7 Coastal and Shelf Sediment Transport Processes and Products of the Northern Gulf of Mexico (Posters)

Monday, 21 March 2016
8:00 AM - 5:30 PM
Riverview B

FAR-FIELD FINE SEDIMENT DISPERSAL IN FOURLEAGUE BAY, LOUISIANA: A POSSIBLE ANALOG FOR LARGE RIVER-SEDIMENT DIVERSIONS AND COASTAL WETLAND RESTORATION

Paper number: 7-4
Program: Theme Sessions
Time: 8:00 AM – 5:30 PM

Authors

Abstract

Large river-sediment diversions are being proposed as primary tools for wetland restoration and land building in the Mississippi River Delta. To date, much emphasis in the study of diversion performance has focused on proximal sand-rich deposition. To better understand far-field dispersal and deposition of fine sediments, which account for the majority of sediment discharge, sediment cores from Fourleague Bay, Louisiana and adjacent marshes are being analyzed for 7Be, a naturally occurring radioisotope, as well as mineral and water content. Fourleague bay is 20 km long, extending southeast from outlets of the Atchafalaya River. During 2015, time-series cores have been collected from ten sites, five located in the bay and five from the marshes, and have been analyzed for 7Be using gamma spectrometry. All sites fall within a distance of 9 km to 25 km from the outlet of the Atchafalaya River. Preliminary results show that cores sampled during the early summer season, collected July 2015, contain higher activity of 7Be in the marsh cores, with no detectable 7Be contained in bay cores. The highest activity of 7Be, 3.2 ± 0.79 dpm/g, was found in the top two centimeters of the marsh core closest to the river mouth, site FLM-1. No activity was detectable beyond a depth of 4-6 cm. Surficial activity declined in samples further from the river mouth, with the lowest detectable value being 1.8 ± 0.72 dpm/g in the top two centimeters of site FLM-5. The majority of cores taken late summer, September 2015, indicate an increase in activity. The largest increase was seen at FLB-3, rising from undetectable amounts of 7Be during July to 1.7 ± 0.54 dpm/g in the top two centimeters. Results show that the range of influence for fine sediment delivery to wetlands is > 10 km, suggesting that the area that may be nourished sediment from a large diversion extends far beyond the footprint of proximal sandy deltaic deposits.

Geological Society of America Abstracts with Programs. Vol. 48, No. 1

doi: 10.1130/abs/2016SC-273784

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