Accumulation and transportation of natural radionuclides in estuary

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Natural atomospheric radio-nuclides, unsupported ^<210>Pb (^<210>Pb minus ^<214>Bi), and ^7Be in three estuarine sediments from Tatara-Umi estuary were measured. Their profiles of the silty sediments from tidal flat are fitted down to 30 cm on a simplest equation for diffusion (mixing) with the coefficients from 1 to 8 x10^<-7> cm^<2s>ec^<-1>. The monthly profiled of ^7Be in tidal flat sediments show no different mixing on season. This mixing is faster than those expected from microcosmic experiments. The upper 7,8 cm of the silty sediments from reed marsh are well mixed, probably owing to the growth of roots of reeds. Under the well mixed layr, ^<210>Pb and ^7Be are decreased with the depth in a similar manner as tidal flat sediments. In seaside sand sediments their nuclides do not absorbed.The radio-nuclides of ^<22>Na, ^<85>Sr, ^<134>Cs, ^<59>Fe, ^<54>Mn, ^<57>Co and ^<65>Zn had been spiked on untreated or heated estuarine sediments. After 1,2 or 3 months, the profiles of their radio-activities were measured by g-spectrometry simultaneously. In heated samples, Na and Sr are transported down to the bottom of 12cm, Cs down to 3-4 cm, and other elements are hardly transported. In untreated samples, Fe, Mn, Co and Zn are transported down to 4-5 cm and several samples showed peaks, which suggest bioturbation and conveyor-belt deposit feeders. The bioturbation were heterogeneous in time and place in Tatara-Umi estuary. The transfer of these elements can be simulated by an advection-diffusion-reaction model.