Watershed land use and river engineering drive wetland formation and loss in the Mississippi River birdfoot delta

Andrew W. Tweel and R. Eugene Turner

Limnol. Oceanogr., 57(1), 2012, 18-28 | DOI: 10.4319/lo.2012.57.1.0018

ABSTRACT: The Mississippi River basin was developed for agriculture at an unprecedented scale and intensity within the last 200 yr. These changes favored erosion and sediment transport, which were subsequently reduced by soil conservation practices, the trapping of sediment behind large reservoirs, and channel engineering. We discuss the relationship between sediment loading and the growth, loss, and stability of wetlands in the Mississippi River birdfoot delta (MRBD). We report an anthropogenically driven increase in mean suspended sediment concentrations in the Mississippi River below New Orleans, from a modeled 350 mg L-1 (174 × 109 kg yr-1) at the end of the 18th century to a measured maximum of 675 mg L-1 (348 × 109 kg yr-1) in the late 19th century, followed by a sharp reduction, and then a period of stabilization at 157 mg L-1 (91 × 109 kg yr-1) after 1962. Changes in wetland area of the MRBD over the past two centuries reflect variations in sediment supply during periods of increasing, decreasing, and stable sediment loading, and are distinct from wetland loss patterns in other areas of coastal Louisiana. The rapid growth of the MRBD until the 1930s, which has been used as a reference for one of the world's largest wetland restoration efforts, may not be a suitable archetype for the majority of the coast. Additionally, future variation in sediment supply to the MRBD would likely change the total wetland area of the MRBD.

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