Characteristics And Sources Of Soil Dissolved Organic Matter In Typical Ecosystems In Tianjin

With the intensification of global warming,pedosphere has attracted extensive attention as an important carbon pool in the global carbon cycle.Dissolved organic matter（DOM）is the most active organic carbon pool in soil,and its abundance is generally expressed by dissolved organic carbon（DOC）.As important carbon sinks in the world,forests,oceans and lakes are deeply involved in the process of global carbon cycle.In recent years,a large number of industrial and agricultural wastewater and human activities have affected the distribution and source of soil DOM.Taking the soils and/or sediments of Baxianshan forest,Yuqiao reservoir,Duliujian river estuary and the near coasts of Bohai Sea as the research object,the characteristics of DOC were analyzed by using Fourier infrared spectroscopy,UV-vis spectroscopy and three-dimensional fluorescence spectroscopy.Then,the spatial distribution,sources and influencing factors of DOM were discussed from the combination of DOC and environmental factors.The findings of the structural composition,distribution characteristics and sources ofl DOM in different typical ecosystems in Tianjin will help us get a better understanding of the carbon sink capacity of different ecosystems,and provide basic data and new ideas for achieving the"double carbon"goal.The main results of the study are as follows:（1）The types of soil functional groups in different ecosystems are roughly the same.Most absorption peaks belong to sugars,fats,amino acids,phenolic compounds,aromatic hydrocarbons and silicate minerals,and water content（MC）,p H,total nitrogen（TN）,electrical conductivity（EC）,total carbon（TC）and total phosphorus（TP）have significant impacts on the distribution of soil functional groups.（2）The highest DOM abundance was in forest ecosystem.With the decreases of altitude gradient,DOC concentration increases first and then decreases.The spatial distribution of DOC in the sediments of Duliujian river estuary and Yuqiao reservoir are high in the center and low around the water ecosystems.The spatial distribution of DOC in the sediments of the coasts of Bohai Sea is high near the coast and low far from the coast.CDOM concentration and DOC concentration have similar distribution changes in all the study ecosystems.At the same time,EC,MC and p H are significantly negatively correlated with DOC concentration,while TC and TN are significantly positively correlated with DOC concentration.（3）According to the UV absorption spectrum parameters,DOM of the forest,reservoir,coasts and estuary are both exogenous and endogenous.SUVA₂₅₄ was significantly positively correlated with SUVA₂₆₀,indicating that the hydrophobicity of DOM was closely related to the aromatic structure.E₂/E₃ was positively correlated with E₃/E₄,and the molecular weight of humus was significantly correlated with the degree of humification.（4）According to the parallel factors analysis,the different components of different ecosystems are mainly protein-like and humus-like things.DOM in forest soil mainly comes from exogenous input,and its capacity for self generating is low.DOM in reservoir sediment mainly comes from the dual roles of endogenous and exogenous inputs,and its capacity for self generating is high.DOM in estuarine sediment mainly comes from the dual roles of endogenous and exogenous inputs,and the capacity for self generating is relatively moderate.DOM in coastal sediment comes from the dual roles of endogenous and exogenous inputs,and its capacity for self generating is high and produced by new organisms of bacteria.（5）According to the numerical analysis of r（A/C）and r（T/C）,except the soil of forest ecosystem,the sediments of other aquatic ecosystems had been polluted in varying degrees.On the whole,pollution of the sediment in coasts of Bohai Sea is the most serious of all.