Grain Size And Geochemical Characteristics Of Core Sediments And Its Environmental Significance In Tidal Flat From Haizhou Bay

Haizhou Bay is the region where oceans and rivers have very strong interaction,and the area is also an important economic zone in Jiangsu province.The grain size of four sediment cores(HZ01?HZ02?HZ03 and HZ04)in tidal flat from Haizhou Bay were analyzed,researched major-elements,trace elements and REE analysis of HZ02 core,coming with the 137Cs isotope dating of sediment HZ02 core.This paper discussed the distribution characteristics of grain size and geochemical elements of tidal flat in Haizhou Bay over the past the century.It's also discussed the effects of sedimentary environment response to the human activities.Several mainly conclusions includes have been made as follows:(1)The sediment in the middle and upper intertidal zone are mainly made of silts.The sediment in the bottom intertidal zone is mainly composed of silts and sands.Vertically,sediment size in core HZ01 gradually changes from fine to coarse with the depth changes from the bottom to the top,while opposite trend changes in cores HZ03 and HZ04.The affected tidal flat dynamic process resulted from the large-scale reclamation around northern Linhong estuary of 1950s would possibly trigger grain size vertical changes in core HZ01.The changes in grain size in cores HZ03 and HZ04 are related to deposition elevation and weakening hydrodynamic condition,because the Linhong River inputs sediments to the bay and expands towards the sea area continuously.(2)In descending order,the relative average concentrations of heavy metals is Mn>Zn>Cr>Ni>Cu>Pb>As.The concentrations of 7 heavy metals increased gradually since 1980,and increased rapidly after 1990.The assessment results of these 7 heavy metals from core sediments in Haizhou Bay show that there are mild to moderate pollution existed by using 5 different assessment methods.Sources of the heavy metals can be divided into three groups:the first group,such as Cr,Ni,Cu and Zn,is derived from industrial and urban pollution emissions;the second group is Mn and As,which may come from agricultural pollution;and the last group is Pb,which probably comes from harbor traffic.(3)In descending order,the relative average concentrations of major-elements is Al>Fe>Ca>K>Na>Mg>Ti,and the change of the major elements have a similar regularity from the bottom to the top;trace elements concentrations also have the same trend,which varies greatly before 1958,after that it tends to be stable.The study also shows that most elements of the sediments don't correlate with the grain-size of the HZ02 core so well.The REE patterns indicated that the sediments originated are matter from the mainland.Therefore,the terrestrial sources control and effect on the sedimentary environment.The sediments sources from Linhong River,followed by the old Yellow River and Yellow River before 1958.The construction of Shilianghe reservoir leads to the reduction of minerals source from Linhong River and the increase of provenance from the open sea after 1958.(4)It's proved that sedimentary environment have a response to human activities according to the indicators such as the grain size,major-elements,trace elements,and REE of HZ02 core.These indicators aslo reveal the profound changes of sedimentary environment of Haizhou Bay which is connected with the human activity directly.