Spatial And Temporal Distribution Characteristics Of DOM In Water Bodies Of Xi’an City And The Influence Of Drainage Outlets On It

Dissolved Organic Matter(DOM)widely exists in lakes,rivers,oceans,rainwater and other natural water bodies.It is a mixture of a variety of Organic Matter,including fulvic acid,humic acid,aromatic polymer and other soluble Organic Matter.DOM has attracted extensive attention because of its large number and variety of functional groups.Studies have found that DOM can interact with heavy metal ions or organic pollutants,which provides a new idea for the treatment of soil or water pollution.DOM is an important nutrient in water environment,which provides necessary elements for the metabolism of various microorganisms in water.At the same time,DOM is also an important carbon pool in the water environment.Its storage is equivalent to that of atmospheric carbon pool,and it is an indispensable part of the global carbon cycle.Studies have shown that DOM will decompose when exposed to light,generating carbon dioxide,inorganic salts and small molecular organic compounds,among which carbon dioxide will enter the atmosphere to participate in the carbon cycle,while small molecular organic compounds will be used by microorganisms and eventually be converted into carbon dioxide and enter the atmosphere.The contents and types of organic matter in DOM in different water bodies are different,which are affected by environmental factors.Therefore,some scholars take DOM as an indicator to measure the quality of water quality and divide it into endogenous DOM affected by sewage and exogenous DOM affected by natural environment.DOM composition and structure are very complex,so how to characterize the DOM becomes the focus.Three-dimensional fluorescence spectroscopy(3D-EEM)utilizes a variety of components with fluorescence characteristics such as proteins and aromatic hydrocarbons in DOM to analyze and characterize DOM.Three-dimensional fluorescence spectroscopy has the characteristics of low dosage,high sensitivity and no damage to the sample,and compared with the traditional two-dimensional fluorescence spectrum analysis,three-dimensional fluorescence spectroscopy can provide the peak of fluorescence peak and facilitate the comparison of the relative content of each fluorescence component.DOM 3D fluorescence analysis results can also be used to calculate fluorescence characteristic parameters,which can trace the source of DOM in water and distinguish endogenous and exogenous DOM.During the spring and autumn points collected xi river pollution serious Zao He,action and ba river water samples,including the surface and on the river,the sewage near the outlet of the water samples after processing,the determination of total organic carbon(TOC),three-dimensional fluorescence spectrometry(3D-EEM)and parallel factor analysis(PARAFAC)technology,the analysis of water samples in the DOM.The results of parallel factor analysis showed that among the three rivers in spring,Zao River was the most severely polluted,followed by Ba River,and Chan River was the least polluted.In autumn,the contents of proteinoid components in the three rivers all decreased significantly,indicating that the pollution degree of the water was reduced,and the change of the Zao River was the most obvious.This change was related to the factors affected by the season,such as temperature,and the closure of part of the drainage outlets.As can be seen from the fluorescence characteristic parameters,in DOM of the three rivers,autogenesis accounted for a large proportion,while in humus,endogenous humus accounted for a large proportion,indicating that microbial metabolism was more active in the three rivers.In autumn,FI index increases while Bix index decreases,which may be caused by the influence of temperature and other conditions.The three-dimensional fluorescence spectra of the three river samples generally show 2-4 peaks,the upstream and downstream water samples that are less polluted can show 4 peaks,the middle water samples that are more polluted through the urban area can only show 2 peaks,and the three-dimensional fluorescence spectra of the Zao River water sample is particularly obvious.The three-dimensional fluorescence spectra in autumn are significantly different from those in spring.It can be clearly seen that the fluorescence peaks in some maps change from 2 to 3 or 4.Meanwhile,the fluorescence peaks shift to humus-like substances,and the fluorescence peaks in humus-like areas increase,indicating that the proportion of humus-like components in autumn water samples increases,and the water quality gradually gets better.The turbidity,total dissolved solids and dissolved oxygen contents of water samples in autumn are lower than those in spring,which also supports this conclusion.