Particle dynamics of ~7Be, ~210Pb and the implications of sedimentation of heavy metals in the Wenjiao/Wenchang and Wanquan River estuaries, Hainan, China

摘要

Radionuclides (i.e., Be and Pb) can be used to trace particle and sediment dynamics and to quantify coastal oceanic processes with time scales ranging from a few days to a hundred years. Here, we study the settling dynamics of suspended particles and the implication by sedimentary heavy metals in the Wenjiao/Wenchang River and Wanquan River estuaries through the measurement of the paniculate ~7Be and ~210Pb nuclides. Activity in the paniculate phase had a range of 2.1-54.5 and 4.6-67.9 Bq kg~-1 for ~7Be and excess ~210Pb (~210Pb-xs), respectively, in the Wenjiao/Wenchang River estuary. In the Wanquan River estuary, activity is in the range of 1.2-43.5 Bq kg~-1 for ~7Be and 6.2-194.5 Bq kg~-1 for ~210Pb-xs. At the same time, activity in the dissolved phase had a range of 0.46-1.26 and 0.30-1.17 Bq m~-3 for ~-7Be and ~-210Pb, respectively, in the Wenjiao/Wenchang River estuary; ranges of 0.10-2.31 and 0.09-1.87 Bq m~-3 for ~-7Be and ~-210Pb, respectively, were observed in the Wanquan River estuary. The distribution coefficients (K-d) for the two nuclides decreased within increased in suspended particle matters (SPM) concentration and/or salinity in Wanquan River estuary. The residence times of particulate ~7Be and ~210Pb-xs had ranges of 0.4-1.6 and 1.65-5.15 days, respectively, in the Wenjiao/Wenchang River estuary; and ranges of 0.02 -3.2 and 0.61-4.44 days, respectively in the Wanquan River estuary. All residence times for the two nuclides increased in the seaward direction. In the Wenjiao/Wenchang River estuary, we found that 11.8 -21.0% of Cu, 3.0-9.0% of Zn and 43.2-69.9% for Cd is removed from the water column and deposited into the estuary, and 24.2-34.8% for Cu, 7.2-23.8% for Zn, and 70.0-82.5% for Cd in the Wanquan River estuary, respectively.