Adsorption and sequestration of soil-dissolved organic matter by ferrihydrite
A ferrihydrite was synthesized from ferric chloride and sodium hydroxide using the hydrolysis method.The absorption behavior of soil-dissolved organic matter(DOM)on ferrihydrite was studied by mixing different concentrations of ferrihydrite with soil-extracted DOM solution.UV-Vis absorption spectra analysis showed that in the range of 10-30 g·L-1 ferrihydrite concentration,the adsorption capacity of ferrihydrite to soil DOM is positively correlated with ferrihydrite concentration.The significant decrease in the absorption slope S275-295 indicates that ferrihydrite preferentially adsorbs macromolecular aromatic compounds in soil DOM.Three-dimensional fluorescence spectra coupled parallel factor model(EEM-PARAFAC)analysis showed that soil DOM comprises three fluorescent components.They were humus-like component C1(Ex/Em=240/410),tryptophan-like component C2[Ex/Em=290(240)/350],and tyrosine-like component C3(Ex/Em=270/300).The fluorescent intensity of the three components showed a significant decreasing trend with incubation time.The decrease in the humic-like C1 component was greater than for the protein-like components of C2 and C3.After adsorption,soil DOM's humification index(HIX)decreased significantly.Meanwhile,the biological index(BIX)increased significantly,indicating that the relative proportion of humus fraction in soil DOM decreased and the relative proportion of autogenetic fraction increased with the process of adsorption.In conclusion,ferrihydrite has a significant adsorption and removal effect on soil DOM,and the adsorption effect on macromolecular humus is more potent than that of small molecular amino acids.The retention of soil DOM molecules by ferrihydrite can increase the bioavailability of soil organic matter and improve the soil environment.
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