Distribution Of Heavy Metal And Its Effect Of Water Level And Salinity In Sediments In Soil Of The Yellow River Estuary

With the decrease of fresh water supply source of the Yellow River,the wetland soil of the Yellow River Estuary faces different degrees of damage and influence due to the artificial disturbance of agricultural reclamation,oil field construction and urban development.Soil is one of the main environmental elements of wetland ecosystem,and also major sink of heavy metal pollutants.Different frcations of heavy metals have different effects on the environment.Heavy metals will migrate and transform when the natural environment changes,thus causing harm to the environment.Therefore,it can be assessed that importance to study the distribution of heavy metals and their migration and transformation in estuarine wetland soil.In this study,we selectd natural wetlands in different vegetation communities in the Yellow River Delta as study areas.In these areas,different vegetation covers-Calamagrostis pseudophragers-tyhya orientalis,Phragmites australis,Tamarix chinensis,Suaeda glauca and Tamarix chinensis were selected,respectively.Soil samples were collected from different depths(0-50 cm).The heavy metals Cr,Cu,Zn,Cd and Pb,in each soil sample were determined.The results showed that heavy metals were mainly concentrated in the soil at 0-20 cm.In different vegetation cover prfiles,heavy metals decreased with the increase of soil depth,mostly because the regulation of element accumulation by plant communities in factors such as salinity,root distribution and organic matter.The Index of Geoaccumulation elucidated that pollution level of Cr and Cd were higher among the 5 studied heavy metals in soil of the Yellow River Estuary,among which Cr was at the level of no pollution to moderate pollution,and Cd was at the level of moderate pollution to intensive pollution.This may affected by the petroleum exploitation,emission pollutants,fertilizer use and other human activities.The incubation experiment samples were collected in a site with low salinity and lesser impact of water.Results showed that the main fraction of Cr,Cu,Zn and Pb was residual fraction.Cd was manily in the fraction of weak-acid fraction existing in the soil of the Yellow River Estuary.Incubation experitiment results showed that,with the increase of culture time,the proportion of Cu and Pb weak-acid fraction decreased under different flooded conditions,while Cd weak-acid fraction tend to increased.The Cr reducible indicated a trend of decreasing first and then rising in no-flood and flooded treatment.The oxidizable fraction of Cr increased in different flooding treatments,and the oxidizable fraction of Cd increased with the increase of culture time.Except for the low Cr residual fraction in the first week,the Cr residual fraction accounted for a high amount in the other samples,and the Cd residual fraction showed a decreasing trend with the increased of culture time.Analysis of GLM showed that flooding had a significant impact on the morphology of Cr and Pb,different flooding conditions and the oxidizable fraction of Cr,Zn and Cd had a significant impact,and flooding had a significant impact with the weak-acid fraction,reducible fraction and residual fraction of Cu.The weak-acid,reducible and oxidizable fraction of Cd increased with the increase of salinity,while the residual states of Cu,Cr and Pb have lower contents at high salinity,it showed that the increase of salinity increased the risk of Cd,high salinity could help reduce the risk of migration of Cu,Cr and Pb,and salinity have no significant effect of Zn morphology change.This study had a scientific understanding of the transfer and transformation of heavy metals in the intertidal soil of the Yellow River estuary under the condition of water and salinity was put forward.