福建漳江口红树林湿地溶解无机碳横向输送的研究

Lateral Transport of Dissolved Inorganic Carbon in a Mangrove Wetland in Zhangjiang Estuary,Fujian Province

红树林作为地球上最富碳的生态系统之一,是重要的蓝色碳汇。孔隙水/海底地下水排放(Submarine Groundwater Discharge,SGD)作为陆海交互作用的重要过程,是红树林碳横向输送的重要途径。本研究于2017年4月在福建省云霄县漳江口红树林潮沟处进行为期24 h的时间序列观测,并采集了河流(漳江)、孔隙水和生活污水样品,进行了镭(Ra)同位素、溶解无机碳(Dissolved Inorganic Carbon,DIC)、总碱度(Total Alkalinity,TA)、pH、流速的测定,量化了红树林溶解碳的横向输送(包括孔隙水输送和地表水输送)通量。结果表明,表层水体中DIC浓度与Ra活度(SGD示踪剂)呈正相关关系,孔隙水是潮沟DIC的重要来源,高于河流输入和污水排放。基于Ra质量平衡模型和潮动力模型估算的孔隙水交换速率为(0.2±0.1)m/d。红树林通过孔隙水交换输送至潮沟的单位红树林面积的DIC、TA、溶解有机碳(Dissolved Organic Carbon,DOC)和游离CO_(2)的通量分别为1013、1008、332和52 mmol/(m2·d);潮沟水体在潮汐作用下横向输送至河口的单位河道面积的DIC、TA、DOC和游离CO_(2)的通量分别是1136、1349、131和170 mmol/(m2·d),溶解碳主要以DIC的形式输出(占比82%)。漳江口红树林通过孔隙水向潮沟输送的溶解碳通量(3.9×104 mol/d)贡献了潮沟地表水横向输送DIC通量的89%,占红树林植被固碳量的23%,与漳江口红树林沉积物的碳埋藏量(3.2×104 mol/d)相当,是海岸带蓝碳收支的重要组成部分。

Mangroves,one of the Earth’s most carbon-rich ecosystems,serve as important blue carbon sinks.Submarine Groundwater Discharge(SGD),an important land-sea interaction process,plays a crucial role in the lateral transport of carbon within mangrove ecosystems.In this study,we conducted a 24-hour time series observation in the tidal creek of Zhangjiang Mangrove in Yunxiao County,Fujian Province,in April 2017.We collected samples from river,pore water and domestic sewage.Measurements of radium(Ra)isotopes,dissolved inorganic carbon(DIC),total alkalinity(TA),pH,and flow velocity were taken to quantify the flux of dissolved carbon in mangroves,encompassing both pore water and surface water transport.The results show that DIC concentration in surface water is positively correlated with Ra activity(SGD tracer),and pore water serves as a significant source of DIC in tidal creek,which is higher than river(Zhangjiang)input and sewage discharge.Based on the Ra mass balance model and the tidal dynamic model,we estimated the pore water exchange rate to be approximately(0.2±0.1)m/d.The fluxes of DIC,TA,dissolved organic carbon(DOC),and free CO_(2) per unit mangrove area were measured at 1013,1008,332,and 52 mmol/(m2·d),respectively.Under the influence of tides,the fluxes of DIC,TA,DOC,and free CO_(2) per unit area of tidal channel water transported to the estuary were recorded at 1136,1349,131,and 170 mmol/(m2·d),respectively.The primary export form of dissolved carbon was DIC,constituting 82%of the total.The dissolved carbon flux,totaling 3.9×104 mol/d,transported by the Zhangjiang Mangrove to the tidal creek contributed 89%of the lateral DIC flux conveyed by the surface water of the tidal creek.Additionally,it accounted for 23%of the carbon sequestration of mangrove vegetation,a proportion comparable to the carbon buried in the sediment of the Zhangjiang mangrove forest(3.2×104 mol/d).This study represents a significant component of the coastal blue carbon budget.