Distribution Characteristics And Influencing Factors Of Organic And Inorganic Carbon In Tidal Flats And Salt Marshes Along The Coast Of Northern Jiangsu

Tidal flats and salt marshes are located in the interactive zone between the ocean and the land,and are sensitive to natural changes,human activities,and global changes.They are the main interface for most terrestrial carbon to enter the marine environment.Due to this zone characterized by high primary productivity,continuous deposition and relatively low decomposition rate,large amounts of organic carbon(OC)and inorganic carbon(IC)are stored,which play an important role in global climate change.Therefore,a clear understanding of the distribution characteristics of OC and IC in this zone and their influencing factors is crucial to understanding their impact on global climate change.Therefore,in this paper,the surface sediments of 4 tidal flats sections(Sheyang(Sect-1),Doulong(Sect-2),Dongtai(Sect-3),Jianggang(Sect-4))along the northern coast of Subei and the columnar sediments under Spartina alterniflora and Phragmites australis in salt marshes are used as the research objects.The OC and IC content of tidal flat and salt marsh sediments,the physical and chemical properties of tidal flat(grain size,nutrient elements(N,P,S),p H,salinity(SAL)),and physical and chemical properties of salt marsh sediments(grain size,nutrient elements(N,P,S),p H,salinity(SAL),water content)were measured,and the stable carbon isotope composition(?¹³C)of organic carbon in tidal flat sediments were analyzed.The distribution characteristics of OC and IC in the two sedimentary environments were discussed respectively.And the main factors affecting the distribution of OC and IC distribution in the two sedimentary environments are revealed.At the same time,a two-terminal element model based on the?¹³C evaluated the contribution rate of land-source and sea-source organic carbon in the tidal flat area,in order to further understand the influence mechanism of the distribution of organic carbon sources.Research shows:(1)The average contents of OC and IC in the surface sediments of the 4 sections under the tidal flat system are respectively 0.74g/kg?3.87g/kg,8.10g/kg?10.73g/kg,and the OC spatial differentiation of each section is far greater than that of IC,and both OC and IC show a gradually increasing trend from sea to land.The important influencing factors of OC and IC in the tidal flat system are the sediment size and N content.As an important environmental element,vegetation along the tidal flat has a profound impact on the distribution trend of OC and IC from sea to land.The greater the vegetation coverage,the greater the contribution to OC and the stronger the interception of OC and IC.The effect of vegetation on OC and IC is significant.(2)The average OC content of sediment under Spartina alterniflora and Phragmites australis in salt marsh is between 3.22g/kg?4.11g/kg,0.96g/kg?1.36g/kg,and the average content of IC is respectively between 7.90g/kg?8.85g/kg,7.90g/kg?9.25g/kg.The OC and IC contents of the sediments covered by Spartina alterniflora and Phragmites australis both decreased with the increase of depth.The OC content of the sediments covered by Spartina alterniflora is much higher than that of Phragmites australis,and the IC content is not much different.The vegetation type has a significant impact on OC.The main influencing factors of OC under Spartina alterniflora in salt marsh were sediment size,N content and water content,and the main influencing factors of IC under Spartina alterniflora in salt marsh were sediment size and OC.(3)The trends of OC and IC under the tidal flat and salt marsh systems are consistent,and they show a positive coupling relationship.For tidal flats,this coupling relationship is largely due to the greater contribution of nearshore vegetation to OC and the strong retention capacity of IC.At the same time,it does not rule out that OC can promote IC to a certain extent.The salt marsh system may also be affected by the specific depositional environment and the contribution of OC to IC.(4)The average values of?¹³C of the 4 sections are-26.57‰,-26.10‰,-25.77‰,-22.47‰.Affected by the conditions of the coastal estuary,the OC of Sect-1,Sect-2,and Sect-3 are mainly terrigenous contributions,and the average terrigenous contribution are 82.09%,76.22%,72.11%respectively.The OC of Sect-4 is mainly contributed by sea sources,and the average sea source contribution is 69.17%.The?¹³C values of the four sections and the contribution of marine organic carbon calculated based on the two-end element model to the four sections gradually increase from sea to land.On the one hand,they are affected by the higher?¹³C value of the nearshore C4plant Spartina alterniflora itself.On the other hand,it is due to the weakening of marine hydrodynamics on the shore to enrich marine organic carbon deposits.