Publication Date:
2013-03-01
Description:
[1] The time scale of transport processes in estuarine and coastal regions can be evaluated using natural radionuclides with different half-lives. The distribution patterns of 7 Be, 210 Pb and 234 Th in the water column from April to July 2008 were used to calculate the removal and residence times in the Changjiang Estuary. The results showed that the maximum particulate activities of 7 Be, 210 Pb and 234 Th were observed approximately 150 km downstream (the turbidity maximum zone) of the freshwater end-number. The mean distribution coefficients (K d , cm 3 g -1 ) of the high suspended particulate matter (SPM) group are higher than those of the lower SPM group for 7 Be and 210 Pb; for 234 Th, the reverse is true. Based on a material balance in two-dimensional models of 7 Be, 210 Pb and 234 Th in the Changjiang River mouth, the removal times of these nuclides were approximately 0.66-12, 1.6-21 and 1.2-5.4 d, respectively. The residence times increased toward the seaward side. In the coastal region, the removal times of 7 Be, 210 Pb, and 234 Th calculated by material balance in one-dimensional models were approximately 1.1-26, 1.2-27, and 0.70-23 d, respectively. Moreover, an enhanced resuspension process not only controlled the partitioning of 7 Be, 210 Pb, and 234 Th between the particulate and dissolved phases, but also this process may play a dominant role in controlling the dynamic behavior of SPM in the water column compared with the advection input/output fluxes of the SPM in the river mouth areas. The removal and the resuspension fluxes were comparable in the estuary. Meanwhile, old composition (which deposition into the seabed long time enough for the decay of 7 Be completely) occupied only a small part in the resuspended sediment during resuspension process.
Print ISSN:
0148-0227
Topics:
Geosciences
,
Physics
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