Carbon loss and chemical changes from permafrost collapse in the northern Tibetan Plateau

Abstract

Permafrost collapse, known as thermokarst, can alter soil properties and carbon emissions. However, little is known regarding the effects of permafrost collapse in upland landscapes on the biogeochemical processes that affect carbon balance. In this study, we measured soil carbon and physiochemical properties at a large thermokarst feature on a hillslope in the northeastern Tibetan Plateau. We categorized surfaces into three different microrelief patches based on type and extent of collapse (control, drape, and exposed areas). Permafrost collapse resulted in substantial decreases of surface soil carbon and nitrogen stocks, with losses of 29.6 ± 4.2% and 28.9 ± 3.1% for carbon and nitrogen, respectively, in the 0-10 cm soil layer. Laboratory incubation experiments indicated that control soil had significantly higher CO 2 production rates than that of drapes. The results from Fourier transform infrared spectroscopy analysis showed that exposed soils accumulated some organic matter due to their low position within the feature, which was accompanied by substantial changes in the chemical structure and characteristics of the soil carbon. Exposed soils had higher hydrocarbon and lignin/phenol backbone content than in control and drape soils in the 0-10 cm layer. This study demonstrates that permafrost collapse can cause abundant carbon and nitrogen loss, potentially from mineralization, leaching, photodegradation, and lateral displacement. These results demonstrate that permafrost collapse redistributes the soil organic matter, changes its chemical characteristics, and leads to losses of organic carbon due to the greenhouse gas emission.Permafrost collapse including thaw slumps can occur rapidly in permafrost regions and result in the release of greenhouses gases, particulates, and dissolved organic carbon [Jensen et al., 2014]. In addition, dissolved organic carbon can be released from thawing permafrost [Cory et al., 2013; Wickland et al., 2007], and MU ET AL. PERMAFROST COLLAPSE CAUSED CARBON LOSS

Permafrost collapse shifts alpine tundra to a carbon source but reduces N2O and CH4 release on the northern Qinghai‐Tibetan Plateau

“…At our site, vegetation recovery after thermokarst formation appears to be slower than in Arctic ecosystems. For example, we observed no vegetation recolonization of exposed patches at our study site over 10 years, and at a similar thermo‐erosion feature on the QTP, there was no growth after 20 to 30 years of recovery [ Mu et al, ]. Slow plant recovery has also been observed in central QTP, where vegetation cover showed no increase after 7 years of ecological protection following anthropogenic disturbance [ Cai et al, ].…”

“…This, together with the high‐temperature sensitivity of R eco for exposed patches ( Q 10 = 4), suggests that SOC exposed by thermokarst formation in our study area could be substantially more vulnerable to mineralization following thaw than SOC from other permafrost regions [ Jensen et al, ]. However, considerably more empirical and conceptual research concerning relative biodegradability, climatic differences, hydrological changes, and site level variability is needed before coming to firm conclusions about regional patterns of vulnerability of carbon stocks following permafrost degradation [ Mu et al, ; Olefeldt et al, ].…”

“…For ice‐rich permafrost, thawing can trigger surface collapse due to melting of ground ice, a process termed thermokarst [ Abbott and Jones , ; Kokelj and Jorgenson , ]. As opposed to top‐down permafrost thaw, which gradually exposes previously frozen organic matter to decomposition, thermokarst abruptly exposes the whole soil column, influencing not only carbon and nitrogen stocks but also their chemical characteristics and rate of mineralization [ Mu et al, ]. Thermokarst formation reorganizes surface topography, creating complex and dynamic microtopography that can alter soil hydrothermal conditions, redox conditions, and consequently the production of CO 2 , CH 4 , and N 2 O in affected soil [ Abbott and Jones , ; Jensen et al, ].…”

Selective Leaching of Dissolved Organic Matter From Alpine Permafrost Soils on the Qinghai‐Tibetan Plateau

“…Previous studies have shown that the total potential soil CO 2 emission on the QTP ranges from 737.90–4224.77 g CO 2 m −1 y −1 , and thawing‐induced CO 2 emissions from permafrost soils would increase general soil respiration by at least about one third on average at a temperature of 5°C (Bosch et al, ). A laboratory incubation experiment indicated that the soils from the AL and PL on the QTP had similar CO 2 ‐emitting potentials (Chen et al, ), while another study suggested that control (nonexposed) soils had significantly higher CO 2 production rates than drape (exposed) soils in a permafrost collapse area on the northern QTP (Mu et al, ). Nevertheless, the abundant carbon stock (~29.6 ± 4.2%; Mu et al, ) was lost during the permafrost thaw and collapse processes, potentially from mineralization, leaching, photodegradation, and lateral displacement.…”

“…A laboratory incubation experiment indicated that the soils from the AL and PL on the QTP had similar CO 2 ‐emitting potentials (Chen et al, ), while another study suggested that control (nonexposed) soils had significantly higher CO 2 production rates than drape (exposed) soils in a permafrost collapse area on the northern QTP (Mu et al, ). Nevertheless, the abundant carbon stock (~29.6 ± 4.2%; Mu et al, ) was lost during the permafrost thaw and collapse processes, potentially from mineralization, leaching, photodegradation, and lateral displacement. A recent study for three Tibetan rivers (the Yellow, Yangtze, and Yarlung Tsangpo) showed that the mean radiocarbon age of DOM was 511 ± 294 years before present (BP) during high flow period (August to September 2014), suggesting the significant export of preaged permafrost carbon into the Tibetan rivers (Qu et al, ).…”