Implication scientifique et perspectives

Malgré la croissance rapide de la littérature sur les mares de thermokarst au cours des dernières années, une grande partie des études s’est limitée aux régions de pergélisol de type yedoma et aux sites situés à proximité d'installations de recherche bien établies, comme le sud de l'Alaska, le nord de la Suède, et certaines parties du nord de la Russie. Les lacs des autres régions du pergélisol, y compris le thermokarst des tourbières dont la teneur en carbone est beaucoup plus élevée que celle du pergélisol du type yedoma, ont reçu moins d'attention, en partie à cause de leur difficulté d'accès. Pour des raisons similaires, la dynamique hivernale du CH4 et du CO2 reste largement énigmatique pour la plupart des types de mares de thermokarst. En outre, les paysages de thermokarst sont sujets à des changements rapides, en particulier en réponse au réchauffement accéléré de l'hémisphère Nord lié au changement climatique. En conséquence, cette recherche offre une meilleure compréhension du fonctionnement des écosystèmes des mares de thermokarst des sols minéraux et plus particulièrement de ceux liés au thermokarst des tourbières. Plus précisément, cette étude attire l'attention sur les taux exceptionnellement élevés d'émissions de CH4 et de CO2 associés aux lacs de palse, un type d'écosystème dominant dans les tourbières de pergélisol, ainsi que sur les profils distinctifs de ces émissions (dominés par la diffusion). De plus, les mares de lithalse du nord du Québec sont caractérisées par un type particulier d'émissions, avec des taux de diffusion croissants associés à une plus grande dégradation du pergélisol. Ces observations uniques apportent une nouvelle perspective sur les principales sources de variabilité de leurs émissions de CH4 et de CO2, y compris l'hétérotrophie bactérienne et le possible lien entre la méthanotrophie et le degré de dégradation du pergélisol.

Enfin, cette étude souligne l'importance de compléter les estimations estivales des émissions de CH4 et de CO2 des mares de thermokarst avec des mesures pendant la période de fonte de la glace au printemps, lors de la période du mélange automnal et avec des mesures sous la glace. De nouvelles approches technologiques seront nécessaires pour mesurer adéquatement ces flux, tels que les détecteurs laser et les systèmes d'imagerie aéroportés. Les périodes de mélange ont été jugées particulièrement importantes afin de quantifier avec précision les émissions totales de GES des lacs, et en fonction de la morphométrie du lac qui peut jouer un rôle clé en permettant ou non le mélange complet de

la colonne d'eau du lac.

Les résultats de cette étude ont révélé les propriétés distinctives de certains types de mares de thermokarst et les principales sources de variabilité de leurs émissions de CH4 et de CO2. Il convient toutefois de noter que ces conclusions reposent sur un nombre limité de lacs étudiés et de courtes périodes d'échantillonnage. Des recherches supplémentaires sont donc nécessaires pour quantifier avec précision les émissions totales de GES de ces paysages. En particulier, l'effet de la taille et de la profondeur des mares sur le régime de mélange des lacs devrait être examiné sur un éventail plus large de morphométrie des mares. Nous aurons besoin de connaître la superficie de ces écosystèmes pour fournir une estimation robuste du flux total de gaz à effet de serre provenant de tous les lacs de thermokarst des paysages de lithalse et des tourbières de pergélisol du nord. Compte tenu de la vaste superficie de ce dernier type de paysage (1,4 million de km2_{; Tarnocai et al.,} 2009) et des taux d'émission élevés, il est nécessaire de développer des approches exploitant la télédétection en plus de l’instrumentation d’un plus grand nombre de systèmes afin d’obtenir une estimation plus précise. De plus, une couverture saisonnière complète est requise pour la mise à l'échelle, la modélisation et des estimations fiables du bilan du carbone dans l'Arctique, qui se réchauffe rapidement.

Bibliographie

Abbott, B.W., J. B. Jones, E. A. G. Schuur, et al. 2016. Biomass offsets little or none of permafrost carbon release from soils, streams, and wildfire: an expert assessment. Environmental Research Letters 11: 034014. doi:10.1088/1748-9326/11/3/034014. Abell G. C., A. T. Revill, C. Smith, A. P. Bissett, J. K. Volkman, and S. S. Robert. 2010.

Archaeal ammonia oxidizers and nirS-type denitrifiers dominate sediment nitrifying and denitrifying populations in a subtropical macrotidal estuary. The ISME Journal 4: 286-300. doi:10.1038/ismej.2009.105.

Abnizova, A., J. Siemens, M. Langer, and J. Boike. 2012. Small ponds with major impact: The relevance of ponds and lakes in permafrost landscapes to carbon dioxide emissions, Global Biogeochemical Cycles 26: GB2041.

doi:10.1029/2011GB004237.

ACIA. 2005. Arctic Climate Impact Assessment Scientific Report. Cambridge University Press, Cambridge, UK

Allan, J., J. Ronholm, N. C. S. Mykytczuk, C. W. Greer, T. C. Onstott, and L. G. Whyte. 2014. Methanogen community composition and rates of methane consumption in Canadian High Arctic permafrost soils. Environmental Microbiology Reports 6: 136-144. doi:10.1111/1758-2229.12139.

Allard, M., and K. Seguin, M. 1987. Le pergélisol au Québec nordique : bilan et perspectives. Géographie physique et quaternaire 41: 141-152.

doi:10.7202/032671ar.

Allard, M., D. Sarrazin, and E. L'Hérault. 2017. Borehole and near-surface ground temperatures in northeastern Canada, v. 1.3 (1988-2016). Nordicana D8. doi:10.5885/45291SL-34F28A9491014AFD.

An, W., and M. Allard. 1995. A mathematical approach to modelling palsa formation: insights on processes and growth conditions. Cold Regions Science and Technology 23: 231-44. doi:10.1016/0165-232X(94)00015-P.

APHA, AWWA, and WEF. 1998. American Public Health Association (APHA), American Water Works Association (AWWA), and Water Environment Federation (WEF). 1998. Standard Methods for the Examination of Water and Wastewater 20th Edition. United Book Press, Inc., Baltimore, Maryland.

Arlen-Pouliot, Y., and N. Bhiry. 2005. Palaeoecology of a palsa and a filled thermokarst pond in a permafrost peatland, subarctic Québec, Canada. The Holocene 15: 408- 419. doi:10.1191/0959683605hl818rp.

Arp, C.D., and B. M. Jones. 2009. Geography of Alaska lake districts: Identification, description and analysis of lake-rich regions of a diverse and dynamic state. Reports 40 pp., U.S. Geological Survey, Reston, VA.

Arp, C.D., B.M. Jones, G. Grosse, A.C. Bondurant, V.E. Romanovsky, K.M. Hinkel, and A.D. Parsekian. 2016. Threshold sensitivity of shallow Arctic lakes and sublake permafrost to changing winter climate. Geophysical Research Letters 43: 6358- 6365. doi:10.1002/2016GL068506.

Azam, F., T. Fenchel, J. G. Field, J. S. Gray, L. A. Meyer-Reil, and F. Thingstad. 1983. The ecological role of water-column microbes in the sea. Marine Ecology Progress Series 10: 257-263. doi:10.3354/meps010257.

Bapteste, E., C. Brochier, and Y. Boucher. 2005. Higher-level classification of the Archaea: evolution of methanogenesis and methanogens. Archaea 1: 353-363.

doi:10.1155/2005/859728.

Bastien, J., A. Tremblay, and L. LeDrew. 2009. Greenhouse gas fluxes from Smallwood Reservoir and natural water bodies in Labrador, Newfoundland, Canada.

Verhandlungen des Internationalen Verein Limnologie 30: 858-861. doi:10.1080/03680770.2009.11902257.

Bastviken, D., L. Persson, G. Odham, and L. Tranvik. 2004. Degradation of dissolved organic matter in oxic and anoxic lake water. Limnology and Oceanography 49: 109-116. doi:10.4319/lo.2004.49.1.0109.

Bastviken, D., J. J. Cole, M. L. Pace, and M. C. Van de Bogert. 2008. Fates of methane from different lake habitats: Connecting whole-lake budgets and CH4 emissions. Journal of Geophysical Research 113: G02024. doi:10.1029/2007JG000608. Bastviken, D., L. Tranvik, J. A. Downing, P. M. Crill, and A. Enrich-Prast. 2011.

Freshwater methane emissions offset the continental carbon sink. Science 331: 50. doi:10.1126/science.1196808.

Bégin, P.N., and Vincent, W.F. 2017. Permafrost thaw ponds as habitats for abundant rotifer populations. Arctic Science 3: 354-377. doi: 10.1139/AS-2016-0017.

Bhiry, N., A. Delwaide, M. Allard, et al. 2011. Environmental change in the Great Whale River Region, Hudson Bay: Five decades of multidisciplinary research by Centre d'études nordiques (CEN). Ecoscience 18: 182-203. doi:10.2980/18-3-3469. Bhiry, N., S. Payette, and É. C. Robert. 2007. Peatland development at the arctic tree line

(Québec, Canada) influenced by flooding and permafrost, Quaternary research 67: 426-437. doi:10.1016/j.yqres.2006.11.009.

Biesinger, Z., E. B. Rastetter, and B. L. Kwiatkowski. 2007. Hourly and daily models of active layer evolution in Arctic Soils. Ecological Modelling 206: 131-146. doi:10.1016/j.ecolmodel.2007.03.030.

Bigelow, N. H., L. B. Brubaker, M. E. Edwards, et al. 2003. Climatic change and Arctic ecosystems I. Vegetation changes north of 55oN between the last glacial maximum, mid-Holocene, and present. Journal of Geophysical Research: Atmospheres 108: 2169. doi:10.1029/2002JD002558.

Blois, J. L., J. W. Williams, M. C. Fitzpatrick, S. T. Jackson, and S. Ferrier. 2013. Space can substitute for time in predicting climate-change effects on biodiversity. Proceedings of National Academy of Science USA 110: 9374-9379. doi:10.1073/pnas.1220228110.

Bogard, M. J., P. A. Del Giorgio, L. Boutet, M. C. G. Chaves, Y. T. Prairie, A. Merante, and A. M. Derry. 2014. Oxic water column methanogenesis as a major component of aquatic CH4 fluxes. Nature Communications 5: 5350. doi:10.1038/ncomms6350. Boike, J., T. Grau, B. Heim, F. Günther, M. Langer, S. Muster, S., Gouttevin, I., and S.

Lange. 2016. Satellite-derived changes in the permafrost landscape of central Yakutia, 2000-2011: Wetting, drying, and fires. Global Planet Change 139: 116- 127. doi:10.1016/j.gloplacha.2016.01.001.

Bonilla, S., V. Villeneuve, and W. F. Vincent. 2005. Benthic and planktonic algal

nutrient enrichment. Journal of Phycology 41: 1120-1130. doi:10.1111/j.1529- 8817.2005.00154.x.

Bouchard, F., P. Francus, R. Pienitz, and I. Laurion. 2011. Sedimentology and

geochemistry of thermokarst ponds in discontinuous permafrost, subarctic Quebec, Canada. Journal of Geophysical Research 116: G00M04.

Bouchard, F., P. Francus, R. Pienitz, I. Laurion, and S. Feyte. 2014. Subarctic thermokarst ponds: Investigating recent landscape evolution and sediment dynamics in thawed permafrost of northern Québec (Canada). Arctic, Antarctic and Alpine Research 46: 251-271. doi:10.1657/1938-4246-46.1.251.

Bouchard, F., I. Laurion, V. Prieskienis, D. Fortier, X. Xu, and M. J. Whiticar. 2015. Modern to millennium-old greenhouse gases emitted from ponds and lakes of the Eastern Canadian Arctic (Bylot Island, Nunavut), Biogeosciences 12: 7279-7298. doi:10.5194/bg-12-7279-2015.

Bouchard, F., L. A. MacDonald, K. W. Turner, J. R. Thienpont, A. S. Medeiros, B. K. Biskaborn, J. Korosi, R. I. Hall, R. Pienitz, and B. B. Wolfe. 2016. Paleolimnology of thermokarst lakes: A window into permafrost landscape evolution. Arctic Science 3: 91-117. doi:10.1139/as-2016-0022.

Boudreau, B. P., B. S. Gardiner, and B. D. Johnson. 2001. Rate of growth of isolated bubbles in sediments with a diagenetic source of methane. Limnology and Oceanography 46: 616-622, 1578(erratum). doi:10.4319/lo.2001.46.3.0616, 10.4319/lo.2001.46.6.1578.

Brankovits, D., J. W. Pohlman, H. Niemann, M. B. Leigh, M. C. Leewis, K. W. Becker, T. M. Iliffe, F. Alvarez, M. F. Lehmann, and B. Phillips. 2017. Methane- and dissolved organic carbon-fueled microbial loop supports a tropical subterranean estuary ecosystem. Nature Communications 8: 1835. doi:10.1038/s41467-017-01776-x. Breton, J., C. Vallieres, and I. Laurion. 2009. Limnological properties of permafrost thaw

ponds in northeastern Canada. Canadian Journal of Fisheries and Aquatic Science 66: 1635-1648. doi:10.1139/F09-108.

Brook, E. J., S. Harder, J. Severinghaus, E. J. Steig, and C. M. Sucher. 2000. On the origin and timing of rapid changes in atmospheric methane during the last glacial period, Global Biogeochemical Cycles 14: 559-572.

Brown, J., O. Ferrians, J. A. Heginbottom, and E. Melnikov. 2002. Circum-Arctic Map of Permafrost and Ground-Ice Conditions, Version 2. [Subset: Ground Ice]. Boulder, Colorado USA. NSIDC: National Snow and Ice Data Center. [Date Accessed: 2017- 11-27]

Calmels F., and M. Allard. 2004. Ice segregation and gas distribution in permafrost using tomodensitometric analysis. Permafrost and Periglacial Processes 15: 367-378. doi:10.1002/ppp.508.

Calmels, F., M. Allard, and G. Delisle. 2008. Development and decay of a lithalsa in northern Quebec: a geomorphological history. Geomorphology 97: 287-299. doi:10.1016/j.geomorph.2007.08.013.

Carignan, R. 1998. Automated determination of carbon dioxide, oxygen, and nitrogen partial pressures in surface waters. Limnology and Oceanography 43: 969-975. doi:10.4319/lo.1998.43.5.0969.

Casper, P., S. C. Maberly, G. H. Hall, and B. J. Finlay. 2000. Fluxes of methane and carbon dioxide from a small productive lake to the atmosphere. Biogeochemistry 49: 1-19. doi:10.1023/A:1006269900174.

Chadburn, S. E., E. J. Burke, P. M. Cox, P. Friedlingstein, G. Hugelius, and S. Westermann. 2017. An observation-based constraint on permafrost loss as a function of global warming. Nature Climate Change 7: 340.

doi:10.1038/nclimate3262.

Chaudhary, N., P. A. Miller, and B. Smith. 2017. Modelling past, present and future peatland carbon accumulation across the pan-Arctic region. Biogeosciences 14: 4023-4044. doi:10.5194/bg-14-4023-2017.

Christensen, T., M. Jackowicz-Korczyn’ski, M. Aurela, P. Crill, M. Heliasz, M.

Mastepanov, and T. Friborg. 2012. Monitoring the multi-year carbon balance of a subarctic palsa mire with micrometeorological techniques. Ambio 41: 207-217. doi:10.1007/s13280-012-0302-5.

Cohen, S. J. 1997. What if and so what in northern Canada: Could climate change make a difference to the future of the Mackenzie Basin. Arctic 50: 293-307.

Cole, J. J., and N. F. Caraco. 1998. Atmospheric exchange of carbon dioxide in a low-wind oligotrophic lake measured by the addition of SF6. Limnology and Oceanography 43: 647-656. doi:10.4319/lo.1998.43.4.0647.

Conrad, R. 2005. Quantification of methanogenic pathways using stable carbon isotopic signatures: a review and a proposal. Organic Geochemistry 36: 739-752.

doi:10.1016/j.orggeochem.2004.09.006.

Coplen, T. B. 2011. Guidelines and recommended terms for expression of stable-isotope- ratio and gas-ratio measurement results. Rapid Communication in Mass

Spectrometry 25: 2538-2560. doi:10.1002/rcm.5129.

Crevecoeur, S., W. F. Vincent, J. Comte, A. Matveev, and C. Lovejoy. 2017. Diversity and potential activity of methanotrophs in high methane-emitting permafrost thaw ponds. PLoS ONE 12: 1-22. doi:10.1371/journal.pone.0188223.

Crevecoeur, S., W. F. Vincent, and C. Lovejoy. 2016. Environmental selection of planktonic methanogens in permafrost thaw ponds. Scientific Reports 6: 31312. doi:10.1038/srep31312.

Crevecoeur, S., W. F. Vincent, J. Comte, and C. Lovejoy. 2015. Bacterial community structure across environmental gradients in permafrost thaw ponds: Methanotroph- rich ecosystems. Frontiers in Microbiology 6: 192. doi:10.3389/fmicb.2015.00192. Crusius J., and R. Wanninkhof. 2003. Gas transfer velocities measured at low wind speed

over a lake. Limnology and Oceanography 48: 1010-1017. doi:10.4319/lo.2003.48.3.1010.

Dällenbach, A. T., J. Blunier, B. Flückiger, J. Stauffer, D. Chappellaz, and D. Raynaud. 2000. Changes in the atmospheric CH4 gradient between Greenland and Antarctica during the last Glacial and the transition to the Holocene. Geophysical Research Letters 27: 1005-1008.

Delmotte, M. 2004. Atmospheric methane during the last four glacial-interglacial cycles: Rapid changes and their link with Antarctic temperature. Journal of Geophysical Research 109: D12104. doi:10.1029/2003JD004417.

DelSontro, T., D. F. McGinnis, B. Wehrli, and I. Ostrovsky. 2015. Size does matter: Importance of large bubbles and small-scale hot spots for methane transport. Environmental Science and Technology 49: 1268-1276. doi:10.1021/es5054286. Deshpande, B. N., S. Crevecoeur, A. Matveev, and W. F. Vincent. 2016. Bacterial

production in subarctic peatland lakes enriched by thawing permafrost. Biogeosciences 13: 4411-4427. doi:10.5194/bg-13-4411-2016.

Deshpande, B. N., S. MacIntyre, A. Matveev, and W. F. Vincent. 2015. Oxygen dynamics in permafrost thaw lakes: Anaerobic bioreactors in the Canadian subarctic.

Limnology and Oceanography 60: 1656-1670. doi:10.1002/lno.10126.

Deshpande, B. N., F. Maps, A. Matveev, and W. F. Vincent. 2017. Oxygen depletion in subarctic peatland thaw lakes. Arctic Science 3: 406-428. doi:10.1139/AS-2016- 0048.

Ducharme-Riel, V., D. Vachon, P. A. del Giorgio, and Y. T. Prairie. 2015. The relative contribution of winter under-ice and summer hypolimnetic CO2 accumulation to the annual CO2 emissions from northern lakes. Ecosystems 18: 547-559.

doi:10.1007/s10021-015-9846-0.

Elvert, M., J. W. Pohlman, K. W. Becker, B. Gaglioti, K. U. Hinrichs, and M. J. Wooller. 2016. Methane turnover and environmental change from Holocene lipid biomarker records in a thermokarst lake in arctic Alaska. Holocene 26: 1766-1777.

doi:10.1177/0959683616645942.

Emmerton, C. A., St. Louis, V. L., Lehnherr, Graydon, J. A., Kirk, J. L., and K. J. Rondeau. The importance of freshwater systems to the net atmospheric exchange of carbon dioxide and methane with a rapidly changing High Arctic watershed. Biogeoscience 13: 5849–5863. doi: 10.5194/bg-13-5849-2016.

Fenchel, T. 2008. The microbial loop - 25 years later. Journal of Experimental Marine Biology Ecology 366: 99-103. doi:10.1016/j.jembe.2008.07.013.

Fillion, M.-È., N. Bhiry, and M. Touazi. 2014. Differential development of two palsa fields in a peatland located near Whapmagoostui-Kuujjuarapik, Northern Québec, Canada. Arctic, Antarctic and Alpine Research 46: 40-54. doi:10.1657/1938-4246-46.1.40. Galand, P. E., K. Yrjälä, and R. Conrad. 2010. Stable carbon isotope fractionation during

methanogenesis in three boreal peatland ecosystems. Biogeosciences 7: 3893-3900. doi:10.1111/gcb.13281.

Gao, X., C. A. Schlosser, A. Sokolov, K. Walter-Anthony, Q. Zhuang, and D. Kicklighter. 2013. Permafrost degradation and methane: low risk of biogeochemical climate- warming feedback. Environmental Research Letters 8: 035014. doi:10.1088/1748- 9326/8/3/035014.

Gebert J., B. K. Singh, Y. Pan, L. Bodrossy. 2009. Activity and structure of methanotrophic communities in landfill cover soils. Environtal Microbiology Reports 1: 414–423. doi:10.1111/j.1758-2229.2009.00061.x.

GIEC (IPCC). 2013. Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change.T. F. Stocker, D. Qin, G.-K. Plattner, M. Tignor, S. K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex, and P. M. Midgley [eds.] Cambridge, United Kingdom and New York, NY, USA doi:10.1017/ CBO9781107415324.005.

GIEC (IPCC). 2014. Climate Change 2014: Synthesis Report. Contribution of Working Groups I, II and III to the Fifth Assessment Report of the Intergovernmental Panel

on Climate Change [Core Writing Team, R.K. Pachauri and L.A. Meyer [eds.]. IPCC, Geneva, Switzerland, 151 pp.

Glew, J. R. 1991. Miniature gravity corer for recovering short sediment cores. Journal of Paleolimnology 5: 285-287.

Golterman, H., and R. Clymo [eds.]. 1971. Methods for Chemical Analysis of Fresh Waters. IBP handbook No. 8, 3rd edition for the International Biological Programme, Blackwell.

Grant, R. F., E. R. Humphreys, and P. M. Lafleur. 2015. Ecosystem CO2 and CH4 exchange in a mixed tundra and a fen within a hydrologically diverse arctic landscape: 1. Modeling versus measurements. Journal of Geophysical Research: Biogeosciences 120: 1366-1387. doi:10.1002/2014JG002888.

Grossart, H.-P., K. Frindte, C. Dziallas, W. Eckert, and K. W. Tang. 2011. Microbial methane production in oxygenated water column of an oligotrophic lake. Proceedings of the National Academy of Sciences U. S. A. 108: 19657–19661. doi:10.1073/pnas.1110716108.

Grosse, G., B. Jones, and C. Arp. 2013. 8.21 Thermokarst lakes, drainage, and drained basins. In Treatise on Geomorphology. J. F. Shroder [ed.], pp. 325-353. Academic Press, San Diego. doi:10.1016/B978-0-12-374739-6.00216-5.

Grosse, G., L. Schirrmeister, and T. J. Malthus. Application of Landsat-7 satellite data and a DEM for the quantification of thermokarst-affected terrain types in the periglacial Lena-Anabar coastal lowland. Polar Research 25: 51-67. doi:10.1111/j.1751- 8369.2006.tb00150.x.

Grosse, G., S. Goetz, A. D. McGuire, V. E. Romanovsky, and E. A. G. Schuur. 2016. Changing permafrost in a warming world and feedbacks to the Earth system. Environmental Research Letters 11: 040201. doi:10.1088/1748-9326/11/4/040201. Hampton, S. E., et al. 2017. Ecology under lake ice. Ecology Letters 20: 98-111.

doi:10.1111/ele.12699.

Hampton, S. E., M. V. Moore, T. Ozersky, E. H. Stanley, C. M. Polashenski, and A. W. Galloway. 2015. Heating up a cold subject: prospects for under-ice plankton research in lakes, Journal of Plankton Research 37: 277-284.

doi:10.1093/plankt/fbv002.

He, R., M. J. Wooller, J. W. Pohlman, J. Quensen, J. M. Tiedje, and M. B. Leigh. 2012. Shifts in identity and activity of methanotrophs in Arctic lake sediments in response to temperature changes. Applied Environmental Microbiology 78: 4715- 4723. doi:10.1128/AEM.00853-12.

Heimann M., and M. Reichstein. 2008. Terrestrial ecosystem carbon dynamics and climate feedbacks. Nature 451: 289-292. doi:10.1038/nature06591.

Hilbert, D. W., N. Roulet, and T. Moore. 2000. Modelling and analysis of peatlands as dynamical systems. Journal of Ecology 88: 230–242. doi:10.1046/j.1365- 2745.2000.00438.x.

Hinzman, L. D., C. J. Deal, A. D. McGuire, S. H. Mernild, I. V. Polyakov, and J. E. Walsh. 2013. Trajectory of the Arctic as an integrated system. Ecological Applications 23: 1837-1868. doi:10.1890/11-1498.1.

Hofmann H. 2013. Spatiotemporal distribution patterns of dissolved methane in lakes: How accurate are the current estimations of the diffusive flux path? Geophysical

Hofmann, H., L. Federwisch, and F. Peeters. 2010. Wave-induced release of methane: Littoral zones as a source of methane in lakes. Limnology and Oceanography 55: 1990-2000. doi:10.4319/lo.2010.55.5.1990.

Holgerson, M.A., and P.A. Raymond. 2016. Large contribution to inland water CO2 and CH4 emissions from very small ponds. Nature Geoscience 9: 222-226.

doi:10.1038/ngeo2654.

Hopkins, D. M. 1949. Thaw lakes and thaw sinks in the Imuruk Lake area, Seward Peninsula, Alaska. Journal of Geology 57: 119-131. doi:10.1086/625591. Hugelius G., J. Strauss, S. Zubrzycki, J. W. Harden, E. A. G. Schuur, C. L.Ping, L.

Schirrmeister, G. Grosse, and G. J. Michaelson. 2014. Estimated stocks of circumpolar permafrost carbon with quantified uncertainty ranges and identified data gaps. Biogeosciences 11: 6573-6593. doi:10.5194/bg-11-6573-2014. Huttunen, J. T., J. Alm, A. Liikanen, S. Jutinen, T. Larmola, T. Hammar, J. Silvola, and

Martikainen, P.J. 2003. Fluxes of methane, carbon dioxide and nitrous oxide in boreal lakes and potential anthropogenic effects on the aquatic greenhouse gas emissions. Chemosphere 52: 609-621. doi:10.1016/S0045-6535(03)00243-1. Jones, B. M., G. Grosse, C. D. Arp, M. C. Jones, K. M. Walter Anthony, and V. E.

Romanovsky. 2011. Modern thermokarst lake dynamics in the continuous permafrost zone, northern Seward Peninsula, Alaska. Journal of Geophysical Research 116: G00M03. doi:10.1029/2011JG001666.

Kane, D.L., L. D. Hinzman, J. P. Zarling. 1991. Thermal response of the active layer to climatic warming in a permafrost environment. Cold Regions Science and Technology 19: 111-122. 10.1016/0165-232X(91)90002-X.

Kanevskiy, M., T. Jorgenson, Y. Shur, J. A. O’Donnell, J. W. Harden, Q. Zhuang, and D. Fortier. 2014. Cryostratigraphy and permafrost evolution in the lacustrine lowlands of west-central Alaska. Permafrost and Periglacial Processes 25: 14-34.

doi:10.1002/ppp.1800.

Kankaala, P., J. Huotari, E. Peltomaa, T. Saloranta, and A. Ojala. 2006. Methanotrophic activity in relation to methane efflux and total heterotrophic bacterial production in a stratified, humic, boreal lake. Limnology and Oceanography 51: 1195-1204. doi:10.4319/lo.2006.51.2.1195.

Kaplan, J. O., N. H. Bigelow, I. C. Prentice, et al. 2003. Climate change and Arctic ecosystems: II. Modeling, paleodata-model comparisons, and future projections. Journal of Geophysical Research 108: D18 8171. doi:10.1029/2002JD002559. Karlsson J., T. R. Christensen, P. Crill, et al. 2010. Quantifying the relative importance of

lake emissions in the carbon budget of a subarctic catchment, Journal of Geophysical Research 115: G03006. doi:10.1029/2010JG001305.

Kessler, M. A., L. J. Plug, and K. M. Walter Anthony. 2012. Simulating the decadal- to millennial-scale dynamics of morphology and sequestered carbon mobilization of two thermokarst lakes in NW Alaska. Journal of Geophysical Research 117: G00M06. doi:10.1029/2011JG001796.

Kling, G. W., Kipphut, G. W., and Miller, M. C. 1991. Arctic lakes and streams as gas conduits to the atmosphere: implications for tundra carbon budgets. Science 251: 298-301. doi: 10.1126/science.251.4991.298.

Kokelj, S. V., and M. T. Jorgenson. 2013. Advances in thermokarst research. Permafrost and Periglacial Processes 24: 108-119. doi:10.1002/ppp.1779.

Kruger J. P., J. Leifeld, and C. Alewell. 2014. Degradation changes stable carbon isotope depth profiles in palsa peatlands. Biogeosciences 11: 3369-3380. doi:10.5194/bg- 11-3369-2014.

Kuhry P. 2008. Palsa and peat plateau development in the Hudson Bay lowlands, Canada: timing, pathways and causes. Boreas 37: 316-327. doi:10.1111/j.1502-

3885.2007.00022.x.

Langer, M., S. Westermann, K. Walter Anthony, K. Wischnewski, and J. Boike. 2015. Frozen ponds: production and storage of methane during the Arctic winter in a lowland tundra landscape in northern Siberia, Lena river delta. Biogeosciences 12: 977–990. doi:10.5194/bg-12-977-2015.

Laurion, I., W. F. Vincent, S. MacIntyre, L. Retamal, C. Dupont, P. Francus, and R.

Pienitz. 2010. Variability in greenhouse gas emissions from permafrost thaw ponds. Limnology and Oceanography 55: 115-133. doi:10.4319/ lo.2010.55.1.0115.

Lee, H., E. A. G. Schuur, K. S. Inglett, M. Lavoie and J. P. Chanton. 2012. The rate of permafrost carbon release under aerobic and anaerobic conditions and its potential effects on climate. Global Change Biology 18: 515-527. doi:10.1111/j.1365- 2486.2011.02519.x.

Lehner, B. and P. Doll. 2004. Development and validation of a global database of lakes, reservoirs, and wetlands. Journal of Hydrology 296: 1-22.

doi:10.1016/j.jhydrol.2004.03.028.

Lewis, W. M. Jr. 1983. A revised classification of lakes based on mixing. Canadian Journal of Fishery and Aquatic Sciences 40: 1779-1787. doi:10.1139/f83-207.

Liebner, S., L. Ganzert, A. Kiss, S. Yang, D. Wagner, and M. M. Svenning. 2015. Shifts in methanogenic community composition and methane fluxes along the degradation of discontinuous permafrost. Frontiers in Microbiology 6: 356.

doi:10.3389/fmicb.2015.00356.

Lindgren, P. R., G. Grosse, K. M. Walter Anthony, and F. J. Meyer. 2016. Detection and spatiotemporal analysis of methane ebullition on thermokarst lake ice using high-