Drowning of the Mississippi Delta due to insufficient sediment supply and global sea-level rise

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Abstract

Over the past few centuries, 25% of the deltaic wetlands associated with the Mississippi Delta have been lost to the ocean1. Plans to protect and restore the coast call for diversions of the Mississippi River, and its associated sediment, to sustain and build new land2,3. However, the sediment load of the Mississippi River has been reduced by 50% through dam construction in the Mississippi Basin, which could affect the effectiveness of diversion plans4,5,6. Here we calculate the amount of sediment stored on the delta plain for the past 12,000 years, and find that mean storage rates necessary to construct the flood plain and delta over this period exceed modern Mississippi River sediment loads. We estimate that, in the absence of sediment input, an additional 10,000–13,500 km2 will be submerged by the year 2100 owing to subsidence and sea-level rise. Sustaining existing delta surface area would require 18–24 billion tons of sediment, which is significantly more than can be drawn from the Mississippi River in its current state. We conclude that significant drowning is inevitable, even if sediment loads are restored, because sea level is now rising at least three times faster than during delta-plain construction.

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Figure 1: Geologic map of the Mississippi River delta plain.
Figure 2: Suspended sediment loads for the lower Mississippi River at Tarbert Landing, Mississippi, the Atchafalaya River at Simmesport, Louisiana, and for the combined Mississippi and Atchafalaya, obtained by summing the two data sets.
Figure 3: Predictions of relative sea-level change, submergence and land loss.
Figure 4: Sediment mass balance for the delta region with modern sediment loads, and with hypothetical restored sediment loads.

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Acknowledgements

This analysis was supported by the Harrison Professorship in the Department of Geology and Geophysics at Louisiana State University (M.D.B.), the LSU Boyd Professorship at Louisiana State University (H.H.R) and a US National Science Foundation grant (M.D.B.). We thank M. Garvin, Louisiana State University Department of Geology and Geophysics, for processing satellite imagery and DEM data to create submergence maps, and we thank numerous colleagues for discussions about the Mississippi delta region, coastal restoration, the subsidence problem and sea-level change over the years. We benefited greatly from comments by T. Törnqvist.

Author information

Modelling of submergence and sediment mass balance was conducted by M.D.B. Previous work on the lower Mississippi Valley, the Mississippi Delta and the Gulf of Mexico shoreline by H.H.R. and M.D.B. provided data and context for this study.

Correspondence to Michael D. Blum.

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