喀斯特流域是岩石风化碳汇的关键区域,同时也是CO2 逸散研究的热点区域.为探究喀斯特地下河涌出后CO2 分压(pCO2)及其逸散通量的时空变化格局,选择喀斯特流域巴马盘阳河为对象,分析水体的pH、碱度、总溶解性固体(TDS)、溶解无机碳(DIC)、溶解有机碳(DOC)、pCO2 的时空变化特征,探讨pCO2 的调控因素并估算了CO2 逸散通量.结果表明,流域内地下水碱度、TDS、DIC和pCO2 显著高于地表水,表明喀斯特碳酸盐风化释放大量DIC进入地下水,地下水涌出后产生CO2 逸散降低了地表水DIC含量和pCO2.在时间尺度上,旱季常规地表、地下水的碱度、TDS、DIC、pCO2、CO2 逸散通量均显著高于雨季,主要归结于雨季雨水的稀释效应.然而次降雨事件下地表、地下水的pH、碱度、TDS、DIC、DOC、pCO2 无显著性差异,可能由于降雨量不足或降雨持续时间短.研究期间,巴马盘阳河流域地表水、地下水CO2 逸散通量范围分别为-0.10～9.20 kg C m-2 year-1,-0.12～17.28 kg C m-2 year-1,平均CO2 逸散通量分别为 1.06±1.46 kg C m-2 year-1 和 2.40±3.14 kg C m-2 year-1,远高于全球主要大型流域的平均CO2 逸散通量(0.64 kg C m-2 year-1).阐明喀斯特流域的CO2 逸散通量及其时空变化特征对准确评估河流碳收支状况与评估岩石风化碳汇具有重要意义.
Spatiotemporal patterns of CO2 efflux fluxes from the outflow of karst underground river:A case study of the Panyang river in Bama,Guangxi
Karst basins are key regions for rock weathering and carbon sinks.Because water bodies in karst basins contain high concentrations of dissolved inorganic carbon(DIC),and can affect carbon cycle through both lateral migration of DIC and vertical efflux of CO2,they become research hotspots for CO2 efflux.Although there have been many studies on CO2 efflux fluxes in karst rivers,our understanding is still limited in terms of the spatiotemporal variations in CO2 efflux fluxes of water bodies from the outflow of karst underground rivers.In order to explore the spatiotemporal patterns of partial pressure of carbon dioxide(pCO2)and CO2 efflux flux from the outflow of karst underground rivers,this study focused on the Panyang river in Bama in the karst area of Southwest China.Monthly routine sampling of surface water and groundwater as well as sampling based on rainfall events was conducted from July 2022 to April 2023.The spatiotemporal variations of pH,alkalinity,total dissolved solids(TDS),DIC,dissolved organic carbon(DOC)and pCO2 in both the surface water and underground water were explored.The relationships between DIC,DOC and pCO2,as well as the relationships between TDS,alkalinity,and DIC,were also analyzed.The controlling factors of pCO2 were discussed,and the CO2 efflux flux was estimated.The results showed that alkalinity,TDS,DIC and pCO2 of groundwater in the basin were significantly higher than those of surface water,indicating that karst carbonate weathering released a large amount of DIC into groundwater,and the outflow of groundwater resulted in the CO2 efflux,reducing the DIC content and pCO2 of surface water.There was no significant difference in DIC concentrations and pCO2 of surface water from upstream to downstream,indicating that groundwater could release CO2 into the atmosphere in a short time and quickly reached equilibrium.During the rainy season,DIC and pCO2 of groundwater showed an increasing trend from upstream to downstream,while during the dry season,they showed a decreasing trend,indicating that rock weathering during groundwater recharge is an important source of inorganic carbon in groundwater.Alkalinity,TDS,DIC,pCO2 and CO2 efflux flux of surface water and groundwater during the dry season were significantly higher than those during the rainy season,mainly due to the dilution effect of rainwater during the rainy season.In addition,there were high DOC concentrations during the dry season,and the mineralization of DOC contributed directly to CO2 production,which also led to higher pCO2 in the dry season compared to the rainy season.Overall,there were no significant differences in pH,alkalinity,TDS,DIC,DOC and pCO2 of surface water and groundwater under rainfall events,possibly due to insufficient rainfall or its short duration.However,several samples during rainfall events showed significantly higher pCO2 than in the regular rainy seasons,because the continuous heavy rainfall likely raised the water level of underground rivers and supplied high CO2 concentrations from groundwater to surface rivers.There was no significant correlation between DOC and pCO2,possibly because the carbon input from other sources disrupted the coupling relationship between DOC and pCO2.These sources include soil CO2,organic carbon synthesized by CO2 that was absorbed by photosynthesis of plants,and human activities.A large amount of carbonate and other salt-based ions released from carbonate rocks into groundwater through dissolution increased DIC content,TDS and alkalinity,which contributed to a significantly positive correlation between DIC and indicators such as alkalinity and TDS.The CO2 efflux flux of surface water in the Panyang river basin during the dry season(2.05±1.89 kg C m-2 year-1)was significantly higher than that during the rainy season(0.40±0.30 kg C m-2 year-1),and the CO2 efflux flux of groundwater during the dry season(4.72±4.15 kg C m-2 year-1)was about 4.6 times higher than that during the rainy season(1.03±0.74 kg C m-2 year-1).During the study period,the CO2 efflux fluxes of surface water and groundwater in the Panyang river basin ranged from-0.10 to 9.20 kg C m-2 year-1 and-0.12 to 17.28 kg C m-2 year-1,with average CO2 efflux fluxes of 1.06±1.46 kg C m-2 year-1 and 2.40±3.14 kg C m-2 year-1,respectively,which were much higher than the average CO2 efflux fluxes of major global river basins(0.64 kg C m-2 year-1).Understanding the CO2 efflux flux and its spatiotemporal variations in karst basins is of great significance for us to accurately assess the carbon budget of rivers and to evaluate the role of rock weathering as a carbon sink.
karst springdissolved inorganic carbonriver CO2 partial pressureCO2 efflux flux
万方数据
