Effect Of Dissolved Organic Matter On Mercury Release From Soil/Water/Air Interface

Dissolved organic matter (DOM) is an important and active component in both terrestrial and aquatic ecosystem,while soil DOM plays an important role in the pedogenesis. It has become a hotspot in environment science. It have vital function on chemical and biological process in soil and water body such as absorption, complexation, chelate, flocculation, deposit, redox because of the functional groups carboxyl, carbonyl, amido and hydroxy.The main affecting mechanisms of soil DOM on environment behaviors of Hg were summarized as complexing with Hg²⁺,competing with Hg²⁺ for adsorption sites,and affecting soil pH value. In this paper.typical soil of Chongqing were collected and then mercury adsorption-desorption characteristics of soil which were added different kinds of dissolved organic matter were studies depdending on adsorption-desorption experiments.On the other hand, mercury release characteristics and relations with environment factors were discussed in different types of soil with different added dissolved organic matter during flooding by simulated experiments.Effect of three types of DOMs extracted from Humics(DOM_H), rice straw(DOM_R) and pig materials(DOMp) on isotherm adsorption of Hg²⁺ in yellow soil and neutral purple soil.The maximum adsorption of Hg²⁺ was reduced by the additions of DOM_H, DOM_Rand DOM_P.The least of yellow soil of the maximal amount was DOM_H which is 250μg/g and neutral purple soil was DOM_H too which is 270.27μg/g.The range of the maxomum adsorption of Hg²⁺ decreased from 40% to 22.6%,and the neutral purple soil from 43.3% to 27.6%. DOM will have a significant effect on the retardation of Hg²⁺ and it can scramble for Hg²⁺ with soil colloids by competitive sorption which reduced the adsorption capacity of Hg²⁺ in soil.And the different source and extraction method of DOM have different function on Hg²⁺.The results of Hg²⁺ adsorption to two soil which were added three differert dissolved organic matter could be fitted to three isothermal adsorption equations including Langmuir,Freundlich,Temkin, among which Langmuir equation was the most effective. We can discover from Freundlich,it have reduced the sorption to Hg²⁺ of siol to some extent,but it was unsharpness among diffrernt DOM.In this paper,we ueded several kinetics equations.The results indicated that the kinetic characteristics of adsorption and desorption of differem soil which added different DOM were similar.The adsorption reaction velocity have had reduced in yellow adding DOM.The neutral purple soil was similar with yellow soil.After flooding mercury contents in water have peak values during flooding ,and the more dissolved organic matter added in soil ,the more was mercury content of water.The maximal release flux of mercury of yellow soil was D4 which is 465ng/L and neutral purple which was 577ng/L.The Hg²⁺ content in water rose with level increasing of DOM both in yellow soil and neutral purpl soil,the order was DOM_H>DOM_R>DOM_P>CK .Among assayed factors in this experiment,only pH,conductivity,dissolved oxygen were better correlative with mercury content in water,others were not obvious.Dissolution balance times of soil basicity were basically correspondent with changes of mercury content in water.Water-air exchange fluxes of mercury reduced with the increase of DOM contents in soil after flooding ,and balance time was longer.The fluxes of mercury were higher than yellow soil and neutral purple soil adding DOM.The different between the same level about DOM_R and DOM_P were not obvious.Among assayed factors in this experiment,DOM have had effecte to some extent.In water-air exchange stage,mercury release flux had a positively relationship with solar radiation.In the whole course ,mercury release flux was significantly correlative with pH.But mercury release flux of soils was negatively correlated with conductivity of water and dissolved oxygen of water.Content of total mercury of soils had great change in flooding course which added DOM.The total mercury losing of yellow soil were more than neutral purple soil. The mercury release into atmosphere from soils was preliminary estimated based on measurement data by dynamic flux chamber method, associated with climate characteristic of Chongqing. The result showed that the total conten ts of mercury in different soils decreased after experiment, and the mercury amount released from soils were less than the lost amount of total mercury in soils.