岩溶湿地表层水体CO2分压时空分布特征及其扩散通量

Spatiotemporal distribution of carbon dioxide partial pressure and its diffusion flux in surface water of Karst wetland

为揭示岩溶湿地表层水体二氧化碳分压(pCO_(2))的时空分布规律及其扩散通量,以我国最大的岩溶湿地贵州威宁草海为研究对象,分别于2019年7月(丰水期)和12月(枯水期)通过网格布点法,系统采集草海表层湿地水体,测定水样理化指标和离子组成,利用PHREEQCI软件计算水体pCO_(2),并基于Cole提出的气体扩散模型估算水-气界面二氧化碳(CO_(2))的扩散通量.结果表明:草海湿地表层水体丰水期pCO_(2)的变化范围为0.44~645.65μatm,平均值为(55.94±124.73)μatm;枯水期变化范围为35.48~707.95μatm,平均值为(310.46±173.54)μatm;丰水期水体整体pCO_(2)低于枯水期,空间上两期水体均呈现东部区域及河流入湖口处pCO_(2)较高,而中西部区域pCO_(2)欠饱和的特征.水-气界面CO_(2)的扩散通量在丰水期变化范围为-43.27~27.16 mmol/(m^(2)·d),平均值(-34.49±12.93)mmol/(m^(2)·d),枯水期变化范围为-33.36~28.15 mmol/(m^(2)·d),平均值(-8.02±15.85)mmol/(m^(2)·d),与其他岩溶湖库相比,水生植物丰富的草海在两个极端水文期CO_(2)扩散通量相对较低,总体表现为大气CO_(2)的汇.

In order to explore the temporal and spatial distribution of the partial pressure of carbon dioxide(pCO_(2))and its diffusion flux in the surface water of karst wetland,the largest karst wetlands in China,Weining Chaohai,Guizhou Province,was selected as the research object.The surface wetland water of Lake Caohai was systematically collected through the method of grid placement in July(wet season)and December(dry season),respectively,in 2019.The physicochemical parameters and ion composition of the water samples were measured,the pCO_(2)of the water was calculated by PHREEQCI,and the diffusion flux of carbon dioxide(CO_(2))at the water-air interface was estimated base on the gas diffusion model proposed by Cole.The results show that the variation of pCO_(2)in the surface water of Lake Caohai wetland ranges from 0.44μatm to 645.65μatm in the wet season,with an average value of(55.94±124.73)μatm,while 35.48μatm to 707.95μatm in the dry season,with an average value of(310.46±173.54)μatm.In general,the distribution of pCO_(2)was higher in dry season than in wet season,and higher in the eastern lake area and the entrance of river to the lake but undersaturated in the midwest area of the study region,spatially.The diffusion flux of CO_(2)in Lake Caohai wetland water ranges from-43.27 mmol/(m^(2)·d)to 27.16 mmol/(m^(2)·d),with an average value of(-34.49±12.93)mmol/(m^(2)·d)in the wet season,while ranges from-33.36 mmol/(m^(2)·d)to 28.15 mmol/(m^(2)·d),with an average value of(-8.02±15.85)mmol/(m^(2)·d)in the dry season.Compared with other karst lakes and reservoirs,Lake Caohai,which is rich in aquatic plants,has relatively low CO_(2)diffusion flux during the two extreme hydrological periods,and is generally a sink of atmospheric CO_(2).