张陶,
李建鸿,
蒲俊兵^,,
吴飞红,
袁道先
中国地质科学院岩溶地质研究所, 自然资源部/广西壮族自治区岩溶动力学重点实验室, 广西 桂林 541004

基金项目: 广西自然科学基金项目(批准号:2017GXNSFFA198006)、国家自然科学基金项目(批准号:41977166、41907172和41572234)和中国地质科学院基本科研业务费项目(批准号:2020004)共同资助


详细信息

作者简介: 张陶, 男, 30岁, 助理研究员, 岩溶碳循环与岩溶环境学, E-mail:zhangtao@karst.ac.cn

通讯作者: 蒲俊兵, E-mail:junbingpu@karst.ac.cn

中图分类号: P597⁺.2;P641.134

收稿日期:2020-02-11
修回日期:2020-05-08
刊出日期:2020-07-30

Sources and controlling mechanisms of CO₂ exchange across water-air interface in summer in two typical transects of Guijiang River, China

Zhang Tao,
Li Jianhong,
Pu Junbing^,,
Wu Feihong,
Yuan Daoxian
Key Laboratory of Karst Dynamics, Ministry of Natural Resources&Guangxi Zhuang Autonomous Region, Institute of Karst Geology, Chinese Academy of Geological Sciences, Guilin 541004, Guangxi



More Information

Corresponding author: Pu Junbing,E-mail:junbingpu@karst.ac.cn

MSC: P597⁺.2;P641.134

--> Received Date: 11 February 2020
Revised Date: 08 May 2020
Publish Date: 30 July 2020


摘要
摘要:河流系统水-气界面CO₂交换是全球水体碳循环的重要组成部分，但其来源、通量及控制机制一直存在较大争议。针对这一问题，本研究在南方亚热带河流（桂江）选择干流上游非岩溶区大面圩断面（DM）和下游岩溶区普益断面（PY）开展不同地质背景影响下水-气界面CO₂交换的高分辨率监测研究，并结合相应的大气环境参数、水化学参数以及碳同位素（Δ¹⁴C和δ¹³C）数据，分析水-气界面CO₂交换强度和方向的变化、碳来源及其控制机制。结果显示，两个断面CO₂交换强度表现出相似的白天下降夜间上升的昼夜变化模式，且都受到水生光合生物新陈代谢过程的控制。通过河水DIC和POC的Δ¹⁴C和δ¹³C值分析表明，桂江干流岩溶区河段（DM-PY河段）河水中DIC来源受到碳酸盐岩风化端元的影响，但在上游DM断面也受到了大气CO₂的影响，出现了显著的吸收大气CO₂。随着河流进入岩溶区，碳酸盐岩风化作用影响显著增强，为水生植物的生长提供了丰富的碳源，也影响了河流POC的变化，并改变了CO₂交换的方向。因此，桂江干流水气界面CO₂交换的变化受到水体内部水生光合生物新陈代谢过程和外部碳来源的共同控制。总之，由于河流中显著的水生生物代谢过程，桂江干流不仅出现了直接吸收大气CO₂的现象，同时也限制了CO₂脱气，形成了可观的碳汇通量，达到249.95 t/d，约为0.089 Tg C/a。
关键词: 桂江/
CO₂交换/
碳同位素/
水生光合生物/
代谢过程

Abstract:The Guijiang River (GJR) is the first order tributary of the Pearl River, which originates from Mao'ershan Mountain at an elevation of 2142 m. The river is 438 km long and drains an area of 18790 km². The regional climate is dominated by the East Asian Monsoon, which is characterized by a cold-dry winter from late November through March and a hot-rainy summer from April through October. The annual average temperature is about 20℃ in the GJR catchment from south to north, and has significant spatial differences. Carbonate rock (mainly of limestone) outcrops account for about 51% of the GJR drainage basin, most of which occur in the upper and middle parts of the drainage basin. We chose two typical transects for carrying out high-resolution diel monitoring and sampling during August 24 and 25, 2016, which represents two rock types in the GJR catchment:The upstream site, DM (25°20'59″N, 110°19'21″E) is located at the upstream edge of the middle reach and underlain by carbonate and siliciclastic rock. The downstream site, PY (24°40'37″N, 110°35'59″E) is located at the downstream edge of the middle reach and is underlain by pure carbonate rocks. Here, we measured CO₂ fluxes across the air-water interface at both DM and PY sections by floating chamber designed independently, and combined the corresponding atmospheric environmental parameters (air temperature and wind speed), hydrochemical parameters (water temperature, pH, DO and dissolved inorganic carbon (DIC)) and carbon isotopes (Δ¹⁴C and δ¹³C) of particulate organic carbon (POC) and DIC to assess variations, sources and controlling mechanism on intensity and direction of CO₂ exchange. The results showed that the intensity of CO₂ exchange across the water-air interface displayed similar diurnal pattern of decreasing in daytime and increasing at night at the two sections in the main stream of the Guijiang River, which is controlled by metabolism process of sub-aquatic community. The average δ¹³C_DIC and Δ¹⁴C_DIC value were -11.02±0.67 ‰ and -151.6±5.9 ‰ at DM, respectively, which implies that the DIC was affected by the carbonate weathering and atmospheric CO₂ and resulting in absorption of atmospheric CO₂. However, a more negative mean value of Δ¹⁴C_DIC (-366.7±18.9 ‰) and a more positive mean value of δ¹³C_DIC (-10.43±0.17 ‰) occurred at PY, indicating that the carbonate rocks weathering increases significantly. Additionally, aquatic plants utilized the DIC from karst processes to form a negative Δ¹⁴C_POC value indicating that the carbonate rocks weathering provided abundant carbon sources for the growth of aquatic plants to affect the sources of POC in the river, and changing the direction of CO₂ exchange. Therefore, the variations of CO₂ exchange intensity and direction were jointly controlled by the internal process of metabolism of sub-aquatic community and the external carbon sources. In conclusion, due to the strong aquatic metabolic processes under different geological feature in the main stream of Guijiang River, the research transections did not only directly absorb atmospheric CO₂ at some time, but also further limit CO₂ degassing, which resulted in a considerable carbon sink flux of 249.95 t/d, about 0.089 Tg C/a.
Key words:Guijiang River/
CO₂ exchange/
carbon isotopes/
sub-aquatic community/
metabolism process



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