APPLICATION OF ¹³⁷Cs CHRONOLOGY TO COASTAL SALT MARSHES

Salt marshes are a widespread coastal and estuarine environment,and geomorphologically are composed of an approximately leveling,vegetated platform dissected by network of typically blind-ended channels. It is important for studying the depositional processes and sedimentation rates to understand deeply the interaction between human activities and coastal system. ¹³⁷Cs chronology is an effective technique for studying modern sedimentation rates since 20 years. ¹³⁷Cs is an artificial radioactive isotope introduced into the natural environment since the start of the atmospheric nuclear weapon testing in the 1950s. ¹³⁷Cs can be exchanged and adsorbed in the surface sediment and buried through the air-water interface and water-sediment interface,and four dating markers(1954,1963,1974 and 1986)which correspond to the onset and peaks discharge of ¹³⁷Cs can be identified and the sedimentation rates in different periods can be calculated. ¹³⁷Cs chronology is used widely to study sedimentation rates in lakes,continental shelves,bays and tidal flats,and gives better study results. The ¹³⁷Cs chronology needs high stability of strata in study area,and its concentration is influenced by clay content and sorting degree of sediments. The root system of the salt marsh vegetation can extend deeply downwards and disturb the stratum sequence. Then it is difficult to identify the characteristic peak,and thus other techniques are needed to do comprehensive estimation.