The Dynamic Change Of Dissolved Organic Matter And Its Effects On The Sorption-desorption Behavor Of Copper And Zinc

Dissolved organic matter(DOM) is defined as it can be extracted by water,acid and alkali,like organic matter in water,soil solution and organic materials.The operation definiation of DOM is defined through filtration,the size limit,which is used to differentiate DOM from particulate organic matter,is somewhat arbitrary,but there is an almost universal consensus that it is around 0.45μm.In the past 20 years,much progress has been made in the understanding of DOM functions in terrestrial and aquatic ecosystems.In the presence of DOM,weathering rates can be accelerated,and DOM plays a central role during podsolisation. Furthermore,DOM contains organically bound nutrients such as N,P and S,and DOM dynamics will therefore also affect their mobility and availability.Today,it is commonly acknowledged that DOM can affect the solubility,biodegradation and mobility of heavy metal and thus contributes to pollutant transport or to micronutrient availability.For more concentrated on heavy metal pollution,studying the relationship between DOM and heavy metal pollutants will be the frontier of soil science,ecology and environment science.The dynamic of DOM derived from various stages of crop straw decomposition have been studied in this research,its effect on the sorption-desorption behavior of Copper(Cu) and Zinc(Zn) in soil had been also studied.The main results as follows:(1) The dynamic changes of DOM derived from crop straw decomposition was studied by using chemical analysis.The results showed that the content and constituents of DOM was in dynamic changes at all the incubation stages.At the initial decomposition stages,the DOM orignated from water-dissolved matter derived from organic materials,temperately,the primary composition of DOM was carbonhydrates and micromolecular organic acid,its hydrophile was a little strong. With crop straw decomposition,the DOM origanted from the product of cellulose and hemicellulose decomosition.Temperately,the DOM were macromolecular matter, its aromaticity and hydrophobic nature increased.The DOC,dissolved nitrogen, dissolved sugar and phenol acid increased gradually until constant after 91 days' incubation,but the compositions were still changing.(2) During the crop straw decomposition,theâ–³logK value increased at first, then decreased,while A₂₈₀,A₂₅₄ and E₄/E₆ increased,which indicated that the aromaticity and oxidation degree of DOM increased,their molecular structure became less aliphatic and more complex.(3) Cellulose and hemieellulose are the main components of crop straw,the other components,such as lignin,alcohol-benzene dissolubility,water-soluble organic compounds are comparatively fewness.Alcohol-benzene dissolubility and water-soluble organic compounds are be decomposed first,hemicellulose and cellulose are be decomposed second,lignin is hard to be decomposed.(4) Sorption of model pollutants in soil was biphasic,a fast sorption phase followed by a slow sorption phase.The equilibrium reached in 5 hours.Likewise, desorption were biphasic,too,containing a fast phase no more than 5 hours,in which a small portion model pollution adsorbed in soil desorbed into aqueous phase quikly, however,the other portion seemed to be resistant to desorption.It was found that the sorption-desorption hystersis of Cu in soil was statistically significant.The Freundlich model can comletely explained the mechanism of Cu and Zn sorption and desorption.(5) Within the selected concentration range of the Cu and DOM in this study, 0d-DOM increased the pH of sorption-desorption system,significantly decreased the hysteresis index of soil Cu,greatly reduced the sorption capacity of soil Cu,and accelerated the desorption of soil Cu.Further,there is significant difference(p＜0.01) between the 0day phase of DOM and other phases of DOM.Other decomposition phases of DOM could also increased the pH sorption desorption system.When soil Cu concentration was low,it decreased the hysteresis index of soil Cu,restrained the sorption of soil Cu,and accelerated the desorption of soil Cu,because chelated's effect was better than pH's effect at this time.On the other hand,when soil Cu concentration was relatively high,it increased the sorption of soil Cu,reduced the desorption of soil Cu,and increased the hysteresis index of soil Cu.(6) 0d-DOM could increase the pH sorption-desorption system,significantly decrease the hysteresis index of soil Zn too,greatly reduced the sorption capacity of soil Zn,and accelerated the desorption of soil Zn.Further,there is significant difference(p＜0.01) between other phases of DOM.Other decomposition phases of DOM could also increased the pH sorption desorption system,but significantly increased the hysteresis index of soil Zn,accelerated the sorption of soil Zn,and restrained the desorption of soil Zn.