桂江典型断面夏季水-气界面CO2交换的碳源与机制  

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

作　　者：张陶[1] 李建鸿[1] 蒲俊兵[1] 吴飞红[1] 袁道先[1] 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)

机构地区：[1]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

出　　处：《第四纪研究》2020年第4期1048-1057,共10页Quaternary Sciences

基　　金：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);中国地质科学院基本科研业务费项目(批准号:2020004)共同资助。

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(△^14C和δ^13C)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△14C和δ^13C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.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(Δ^14C and δ^13C)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 averageδ^13CDIC andΔ^14CDIC value were-11.02±0.67‰and-151.6±5.9‰at DM,respectively,which implies that

关 键 词：桂江 CO2交换 碳同位素 水生光合生物 代谢过程 

分 类 号：P597.2[天文地球—地球化学] P641.134[天文地球—地质学]