Environmental Geochemical Study Of The East China Intertidal Zone

The area of intertidal zone in Eastern China is about 11056.48 km2,which accounts for half of the total intertidal area in China and constitutes a critical backup of land resource.However,current researches are mainly limited to investigations done in a small region and based on a small number of measurements,and there is a lack of a systematic investigation focusing on geochemical characteristics in the whole zone and changes caused by reclamation time in Eastern China intertidal zone.Based on a multi-purposed 1/250,000 geochemical survey in East China intertidal zone organized by China Geological Survey,1906 samples of surface sediments(soils)were taken and 54 geochemical indexes measured for each sample.In this dissertation,multivariate statistics were applied to analyze the data obtained by the project,focused on studying concentration and distribution of heavy metals and nutrition elements in the whole zone and their correlation to other geochemical indexes,and on evaluating the pollution statue of heavy metals and eutrophication in the East China intertidal zone.Two typical areas,Dafeng and Rudong in Jiangsu province,were then chosen to study the changes of physical properties,contents of major elments,heavy metals,nutrient elements,salt etc.,in intertidal soils of after different length of reclamation time.The main conclusions reached in this dissertation are as the followings:1.Through a study on the content distribution and enrichment factors of heavy metals and their correlation with other geochemical indexes,the concentration in the East China intertidal zone as a whole is believed to be relatively low,lower than those of most estuaries in the world.And the pollution of heavy metals is not very serious as believed before.2.In the East China intertidal zone,content distribution of heavy metals shows different styles for different region,i.e.,from north to south,Jiangsu province,Shanghai Municipal,Zhejiang prvince and Fujiang province.It is revealed in this dissertation that contents of heavy metals in Jiangsu is usually lower than in other regions,with a relatively low pollution level of heavy metals,while the concentration distribution of Zhejiang and Shanghai is quite diffent,with higher average concentrations and double peaked distribution showed in histigram,demonstrate a reasonably strong pollution of heavy metals in the intertidal zone of these two regions.Fujiang show a different senario,showing a high background concentration of heavy metals and a less degree of superimposition.Compared to their contents on regional rocks,heavy metals show some degree of enrichment in the East China intertidal zone,especially As and Hg which have reached moderate enrichemnt with enrichment factor EF>2.0.Cr is the next enriched element,while the enrichment of other heavy metals is neglecable,with only a small propotion of moderate enrichment.3.Pb,Zn,Hg,Cu,Ni and As are proved to be a closely correlated group of heavy metals,indicating a similar resource from the weathering of regional rock and affected by authropogenic activities.Factor analysis also demonstrates that this association of heavy metals is believed to be mainly capture by the sediments by adsorption by Fe-Mn oxides,clay minerals(characterized by high aluminum contents),and organic,and be affected by the physicochemical properties of the sediments,benefiting from an acid condition.4.Contents of total nitrogen(N)and total organic carbon(OrgC)is not high as believed previously,Phosphorous content in the East China intertidal zone is generally of modeate level,with large values in some isolated sampling sites,indicating some localized eutrophication.,but N,P and OrgC show a different pattern of concentration distribution for different regions(provinces and municipal).5.Soil physicochemical property of lands with different reclamation durations at two typical reclamation areas(named Dafeng and Rudong)were analyzed and the result indicated a similar variation trend of soil particle sizes in both areas.Soil particle size decreased along with the increase of reclamation time.Soil clay contents presented increase trend with increased reclamation time.By contrast,soil sand contents had opposite change trends.Both soil pH and inorganic salt presented decreased trends with increased reclamation duration,along with the change of composition of base cations.The ratio of Na+ and Cl-decreased while the ratio of Ca2+,Mg2+,SO42-,and HCO3-increased as the reclamation durations went by.For other elements,the total contents of Cd,Hg,N,P,F,and I presented increasing trends as reclamation durations increase,whereas the contents of As,Cl,and Br decreased.6.Soil weathering index indicated that the soil development was different in the two areas.Dafeng reclamation area showed the process of Si enrichment and poor Al Fe,while Rudong showed inverse process.At the same time,desalinate and decalcification were noted both in the two areas.7.The changes of soil grain size,OM,macroelements,pH have important and different impacts on heavy metals,halogen elements,and N,P,which indicated that the physicochemical property changes along reclamation was crucial for the changes of elements.The changes of Na/K,silica-alumina ratio,silica-sesquioxide ratio in soil development can reveal the essential reason for the difference of heavy metals,halogen elements,N and P changes in the two reclaimed areas.8.The analysis on soil physicochemical properties with different land uses in Dafeng and Rudong indicated that soil particle sizesdistributed evenly in human-dominated land uses such as cropland.Moreover,the human-dominated land uses were characterized by high clay and silt contents.The contents of inorganic salt of cropland,fishpond,and forestland were significant lower than those in tidal flats and barren land.In tidal flats and barren land,the major base cations were Cl and Na,while they were Ca2+,Mg2+,HCO3,and SO42-in cropland and forest land.Cd,Hg,Cu,N,P,organic carbon,I,and F accumulated in cropland,forest land,and fishpond,whereas As,Cl,and Br accumulated in tidal flats and barren lands.Land uses exert significant impacts on soil-forming process.The soil weathering indexes such as Na/K,silica-alumina ratio,silica-sesquioxide ratio of cropland,forest land and fishpond were remarkably higher than those in tidal flats and barren land.