HR: 1330h
AN: H33A-07    [Abstracts]
TI: Source Determination and Residence Time Indications of Suspended Sediment for the Mississippi River
AU: * Stewart, C M
EM: cstewar1@tulane.edu
AF: Tulane University, Department of Earth and Environmental Sciences 120 Dinwiddie Hall, New Orleans, LA 70123 United States
AU: McKee, B A
EM: bmckee@tulane.edu
AF: Tulane University, Department of Earth and Environmental Sciences 120 Dinwiddie Hall, New Orleans, LA 70123 United States
AU: Duncan, D D
EM: dduncan@tulane.edu
AF: Tulane University, Department of Earth and Environmental Sciences 120 Dinwiddie Hall, New Orleans, LA 70123 United States
AU: Ferrell, R E
EM: rferrell@lsu.edu
AF: Louisiana State University, Department of Geology and Geophysics E146 Howe-Russell Building, Baton Rouge, LA 70803 United States
AB: Characterization of suspended particulates in large river systems is important and challenging. The world's 25 largest rivers, in terms of sediment discharge, account for approximately 40% of the fluvial sediments that enter the ocean. Particulates that enter the ocean from rivers are the products of integrated basin-wide processes. This study focuses on the development of a suite of proxies that give insight to the source and system-wide residence time of particulates discharged by rivers to the coastal zone. To completely characterize the suspended sediments in a major river system, regular sampling over longer periods of time is necessary. A river's suspended load is highly variable over a range of time scales; therefore high temporal resolution sampling is required. Continuous, regular sampling incorporates not only seasonal and annual change, but it also allows interpretation for differences on a sub-seasonal scale. Biweekly sampling of the Mississippi River was performed from March 2002 through December 2004. Previous studies have used short-lived radionuclides (⁷Be, ¹³⁷Cs, and ²¹⁰Pb) to determine sediment source and residence time in small agricultural watersheds. Using the same approach in a large river system is more challenging because sources and sinks are more numerous and complex and residence times change from smaller to larger systems. As a result of these complexities, the use of short-lived radioisotopes alone was not completely diagnostic in the Mississippi River system. Trends in ⁷Be and ¹³⁷Cs activities appear to be driven by mixing of old and new sediments. Therefore, both source and residence time effects control the observed radioisotope activities. Additional examinations of grain size, ²³⁴U/²³⁸U isotope activity ratios, and sediment mineralogy were done to better evaluate basin sources. Four up-basin sampling trips were also performed in February, April, July, and November of 2004. The upper Mississippi, Missouri, Ohio, and Arkansas rivers were sampled each time. These end-member samples are essential to determining primary source, residence time, and are used in a semi-quantitative mass balance analysis for the Mississippi River system. When done in conjunction with basin source indicators, the mass balance approach sheds light on how the main stem of the Mississippi River influences particle retention times, long term storage, and particle alterations.
DE: 1815 Erosion and sedimentation
DE: 1894 Instruments and techniques
DE: 4558 Sediment transport
SC: Hydrology [H]
MN: 2005 Joint Assembly