Environmental evolution records reflected by radionuclides in the sediment of coastal wetlands: A case study in the Yellow River Estuary wetland

摘要

Vertical profiles of environmental radionuclides (Pb-210, Cs-137, U-238, Th-232, Ra-226 and K-40) in a sediment core (Y1) of the Yellow River Estuary wetland were investigated to assess whether environmental evolutions in the coastal wetland could be recorded by the distributions of radionuclides. Based on Pb-210 and Cs-137 dating, the average sedimentation rate of core 11 was estimated to be 1.0 cm y(-1). Vertical,, distributions of natural radionuclides ((238)u Th-232 Ra-226 and K-40) changed dramatically, reflecting great changes in sediment input. Concentrations of U-238, Th-232, Ra-226 and K-40 all had significant positive relationships with organic matter and clay content, but their distributions were determined by different factors. Factor analysis showed that U-238 was determined by the river sediment input while Ra-226 was mainly affected by the seawater erosion. Environmental changes such as river channel migrations and sediment discharge variations could always cause changes in the concentrations of radionuclides. High concentrations of U-238 and Ra-226 were consistent with high accretion rate. Frequent seawater intrusion decreased the concentration of Ra-226 significantly. The value of U-238,(226) Ra tended to be higher when the sedimentation rate was low and tide intrusion was frequent. In summary, environmental evolutions in the estuary coastal wetland could be recorded by the vertical profiles of natural radionuclides. (C) 2016 Elsevier Ltd. All rights reserved.