The effect of decreasing permafrost stability on ecosystem carbon in the northeastern margin of the Qinghai–Tibet Plateau

Abstract

The objective of this study is to investigate the effect of decreased permafrost stability on carbon storage of the alpine ecosystems in the northeastern margin of the Qinghai–Tibet Plateau. During July and August 2013, we selected 18 sites in five types of permafrost (stable, substable, transitional, unstable, and extremely unstable) regions. We measured aboveground phytomass carbon (APC) and soil respiration (SR), soil inorganic carbon (SIC), soil organic carbon (SOC), belowground phytomass carbon, and soil properties down to 50 cm at same types of soils and grasslands. The results indicated that ecosystem carbon in cold calcic soils first decreased and then increased as the permafrost stability declined. Overall, decreasing permafrost stability was expected to reduce ecosystem carbon in meadows, but it was not obvious in swamp meadows and steppes. APC decreased significantly, but SIC and SOC in steppes first decreased and then increased with declining permafrost stability. Soil clay fraction and soil moisture were the controls for site variations of ecosystem carbon. The spatial variations in SR were possibly controlled by soil moisture and precipitation. This meant that alpine ecosystems carbon reduction was strongly affected by permafrost degradation in meadows, but the effects were complex in swamp meadows and steppes.

Carbon Isotopic Evidences for Gas Hydrate Release and Its Significance on Seasonal Wetland Methane Emissions in the Qilian Mountains Permafrost

“…The measured carbon isotope compositions of methane (δ 13 C CH4 ) were between − 49.6‰ and − 34.6‰ with the average of -45.2‰, simillar as the range of the headspace gases from gas hydratebearing drill cores retrieved from the depth of 104.6m to 397.99m of the DK-8 (generally from − 38.3‰ to -53.2‰ with the average of -43.6‰) 23 . They are charcterized by less negative δ 13 C CH4 values, which are typical of thermogenically-derived methane source (-48‰ to -35‰) 33 .…”

“…The Qinghai-Tibet Plateau is the largest high-altitude permafrost region on Earth, with a wetland area coverring approximately 130,000 km 2 10 . Permafrost wetlands in the Qinghai-Tibet Plateau have received considerable attention, not only because the effects of climate warming on carbon ecosystems and wetlands emission are higher sensitive at high latitudes [11][12][13][14][15] , but also because this region holds vast amounts of soil organic carbon [16][17][18] stored in permafrost as well as thermogenic hydrocarbons in form of gas hydrates [19][20][21] . Climate warming has likely similar effects on greenhouse gases production in deep permafrost as in surface soils 14 .…”

“…Previous studies about gas hydrate in the Qinghai-Tibet Plateau indicated that the hydrocarbon gases in gas hydrates can effuse towards the land surface through microseepag 29 and may have an impact on the surface carbon circulation system, forming a key source of wetland methane emissions 19,30−32 . Until now there is only one recent study 32 that provided evidence of gas hydrate release as a new source of methane emissions from wetland soils in permafrost regions of the Qinghai-Tibet Plateau, which was identi ed by four high methane emission uxes of 10.4 ~ 76.0 mg/m − 2 h − 1 and δ 13 C CH4 values between − 48.0‰ and − 42.2‰ in the soil free gas during August. Howerver, the maganitude and timing of gas hydrate release and its impact on wetland methane emission and atmospheric methane concentration in the Qinghai-Tibet Plateau remains not fully understood.…”

“…The gases of gas hydrates from the Muli permafrost regions in the Qinghai-Tibet Plateau are mainly of thermogenic origin 33 , with a δ 13 C CH4 value ranging from − 52.7‰ to -31.3‰. The thermogenic methane is generally enriched in 13 C compared with bacterial methane that has δ 13 C CH4 values more negative than − 50‰ and up to -100‰. The carbon isotope signatures of methane are useful to distiguish methane sources of thermogenic or biogenic origin.…”

“…Nervertheless, the carbon isotope separation (ε C ) between CH 4 and CO 2 (de ned by ε C ≈ δ 13 C CO2δ 13 C CH4 ) can remain consistent despite large variaitons in the actual δ 13 C CH4 values and indicative of the particular methanogenic pathway 34 . Accordingly, the δ 13 C CH4 values in combination with the coexisting isotope information (ε C ) on CO 2 and CH 4 may be adequate to reliably distiguish methane sources.…”