Changing climate in northern regions is causing permafrost to thaw with major implications for the global mercury (Hg) cycle. We estimated Hg in permafrost regions based on in situ measurements of sediment total mercury (STHg), soil organic carbon (SOC), and the Hg to carbon ratio (RHgC) combined with maps of soil carbon. We measured a median STHg of 43 ± 30 ng Hg g soil−1 and a median RHgC of 1.6 ± 0.9 μg Hg g C−1, consistent with published results of STHg for tundra soils and 11,000 measurements from 4,926 temperate, nonpermafrost sites in North America and Eurasia. We estimate that the Northern Hemisphere permafrost regions contain 1,656 ± 962 Gg Hg, of which 793 ± 461 Gg Hg is frozen in permafrost. Permafrost soils store nearly twice as much Hg as all other soils, the ocean, and the atmosphere combined, and this Hg is vulnerable to release as permafrost thaws over the next century. Existing estimates greatly underestimate Hg in permafrost soils, indicating a need to reevaluate the role of the Arctic regions in the global Hg cycle.
Abstract. Fluxes of CO2 and CH 4 through a seasonal snowpack were measured in and adjacent to a subalpine wetland in Rocky Mountain National Park, Colorado. Gas diffusion through the snow was controlled by gas production or consumption in the soil and by physical snowpack properties. The snowpack insulated soils from cold midwinter air temperatures allowing microbial activity to continue through the winter. All soil types studied were net sources of CO2 to the atmosphere through the winter, whereas saturated soils in the wetland center were net emitters of CH 4 and soils adjacent to the wetland were net CH 4 consumers. Most sites showed similar temporal patterns in
Carbon dioxide (CO2) accumulates under lake ice in winter and degasses to the atmosphere after ice melt. This large springtime CO2 pulse is not typically considered in surface‐atmosphere flux estimates, because most field studies have not sampled through ice during late winter. Measured CO2 partial pressure (pCO2) of lake surface water ranged from 8.6 to 4,290 Pa (85–4,230 µatm) in 234 north temperate and boreal lakes prior to ice melt during 1998 and 1999. Only four lakes had surface pCO2 less than or equal to atmospheric pCO2, whereas 75% had pCO2 >5 times atmospheric. The δ13CDIC (DIC = ΣCO2) of 142 of the lakes ranged from –26.28‰ to +0.95‰. Lakes with the greatest pCO2 also had the lightest δ13CDIC, which indicates respiration as their primary CO2 source. Finnish lakes that received large amounts of dissolved organic carbon from surrounding peatlands had the greatest pCO2. Lakes set in noncarbonate till and bedrock in Minnesota and Wisconsin had the smallest pCO2 and the heaviest d13CDIC, which indicates atmospheric and/or mineral sources of C for those lakes. Potential emissions for the period after ice melt were 2.36 ± 1.44 mol CO2 m−2 for lakes with average pCO2 values and were as large as 13.7 ± 8.4 mol CO2 m−2 for lakes with high pCO2 values.
Quantification of the components of ecosystem respiration is essential to understanding carbon (C) cycling of natural and disturbed landscapes. Soil respiration, which includes autotrophic and heterotrophic respiration from throughout the soil profile, is the second largest flux in the global carbon cycle. We measured soil respiration (soil CO 2 emission) at an undisturbed mature jack pine (Pinus banksiana Lamb.) stand in Saskatchewan (old jack pine, OJP), and at a formerly continuous portion of the stand that was clear-cut during the previous winter (clear-cut, CC). Tree harvesting reduced soil CO 2 emission from~22.5 to~9.1 mol CO 2 ⋅m -2 for the 1994 growing season. OJP was a small net sink of atmospheric CO 2 , while CC was a net source of CO 2 . Winter emissions were similar at both sites. Reduction of soil respiration was attributed to disruption of the soil surface and to the death of tree roots. Flux simulations for CC and OJP identify 40% of CO 2 emission at the undisturbed OJP site as near-surface respiration, 25% as deep-soil respiration, and 35% as tree-root respiration. The near-surface component was larger than the estimated annual C input to soil, suggesting fast C turnover and no net C accumulation in these boreal uplands in 1994.Résumé : La quantification des composantes de la respiration de l'écosystème est essentielle à la compréhension du recyclage du carbone (C) dans les milieux naturels et perturbés. La respiration du sol, qui inclut la respiration autotrophe et hétérotrophe de l'ensemble du profil de sol, est le deuxième plus large flux dans le cycle global du carbone. Nous avons mesuré la respiration du sol (émission de CO 2 du sol) dans un peuplement non perturbé et mature de pin gris (Pinus banksiana Lamb.) en Saskatchewan, ainsi que dans une portion du même peuplement qui fut coupée à blanc durant l'hiver précédant. La récolte des arbres a réduit l'émission de CO 2 du sol de~22,5 à~9,1 mol de CO 2 /m 2 pour la saison de croissance de 1994. Le vieux peuplement de pin gris constituait un faible puits net de CO 2 atmosphérique, tandis que la coupe à blanc représentait une source nette de CO 2 . Les émissions hivernales étaient similaires sur les deux sites. La réduction de la respiration du sol a été attribuée à la perturbation de l'horizon de surface et à la mortalité des racines des arbres. Les simulations de flux pour la coupe à blanc et le vieux peuplement de pin gris ont permis d'estimer que 40% de l'émission de CO 2 dans le vieux peuplement de pin gris venait de la respiration près de la surface du sol, 25% de la respiration en profondeur dans le sol et 35% de la respiration des racines des arbres. La composante près de la surface était plus grande que l'apport annuel estimé de C au sol, ce qui suggère que C se renouvellait rapidement sans aucune accumulation nette de C dans ces plateaux boréaux en 1994. [Traduit par la Rédaction]
Frontiers in Earth Science | www.frontiersin.org October 2019 | Volume 7 | Article 275 Textor et al. DOC Turnover in Alaskan Watersheds modern, stable DOC sources. Thus, future projections of carbon turnover in northern high-latitude region streams may not have to account for a priming effect. KEY POINTS -Biodegradability of DOC followed a continuum from relatively stable stream DOC to relatively biolabile DOC from permafrost, active layer organic soil, and vegetation leachates. -DOM composition, especially the relative contribution of aliphatic compounds, largely controlled biodegradability and we observed evidence for selective utilization/preservation of certain compounds with depth in soil horizons. -Nutrient availability played a role in DOC biodegradability, while priming did not appear to be a relevant mechanism for enhancing DOC biodegradation.
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