杨茜茜^1,,
廖佩琳¹,
孙渝雯¹,
刘双圆¹,
谢雨婷¹,
钟庆祥¹,
吴迪¹,
高全洲^1,2,,
1. 中山大学地理科学与规划学院, 广东省城市化与地理环境空间模拟重点实验室, 广东 广州 510275
2. 南方海洋科学与工程广东省实验室(珠海), 广州 珠海 519080

基金项目: 国家自然科学基金项目（批准号：41871014）和国家自然科学基金-广东联合基金重点项目（批准号：U1901209）共同资助


详细信息

作者简介: 杨茜茜, 女, 23岁, 硕士研究生, 自然地理学专业, E-mail: yangxx35@mail2.sysu.edu.cn

通讯作者: 高全洲, E-mail: eesgqz@mail.sysu.edu.cn

中图分类号: P592, P534.63⁺2

收稿日期:2021-05-18
修回日期:2021-07-29
刊出日期:2021-11-30

Discussion on the measurement methods of dissolved inorganic carbon concentration in weak acid runoff of Dinghushan forest headwater catchment in Zhaoqing City, Guangdong Province

YANG Qianqian^1,,
LIAO Peilin¹,
SUN Yuwen¹,
LIU Shuangyuan¹,
XIE Yuting¹,
ZHONG Qingxiang¹,
WU Di¹,
GAO Quanzhou^1,2,,
1. Guangdong Key Laboratory for Urbanization and Geo-simulation, School of Geography and Planning, Sun Yat-sen University, Guangzhou 510275, Guangdong
2. Southern Marine Science and Engineering Guangdong Laboratory(Zhuhai), Zhuhai 519080, Guangdong


More Information

Corresponding author: GAO Quanzhou,E-mail:eesgqz@mail.sysu.edu.cn

MSC: P592, P534.63⁺2

--> Received Date: 18 May 2021
Revised Date: 29 July 2021
Publish Date: 30 November 2021


摘要
摘要:流域源区水-土界面联系密切，源区径流对碳的输送构成全球碳循环的重要环节。但现有研究对源区径流的水化学特征和碳的生物地球化学循环认识不足。本研究以广东肇庆鼎湖山森林源区为研究区域，分析了干季土壤水、地下水和地表水的化学组成；用顶空平衡法测量了地下水和地表水中游离CO₂的含量，并与自动酸化法和滴定法测量的游离CO₂含量对比，结合近年来文献中有关源区低阶河流游离CO₂含量的测量数据，探讨了各种测量方法在源区溪流溶解无机碳（DIC）或游离CO₂含量分析中的适用性。结果表明，研究区域受土壤自然酸化和酸沉降影响，径流水体总体为弱酸性（pH均值5.37±1.23），Ca²⁺和NO₃^-为水体主要的阳离子和阴离子。自然保护区地下水游离CO₂含量（13.18±6.89 mg C/L）较高，向下游其含量先降低后略为升高。东、西沟上游河段水体游离CO₂主要来源于地下水的注入，下游受河流水体有机质的分解和水生生物的呼吸作用影响较大。自动酸化法和滴定法低估了弱酸性、低碱度源区溪流水体DIC含量；顶空平衡法、水气分离法可直接测量水中游离CO₂含量且精度较高；酸化顶空法是近年来直接测量源区溪流DIC含量最常用的方法。顶空平衡法、水气分离法和酸化顶空法都能够有效避免CO₂逃逸对测量结果的影响。
关键词: 森林源区/
溪流/
水化学组成/
游离CO₂/
溶解无机碳

Abstract:Accurate measurement of DIC concentration in streams is the key to study the carbon cycle in the headwater catchment. Dinghushan Nature Reserve(23.16°~23.19°N, 112.51°~112.56°E) is located in Zhaoqing City, midwestern Guangdong Province, covering an area of 11.55 km². The regional climate is dominated by the subtropical monsoon climate, which annual mean temperature is 21℃ and has distinct wet season and dry season. The dry season is from October to March of the following year, and the wet season is from April to September, which accounts for more than 80% of the annual precipitation. The bedrock is mainly sandstone and sand shale of Devonian system. The soil types include latosolic red soil, yellow soil, and mountain shrub meadow soil, which are vertically distributed, with serious natural acidification, and the pH value is between 4.1 and 4.9. There are two small streams in the Dinghushan Nature Reserve, the East and West Gully, which are the same order streams in the upper reaches of the headwater catchment. At the exit of the nature reserve the two streams merge and flow into the Shuigan Canal, then the Shuigan Canal drains into the Houli River and finally into the Xijiang River.
The soil infiltrating water, groundwater and surface water were collected in dry season(December 2020) of the Dinghushan headwater catchment. The hydrochemical characteristics, such as electrical conductivity, pH value, cation and anion concentration were analyzed. Concentration of free CO₂ in groundwater and small streams were measured by headspace equilibration method and compared with that measured by automatic acidified methods and titration. Meanwhile, combined with the data of free CO₂ concentration in headwater streams of recently published literature, the applicability of these methods in lower-order streams were discussed.
The results showed that because of the natural acidification of soil and acid deposition, the water is weakly acidic(pH mean value 5.37±1.23). The main cation and anion in runoffs were Ca²⁺(209.0±260.5 μmol/L) and NO^3-(437.1±628.0 μmol/L), respectively. The main sources of ions are silicate rock mineral weathering and acid deposition. The concentration of free CO₂ in groundwater(13.18±6.89 mg C/L) was the highest and springs were the hotspots for CO₂ escape. When groundwater entered the stream, lots of CO₂ was emitted from the water, the concentration of free CO₂ in stream decreased sharply. Then the concentration of free CO₂ increased slowly in the downstream reaches(the Shuigan Canal and the Houli River). In the East and West Gully, DIC mainly existed in the form of free CO₂ which mainly came from groundwater input. With the increased of pH value in the Shuigan Canal and the Houli River, HCO₃^- became the main form of DIC, and free CO₂ was more affected by the decomposition of organic matter and respiration of aquatic organisms in rivers. The automatic acidification method and titration method underestimate the DIC content of the stream water in the weakly acidic and low-alkalinity source areas. The headspace balance method and the water-gas separation method can directly measure the free CO₂ content in the water with high accuracy. The acidification headspace method is the most commonly used method to direct measure the DIC content of streams in the headwater catchment in recently years. The headspace balance method, the water-gas separation method and the acidification headspace method can effectively avoid the influence of CO₂ escape on the measurement results.
Key words:forest headwater catchments/
streams/
hydrochemical compositions/
free CO₂/
dissolved inorganic carbon



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