Riverine CO2 variations in permafrost catchments of the Yangtze River source region: Hot spots and hot moments

Chunlin Song; Genxu Wang; Xiangyang Sun; Yang Li; Silu Ye; Zhaoyong Hu; Juying Sun; Shan Lin

doi:10.1016/j.scitotenv.2022.160948

Riverine CO₂ variations in permafrost catchments of the Yangtze River source region: Hot spots and hot moments

Sci Total Environ. 2023 Mar 10:863:160948. doi: 10.1016/j.scitotenv.2022.160948. Epub 2022 Dec 14.

Authors

Chunlin Song¹, Genxu Wang², Xiangyang Sun¹, Yang Li¹, Silu Ye¹, Zhaoyong Hu¹, Juying Sun¹, Shan Lin¹

Affiliations

¹ State Key Laboratory of Hydraulics and Mountain River Engineering, College of Water Resource and Hydropower, Sichuan University, Chengdu, China.
² State Key Laboratory of Hydraulics and Mountain River Engineering, College of Water Resource and Hydropower, Sichuan University, Chengdu, China. Electronic address: wanggx@scu.edu.cn.

PMID: 36526176
DOI: 10.1016/j.scitotenv.2022.160948

Abstract

Rivers and streams are pivotal modulators in regional and global carbon cycles, but riverine CO₂ flux is still uncertain for permafrost watersheds. Here we present the seasonal CO₂ partial pressure (pCO₂) and CO₂ emission flux (FCO₂) of 8 rivers and streams in the Yangtze River source region (YRSR), which have high permafrost coverage and seasonally thawed active layer. The YRSR rivers and streams are generally supersaturated with CO₂, although there are a few sites with CO₂ undersaturation during spring. The small headwater streams are CO₂ hot spots that show significantly higher pCO₂ (52 % higher) and FCO₂ (792 % higher) than larger rivers. Both pCO₂ and FCO₂ show distinct seasonality across the study sites. pCO₂ and FCO₂ peak in summer and exhibit much lower levels in autumn and spring, indicating that hot moments of riverine CO₂ occur in summer. Seasonal pCO₂ and FCO₂ variations are jointly controlled by hydrology, active layer dynamics and associated processes. The warm summer causes active layer thaw and highly active soil respiration, which release a large quantity of soil carbon and increase the CO₂ sources via strengthened hydrologic connectivity. The high rainfall and more thaw-released water in summer bring high discharge, which can increase the water velocity and gas exchange rate and thus CO₂ emission flux. Most of the variances of seasonal FCO₂ (95 %) can be explained by hydrology and active layer thaw depth. Nevertheless, the hydrological process and seasonally thawed active layer over Qinghai-Tibet Plateau (QTP) play crucial roles in riverine carbon export due to the summer monsoon-dominated climate in QTP. Our results suggest that full seasonal coverage of CO₂ dynamics is essential to quantify the annual CO₂ flux accurately. Changing climate and warming permafrost may alter the annual CO₂ emission due to deeper flow paths, hydrology changes, and longer emission windows throughout the year.

Keywords: CO(2) emission; CO(2) partial pressure; Permafrost; Qinghai-Tibet Plateau; Riverine carbon.