Vertical Distribution Of Dissolved Organic Matter In The Acid Mine Drainage Reservoir And The Molecular Component Characterization

Acid mine drainage(AMD)is one of the typical extreme environments on earth.Identification of the source and components of soluble organic matter(DOM)is helpful to understand the natural evolution process of AMD water bodies,which is of guiding significance for AMD restoration.In this paper,Fourier transform ion cyclotron resonance mass spectrometry(FT-ICR MS)and three-dimensional fluorescence(3D-EEM)were combined to analyze the source and component characteristics of the DOM in an AMD library.The results are as follows:(1)DOM in June,October 2018 and March 2019:3D-EEM identified that DOM samples of June 2018 only contained tryptophan fluorescence peaks,however,fulvic acid and tryptophan fluorescence peaks were both identified in October 2018 and March 2019.The results of FI,HIX and BIX indicated that DOM in June 2018 mainly came from internal sources,however,the samples of the last two quarters were influenced by both internal and external sources.On the molecular level,FT-ICR MS further revealed that DOM mainly contains three categories of compounds(CHO,CHON,CHOS,CHONS).It should be noted that CHONS compounds were only detected in the samples in October 2018,and the compound type diagram showed that compared with the first quarter,DOM samples in the latter two quarters have more abundant compound types.The content of endogenous components in samples in June 2018 was relatively high(66-75%),and the content of endogenous components in samples in the next two quarters(October 2018 and March 2019)was relatively low.(2)The spatial distribution characteristics and source of DOM in June,2018: 3D-EEM identified that DOM contained two dominant substances in the fluorescence components,namely endogenous tryptophan fluorescence peaks and exogenous fulvic acid fluorescence peaks.The results of FI,HIX and BIX indicated that DOM was mainly endogenous.FT-ICR MS results show that DOM mainly contains three major categories of compounds(CHO,CHON,CHOS).In terms of spatial distribution,CHON compounds dominated at 0.5 m,while CHO compounds dominated.The content of lipids,sugars and aromatic structures in DOM is the highest.As the depth increases,the lipid content first increases and then decreases.The spatial variation trend of saccharide and aromatic structure was opposite.(3)DOM of surface water in June,2019: 3D-EEM results showed that,compared ith the far-shore point(point 3),the exogenous fulvic acid fluorescence peaks identified at the near-shore point(point 1 and 2)were stronger.The results of the three-dimensional fluorescence characteristic indexes(FI,HIX,BIX)showed that point 1 and point 2 may contain both exogenous and endogenous DOM,while point 3 was mainly endogenous DOM generated by the metabolism of algae and water microorganisms due to its distance from the offshore.At the molecular level,FT-ICR MS further indicates that the relative content of endogenous components(lipids,aliphatic/protein,carbohydrates)is the lowest(30%)at point 1,while the relative content is relatively high at points 2 and 3.