Impact On Lake Sediment Phosphorus Adsorption Characteristics And Structure Of Plant Dissolved Organic Matter

By using UV-vis, Fourier transform infrared (FT-IR) and the three-dimensional excitation emission matrix fluorescence (3DEEM) spectroscopies, chemical structures of the water dissolved organic matters (DOM) extracted from the typical terrestrial and aquatic plant in or around Lake Dianchi were investigated. The results showed that the characters of UV-visible spectra were similar between the DOMs derived from the terrestrial and the aquatic plants. Ultraviolet absorbance of the DOM samples decreased monotonically with increase of wavelength. The SUV A254values of DOM derived from the terrestrial plants were greater than those from aquatic ones, which indicated the higher humification degree of the DOM from the terrestrial A250/A365values of the leaf DOMs were less than those from the stems, which illustrated that the aromaticity and molecular weight of leaf DOMs were higher than those of stem DOMs. The characteristic peaks of—COO-,—CH2,—C=O,—OH and—NH2were clearly shown in DOMs from both terrestrial and aquatic plants, and they were the main function groups in DOMs of these species. The3D-EEM spectrum showed that the DOMs from stems of the terrestrial plant contained fulvic acid and there was humic acid in the leaf DOMs of these species. DOMs (stem and leaves) derived from the aquatic plants mainly contained fulvic acid, except the water hyacinth which had humic acid in its DOM. Excepting water hyacinth, DOMs from stems of all the other plants contained the tryptophan-like organic matters, but there were no similar fluorophore showed in their leaf DOMs.Ground dry leaves of two emerged macrophytes Zizania Caduciflora and Phragmites australis from Lake Dianchi were soaked in distilled water in laboratory to track their DOM release process.The results showed that:(1) during soaking, concentration of DOMhich was released to the overlying water by the two speciesincreased at first, then reduced and increased again at last. Concentrations of DOC, DON, and DOP released by both species reached their peaks at the8th,8th, and24th hour, respecitvely;2) the two species showed the same DOM release trend, i.e., release rates and intensities of DOC, DON, and DOP by both species reached the peaks at the8th hour, and for both of them, the release rates and intensities of DOC, DON, and DOP at the8th hour decreased in the order of DOC>DON>DOP;(3) the SUVA254value obtained by the UV-visible spectroscopy increased at first and then decreased;4)Fourier transform infrared (FT-IR) spectroscopy showed that the characteristic peak—OH disappeared during the decomposion process;5)intensity of the humic-acid fluorescence peak as showed by the3D-EEM fluorescence intensity (F/DOC) increased along with degradation.The kinetic adsorption of P from DOM of Z. caduciflora and P.australis to sediment of Lake Dianchi was studied. Effects of plant DOM on the P adsorption to sediment were investigated and P absorption without addition of DOM was set as the blank. The results showed that:The kinetic adsorption process of P to sediment was divided into two stages:the fast adsorption stage in the initial four hours, and the slow adsorption stage from the4th to24th hour. The adsorption equilibrium reached at the24th hour. In the first stage,90.86%and87.07%of the adsorption of P from DOM of Z. caduciflora and P.australis, respectively finished. During the adsorption process, total adsorption capacity and adsorption rate of P from DOM of Z. caduciflora were higher than those of P from DOM of P.australis. The maximum adsorption rates of P from DOM of Z. caduciflora [0.33mg·(g·L)-1] and P. australis [0.23mg·(g—L)-1] reached within the initial2h. Diffusion equation had the best simulation on adsorption of P from the DOM to sediment of Lake Dianchi. The kinetic curves of P adsorption with and without DOM were similar. Addition of DOM delayed the time for equilibrium from the4th to24th hour, and made the adsorption rate slower than the blank. However, the adsorption capacity was still1.66mg·g-1. The dual constant equation was the best one to describe the real effect of plant DOM on P adsorption to the sediment.