Study On Characteristics And Ecological Risk Of Heavy Metals In Surface Sediments Of Dongda River Wetland In Dianchi Lake

Dianchi Lake is the mother lake of Kunming,but its ecological function and utilization value have been seriously affected by water environmental pollution for many years.After years of restoration and treatment,the Dianchi water environment is generally improving,but the problems of low submerged plant coverage,low biodiversity and unstable ecological conditions in estuarine wetlands still exist.Estuarine wetlands are the interaction zone between rivers and lakes,characterized by rich biodiversity and bearing important ecological service functions,but also a place for heavy metal enrichment and conversion.At present,the study of heavy metals in sediments of Dianchi Lake watershed is mainly focused on Dianchi sediments,and less attention has been paid to heavy metals in sediments of estuarine wetlands.Studying the status of heavy metal pollution in estuarine wetlands and evaluating its ecological risk is of positive significance for the safety of estuarine wetlands ecosystems and biodiversity conservation.This paper takes Dongda River wetland of Dianchi Lake as the research object,this paper systematically studies the heavy metals Zn,Cu,Ni,Pb,Cr,As and Cd in the sediments of Dongda River wetland from the sediment environment,the sediment properties,the total amount of heavy metals in the sediment,the characteristics of its occurence form,the heavy metal pollution of wetland plants and the heavy metal pollution assessment,so as to understand the ecological hazards of heavy metals in the estuarine wetlands of Dianchi Lake.The conclusions of this paper are as follows.（1）The water environment parameters such as p H,temperature,total dissolved solids and dissolved oxygen in the Dongda River wetlands showed different spatial distribution characteristics.The p H of the water is predominantly neutral to weakly alkaline,showing that the eastern>the western>the central.The water temperature showed that the western>the central>the eastern.Total dissolved solids are lower than the limit value of domestic drinking water sanitation standards,showing that the central>the western wetland>the eastern.The dissolved oxygen classes ranged from Class I to poor V,showing that the western>the eastern>the central part of the wetland.The cations of the East River wetland water bodies were dominated by Na⁺,and the anions were dominated by Cl^-and SO₄^2-.Zn,Cu,Ni,Pb,Cr,As and Cd in the water all meet the Class I surface water standard.The eastern part of the wetland has high levels of heavy metals in the water column under the influence of the drainage ditch.（2）The surface sediment p H of the Dongda River wetland is predominantly neutral and alkaline,showing that the eastern>the western>the central,which is consistent with the p H distribution characteristics of the overlying water.Both sediment organic matter and carbonate showed that the eastern>the central>the western.The magnetic material in the sediment is mainly paramagnetic,and the magnetic particles are mainly from the slightly coarser size fraction,with a high content of superparamagnetic particles.The sediment components are concentrated in the range of clayey chalk,sand-chalk-clay,and sandy chalk.Both the median and mean sediment grain size showed the western>the eastern>the central.The sediment particles are sub-symmetrical in character,with a constant peak state and a poor to very poor sorting coefficient.（3）The average concentrations of Zn,Cu,Ni,Pb,Cr,As,and Cd in the surface sediments of the Dongda River wetland were 221.38,30.40,29.19,79.73,154.00,13.87,and 0.62 mg·kg^-1 respectively,which were 2.7,1.2,1.0,2.5,2.3,1.1,and 3.1times higher than the background values of sediments in the southern China water system times.The average content of all seven heavy metals showed a characteristic of the central>the eastern>the western,which was more influenced by human activities.（4）The active states of Pb,Cu and Zn in the surface sediments of the Dongda River wetland are high,while the active states of Ni and Cr are low,but they are all dominated by heavy metals in the residue fraction.The mild acid-soluble fractions of the five heavy metals did not show significant response characteristics with each water environment parameter.Positive correlation between residue fraction and total dissolved solids in the overlying water.The reducible state is positively correlated with clay and negatively correlated with very fine sand.The response of each fugitive form of heavy metals to the overlying water is different due to their own characteristics.The percentages of heavy metal release are Zn>Ni>Cu>Pb>Cr.（5）Five species of plants in the Dongda River wetland（Pontederia cordata L,Thalia dealbata Fraser,Phragmites australis（Cav.）Trin.ex Steud,Canna indica L.var.flava Roxb and Typha orientalis Presl）have strong enrichment capacity for Ni,Cu,and As.The enrichment capacity was from strong to weak as Pontederia cordata L>Thalia dealbata Fraser>Phragmites australis（Cav.）Trin.ex Steud>Canna indica L.var.flava Roxb>Typha orientalis Presl.Five species of plants have stronger migration capacity for Cu and Zn.The migration ability from strong to weak was Canna indica L.var.flava Roxb>Phragmites australis（Cav.）Trin.ex Steud>Typha orientalis Presl>Thalia dealbata Fraser>Pontederia cordata L.（6）The results of thepollution assessment show that the surface sediment Pb of the Dongda River wetland reaches light pollution,and Cu,Zn,Ni and Cr are non-polluting.The geoaccumulation index pollution evaluation results show that the Dongda River wetland surface sediment Cd reached moderate pollution,Zn,Pb,Cr is light pollution,Cu,As,Ni is no pollution,the pollution situation shows that the central>the eastern>the western.The results of theecological risk assessment show that the surface sediment Zn of the Dongda River wetland pose a moderate risk to the environment,Ni,Pb and Cr pose a low risk to the environment,and Cu poses no risk to the environment.The evaluation results of the potential ecological risk index method showed that the hazard of heavy metals in the surface sediment of the Dongda River wetland was Cd>Pb>As>Cu>Ni>Cr>Zn,with Cd reaching strong ecological hazards,Pb,As,Cu,Ni,Cr and Zn being minor ecological hazards.The comprehensive potential ecological risk within the wetland is expressed as the central>the western>the eastern.The central reaches moderate ecological hazard,the eastern and the western part are minor ecological hazards.Element Cd is the main contributing element to the comprehensive potential ecological hazard.