The Analysis On Temporal And Spatial Distribution Of Magnetic Parameters And Its Main Influencing Factors Of Dongyang River,Jinhua,China

Environmental magnetism is widely used to geosciences research by characterizing magnetic minerals including magnetic mineral assemblage and grain size,such as the river and estuary study.Dongyang River is an important tributary of the Qiantang River,and there is valuable environmental information contained in its sediments.In this paper,magnetic properties,particle size and geochemistry of the surface(BT1-50)and core(HZ,45 cm in length;SLT,48 in length;JSC,33 cm in length)sample of the Dongyang River are examined.And on the basis of chronology,the effects on magnetic properties are researched.The main conclusion are showed as follows:Ferrimagnetic minerals magnetite dominates the magnetic properties of the intertidal sediments in the study area,together with the contributions of anti ferromagnetic minerals,and concentration in superpara magnetism(SP)particle is very low.In Dongyang River catchment,magnetic mineral content is declining,and grain size is being fine from upstream down to downstream overall.Profile HZ is given priority to silty sand,SLT and JSC are given priority to sandy silt,surface sediment composition mainly includes sandy silt,clay silt and silty sand.The particle size of profile HZ,SLT and JSC indicates the different hydrodynamic conditions.It is concluded that the core location,core length,overlying water and human activitie are concerned.Along the river,sediment particles became fine overall.All heavy metal elements in the sediments were accumulated and enriched,and heavy metal Cu pollution is the most serious.Vertical variations of heavy metal content shows that the effect of Cu pollution is large and the duration is long over the last one hundred years.From spatial perspective,Cu,Pb and Zn change a lot,and the the source analysis shows that Zn,Cu,Ni,Cr may have the same source.Profile SLT It is more serious underpart the profile SLT,while surface sediment indicated that the Yiwu and Dongyang urban district has higher pollution degree,Wucheng District has nethermore pollution degree,and Dongyang rural township district and Jindong district has the lowermost pollution degree.It is found that SD magnetic mineral reside primarily in the fine-grained sediments while coarse grained magnetic mineral enriched in the fraction of coarse grains sediments.The natural source of Dongyang River is stable which shows that it is not the main factor of magnetic property change.Fine-grained ferrimagnetic mineral has significant adsorption of heavy metals.Howhver,the effect of heavy metals on magnetic property tend to be covered in core HZ,JSC and Dongyang rural township district.It is developed in oxidized and shallow water environment overall of core JSC,HZ and SLT.