Freeze-thaw processes of active layer regulate soil respiration of alpine meadow in the permafrost region of the Qinghai-Tibet Plateau

Abstract

Abstract. Freezing and thawing action of the active layer plays a significant role in soil respiration (Rs) in permafrost regions. However, little is known about how the freeze-thaw process regulates the Rs dynamics in different stages for the alpine meadow underlain by permafrost on the Qinghai-Tibet Plateau (QTP). We conducted continuous in-situ measurements of Rs and freeze-thaw process of the active layer at an alpine meadow site in the Beiluhe permafrost region of QTP to determine the regulatory mechanisms of the different freeze-thaw stages of the active layer on the Rs. We found that the freezing and thawing process of active layer modified the Rs dynamics differently in different freeze-thaw stages. The mean Rs ranged from 0.56 to 1.75 μmol/m2s across the stages, with the lowest value in the SW stage and highest value in the ST stage; and Q10 among the different freeze-thaw stages changed greatly, with maximum (4.9) in the WC stage and minimum (1.7) in the SW stage. Patterns of Rs among the ST, AF, WC, and SW stages differed, and the corresponding contribution percentages of cumulative Rs to annual total Rs were 61.54, 8.89, 18.35, and 11.2 %, respectively. Soil temperature (Ts) was the most important driver of Rs regardless of soil water status in all stages. Our results suggest that as the climate warming and permafrost degradation continue, great changes in freeze-thaw process patterns may trigger more Rs emissions from this ecosystem because of prolonged ST stage.

Vegetation Mediated Mercury Flux and Atmospheric Mercury in the Alpine Permafrost Region of the Central Tibetan Plateau

“…Mean annual air temperature is −5 °C with maximum of 18 °C and minimum of −30 °C. 30 The study region lies over the continuous permafrost zone with maximum active layer thickness ranging between 1 and 4.3 m. There are limited point sources of anthropogenic Hg emissions in this region, with the nearest town of Anduo located 110 km south and 400 m lower altitude of the research station. Due to its close proximity to the Qinghai-Tibet highway (∼0.5 km), one possible source of anthropogenic Hg emissions could be transportation at Tanggula station (e.g., gasoline and diesel combustion).…”