Study On The Partition And Influence Mechanism Of Trace Element In Typical Karst Wetland

As one of the three major ecosystems on earth,wetland bred 20% of the known species,though it made up only 6% of the earth.Wetland had irreplaceable ecological function,therefore,it was called “the kidney of the earth”.Although the wetland was a very important ecosystem,the interior was fragile and vulnerable to pollutants.Trace elements had potential ecological risk of long-term and accumulated transformation in the wetland.Especially in recent years,due to human industrial production,agricultural fertilization,geological setting and mining activities,sewage irrigation and other factors made steady accumulation of the trace elements in wetland,caused pollution of the trace elements increasing and brought great damage to ecological function of wetland.This study takes Yunnan-Guizhou plateau wetland-Caohai wetland as the research object,comprehensively studied Caohai wetland water chemical environment,wetland water,environmental geochemical characteristics of trace elements in sediments,and trace element distribution,the forms of existence under the influence of water chemistry conditions and the influence mechanism were discussed,mainly draw the following conclusion:(1)Caohai wetland water body was influenced by carbonate karst erosion,the main cation were Ca2+,Mg2+,the main anion were HCO3-,SO42-in water body.Under the control of the influence of wetland in the geochemical process,wetland water had obvious seasonal variation,the water chemistry types of wetland water in wet season had Ca-HCO3,Ca-SO4,Mg-HCO3 ? Mg-SO4,in contrast to dry season,due to the effect of water body evaporation,the main chemical type was Ca-HCO3.(2)The trace elements concentration of wet season outweights the dry season.Compared with the other freshwater wetland,the concentration of Pb,Cu,Zn were apparently higher and Cd element part point were higher in the Caohai wetland,it might be related to the local mining activities(zinc smelting method).Health riskassessment and comprehensive pollution index point out Caohai wetland exist pollution of Hg,Cd.(3)With reference to national sediment quality standards,Hg pollution was serious,closely followed by Cd,Zn in Caohai wetland sediments.Temperature,oxidation reduction potential,hydrodynamic conditions,organic matter,particle size,salinity were the influencing factors of trace elements distribution differences in different period of wetland water sediment.Moreover,temperature,hydrodynamic conditions,organic matter and particle size on the sediments had big impactes on the distribution of Cd,Pb,Cr,Cu,Zn in different period water's sediment,belong to the main control factors.Oxidation reduction potential and salinity were the main control factors of Hg and As in sediment.By principal component analysis,the source of Hg was rock weathering,ore combustion and agricultural irrigation,As was mainly derived from agricultural irrigation,Cd and Zn elements mainly from rock weathering and mining activities,Pb mainly from rock weathering and ore combustion,Cr and Cu were mainly rock weathering.The speciation analysis indicated that Cd had the highest exchangeable component in the sediments of Caohai wetland,and its activity coefficient and migration ability were also the largest,which was easy to be used by organisms.When the water environment of Caohai wetland changes,Cd can easily migrate from the sediments to the wetland water body,thus the potential harm to the ecological environment of the lake is the greatest.(4)Used PHREEQC software simulate the existential form of trace elements in Caohai wetland,and the effects of temperature,p H and oxidation-reduction potential on the forms of trace elements were analyzed.With the change of temperature,there are slight changes of the existential form of these trace element,and the main existential forms increased with the increase of temperature,but the content is not obvious.It is worth noting that with the increase of temperature,the contents of hexavalent Cr in water gradually increased.The main existential forms of trace elements in wetland water are greatly affected by p H,andthe change of p H value changed the content of OH-ion.Therefore,the amount of OHbound with trace elements is changed.The value of oxidation-reduction potential will affect the main existential form of As and Cu,the reason is that the valence of the elements is changed and the binding of the elements to anions is affected.