Particle Dynamics in a Managed Navigation Channel Under Different Tidal Conditions as Determined Using Multiple Radionuclide Tracers

Abstract

AbstractParticle dynamics play significant roles in sedimentological and geomorphological processes as well as biogeochemical cycles in estuaries. We collected a suite of water samples from the North Passage of the Changjiang (Yangtze) Estuary during different tidal conditions in summer 2009 to observe variations in the particulate 234Th, 7Be, 210Pb, and 137Cs activities as well as in particle transport, deposition, and resuspension. The mean activities of 7Be and 210Pbex in surface water during low tide were lower than those during high tide. The residence times of 7Be (1.1–3.4 d), 234Th (4.7–28 d), and 210Pb (7.9–34 d) in the North Passage increased with the increase of salinity and suspended particulate matter. The estimated results, based on a two‐dimensional model of 7Be, 234Th, and 210Pb, showed that sedimentary particles in the North Passage experienced net deposition during neap tides whereas those in more seaward areas of the North Passage exhibited net resuspension during spring tides. The 7Be/210Pbex activity ratio in seaward area of the North Passage was lower during spring tide than during neap tide but both were close to values in surface sediments beyond the estuary. Using 7Be/210Pbex and 137Cs/210Pbex activity ratios as tracers, we deduced that most of particles in the North Passage were not derived from the direct deposition of Changjiang input particles but were transported from sediment deposited offshore. These results emphasized the important contributions of offshore inputs to sediments in this channel, which should be considered when conducting channel dredging of other estuarine systems.