大型水库分层期和混合期溶存温室气体空间变化及排放通量

Spatial variations of dissolved greenhouse gases and emission fluxes in a large reservoir during the stratification and mixing periods

水库作为温室气体的重要来源,对区域气候变化有不可忽略的影响。然而,目前对水库溶存温室气体的空间异质性及垂向特征的认知仍然欠缺。为了揭示水库分层期和混合期溶存温室气体空间特征及排放通量,也为厘清水库温室气体产生和排放的关键过程提供重要支撑。研究选择东北地区大型水库——汤河水库为对象,于2021年79月和10月(分别代表水库分层期和混合期)对水库不同位置(坝前、库中和库尾)开展溶存温室气体垂向分层监测。研究结果显示,水库CH 4排放通量变化范围为0.018~0.174 mmol/(m^(2)·d),是大气CH 4的源,空间分布为库尾>库中>坝前;CO_(2)通量为-4.91~58.77 mmol/(m^(2)·d),除分层期东支库尾,其余点位均表现为大气CO_(2)的源,空间分布为坝前>库中>库尾。时间上,分层期CH 4排放通量(0.071±0.044 mmol/(m^(2)·d))高于混合期((0.027±0.008)mmol/(m^(2)·d));分层期CO_(2)排放通量((5.12±5.50)mmol/(m^(2)·d))明显低于混合期((42.76±16.72)mmol/(m^(2)·d))。水温和径流的变化共同影响CH 4和CO_(2)排放通量。结合水库溶存温室气体垂向分布特征,水库CH 4的生成热区主要在坝前和库尾。分层期的水库溶存CH 4在坝前和库中底层大量累积,原因是等温层的持续缺氧以及上下水层的交换能力限制。与国内其它水库温室气体排放通量对比发现,水库的不同时期(分层期和混合期)、空间位置(坝前、库中和库尾)以及库龄是准确评估水库温室气体排放的关键因素。

Reservoirs are pivotal sources of greenhouse gases(GHGs)to the atmosphere that may influence regional climate change.However,the spatial heterogeneity and the vertical characteristics of dissolved GHGs in reservoirs are still poorly understood.This study aimed to reveal the characteristics of greenhouse gases dissolution and emission fluxes in reservoirs during stratification and mixing periods,and to provide important supports to clarify the key processes of GHGs production and emission in reservoirs.We selected Tanghe Reservoir,a large reservoir in Northeast China,and conducted vertical stratified monitoring of dissolved GHGs at different locations(in front of dam,mid,end transects)from July-September and October 2021(representing the stratification and mixing periods,respectively).The results showed that the CH 4 fluxes ranged from 0.018-0.174 mmol/(m^(2)·d)and all sites were the source of CH 4,the spatial distribution of CH 4 fluxes was end>mid>in front of dam.The CO_(2) fluxes ranged from-4.91-58.77 mmol/(m^(2)·d),and all sites were the source of CO_(2) except for the eastern end transect during the stratified period,and the contents of spatial distribution of CO_(2) fluxes was in front of dam>mid>end.In terms of temporal differences,CH 4 fluxes in the stratified period((0.071±0.044)mmol/(m^(2)·d))were higher than in the mixed period((0.027±0.008)mmol/(m^(2)·d)),and CO_(2) fluxes in the stratified period((5.12±5.50)mmol/(m^(2)·d))were lower than the mixed period((42.76±16.72)mmol/(m^(2)·d)),and both water temperature and runoff affected CH 4 and CO_(2) fluxes.The vertical distribution characteristics of dissolved GHGs indicated that the hot zone of reservoir CH 4 generation was mainly in front of dam and end transects.The CH 4 was heavily accumulated in the bottom water of the dam front and mid transects during the stratified period due to the persistent anoxia in the hypolimnion and the limitation of the exchange capacity in the water column.The comparison with other reservoirs GHGs fluxes in China revealed that the different periods(stratification and mixing period),spatial variations(in front of dam,mid,and end transects)and reservoir ages were the key factors for accurate assessment of reservoir GHGs emissions.