昌邑滨海湿地沉积物的放射性核素水平与环境指示意义

利用伽马谱仪测定了昌邑滨海湿地表层沉积物以及沉积物岩芯中放射性核素含量,根据放射性核素的分布,探讨了其对物质来源、人类活动以及其他沉积环境演变事件的指示作用,并估算了研究区域的沉积速率.结果表明,表层沉积物中自然放射性核素238U、232Th、226Ra和40K的平均含量分别为(54.4±11.7)、(57.9±9.7)、(28.6±4.3)和(542±21)Bq·kg~(-1),表层沉积物放射性水平的区域差异反映了物质来源的不同以及人类活动对沉积物特性的影响.根据岩芯中过剩210Pb的分布,计算出近百年来沉积环境稳定的高沼区沉积速率为0.23 cm·a~(-1).在沉积物岩芯中,238U、232Th和226Ra具有较高的变异系数,根据238U和226Ra及其比值的垂直分布,沉积过程可被分为4个阶段:缓慢沉积阶段,受黄河河道迁徙影响下的沉积环境剧烈变化阶段,黄河归流后的稳定阶段,以及在人类活动的影响下的退化、增长交替阶段.放射性核素的变化反映了滨海湿地沉积环境的演变过程,具有重要的环境指示意义.

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 and⁴⁰K 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 excess ²¹⁰Pb, 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.