Distribution and environmental significances of radionuclides in the sediment of the Changyi coastal wetland

The radionuclides contents in the surface sediments and sediment cores were determined by gamma spectrometry method. The distribution of radionuclides and its indication to material sources, human activities and other sedimentary environmental evolution events were discussed and the sedimentation rate was estimated. The results showed that the average activity concentrations of ²³⁸U, ²³²Th, ²²⁶Ra and ⁴⁰K in the surface sediment were (54.4±11.7), (57.9±9.7), (28.6±4.3) and (542±21) Bq·kg^-1, respectively. Regional differences of radioactivity level reflected the material sources and influences of human activities on the sediment characteristics. According to the vertical distribution of excess²¹⁰Pb, the sedimentation rate of high tidal areas was estimated at 0.23 cm·a^-1. In the sediment core, the variable coefficients of ²³⁸U, ²³²Th and ²²⁶Ra contents were high. According to the vertical profiles of ²³⁸U, ²²⁶Ra and ²³⁸U/²²⁶Ra ratio, the process of sedimentation could be divided into four periods: period of slow deposition, period of dramatic change in sedimentary environment caused by great migration of the Yellow River channels, period of stable deposition after the Yellow River ran into one single channel, and period of alternate degradation and growth under the influence of human activities. The vertical variation of radionuclides in the sediment core could serve as an effective environmental indicator since it could record the environmental evolution processes of the coastal wetland.