连续筑坝河流水气界面温室气体排放通量及其影响因素——以青海省湟水支流火烧沟为例

GHG Flux at the Water-Air Interface of Rivers with Cascaded Dams:A Case Study on the Huoshaogou Tributary of Huangshui River,Qinghai Province

河流筑坝后水体环境发生巨大改变,水体温室气体排放通量和排放模式随之发生变化。为了探究筑坝后河流水气界面温室气体排放情况,选取青海湟水支流火烧沟为研究区域,采用静态箱-气相色谱实验法,对4个连续筑坝断面水气界面的3种温室气体二氧化碳(CO2)、甲烷(CH4)、一氧化二氮(N2O)夏季排放通量进行监测,研究河流筑坝前后的温室气体排放通量规律及其影响因素。结果显示:(1)筑坝对河流碳、氮等有机质形成滞留效应,筑坝区温室气体排放通量显著高于未筑坝区,二者排放通量平均相差4.12倍。(2)时间尺度上,CO2排放的最高值主要分布于8月;而CH4排放的高峰值多分布于6月;N2O排放高峰值多分布于7月。(3)空间分布上,CO2排放通量无明显的规律,排放低值-1554.19 mg/(m^2·h)和高值778.84 mg/(m^2·h)均出现在筑坝区;CH4和N2O排放低值均出现在未筑坝区,分别为360μg/(m^2·h)和34.72μg/(m^2·h),而高值均出现在筑坝区,分别为6163.4μg/(m^2·h)和746.7μg/(m^2·h)。(4)不同筑坝段水体温室气体排放通量的影响因素不同,相关分析表明,火烧沟水体CO2排放通量与电导率(Cond)(r=-0.914,P<0.05)、pH(r=-0.907,P<0.05)、总溶解固体(TDS)(r=-0.914,P<0.05)、盐度(Sal)(r=-0.926,P<0.05)以及气温(T)(r=-0.978,P<0.01)呈显著负相关;CH4排放通量与氧化还原电位(ORP)(r=-0.968,P<0.01)、pH(r=0.979,P<0.01)呈显著相关;N2O排放通量与电导率(Cond)(r=0.903,P<0.05)、总溶解固体(TDS)(r=0.904,P<0.05)、气温(T)(r=0.970,P<0.05)以及氧化还原电位(ORP)(r=0.929,P<0.05)呈显著正相关。

Dam construction significantly alters the hydrology and water quality of rivers,leading to dramatic changes in fluxes and patterns of greenhouse gas(GHG)emissions.At present,the processes and mechanisms of the impacts produced by cascaded dams on GHG emissions remain unclear,and relevant research is urgently needed.In this case study,we investigated GHG emission patterns before and after con-struction of four cascaded dams on Huoshaogou River,a tributary of Huangshui River in Qinghai Province.The influence of damming the river on GHG emissions and the environmental variables affecting GHG emissions were analyzed.During the summer of 2017,emission fluxes of carbon dioxide(CO2),methane(CH4)and nitrous oxide(N2O)were monitored across five transects located above and below the four cascaded dams on the Huoshaogou River.The emission fluxes of the three GHGs were determined u-sing the static chambergas chromatography method,and three samples were collected across each transect.Hydrological and water quality parameters were simultaneously monitored to identify the primary factors influencing GHG emissions.Results show that:(1)Cascaded dams retained carbonaceous and nitrogenous organic matter and the GHG emission flux in dammed areas was 4.12times higher than that in undammed areas.(2)The emissions of CO 2,CH 4 and N 2 O peaked,respectively,in August,June and July.(3)The lowest CO 2 emission flux[-1554.19mg/(m^2·h)]and the highest flux[778.84mg/(m^2·h)]both occurred in the dammed area;the lowest flux for both CH 4[360μg/(m^2·h)]and N 2 O[34.72μg/(m^2·h)]occurred in undammed areas,while the respective peak values[6163.4μg/(m^2·h)and 746.7μg/(m^2·h)],occurred in dammed areas.(4)The primary influencing factors of GHG emissions varied among the gases.The CO 2 emission flux was negatively correlated with water conductivity(r=-0.914,P<0.05),pH(r=-0.907,P<0.05),TDS(r=-0.914,P<0.05),salinity(r=-0.926,P<0.05)and air temperature(r=-0.978,P<0.01);CH 4 emission flux was negatively correlated with ORP(r=-0.968,P<0.01)and positively correlated with pH(r=0.979,P<0.01);N 2 O emission flux was positively correlated with conductivity(r=0.903,P<0.05),TDS(r=0.904,P<0.05),T(r=0.970,P<0.05)and ORP(r=0.929,P<0.05).This study provides valuable insights into the complexity of factors influencing GHG emissions at the water-air interface of rivers with cascaded dams.