Influence of Dissolved Organic Matter and Phosphogypsum on the Release of Cadmium in the Soil of the Water Level Fluctuating Zone of the Xiangxi River
This research aims to examine the impact of dissolved organic matter(DOM)and phosphogypsum on the release of cadmium(Cd)in the soil of the water level fluctuating zone(WLFZ)in the Xiangxi River.It focuses on soil samples collected from the WLFZ of the Xiangxi River,with particular attention given to the role of Cynodon dactylon as an external source of DOM.Indoor simulated flooding leaching experiments were carried out to reveal the effects of DOM and phosphogypsum on soil physicochemical properties,DOM characteristics,and heavy metal release under both drying and flooding environments.The results showed that at the initial stage of the experiment,the addition of Cynodon dactylon and phosphogypsum decreased the soil pH value,increased the content of available phosphorus and SO42-,promoted the release of Cd into pore water,but inhibited the migration of Cd into the overlying water.With the extension of culture time,the protein components in DOM were transformed into microbial humus components,leading to an increasing degree of humification(HIX).The Cd concentration in the pore water of all groups decreased under both drying and flooding conditions.DOM,acting as a carbon source for sulfate-reducing bacteria,played a role in immobilizing Cd.The Cd content was negatively correlated with pH,SUVA254(aromatic structure)and HIX,and positively correlated with DOC,Mn,SO42-and available phosphorus content.In each treatment,the addition of phosphogypsum decreased soil pH value,increased H+,and enhanced Cd2+activity.SO42-in phosphogypsum played a reducing role in manganese oxides,leading to the dissociation of Cd bound to manganese oxides and consequently promoting the release of Cd.At the beginning of the experiment,DOM was released during Cynodon dactylon decomposition promoted the release of Cd from soil to pore water;at the end of the experiment,DOM participated in the reduction of SO42-,facilitating the conversion of Cd2+to CdS precipitation and subsequent fixation in the soil.
water level fluctuating zonedissolved organic matterphosphogypsumcadmiumtransfer
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