that is implicative in terms of our understanding and modeling of CH4 ebullition and emissions across the Arctic, perhaps yielding new insights into how net emissions might change in the future.
Biogeochemistry, 2016
Small lakes in northern latitudes represent a significant source of CH 4 to the atmosphere that is predicted to increase with warming in the Arctic. Yet, whole-lake CH 4 budgets are lacking as are measurements of d 13 C-CH 4 and d 2 H-CH 4. In this study, we quantify spatial variability of diffusive and ebullitive fluxes of CH 4 and corresponding d 13 C-CH 4 and d 2 H-CH 4 in a small, Arctic lake system with fringing wetland in southwestern Greenland during summer. Net CH 4 flux was highly variable, ranging from an average flux of 7 mg CH 4 m-2 d-1 in the deep-water zone to 154 mg CH 4 m-2 d-1 along the lake margin. Diffusive flux accounted for *8.5 % of mean net CH 4 flux, with plant-mediated and ebullitive flux accounting for the balance of the total net flux. Methane content of emitted ebullition was low (mean ± SD 10 ± 17 %) compared to previous studies from boreal lakes and wetlands. Isotopic composition of net CH 4 emissions varied widely throughout the system, with d 13 C-CH 4 ranging from-66.2 to-55.5 %, and d 2 H-CH 4 ranging from-345 to-258 %. Carbon isotope composition of CH 4 in ebullitive flux showed wider variation compared to net flux, ranging from-69.2 to-49.2 %. Dissolved CH 4 concentrations were highest in the sediment and decreased up the water column. Higher concentrations of CH 4 in the hypoxic deep water coincided with decreasing dissolved O 2 concentrations, while methanotrophic oxidation dominated in the epilimnion based upon decreasing concentrations and increasing values of d 13 C-CH 4 and d 2 H-CH 4. The most depleted 13 C-and 2 H-isotopic values were observed in profundal bottom waters and in subsurface profundal sediments. Based upon paired d 13 C and d 2 H observations of CH 4 , acetate fermentation was likely the dominant production pathway throughout the system. However, isotopic ratios of CH 4 in deeper sediments were consistent with mixing/transition between CH 4 production pathways, indicating a higher contribution of the CO 2 reduction pathway. The large spatial variability in fluxes of CH 4 and in isotopic composition of CH 4 throughout a single lake system indicates that the underlying mechanisms controlling CH 4 cycling (production, consumption and transport) are spatially heterogeneous. Net flux along the lake margin dominated whole-lake flux, suggesting the nearshore littoral area dominates CH 4 emissions in these systems. Future studies of whole-lake CH 4 budgets should consider this significant spatial heterogeneity.