The Influence Of Seawater Intrusion To Heavy Metal Elements In Soil

The pearl river delta?PRD?is the region with the fastest economic development in China,which has become the largest city group in population and area in the world.Environmental problems are becoming prominent,and people are paying more attention to it.This paper analyzed heavy metals in natural soil from different area on PRD,designed a simulation experiment about the sea-land interaction,investigated the content and distribution characteristics of heavy metals in PRD,the relationship and influence factors between seawater intrusion and mobility of heavy metals in coastal areas.The main conclusions are as follows:1.The content of oxides in the soil from Beijiang area,Xijiang area and coastal areas in PRD is less affected by space and relatively stable.The contents of TFe₂O₃,MgO,CaO,Na₂O and K₂O in the surface soil from PRD gradually increased from the beijiang area to the coastal area,indicating that with the increase of transportation distance,the degree of chemical weathering of the soil increased subsequently.2.The spatial distribution of heavy metal Cd,Cu,Pb and Zn in PRD is extremely heterogeneous and have similar distribution characteristics.The enrichment degree of heavy metals from the beijiang area to the downstream area of sanshui is gradually enhanced,while the enrichment degree of heavy metals in the coastal areas is significantly reduced.3.The results of sea-land interaction simulation experiment showed that seawater with different salinity can cause the mobility of heavy metal elements in soil.Seawater intrusion lead to the mobility of heavy metal elements Cd,Cu,Pb and Zn from soil to aqueous solution,which increased environmental risks.With the increase of experiment time,the concentration of heavy metals in leached water gradually decreased,while the environmental risks decreased.The SO₄^2-from seawater may limit the mobility of heavy metals in soil.4.The mobility of heavy metals in soil by seawater intrusion is influenced by many factors,including concentration of seawater,pH,competitive adsorption,ion exchange reaction and the speciation of heavy metals.The cations from seawater can replace the protons on the surface of soil clay colloid,resulting in the increase of soil pH and the decrease of pH in leach water.The cations in aqueous solution can exchange heavy metal ions follow the order of Ca²⁺>Mg²⁺>K⁺>Na⁺.Under the action of seawater intrusion,the heavy metal elements in the soil can be transformed into the form of easier mobility,which improveed the activity of heavy metals.5.Seawater intrusion caused by natural phenomena such as global warming,tide and storm tide may be the main factors causing the relative lack of heavy metal elements in haizhu-nansha district of guangzhou.The underground water with high ionic strength upward from the bottom into the soil pore water under the capillary effect and diffusion,with the influence of ion exchange and the competitive adsorption,heavy metals mobilized to soil pore water.After the ebb,heavy metal in the upper pore water sink to the bottom of soil undering leaching,portion of which mobilized to the sea with the underground water transportation,others enriched in the bottom of soil.