Research article

Human impact on the historical change of CO₂ degassing flux in River Changjiang

FuShun Wang^1,2 , Yuchun Wang³ , Jing Zhang⁴ , Hai Xu² and Xiuguo Wei⁴

¹Institute of Applied Radiation, School of Environmental and Chemical Engineering, Shanghai University, Shanghai 201800, China

²State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550002, China

³Department of water environment, China Institute of Water Resources and Hydroelectric Power Research (IWHR), Beijing 100038, China

⁴State Key Laboratory of Estuarine and Coastal Research, East China Normal University, Shanghai 200062, China

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Geochemical Transactions 2007, 8:7doi:10.1186/1467-4866-8-7

Published:	9 August 2007

Abstract

The impact of water quality changes in River Changjiang (formally known as the Yangtze River) on dissolved CO₂ and silicate concentrations and seasonal carbon flux in the past several decades (1960s–2000) was evaluated, based on monitoring data from hydrographic gauge. It was found that dissolved CO₂ and silicate in Changjiang decreased dramatically during this decades, as opposed to a marked increase in nutrient (e.g. NO₃^-) concentrations. Our analyses revealed that dissolved CO₂ in Changjiang was over-saturated with the atmosphere CO₂, and its concentration had showed a declining trend since the 1960s, despite that fluvial DIC flux had maintained stable. Analysis results also suggested that the decrease in dissolved CO₂ concentration was attributed to changes on the riverine trophic level and river damming activities in the Changjiang drainage basin. Due to the economic innovation (e.g. agriculture and industry development) across the Changjiang watershed, fertilizers application and river regulations have significantly altered the original state of the river. Its ecosystem and hydrological condition have been evolving toward the "lacustrine/reservoir" autotrophic type prevailing with plankton. Accordingly, average CO₂ diffusing flux to the atmosphere from the river had been reduced by three-fourth from the 1960s to 1990s, with the flux value being down to 14.2 mol.m^-2.yr^-1 in the 1990s. For a rough estimate, approximately 15.3 Mt of carbon was degassed annually into the atmosphere from the entire Changjiang drainage basin in the 1990s.