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

Abstract

Vertical profiles of environmental radionuclides (210Pb, 137Cs, 238U, 232Th, 226Ra and 40K) 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 210Pb and 137Cs dating, the average sedimentation rate of core Y1 was estimated to be 1.0 cm y−1. Vertical distributions of natural radionuclides (238U, 232Th, 226Ra and 40K) changed dramatically, reflecting great changes in sediment input. Concentrations of 238U, 232Th, 226Ra and 40K all had significant positive relationships with organic matter and clay content, but their distributions were determined by different factors. Factor analysis showed that 238U was determined by the river sediment input while 226Ra 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 238U and 226Ra were consistent with high accretion rate. Frequent seawater intrusion decreased the concentration of 226Ra significantly. The value of 238U/226Ra 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.