SUN Hailong1，LIU Zaihua1，YANG Rui1,2，CHEN Bo1，YANG Mingxing1,3, Zeng Qinrui1
( 1. State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550081, China;
2. College of Public Management, Guizhou University of Finance and Economics, Guiyang 550025, China;
3. School of Resource and Environment Engineering, Guizhou Institute of Technology, Guiyang 550003, China)
Abstract: The carbon sink produced by carbonate weathering based on the H2O–carbonate–CO2–aquatic phototroph interaction on land, is a significant component of CO2 sink. However, the process, mechanisms and controlling factors of such a carbon sink still need to be researched. A method of combining on-site monitoring and in-situ titrating with measurement of samples in laboratory was used in present study to investigate the spatial and seasonal variations of hydrochemistry in the main stream and tributary of the Pearl River. It is found that the hydrochemical compositions of river water were controlled jointly by the rock weathering, climate and aquatic primary production in the basin. For Xijiang River, the spatial variations of hydrochemistry mainly reflected the control of the rock weathering and utilization of DIC by aquatic photosynthesis. The hydrochemistry at all sites displayed similar seasonal variations, lower in summer and higher in spring and winter, but with much less variations than the river discharge. The lower concentrations of HCO-3 and Ca2+ in summer were mainly due to the dilution effect. The concentrations of dissolved oxygen also showed seasonal variations and reflected the seasonal variations of aquatic photosynthetic intensity. At sampling sites with slow flowing clean water, the values of DO were higher in summer and lower in winter, showing the temperature was the controlling factor of aquatic photosynthesis. At other sampling sites, DO showed reverse variations and the light intensity determined by turbidity was the limiting factor of aquatic photosynthesis. The hydrological environment might be the reason for the difference. It was found that the chemostatic behavior of [HCO-3] also existed in Xijiang River, indicating the variations in discharge played a more important role in controlling the variations in the carbon sink flux than the variation in [HCO-3]. It was also found that the autochthonous organic carbon sink produced by biological carbon pump was about 40% of the dissolved inorganic carbon sink calculated by the traditional model. Therefore, autochthonous organic carbon sink must be considered in the assessment of total rock weathering-related carbon sink in the Peal River.
Key words: the Pearl River Basin; spatiotemporal hydrochemical variations; carbonate weathering-related carbon sink; chemostatic behavior; biological carbon pump
EARTH AND ENVIRONMENT Vol.45, No.1 Tot No.315, 2017, Page 57-65
