Export of Dissolved Organic Carbon from the Source Region of Yangtze River in the Tibetan Plateau

Xiaoni You,Mika Sillanpää,Qiangqiang Xu,Rong Wang,Chengyong Wu,Xiangying Li

doi:10.3390/su14042441

Abstract

The carbon release and transport in rivers are expected to increase in a warming climate with enhanced melting. We present a continuous dataset of DOC in the river, precipitation, and groundwater, including air temperature, discharge, and precipitation in the source region of the Yangtze River (SRYR). Our study shows that the average concentrations of DOC in the three end-members are characterized as the sequence of groundwater > precipitation > river, which is related to the water volume, cycle period, and river flow speed. The seasonality of DOC in the river is observed as the obvious bimodal structure at Tuotuohe (TTH) and Zhimenda (ZMD) gauging stations. The highest concentration appears in July (2.4 mg L−1 at TTH and 2.1 mg L−1 at ZMD) and the secondary high value (2.2 mg L−1 at TTH 1.9 mg L−1 at ZMD) emerges from August to September. It is estimated that 459 and 6751 tons of DOC are transported by the river at TTH and ZMD, respectively. Although the wet deposition flux of DOC is nearly ten times higher than the river flux, riverine DOC still primarily originates from soil erosion of the basin rather than precipitation settlement. Riverine DOC fluxes are positively correlated with discharge, suggesting DOC fluxes are likely to increase in the future. Our findings highlight that permafrost degradation and glacier retreat have a great effect on DOC concentration in rivers and may become increasingly important for regional biogeochemical cycles.

Highlights

The dissolved organic carbon (DOC) amounts in river ecosystems are potentially increasing with global warming as the extensive release from permafrost and glaciers occurs [1,2]
The results indicate that the isotopic signature of particulate organic matter (POM) is similar to that of the surface soil along the riverbank [23], reflecting the typical stable carbon isotope source signatures of terrestrial organic matter [39]
The results show that the variation trend of the DOC concentration at both sites could be explained well by the change in discharge, which follows many previous research studies [37,38,46]

Summary

Introduction

The dissolved organic carbon (DOC) amounts in river ecosystems are potentially increasing with global warming as the extensive release from permafrost and glaciers occurs [1,2]. Glacier ablation causes the release of glacier organic carbon (OC) and enhances water soil/rock interaction and microbial activity by changing the hydrological process in cold regions, affecting the ecological environment and carbon cycle, and reacting on the climate [7,8]. This process depends on the environmental characteristics of the basin, the occurrence conditions, melting sensitivity, and degradation mode of glacier elements [9].

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