Distribution Characteristics Of Dissolved Inorganic Carbon And Inorganic Carbon Sequestration Mechanism Of Coastal Saline-alkali Wetlands In Jiaozhou Bay, China

With the increase of atmospheric CO₂ concentration,the problem of“missing sink”in the field of global change and carbon cycle has attracted more and more attention of international academia.As the latest discovery that may explain the problem of“missing sink”,the inorganic carbon sequestration process of aline-alkali soil has aroused extensive and intense discussion.In this study,estuary wetlands of Dagu River and Yanghe River,located in Jiaozhou Bay,were selected as the study areas.The soil samples were collected by stratified sampling in the mudflat which is parallel to the coastal zone and the river flat which is perpendicular to the coastal zone.We determined to use the soil dissolved inorganic carbon?DIC?content,relevant ion content,as well as soil physical and chemical properties to analyse the distribution characteristics of soil DIC and the factors.Indoor simulation experiments about the CO₂absorption process of soil samples were carried out with different salinity and alkalinity to analyse the leaching characteristics of coastal saline-alkali soil,and to explore the effects of soil salinity and alkalinity on soil inorganic carbon sequestration capacity.Carbon isotope tracer experiments were carried out to determine the mechanism of atmospheric CO₂ inorganic absorption.The migration and transformation of soil DIC which produced by CO₂ absorption process were also preliminarily discussed.The main conclusions are as follows:In the direction of parallel to the coastal zone,the farther from the estuary,the higher DIC content of the soil.Scouring action of water bodies led to the lowest content of soil DIC content in the river estuary.In the direction of perpendicular to the coastal zone,soil DIC content decreased first and then increased with the rising distance from sea,which were mainly affected by human activities.Invasion of spartina alterniflora caused the lower soil DIC content than that in mudflat,which was due to the root transformation of invasive species.Aquaculture activities changed the environmental factors of aquaculture ponds,and then changed the distribution of soil DIC.The DIC content in the surface soil was higher than that in the mudflat,while in the other soil layers were slightly lower than that in the mudflat.Laboratory simulation experiments showed that the leaching processes caused by the tidal and rainfall of coastal wetlands has a synergtic influence on coastal saline-alkali soils.In leaching process,the obvious changing of leached soils and leachates were determined by the strength of interaction between ions and soil colloids,and were related to the precipitation and dissolution equilibrium of ions in soil.The simulated leaching experiments also confirmed that the inorganic carbon sequestration was common in coastal saline-alkali wetlands,and the effects of soil alkalinity on the CO₂ uptake capacity was greater than soil salinity.Simulated leaching experiments showed that?i?the dissolution/precipitation of carbonate system and?ii?the leaching/absorption of atmospheric CO₂ were the two mechanisms of inorganic carbon sequestration in coastal saline-alkali wetlands.And the stable isotope tracer experiments further confirmed that the leaching/absorption of atmosphere CO₂ is the dominate mechanism.The specific mechanism can be speculated as:The atmospheric CO₂ is absorbed by the saline-alkaline soil solutions and then form DIC,which can move to deep soil or eventually enter the ocean through the transport of groundwater.In addition,the salinity and alkalinity of the leached soil can be recovered immediately by the regular tide and rainfall,and the absorption of atmospheric CO₂ by leaching/absorption can be maintained successively and eventually form the carbon sink.