水源地型河流-水库秋冬季水体CO_(2)排放特征

Characteristics of CO_(2) Emission from Water Source River and Reservoir in Autumn and Winter

河流、水库水体是大气CO_(2)的重要排放源。为探究河流-水库连续型水体CO_(2)动态变化特征,文章以中国东南低山丘陵地区水源地型水库——沙河水库及其主要入库河流平桥河为例,于2022年秋季(9月-11月)、冬季(12月-次年2月)进行逐月采样,采用顶空平衡-气相色谱法和漂浮箱-便携式温室气体分析仪法分别对表层水体CO_(2)溶存浓度和水-气界面CO_(2)排放通量进行观测。分析了平桥河、入库口及沙河水库CO_(2)浓度与通量的时空变化及主要影响因素。结果表明:平桥河-沙河水库连续体的CO_(2)浓度和通量的范围分别为0.034~0.415 mmol/L和-7.835~4.481 mmol/(m^(2)·h);CO_(2)浓度及通量在空间上均表现为入库口显著高于平桥河和沙河水库(P<0.05),在季节上表现为秋季显著高于冬季(P<0.05)。平桥河-沙河水库连续体不同区域水体CO_(2)动态的影响因素差异较大,在平桥河主要受DO和pH的影响,在入库口主要受DO、pH和NH_(4)^(+)-N的影响,在沙河水库主要受水温、DO、pH、Chl-a、PO_(4)^(3-)-P、TP、DOC和DIC的影响。研究表明,河流、入库口和水库CO_(2)排放及影响因素具有较强的时空异质性,全面考虑水源地型河流-水库连续体不同区域水体CO_(2)动态变化特征有利于提升区域碳收支估算的准确性。

Rivers and reservoirs are important sources of atmospheric CO_(2) emissions.In order to investigate the dynamics of CO_(2) in a river-reservoir continuum,we analyzed the spatial and temporal changes in CO_(2) concentration and flux and its influencing factors of Pingqiao River,the reservoir inlet,and the Shahe Reservoir in the low-mountain hilly area of southeast⁃ern China.Monthly sampling was conducted in the autumn(September-November)and winter(December-February)of 2022,and headspace equilibrium-gas chromatography and floating chamber-portable greenhouse gas analyzer methods were used to observe the dissolved CO_(2) concentrations in surface water and CO_(2) emission flux at the water-air interface,re⁃spectively.The results showed that CO_(2) concentrations and fluxes in the Pingqiao River-Shahe Reservoir continuum ranged from 0.034 to 0.415 mmol/L and-7.835 to 4.481 mmol/(m^(2)·h),respectively.Spatially,CO_(2) concentrations and fluxes at the reservoir inlet were significantly higher than those in the Pingqiao River and the Shahe Reservoir(P<0.05);seasonally,CO_(2) concentrations and fluxes were significantly higher in autumn than in winter(P<0.05).The influencing factors of CO_(2) dynamics varied considerably in different regions of the Pingqiao River-Shahe Reservoir continuum:CO_(2) concentrations and fluxes in the Pingqiao River were mainly affected by DO and pH,in the reservoir inlet were mainly affected by DO,pH and NH_(4)^(+)-N,and in the Shahe Reservoir were mainly affected by water temperature,DO,pH,Chl-a,PO_(4)^(3-)-P,TP,DOC and DIC.This study demonstrated strong temporal and spatial heterogeneity of CO_(2) emissions and influencing factors in river,in⁃let and reservoir.Therefore,comprehensively considering the characteristics of CO_(2) dynamics in different water regions of the source-type river-reservoir continuum is conducive to improving the accuracy of regional carbon budget.