Aquatic Sciences Meeting, Albuquerque 2001

SS17 Biogeochemical Dynamics of River-Dominated Margins (Disciplinary and Environmental Connections)

Date: Wednesday, February 14, 2001, Time: 2:45:00 PM

Location: Dona Ana

Allison, M, A, Tulane University, New Orleans, USA, malliso@tulane.edu

Coakley, B, J, Tulane University, New Orleans, USA, bcoakle@tulane.edu

SEASONAL AND INTERANNUAL STORAGE OF FINE-GRAINED SEDIMENT IN THE LOWER MISSISSIPPI RIVER: EVIDENCE FROM ACOUSTIC MAPPING AND BOTTOM SAMPLING

Swath bathymetry, subbottom stratigraphy (CHIRP), and bottom character (side-scan sonar) data were collected in conjunction with bottom sampling at two study sites in the lower Mississippi River in December 1999, February and May 2000 to examine spatial and temporal controls on seasonal sediment storage. Maps of bathymetrirc differences between February and May indicate low discharge storage at the English Turn site is superimposed on meter-scale elevation change caused by downriver migration of large bedforms (100-500 m wavelength). CHIRP and sediment data reveal high porosity mud layers up to 50 cm thick are present in water depths shallower than 20 m, with discontinuous deposition between bedforms at greater water depths. The more estuarine Venice site shows low discharge sediment storage up to 200 cm thick, concentrated in the deepest part of the channel thalweg. Geochronological analysis of these deposits indicates that a portion remains stored in the bed over multiple discharge cycles. The magnitude, timing, and location of sediment storage in rivers have profound implications for the transformation of POC and particle-reactive substances prior to their discharge on the margin.

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Aquatic Sciences Meeting, Albuquerque 2001

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