Study On The Effect Of Dissolved Organic Matter At Freezing-Thawing And Snowmelting Processes

The effect of freezing and thawing temperatures, freezing time, and times of freeze-thaw cycles on the spectroscopic characteristics of dissolved organic matter (DOM) in dark-brown and brown earths in Liaoning Province was investigated, which are significantly affected by seasonal freezing-thawing. The results showed that the variations of dissolved organic carbon (DOC) contents, absorbance of ultraviolet light at 254 nm (UV-254), and specific ultraviolet light absorbance (SUVA) soil caused by freezing-thawing were similar:they increased with increasing freezing and thawing temperatures; they decreased initially and then increased, when the freezing time increased; they decreased with increasing times of freeze-thaw cycles. The humification degree of DOM increased and the molecular weight of DOM decreased as a result of freezing-thawing. The contents of fulvic and humic acid-like fluorescent materials in DOM decreased initially and then increased, when the freezing time increased. The contents of fluorescent materials in DOM decreased with increasing times of freeze-thaw cycles.The effect of types and concentrations of chemical ions on the contents and spectroscopy characteristics of dissolved organic matter (DOM) in soil which enters snowmelt runoff, as well as the release of DOM from soil during the melting of snow with different chemical characteristics, was investigated by means of soil leaching experiments and soil column leaching experiments. The soil leaching experiment results showed that the dissolved organic carbon (DOC) concentrations in soil extracts significantly decreased with the increase of Na+, Mg2+ and Ca2+ concentrations. The absorbance of ultraviolet light at 254 nm (UV-254) in soil extracts gradually decreased with the increase of Cl-, SO42-, Mg2+ and Ca2+ concentrations. The specific ultraviolet light absorbance (SUVA) in soil extracts gradually increased with the increase of Na+ and Mg2+ concentrations. When NO3-, SO42- and Na+ concentrations were too high or too low, the intensity of humic acid-and fulvic acid-like fluorescence peaks of DOM in soil extracts was relatively low. The intensity of humic acid-like fluorescence peak of DOM in soil extracts gradually increased with the increase of Cl-、Mg2+ and Ca2+ concentrations. The soil columnleaching experiment results showed that the humic acid- and fulvic acid-like fluorophores were the main fluorescent materials in soil leachate. The snowmelt water which acted as leaching solution, compared with pure water, led to the decrease in DOC concentrations as well as the increase in intensity of soluble microbial byproduct-like fluorescence peak in soil leachates. The freezing-thawing of soil inhibited DOM from desorption from soil and entering leachates. In additon, the freezing-thawing of soil also resulted in the decrease in the relative content of aromatic compounds in soil leachates.The test of new and old snow melt founder showed that the weak acidic conditioned of snow melt water, the higher ion concentration can make more DOC released into the water in the soil; New snow DOM leaching solution contains more soluble microbial metabolites, at the condition of weak acidic relatively in new snow than old snow, snow on ion content in lower case, microbial activity, class more soluble microbial metabolites.