Particle Dynamics in a Managed Navigation Channel Under Different Tidal Conditions as Determined Using Multiple Radionuclide Tracers. Issue 3 (8th March 2021)

• Record Type: Journal Article
• Authors: Wang, Jinlong; Huang, Dekun; Xie, Weiming; He, Qing; Du, Jinzhou
• Is Part Of: Journal of geophysical research. Volume 126:Issue 3(2021)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-03-08
• Subjects: activity ratio -- channel -- deposition -- residence time -- resuspension -- tide; Oceanography -- Periodicals; 551.4605
• DOI: 10.1029/2020JC016683
• Languages: English
• ISSNs: 2169-9275

Abstract

Abstract: Particle 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 234 Th, 7 Be, 210 Pb, and 137 Cs activities as well as in particle transport, deposition, and resuspension. The mean activities of 7 Be and 210 Pbex in surface water during low tide were lower than those during high tide. The residence times of 7 Be (1.1–3.4 d), 234 Th (4.7–28 d), and 210 Pb (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 7 Be, 234 Th, and 210 Pb, 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 7 Be/ 210 Pbex 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 7 Be/ 210 Pbex and 137 Cs/ 210 Pbex 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. Plain Language Summary: We investigated the tidal distribution of particulate activity of 234 Thex, 7 Be, 210 Pbex, and 137 Cs in the North Passage of the Changjiang Estuary in summer 2009. We found that the mean activities of 7 Be and 210 Pbex in surface water during low tide were lower than those during high tide. The residence times of 7 Be (1.1–3.4 d), 234 Th (4.7–28 d), and 210 Pb (7.9–34 d) in the North Passage were positively correlated with salinity and suspended particulate matter. Based on a two‐dimensional model of 7Be, 234Th, and 210Pb, we estimated 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. Using 7 Be/ 210 Pbex and 137 Cs/ 210 Pbex AR 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 there from sediment deposited offshore. These results remind us to reconsider previous cognition that the source of particles in the waterway of estuary was dominated by the riverine input, especially under the background of regime shift in estuarine dynamics caused by the decline in sediment load from the upstream of river. Key Points: Particulate activity of 7 Be, 234 Th, 210 Pb, and 137 Cs varied by tidal condition Sedimentary particles in the seaward part of the waterway underwent net deposition during neap tide and net resuspension during spring tide Sediments derived from the riverine supply were not the dominant source of sediments in the estuarine channel