Date of Graduation

12-2018

Document Type

Thesis

Degree Name

Master of Science in Geology (MS)

Degree Level

Graduate

Department

Geosciences

Advisor

John B. Shaw

Committee Member

Matt Covington

Second Committee Member

Kusum J. Naithani

Third Committee Member

Jill A. Marshall

Keywords

coastal, CRMS, delta, geology, land change, geomorphology, sustainability, wetlands

Abstract

Recent reports estimate that the marshes of the Mississippi Delta receive just 30% of the sediment necessary to sustain current land area1. An extensive monitoring campaign by the USGS and LCPRA provides direct measurements of sediment accumulation, subsidence rates, and deposit characteristics along the coast over the past 10 years2, allowing us to directly evaluate this sediment balance. By interpolating bulk density, organic fraction, and vertical accretion rates from 273 sites, a direct measurement of organic and inorganic sediment accumulation can be made. Results show that a total of 82 MT/year of sediment is delivered to the coast. Using a fluvial sediment discharge of 113 MT/yr1, 52% of the riverine transported sediment is accumulated in the coastal lands of the Mississippi Delta. Assuming an average 9 mm/yr subsidence rate3 and 3 mm/yr sea-level rise1, this accumulation results in a 2.7 MT/yr (3.5%) sediment mass surplus. However, there is a 0.014 km3/yr (5.4%) sediment volume deficit caused by the sediment porosity being too small to fill the accommodation space. About 20 MT/yr inorganic and 6 MT/yr organic sediment initially accumulates in deltaic areas directly nourished by the Mississippi and Atchafalaya rivers, resulting in an initial sediment trapping efficiency of 18%. The remaining sediment must be delivered indirectly to the coast after passing through the ocean, accounting for another 39 MT/yr of inorganic sediment being trapped on coastal marshes. 17 MT/yr organic sediment is produced through marsh plant production. These results suggest that even if current relative sea level rise rates do not change, the gap between accommodation and accumulation is not as dire as previously thought.

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