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.
Highlights
CO2 or carbon flux is the major cause in today's global climate change
Global fluvial export of carbon is a well-documented component in the global carbon cycle and is estimated ca. ~1015 g C.yr-1 [1,2,3,4]. It is relatively small compared with the fluxes at other interfaces, the fluvial carbon flux contributes an important percentage to the regional carbon budget
2.1 Area of study The Changjiang drainage basin is situated within 24°30'– 35°45'N and 90°33'–122°25'E, draining almost one fifth of the total area of China
Summary
CO2 or carbon flux is the major cause in today's global climate change. Rivers, connecting the terrestrial and oceanic ecosystems, plays a unique role in the transportation of weathering products and pollutants from land to ocean. Global fluvial export of carbon is a well-documented component in the global carbon cycle and is estimated ca. ~1015 g C.yr-1 [1,2,3,4] It is relatively small compared with the fluxes at other interfaces (atmosphere-biosphere, atmosphere-ocean), the fluvial carbon flux contributes an important percentage to the regional carbon budget. Carbon exports via rivers are not limited to fluvial discharge. It has been found that river systems actively degasses CO2 into the atmosphere [2,5,6]. As observed in many studies, concentration of CO2 dissolved in rivers, lakes and coastal areas,
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