PNNL

Abstract

Thermokarst lakes on Qinghai-Tibet Plateau (QTP) are significant sources of greenhouse gas emissions, yet the underlying governing processes remain poorly understood. This study refines the Advanced Lake Biogeochemistry Model (ALBM) to characterize the unique environmental and biogeochemical processes of QTP thermokarst lakes. Key improvements include the integration of land vegetation types, microbial abundance, anaerobic methane oxidation (AOM), and groundwater-derived dissolved organic carbon (DOC) inputs. Calibration and validation against field observations demonstrate enhanced performance in simulating thermal and carbon dynamics, successfully capturing the spring CH4 pulse during ice-melt and the dominant contribution of ebullition to annual CH4 emissions. Sensitivity analyses identify surface energy exchange as the dominant control on thermal state, highlighting the rapid atmospheric responsiveness of these shallow alpine lakes. The model further reveals that CO2 fluxes are jointly regulated by hydrological carbon supply and biological uptake, where phytoplankton photosynthesis can substantially offset CO2 emissions. Methanotrophy considerably reduces annual CH4 fluxes, with aerobic oxidation limited by CH4 availability and AOM exerting a stronger effect, particularly on ebullition. Despite remaining challenges like sparse observations and fixed lake depth, the refined model advances understanding of the mechanisms governing carbon emissions from QTP thermokarst lakes, and provides a scalable framework for quantifying permafrost-carbon-climate feedbacks across high-altitude regions.