覃蔡清^1,2,,
李思亮^2,,,
岳甫均²,
丁虎²,
徐胜²,
刘丛强^2,3
1. 西安交通大学人居环境与建筑工程学院, 陕西 西安 710049
2. 天津大学地球系统科学学院, 天津 300072
3. 中国科学院地球化学研究所, 环境地球化学国家重点实验室, 贵州 贵阳 550081

基金项目: 中国科学院(B类)战略性先导科技专项项目(批准号：XDB40000000)和国家自然科学基金委员会国际(地区)合作与交流项目(批准号：41571130072)共同资助


详细信息

作者简介: 覃蔡清, 男, 30岁, 助理教授, 环境地球化学, E-mail: qincaiqing@xjtu.edu.cn

通讯作者: 李思亮, E-mail: siliang.li@tju.edu.cn

中图分类号: P593;X142

收稿日期:2020-12-27
修回日期:2021-03-18
刊出日期:2021-07-30

Biogeochemical processes of dissolved carbon in the karst critical zone and its response to rainstorms

QIN Caiqing^1,2,,
LI Siliang^2,,,
YUE Fujun²,
DING Hu²,
XU Sheng²,
LIU Congqiang^2,3
1. Department of Earth & Environmental Science, School of Human Settlements and Civil Engineering, Xi'an Jiaotong University, Xi'an 710049, Shaanxi
2. Institute of Surface-Earth System Science, School of Earth System Science, Tianjin University, Tianjin 300072
3. State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550081, Guizhou


More Information

Corresponding author: LI Siliang,E-mail:siliang.li@tju.edu.cn

MSC: P593;X142

--> Received Date: 27 December 2020
Revised Date: 18 March 2021
Publish Date: 30 July 2021


摘要
摘要:喀斯特地区良好的水文连通性和丰富的碳酸盐岩使喀斯特关键带碳循环过程十分活跃，并对全球气候变化具有快速响应。为解析流量-溶解性碳浓度-碳同位素(Q-C-I)之间的动态关系以及喀斯特关键带重要的碳生物地球化学过程，本研究在降雨过程中对中国西南典型喀斯特流域——陈旗流域内的雨水、穿林雨、山坡径流、地表水和泉水进行了同步高频采集。结果表明，雨水中的溶解性无机碳(DIC)浓度很低，对地表水和泉水的整体贡献小。地表水和泉水中的DIC浓度随流量增加均表现出"溶质恒定(chemostatic)"行为，生物降解来源的CO₂是主要调控因素，其相对贡献比在采样期间随流量增加而上升，而碳酸盐岩以及大气CO₂的贡献相对较低且在水文变化时波动较小。流量相同时泉水中的DIC浓度及其单位时间的输出量均高于地表水。相比而言，雨水中的溶解性有机碳(DOC)浓度在穿过植被冠层后能上升1倍左右，在随径流从山坡运输到流域洼地的过程中也有上升趋势。地表水和泉水中的DOC浓度均随流量增加而增加，具有积聚效应，在运输过程中主要靠陆源补给，其输出量受控于与降雨情况有关的运输限制。因此，不同赋存形态碳在水文变化中的响应具有差异性，相互之间的转化也可能会改变流域的碳归趋行为。整体而言，流域内强烈的碳酸盐岩风化和农业活动对碳循环、气候以及水环境都会产生潜在影响。未来需要深入研究溶解性碳相互转换的时间尺度和控制机制及其在地表-地下运移过程中与喀斯特关键带结构的相互作用机理。
关键词: 喀斯特关键带/
溶质恒定/
溶解性碳的动态响应/
碳酸盐岩风化/
稳定碳同位素

Abstract:Karst landscapes characterize well hydrologic connectivity and abundant carbonate minerals, making carbon dynamic processes active and responsive to global climate change. The Chenqi catchment(26°15'20″~26°16'9″N, 105°46'3″~105°46'50″E) is a typical karst catchment with an area of 1.25km² in Puding, Guizhou province, Southwest China. It is affected by subtropical monsoonal climate, the annual mean rainfall here is 1140mm, over 80% of which falls in the wet season. Carbonate rocks dominate the lithology in this catchment, over which Quaternary soils are unevenly distributed, thin(mean < 50cm) in hills but thicker(40~100cm) in valley depressions. To analyze the discharge (Q) -dissolved carbon concentrations (C) -carbon isotope (I) relationship, and the vertical distribution and transport mechanism of dissolved carbon among rainwater-throughfall-hillslope runoff-surface water-spring in this karst catchment, we simultaneously conducted continuous in-situ monitoring and field sampling during rainstorms, and measured water quality parameters, dissolved carbon concentrations and isotope compositions. Results showed that the dissolved inorganic carbon(DIC) concentration in rainwater is too low(3.91±0.14mg/L) to contribute a lot to surface water(42.31±1.34mg/L) and spring(51.23±2.46mg/L). DIC concentrations in surface water and spring both showed chemostatic responses to increasing discharge. The mean δ¹³C_DIC in surface water and spring were -13.9±0.4 ‰ and -13.7±0.6 ‰. According to the results of isotope mixing model(Isosource), the dynamic variations of DIC in karst water is mainly regulated by biogenic CO₂(>70%). The relative contribution ratio of biogenic CO₂ to DIC increased with increasing discharge during the sampling period, while the contribution ratios of carbonate and atmospheric CO₂ fluctuated slightly during hydrological variations. DIC concentrations and its export flux per unit time are both higher in spring than in surface water at the same discharge. Dissolved organic carbon(DOC) concentrations in rainwater increased by around one time after passing through the vegetation canopy(1.83±0.57mg/L versus 4.39±0.61mg/L). There was also an uptrend for DOC concentrations during its transportation accompanying with discharge from hillslope(4.36±0.76mg/L) to catchment depression(5.30±1.60mg/L). After infiltrating into epikarst, DOC concentration decreased to 1.83±0.62mg/L in spring water. DOC concentrations in both surface water and spring increased with increasing discharge, showing an accumulation effect. The replenishment of DOC during its transport processes is mainly from terrestrial sources, which is mostly controlled by hydrologic transport limitation related to rainstorms instead of antecedent hydrologic condition. Different chemical speciation of carbon display different responses to rainstorms, the transformation between them can alter carbon fate within catchment. Overall, the strong carbonate weathering and agricultural activities can potentially affect carbon cycle, climate and water environment. In-depth researches are needed in the future to explore the mechanisms of dissolved carbon transformation and its interaction with the structure of karst critical zone.
Key words:karst critical zone/
chemostatic/
dynamic responses of dissolved carbon/
carbonate weathering/
carbon isotopes



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