Spectral Characteristics Of DOM In Water Bodies And Sediments In The Yuan River Basin Under Different Land Use Types

Dissolved organic matter（DOM）refers to natural organic matter that can pass through 0.45μm filter membrane.Its fluorescence properties can be used to indicate pollution of the water environment.In the natural environment,DOM is not only the main carbon source of some microorganisms,but also an important carrier of material exchange between soil and lithosphere（such as biosphere,atmosphere,hydrosphere and lithosphere）.Soil properties and land use types are important factors affecting DOM.It is of great significance to study the water body and sediment DOM in the Yuan River Basin for water environment management in this region.In this paper,three-dimensional excitation-emission matrix fluorescence spectroscopy combined parallel factor analysis（3D-EEM-PARAFAC）,redundancy analysis and principal component analysis and other methods are used to study the difference of spectral characteristics of DOM in water and sediment in Yuan River Basin under different land use types,On this basis,the influence of physical and chemical properties of water and sediment on the spectral characteristics of DOM in water and sediment is further explored.The results of this study can provide theoretical basis for understanding the biogeochemical effects of DOM in water bodies and sediments with different land use types and water quality monitoring in the study area.The main conclusions are as follows:（1）The water quality of Yuan River generally belongs to Class II water,and the concentrations of TP and NH₄⁺in some points only exceed Class III water standard.There is no obvious difference in aromaticity,chromophoric dissolved organic matter（CDOM）concentration,molecular condensation degree of organic matter and humification degree of organic matter in Yuan River between the mainstream and tributaries.The study for different particle size water bodies（raw water with coarse particulate matter,filtered water with fine particulate matter,and ultrafiltered water without particulate matter）show that the aromaticity,CDOM concentration of organic matter in raw water（>0.45μm）are obviously higher than those in filtered water（1k Da-0.45μm）,In the Yuan River,there is little difference between protein-like substances and humic substances in the mainstream and tributaries of Yuan River.According to the spatial distribution of Fn₂₈₀and Fn₃₅₅ values in Yuan River,the water pollution in the lower reaches of Yuan River is more serious than that in the upper reaches.（2）Through 3D-EEM-PARAFAC,one humus-like fluorescent component（C1）and two protein-like fluorescent components（C2 and C3）were extracted from the water.The concentration relationship of the three fluorescent components was C1≈C2>C3,and protein-like substances were the main components.C2 components in the raw water and filtered water in the mainstream of Yuan River basin are significantly different from those in the ultrafiltered water（C1 and C3 components have no significant difference）.Redundancy analysis results show that compared with land use types,hydrochemical characteristics contribute more to spectral characteristics,but hydrochemical characteristics are inevitably affected by land use types.（3）Compared with the areas with serious nitrogen and phosphorus pollution in China,the TP and TN values of sediments in Yuan River basin are relatively low,and the TP content is increasing from upstream to downstream,which is consistent with the changes of most rivers,and the phosphorus pollution in downstream areas is relatively large.According to the analysis of DOM UV-visible spectroscopy（UV-vis）parameters of sediments in Yuan River basin,the DOC concentration and aromaticity of sediments in the lower reaches of Yuan River basin are higher than those in the upper and middle reaches,and the humification degree is slightly stronger.Combined with the land use types of Yuan River,the extensive paddy fields planted in the lower reaches,the pollution is relatively serious,and the accumulation of pollutants leads to the higher DOC concentration.According to the statistical analysis results,there is no significant difference in the humic characteristics of sediment DOM in different river sections,and there is no significant difference in the UV₂₅₄,E2/E4,E3/E4,α₃₅₅ value of sediment DOM between the main stream and tributaries of Yuan River basin.（4）According to the fluorescence spectral index analysis of sediment DOM,it can be seen that the mainstream sediment DOM of Yuan River is mainly imported from terrestrial plants,while the sediment DOM in tributaries has the dual characteristics of endogenous and terrestrial sources,the results presented by the comprehensive analysis of each spectral index indicate that the sediment DOM in Yuan River basin is mainly input from terrestrial sources,and shows a weak autogenous source characteristic,with less contribution from endogenous sources,and strongly influenced by terrestrial input or human activities.（5）The three-dimensional fluorescence analysis of sediment DOM in Yuan River by PARAFAC shows that the fluorescence components of sediment DOM in Yuan River are mainly humus,including humus component（C1）、protein-like component（C2）and humus-like component（C3,C4）.There is a significant correlation between C1,C2and C4,and the correlation coefficient is as high as 0.988,which indicates that these fluorescent components have homology and show the characteristics of terrestrial input.Through the exploration of fluorescence components and spectral index,it can be concluded that each fluorescence component has a significant negative correlation with FI value and a significant positive correlation with BIX value,which indicates that there is a big difference in DOM sources of sediments in Yuan River Basin,and it may be related to the pollution degree and input of internal and external sources of DOM.The correlation analysis between DOM fluorescence components and physical and chemical properties of sediments shows that the fluorescence peak intensity of DOM is positively correlated with TP,which indicates that there is a good correlation between terrestrial humic acids and TP,but the changes of TP and SOM concentrations can’t effectively indicate the source of organic matter and DOM in Yuan River Basin.