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| 引用本文: | 武恩鹏,孙会国,刘文景,徐志方.澜沧江自然河道-梯级水库河流碳迁移转化过程昼夜变化分析.湖泊科学,2025,37(2):517-531. DOI:10.18307/2025.0226 |
| Wu Enpeng,Sun Huiguo,Liu Wenjing,Xu Zhifang.Diel variations in riverine carbon transport and transformation processes in the natural channel-cascade reservoirs continuum of the Lancang River. J. Lake Sci.2025,37(2):517-531. DOI:10.18307/2025.0226 |
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| 澜沧江自然河道-梯级水库河流碳迁移转化过程昼夜变化分析 |
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武恩鹏1，2，孙会国1，2，刘文景1，2，徐志方1，2
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1.中国科学院地质与地球物理研究所, 岩石圈演化与环境演变重点实验室, 北京 100029 ；2.中国科学院大学地球与行星科学学院, 北京 100049
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| 摘要: |
| 河流碳是全球碳循环中的重要组成部分，也是流域内发生的各种自然过程和人类活动的记录载体。梯级水库建设强烈改变河流的自然状态和物质输送，但其对高寒地区河流碳迁移转化过程的影响尚未进行过充分研究。本研究选择澜沧江自然河道及其下游梯级水库河水断面，调查分析了河水基本理化参数、各形式河流碳及其稳定碳同位素的昼夜变化特征，并通过不同断面间的对比研究，揭示了河流碳在自然河道-梯级水库连续体内的迁移转化过程、通量变化及梯级水库对其带来的影响。结果表明，库区水体中的颗粒有机碳浓度较自然河道大幅降低，反映了梯级水库对颗粒态物质的巨大拦截作用（98%悬浮物被拦截）。溶解无机碳与溶解有机碳在自然河道与库区断面的浓度和通量均未发生明显变化，说明梯级水库对河流溶解态物质影响较小。水体二氧化碳分压(pCO2)显示出由自然河道（平均值为689 μatm）向库区（平均值为587 μatm）降低趋势，且在冬季下降幅度更大。溜筒江水文站和功果桥水库两个河水断面的水体物化参数、碳浓度及其稳定碳同位素组成均无显著昼夜差异，且溶解氧与水体pCO2未出现协同变化，说明河流内部水生生物光合作用较弱。结合稳定碳同位素数据指示河流碳来源组成变化及河流碳通量变化，可以推断河流有机碳被大量埋藏在水库底部从而削弱了水体内部有机碳氧化分解过程，并导致库区表层水体pCO2下降。水体营养元素浓度低、水库建成时间短、流量调节频繁等因素是库区水生生物光合作用弱、对河水化学和碳循环影响小的重要原因。可见，澜沧江水库建设导致河流有机碳沉积量大幅增加，同时CO2排放量大幅降低，因而具有净碳汇效应。 |
| 关键词: 河流碳 稳定碳同位素 梯级水库 昼夜变化 澜沧江 |
| DOI：10.18307/2025.0226 |
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| 基金项目:国家重点研发计划项目(2020YFA0607700)；国家自然科学基金项目(41877402)；中国科学院青年创新促进会项目(Y2023014)联合资助 |
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| Diel variations in riverine carbon transport and transformation processes in the natural channel-cascade reservoirs continuum of the Lancang River |
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Wu Enpeng1，2，Sun Huiguo1，2，Liu Wenjing1，2，Xu Zhifang1，2
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1.State Key Laboratory of Lithospheric Evolution and Environmental Change, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029 , P.R.China ；2.College of Earth and Planetary Sciences, University of Chinese Academy of Sciences, Beijing 100049 , P.R.China
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| Abstract: |
| Riverine carbon is an important component of the global carbon cycle, and also provides insights into various natural processes and anthropogenic activities in the catchment. Cascade reservoirs seriously alter the natural state and biogeochemical cycles of rivers, but their effects on the carbon migration and transformation processes of rivers in alpine regions have not been fully investigated. In this study, the natural river section of the Lancang River and its downstream cascade reservoirs were selected to investigate the basic physical and chemical parameters of the river water, as well as the diel variations of riverine carbon contents and stable carbon isotopes. The aim was to investigate the migration and transformation processes of riverine carbon in the natural channel-cascade reservoirs continuum and to explore the influence of cascade reservoirs on carbon cycling through a comparative analysis. The results indicated that the particulate organic carbon content in the reservoir's water column was significantly lower than that in the natural river channel, reflecting the substantial trapping effect of the cascade reservoirs on particulate matter, with 98% of suspended solids being retained. The concentrations and fluxes of dissolved inorganic carbon and dissolved organic carbon exhibited no significant variations between the natural river channel and the reservoir sections, indicating that the cascade reservoirs had a minimal influence on the dissolved substances in the river. However, the partial pressure of carbon dioxide (pCO2) in the water exhibited a decreasing trend from the natural river channel (average 689 μatm) to the reservoir area (average 587 μatm), with a more pronounced decline during the winter season. No significant diel variations were observed in the physicochemical parameters, carbon concentrations, or carbon isotope compositions of the water bodies at the Liutongjiang hydrologic station and the Gongguoqiao Reservoir. Moreover, there was no synergistic change between dissolved oxygen and pCO2, indicating that aquatic photosynthesis within the river was weak. Stable carbon isotope data revealing alterations in carbon sources and carbon fluxes suggested that a substantial amount of riverine organic carbon was sequestered at the bottom of the reservoir. This weakened the internal oxidation were decomposition processes of organic carbon, leading to a decrease in pCO2 in the surface waters of the reservoir. The low nutrient content, short reservoir age and frequent flow regulation were the primary factors contributing to the weak aquatic photosynthesis in the reservoir and its limited impact on river chemistry and the carbon cycle. Overall, the cascade reservoirs in the Lancang River basin had resulted in a significant increase in the deposition of riverine organic carbon with a considerable reduction in CO2 outgassing, thus exhibiting a net carbon sink effect. |
| Key words: Riverine carbon stable carbon isotope cascade reservoir diel variation Lancang River |
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