Study Of Nitrogen Transformation Process On Sediment-water Interface In West Lake

This paper takes the sediment and water of West Lake in Hangzhou as the research objects,and deal with field monitoring and laboratory analysis to investigate the heavy metal and nitrogen pollution situation of West Lake.After the simulation experiments,the paper studied the rate of nitrogen release from sediment and its affecting factors.Using N and O isotopic tracing method and in combined with acetylene inhibition method to detect the nitrate sources and denitrification and nitrification rate.Finally the paper illustrates the main resources of nitrogenous contaminants and migration mechanism.The results presented herein would provide scientific theoretical references for the controlling of water eutrophic pollution.The conclusions were as follows:（1）It shows that the water of West Lake is seriously polluted by nitrogen.Generally,the sediment represent a neutral-weak alkali condition,and ammonium-N is the main form.The annual average value of heavy metals As,Cd,Pb,Co and Zn are all higher than the background value.There is a positive correlation between Cu,Pb,Zn,Cd,Mn and As,and also between Co,Cr,Mn and Ni.The clustering analysis shows the main sources of Cu,Pb,Zn,Cd,Mn and As were natural source and traffic emission.（2）The releasing rate of NH₄⁺-N increases with oxygen concentration,and the releasing rate under aerobic state is 2 times anaerobic state or even 6 times.NO₃^--N releases from overlying water to sediment when it is under anaerobic or low oxygen conditions,but under aerobic state it release from sediment to overlying water.The releasing rate of NH₄⁺-N increases with the rising of temperature and pH level,and releasing rate under 28℃is 1.7 times the rate under 20℃and 3.8 times the rate under8℃.The short period simulation experiment shows that DIN releasing from sediment is14.603t.Long period simulation experiment shows that annual DIN-releasing from overlying water to sediment is 2.92t.（3）It indicates that the main nitrate sources of West Lake are the soil nitrogen,chemical fertilizer and litter organic fertilizer.Denitrification in the overlying water is weak,while in the sediment it is intense.The denitrification rates of area S1 and S12 are24.65μmol·m^-2·d^-1,19.51μmol·m^-2·d^-1,while the nitrification rates are 2.50mmol·m^-2·d^-1,3.10 mmol·m^-2·d^-11 and the ammonification rates are 0.27 mmol·m^-2·d^-1,0.78 mmol·m^-2·d^-1.The denitrification rate is shown significantly negative correlation with dissolved oxygen concentration（p<0.05）and total nitrogen（p<0.01）,while significantlypositive correlation with temperature（p<0.05）.The negative correlation（p<0.01）between nitrification rate and concentration of NH₄⁺-N is significant,but the nitrification rate is negatively and significantly correlated with total nitrogen.To ammonification rate,there is a positive correlation with the dissolved oxygen concentration.