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Cliff R. Hupp(1), Charles R. Demas(2), Daniel E. Kroes(1), Richard H. Day(3), and Thomas W. Doyle(3)
crhupp@usgs.gov
(1)U.S. Geological Survey, 430 National Center, Reston, Virginia 20192,
(2)U.S. Geological Survey, 3535 Sherwood Forest Blvd., Baton Rouge, Louisiana 70816
(3)U.S. Geological Survey, 700 Cajundome Blvd., Lafayette, Louisiana 7050
Abstract
Sediment deposition and storage are important fluvial geomorphic processes that shape landforms, support riparian ecosystems, and provide ecological services, yet documentation and interpretation of sedimentation processes remain incomplete. The central Atchafalaya Basin suffers from high sedimentation in some areas and hypoxia in others. We established 20 floodplain transects that reflect the depositional environments and monitored general and local sediment deposition patterns over a 3‐year period (2000‐2003). Deposition rate, sediment texture, bulk density, and loss on ignition were determined near artificial markers located along transect. Mean sedimentation rates ranged from 2 to 42 mm/yr, percent organic material ranged from about 7 to 28 percent, percent sand (>63 microns) ranged from about 5 to 44 percent, and bulk density varied from about 0.4 to 1.3. The sites were categorized into 5 statistically different groups based on sedimentation rate; these were categorized by parameters that include hydroperiod, source(s) of sediment‐laden water, hydraulic connectivity, flow stagnation, and local geomorphic setting along transect (levee vs. backswamp). Low elevation (long hydroperiod), high hydraulic connectivity to multiple sources of sediment‐laden water, and hydraulic damming (flow stagnation) lead to the highest amounts of sediment trapping; the converse in any of these factors typically diminish sediment trapping. Results suggest the area potentially traps 6.72 billion kg of sediment annually; 820 million kg represent organic materials. Thus, the Atchafalaya Basin plays an important role in sediment storage, including the sequestration of carbon. Findings on local sedimentation patterns may aid in management of flow to control sediment deposition and reduce hypoxia.
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