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

Abstract

Important unknowns remain about how abrupt permafrost collapse (thermokarst) affects carbon balance and greenhouse gas flux, limiting our ability to predict the magnitude and timing of the permafrost carbon feedback. We measured monthly, growing‐season fluxes of CO2, CH4, and N2O at a large thermokarst feature in alpine tundra on the northern Qinghai‐Tibetan Plateau (QTP). Thermokarst formation disrupted plant growth and soil hydrology, shifting the ecosystem from a growing‐season carbon sink to a weak source but decreasing feature level CH4 and N2O flux. Temperature‐corrected ecosystem respiration from decomposing permafrost soil was 2.7 to 9.5‐fold higher than in similar features from Arctic and Boreal regions, suggesting that warmer and dryer conditions on the northern QTP could accelerate carbon decomposition following permafrost collapse. N2O flux was similar to the highest values reported for Arctic ecosystems and was 60% higher from exposed mineral soil on the feature floor, confirming Arctic observations of coupled nitrification and denitrification in collapsed soils. Q10 values for respiration were typically over 4, suggesting high‐temperature sensitivity of thawed carbon. Taken together, these results suggest that QTP permafrost carbon in alpine tundra is highly vulnerable to mineralization following thaw, and that N2O production could be an important noncarbon permafrost climate feedback. Permafrost collapse altered soil hydrology, shifting the ecosystem from a carbon sink to carbon source but decreasing CH4 and N2O flux. Little to no vegetation recovery after stabilization suggests potentially large net carbon losses. High N2O flux compared to Arctic and Boreal systems suggests noncarbon permafrost climate feedback.

Assessing inter-annual and seasonal patterns of DOC and DOM quality across a complex alpine watershed underlain by discontinuous permafrost in Yukon, Canada

“…The predominant signals in the DOM indices observed in WCRB streams correspond well with those reported in the literature for northern and permafrost basins (Walker et al, 2013;Cory et al, 2014), and support conceptual models of coupled runoff generation and DOM transport (Mu et al, 2017). At the onset of freshet and the rise in DOC, SUVA 254 rises while both BIX and FI decline to annual minima.…”

“…At the scale of WCRB and its sub-catchments, results from other research in permafrost regions not experiencing rapid thermokarst that suggest a gradual increase in biodegradability (Spencer et al, 2008;Mann et al, 2015) are not necessarily discernable. However, changes in the DOC concentrations and export are likely due to mineralization and adsorption within the soil profile as thaw increases and active layers expand (Striegl et al, 2007;Mu et al, 2017) with a warming climate. While most conceptual models have focussed on the implications of thaw and thermokarst on DOM (Mu et al, 2017), in this study we had the opportunity to evaluate the influence of increased late summer and fall precipitation, which is a notable feature in fall across much of subarctic Canada (Spence and Rausch, 2005;Spence et al, 2015;DeBeer et al, 2016).…”

Riparian Corridors: A New Conceptual Framework for Assessing Nitrogen Buffering Across Biomes

“…Under temperate conditions, strong seasonal shifts in rainfall and soil moisture patterns entail a decrease in denitrification activity in riparian zones along larger streams (Pinay et al, 1995(Pinay et al, , 2000Tabacchi et al, 1998). Based on existing published data, we forecast that denitrification is not significant in riparian zones along low stream order streams under Mediterranean, arid or arctic climate due to low water availability and/or short residence time of water and solutes (Jones et al, 2005;Bernal et al, 2007;Mu et al, 2017;Poblador et al, 2017). Therefore, we forecast that in Mediterranean and arid regions, denitrification rates are consistently low compared to more humid catchments (Holmes et al, 1996;Bernal et al, 2007;Harms and Grimm, 2010;Lupon et al, 2015;Poblador et al, 2017).…”

Using Persistent Scatterer Interferometry to Map and Quantify Permafrost Thaw Subsidence: A Case Study of Eboling Mountain on the Qinghai‐Tibet Plateau

“…Permafrost temperature at 16-m depth at a borehole (red star in Figure 1a) has increased by about 0.2°C since 2012 (Cao et al, 2018). The study area is characterized by high levels of soil organic carbon and nitrogen stocks in the active layer (Mu et al, 2017). The active layer thickness (ALT) varies from 0.8 to 2.0 m with a mean of about 1.3 m (Cao, Gruber, Zhang, Li, et al, 2017).…”

“…Thermokarst processes also interact with the local hydrological, ecological, and geomorphological processes (Grosse et al, 2011;Jorgenson et al, 2006;Osterkamp et al, 2000;Walvoord & Kurylyk, 2016). Thermokarst subsidence promotes the decay and release of organic carbon stored in the permafrost, which consequently contributes to climatic warming through positive feedbacks (Camila et al, 2014;Mu et al, 2017;Nauta et al, 2015;Schadel et al, 2016;Schuur et al, 2015). In addition, thermokarst subsidence can severely damage buildings and infrastructure stability (Nelson et al, 2001(Nelson et al, , 2002.…”