Impact of Land Cover Types on Riverine CO 2 Outgassing in the Yellow River Source Region

• Published in: Water
• Main Authors: Mingyang Tian, Xiankun Yang, Lishan Ran, Yuanrong Su, Lingyu Li, Ruihong Yu, Haizhu Hu, Xi Xi Lu
• Format: Article in Journal/Newspaper
• Language: English
• Published: MDPI AG 2019
• Subjects: co 2 outgassing; glaciers; permafrost; peatland; grassland; yellow river source region (yrsr); Hydraulic engineering; TC1-978; Water supply for domestic and industrial purposes; TD201-500
• Online Access: https://doi.org/10.3390/w11112243; https://doaj.org/article/6ec384f1eb334aa19fa3e0f3a7553666

Under the context of climate change, studying CO 2 emissions in alpine rivers is important because of the large carbon storage in these terrestrial ecosystems. In this study, riverine partial pressure of CO 2 ( p CO 2 ) and CO 2 emission flux ( F CO 2 ) in the Yellow River source region (YRSR) under different landcover types, including glaciers, permafrost, peatlands, and grasslands, were systematically investigated in April, June, August, and October 2016. Relevant chemical and environmental parameters were analyzed to explore the primary controlling factors. The results showed that most of the rivers in the YRSR were net CO 2 source, with the p CO 2 ranging from 181 to 2441 μatm and the F CO 2 ranging from −50 to 1574 mmol m −2 d −1 . Both p CO 2 and F CO 2 showed strong spatial and temporal variations. The highest average F CO 2 was observed in August, while the lowest average was observed in June. Spatially, the lowest F CO 2 were observed in the permafrost regions while the highest F CO 2 were observed in peatland. By integrating seasonal changes of the water surface area, total CO 2 efflux was estimated to be 0.30 Tg C year −1 . This indicates that the YRSR was a net carbon source for the atmosphere, which contradicts previous studies that conclude the YRSR as a carbon sink. More frequent measurements of CO 2 fluxes, particularly through several diel cycles, are necessary to confirm this conclusion. Furthermore, our study suggested that the riverine dissolved organic carbon (DOC) in permafrost (5.0 ± 2.4 mg L −1 ) is possibly derived from old carbon released from permafrost melting, which is equivalent to that in peatland regions (5.1 ± 3.7 mg L −1 ). The degradation of DOC may have played an important role in supporting riverine CO 2 , especially in permafrost and glacier-covered regions. The percent coverage of corresponding land cover types is a good indicator for estimating riverine p CO 2 in the YRSR. In view of the extensive distribution of alpine rivers in the world and their sensitivity to climate ...