Soil Organic Matter And Its Three-dimensional Fluorescence Characteristics In Coastal Wetlands Of Jiaozhou Bay

This study selected four typical types of wetlands around Jiaozhou Bay including Spartina anglica wetland,the barren wetland,Suaeda glauca wetland,and Phragmites australis wetland,to compare the contents of soil organic matter(SOM)and analyze the contents and characteristic of three-dimensional fluorescence spectrum(3DEEMs)of soil dissolved organic matter(DOM).The aim of this study was to reveal the distribution,sources,migration,and transformation of SOM in coastal wetlands,and to provide the basic information for further revealing the environmental behavior of organic matter in Jiaozhou Bay wetland.The results showed that:(1)The temporal and spatial distributions of SOM in Jiaozhou Bay coastal wetlands were studied.Our results showed that the SOM contents of Spartina anglica wetland,Suaeda glauca wetland,and Phragmites australis wetland all decreased with the increasing soil depth except that the concentration of SOM in the barren wetland showed a decreasing trend first,and then increased slightly along soil profile depth.Spartina anglica wetland ranked the first in SOM content,followed by the barren wetland,Suaeda glauca wetland and Phragmites australis wetland.Seasonally,the SOM contents in Jiaozhou Bay coastal wetlands were in an order of Spring >Summer > Autumn > Winter.The hydrology,climate,vegetation,soil microorganism,and human activity were the important factors influencing temporal-spatial variation of DOM in soil.In addition,the soil parameters including soil salinity,soil moisture content,total nitrogen(TN),pH,and soil bulk density were also measured.Correlation analysis demonstrated that SOM content was positively correlated with soil salinity,moisture content,TN,and C/N.Negative relationships were observed between SOM contents and pH,and between SOM contents and soil bulk density.Soil environmental factors interacted with each other and affected the accumulation of wetland SOM.(2)The storage of SOM in Jiaozhou Bay coastal wetlands was studied.The results showed that the carbon densities of soil profile were in a decreasing order of the barren wetland,Phragmites australis wetland and Suaeda glauca wetland.The above results indicated that there were some differences in the distributions of SOM and carbon density among various types of wetlands.It was mainly related to soil bulk density,topography,temperature,hydrological environment and so on.Further,the carbon stock per unit area of the barren wetland was significantly higher than those of Phragmites australis wetland and Suaeda glauca wetland due to the carbon density and thickness of carbon storage layer playing a significant role in the carbon sink process of coastal wetlands.(3)The spatial distribution of DOM in Jiaozhou Bay coastal wetlands was studied.The results showed that the contents of soil DOM in four types of wetlands alldecreased with the increasing soil depth,and Spartina anglica wetland ranked the first in the contents of soil DOM,followed by the barren wetland,Suaeda glauca wetland and Phragmites australis wetland.The results showed that the SOM pool was unstable,which was not conducive to the accumulation of organic matter.(4)Three dimensional fluorescent characteristics of DOM in Jiaozhou Bay coastal wetlands were studied.The results showed that five fluorescence peaks including B,T,A,D,and C were found in the 3DEEMs,which were assigned to tyrosine-like-,tryptophan-like,phenol-like,soluble microbial byproduct-like,and humic-like substances,respectively.Fluorescence integration(FRI)was applied in the qualitative analysis of five components.The results showed that tryptophan-like,phenol-like,and tyrosine-ike substances ranked in top three in content,soluble microbial byproduct-like and humic-like were not significantly different.Pearson correlation analysis demonstrated that the five components of DOM had a positive correlation between any two,and they were all positively related to DOM contents.In addition,there exist different correlations between the five components of DOM and total phosphorus(TP),available phosphorus(A-P),and TN.The soil DOM in the four types of wetlands was mainly produced by biotic interactions,and the degree of humification was relatively low.