Spectral Characteristics Of Dissolved Organic Matter In The Pi Liqing River Basin And Its Complexation With Hg²⁺

Dissolved organic matter?DOM?is an important component of water and soil.It is rich in functional groups such as carboxyl,hydroxyl and carbonyl groups,and has strong migration,transformation,complexation and adsorption capabilities.Since the1990s,domestic and foreign scholars have conducted a series of studies on DOM in oceans,rivers and lakes.DOM plays a vital role in the carbon cycle of soil,water,ocean and sediment,as well as the environmental behavior of organic pollutants and heavy metals.Therefore,studying the source and characteristics of DOM in the whole basin is an important prerequisite for understanding the role of DOM in the process of pollutant migration and transformation.In this thesis,the Pi Li qing River Basin was selected as the research object.The spectra of water and soil DOM in the basin were studied by means of UV-Vis absorption spectroscopy,three-dimensional fluorescence spectroscopy,parallel factor analysis?PARAFAC?and modified Stern-Volmer model.Characteristics and complexation of soil DOM and Hg²⁺.The main findings are as follows:?1?The content of DOC in Pi Li qing River of the basin is between 7.273 and14.916ppm,with an average of 9.489ppm,and the coefficient of variation is 23.06%.The DOC content of the Tie chang gou ditch is between 6.35 and 12.875ppm,with an average of 9.3ppm and a coefficient of variation of 17.4%.In general,the DOC content is between 6.35 and 14.916 ppm,the average value is 9.459 ppm,and the coefficient of variation is 21.2%,indicating that the spatial difference of DOC content in the water body of the basin is small.?2?The absorption coefficient curve of DOM in water body decreases with increasing wavelength,and there is no obvious characteristic peak.The absorption band is mainly located between 240 and 450 nm,indicating that the main fluorescence peak of dissolved organic matter in the basin is between 240 and 450 nm.?3?The average value of a355 in Pi Li qing River is 2.61/m^-1,and the highest point of a355 is located in the lower reaches of Panjinbulak Village.The average value of a355 in Tie chang gou Ditch is 2.42/m-1,which is the highest value next to the brick kiln.It shows that the discharge of domestic sewage and industrial wastewater will lead to an increase in the content of dissolved organic matter in the water.The average value of SUVA254 in Tie chang gou Ditch is 1.4421 L/?mg·m?,and the average value of SUVA254 in Pili Qing river is 1.1769 L/?mg·m?.The aroma of DOI in Pi li qing River is higher.The average value of SUV260 in Tie chang gou Ditch is 1.3384 L/?mg·m?,the average value of SUVA260 in Pili Qing river is 1.1035,and the hydrophobic component in DOM of Tie chang Ditch Water is more.?4?The content of soil DOC was ranked as grassland>forest land>construction land>farmland>wasteland.The coefficient of variation of DOC content in farmland soil was 38.2%,and the spatial difference was the smallest.The coefficient of variation of DOC content in wasteland was 120.1%,and the difference in spatial distribution was the largest.There is a significant linear relationship between a355,Fn355,and DOC,DOC=0.0048a?355?+0.0096?R²=0.9661?,DOC=0.0001Fn355+0.0128?R²=0.9637?,Fn355=42.658,a?355?+125.63?R²=0.9171?,the temporal and spatial distribution of DOC can be predicted based on a?355?or Fn355.?5?The soil DOM of different elevations changes with elevation,and the fluorescence intensity also changes.From high to low,the FI values of P4^P7 are 1.43,1.60,1.45,1.49,and the BIX of P4 to P7 are 0.52,0.72,0.54,0.53,the change of vegetation type and the change of microbial content in soil.It will affect the DOM,combined with the BIX index and the FI index,indicating that the microbial content at P5?20m elevation?is higher than other elevations.With the increase of depth,the soil DOC content decreased from 0.133 mg/g to 0.105 mg/g,and the soil from shallow to deep FI was 1.50,1.65,and 1.62,respectively,and the BIX index was 0.62,0.75,and0.70 from top to bottom,respectively.The degree of humification of DOM in the topsoil is higher than that of the lower soil,while the exogenous input of microorganisms in the DOM of the lower soil is higher than that in the topsoil.?6?By parallel factor analysis,it is identified that there are three main types of dissolved organic matter in rivers in the basin,C1 Ex/Em=?254/350,432?nm,C2Ex/Em=(257/365,507 Nm,C3 Ex/Em=?245/299,391.1?nm,wherein C1 is UVC humus,C2 is UVA humus,C3 is UVA humus;there are two main dissolved organic components in the soil in the basin.C1 Ex/Em=?256/320,406.4?,C2Ex/Em=?253,497.7?,C1 is UVC type humus,and C2 is UVA type humus.?7?Fluorescence quenching occurs when soil DOM and Hg²⁺are complexed.When Hg²⁺reaches a certain concentration,the fluorescence intensity of DOM is not reduced.The humic acid-like organic matter in grassland soil DOM has stronger complexing ability with Hg²⁺.The complexation ability of fulvic acid organic matter and Hg²⁺in DOM of farmland,construction and living land and wasteland soil is stronger;the complexing ability of DOM and Hg²⁺in grassland soil is stronger.