Lead And Strontium Isotope Characteristics And Environmental Significance Of Sediments In Tianjin Coastal Zone

In this thesis,trace elements and the isotopic compositions of Pb and Sr in the columnar sediments from Tianjin coastal zone were measured.The main purpose of this study is to compare the geochemical characteristics of Pb and Sr isotopes,and to preliminarily explore the sources of Pb and Sr in the sediments of the study area based on the sedimentary environment and other background data,so as to distinguish the effects of nature and human activities on sediments.In addition,the contribution rate of sources is calculated by using the multivariate mixed model.The results show that:1.The range of ²⁰⁷Pb/²⁰⁶Pb in Tianjin coastal sediments is from 0.8471 to 0.8518,and the range of ²⁰⁸Pb/²⁰⁶Pb is from 2.0913 to 2.0993.The mean lead content of the core sediments is 32.91 mg/kg,which is higher than that in the Yellow River Estuary,the Yangtze River Estuary,the East China Sea and the South China Sea,indicating the existence of lead pollution.The correlation analysis shows that there is a significant correlation between ²⁰⁷Pb/²⁰⁶Pb and lead content,suggesting that there may be two sources of lead in columnar sediments.The correlations are not significant between²⁰⁷Pb/²⁰⁶Pb and mean particle size,TOC and pH.2.The ⁸⁷Sr/⁸⁶Sr of sediments in Tianjin coastal zone ranges from 0.714233 to0.715534,showing a trend of“decrease-increase-decrease”from bottom to top.The average content of Sr in columnar sediments is 177.41 mg/kg.The correlation analysis shows that the correlation between ⁸⁷Sr/⁸⁶Sr and strontium content is not significant,suggesting that it may be affected by a variety of terminal substances.There is a high correlation between ⁸⁷Sr/⁸⁶Sr and mean particle size,showing a negative correlation.⁸⁷Sr/⁸⁶Sr increases with the increase of the TOC,but the correlation between ⁸⁷Sr/⁸⁶Sr and pH is not significant.3.Based on the binary mixing model,the average contribution rate of natural sources to Pb is 68.45%in columnar sediments,and that of human activities is31.55%.It is found that coal combustion is the main anthropogenic source,and the main input way is atmospheric deposition.The impact of leaded gasoline is small,and leaded gasoline is no longer the anthropogenic source of lead in the study area after2001.The comparison of lead input pathways shows that the lead discharged by human activities mainly enters the sediments by atmospheric deposition.In addition,the amount of dissolved lead in river water is very small,which indicates that the natural sediments of the Yellow River supply more lead by suspended particulate matter.4.The combined tracing of Pb and Sr isotopes indicates that the source of strontium is affected by a variety of potential pollution sources.Based on the three-end-member model,the mean contribution rates of human activities,seawater and natural sources are 27.43%,15.48%and 57.09%,respectively.It is concluded that the contribution rate of human activities decreases obviously,while the contribution rate of seawater increases gradually with the increase of the sediment depth,indicating that seawater and natural sediments of the Yellow River are the main sources of strontium in Tianjin coastal zone.