Composition,Spectral Characteristics And Source Analysis Of Soils In Different Land Use Types

Using three-dimensional fluorescence spectrophotometry,ultraviolet spectroscopy and EEMs-PARAFAC,etc.,the physical and chemical properties,DOC content,fluorescence and ultraviolet spectroscopy characteristics and sources of DOM in the soil under the vertical characteristics of different land types were clarified.Using the SPSS method,reveal the correlation between the ultraviolet and fluorescence parameters used to express the content,nature and source of DOM in the soil.It is helpful to understand the distribution and properties of DOM in different deep soil profiles and its biogeochemical effects in the natural environment.Through EEMs-PARAFAC analysis,it is determined that the DOM in the soil of educational land,park land,industrial land and agricultural land mainly contains 2 types of humus and type 1 tyrosine,type 1 humus and type 1 tryptophan,type 2 humus,and type 2 respectively.humus.The four types of land use types all contain UV humus with Ex/Em at 245-260 nm/450-465 nm.The water content,pH value and ORP value of the soil samples collected from 0 to 80cm depth were 12.90%-22.22%,7.09-8.59 and 126-187 m V,respectively.The soil is neutral or slightly alkaline,and the pH value of agricultural land is significantly higher than that of educational land,park land and industrial land.The DOC content of DOM in the soil is 30-115 mg/kg.The content of DOC in the soil of 20-40 cm is basically higher in educational land,industrial land and agricultural land.The absorption coefficientα300,α350 andα355 of DOM in the surface soil of educational land,industrial land and agricultural land are basically relatively large.The aromatization degree of DOM in most surface soils is relatively high.The benzene content of DOM in the surface or 20-40 cm soil is relatively large.The degree of ring substitution is basically high.The molecular weight of DOM in industrial land is relatively lower than that in agricultural land.The degree of humification of DOM,the degree of polymerization of the benzene ring C skeleton and the molecular weight in the soil of industrial land are lower than those of educational land.Humic acid is the main component of DOM in the soil of educational land,and fulvic acid is the main component of DOM in the surface soil of industrial land.The FI,BIX,HIX andβ:αvalues of DOM in educational land,park land,industrial land and agricultural land are 1.57–2.32,0.32–1.15,0.64–6.50 and 0.53–0.99,respectively.The humus contained in DOM in the soil is mainly a mixture of terrestrial and biological sources or mainly from biological sources.Compared with other depths of the same type of soil,the humification and aroma of DOM in the surface soil of park land and industrial land are stronger;the proportion of biological sources of DOM in the surface soil of industrial land is the smallest;industrial land soil（20-40 cm）The proportion and biological activity of nascent DOM in the middle DOM are relatively large in the overall DOM.Compared with agricultural land,the proportion of biological sources of DOM in the soil of industrial land at the same depth is relatively large,and the characteristics of autogenic origin are relatively strong,and the proportion of new DOM in the overall DOM and the biological activity are relatively large.Compared with educational land and park land,the humus of DOM in the soil of agricultural land at the same depth has a higher degree of humification,and its aroma and stability are also greater.UV₂₅₄,α₃₀₀,α₃₅₀ andα₃₅₅ of DOM in soil showed a significant positive correlation with each other（P<0.01）.SUVA₂₅₄of DOM in soil is significantly negatively correlated with E₄/E₆ and FI,E₃/E₄ and BIX andβ:α,and UV₂₅₃/UV₂₀₃;SUVA₂₅₄ and HIX are significantly positively correlated,E₂/E₃ is correlated with S_275-295,E₃/E₄,E₄/E₆ and HIX showed a significant positive correlation.The FI,BIX andβ:αof DOM in the soil are significantly negatively correlated with HIX（P<0.01）,and BIX andβ:αare significantly positively correlated（P<0.01）,that is,the stronger the self-generating characteristics of DOM in the soil,the new The greater the proportion of DOM in the overall DOM and its biological activity,the lower the degree of humification.The sum of the fluorescence intensity of fluorescence peak A and the fluorescence intensity of all fluorescence peaks can reflect the organic content or relative content of DOM in the soil.