Circulation and fine-sediment dynamics in the Amazon Macrotidal Mangrove Coast |
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| Authors: | Carlos AF Schettini Nils E Asp Andrea S Ogston Vando JC Gomes Robin L McLachlan Marcus EB Fernandes Charles A Nittrouer Eliane C Truccolo Danilo CL Gardunho |
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| Institution: | 1. Institute of Oceanography, Federal University of Rio Grande, Rio Grande do Sul, Brazil;2. Institute for Coastal Studies, Federal University of Pará, Pará, Brazil;3. School of Oceanography, University of Washington, Washington, USA |
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| Abstract: | The Amazon Macrotidal Mangrove Coast (AMMC) is a large (~7500 km2) contiguous mangrove fringe eastwards from the Amazon River mouth. It encompasses dozens of interconnected bays intercalated with mangrove peninsulas. Mud accumulates on the mangrove flats, whereas the bed of the bays and channels is generally sandy. In this study we investigated the circulation, sediment transport and deposition in a central site at one of these mangrove peninsulas. The study was undertaken during the dry period, when there is no influence of the Amazon River plume and minimum local freshwater inflow. Current and suspended-sediment concentration were monitored in a feeder channel on the mangrove flat along a ~1000 m section oriented along the peninsula axis. Sediment deposition was also measured on the flat. Our results show there was a strong exchange between the neighboring bays. Channel currents were flood dominant, reaching up to >1 m s?1, with residual water and sediment transport westwards. Suspended sediment concentration (SSC) in the channel was directly related to velocity magnitude, ranging between 50 and 350 mg L?1. The flat was flooded in a way that indicated the tidal wave evolves westwards, nearly parallel to the AMMC shoreline. Currents on the flats were much slower than those in the channel and showed slight ebb dominance. However, SSC was higher during the flood than ebb, clearly indicating settling during the current deceleration and limited erosion during the following ebb–flow acceleration. The net sediment transport across the section was 60 tons westwards for the period of the experiment (~4 days). The mean deposition rate was 0.006 kg m?2 s?1 (or 1.4 kg m?2 per tide), which was higher than rates from other reported assessments in mangroves. The set of results indicate very large internal sediment reworking in the AMMC. © 2019 John Wiley & Sons, Ltd. |
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| Keywords: | mangroves tidal circulation mud dynamics tropical systems sediment budget |
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