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5 Integrated Coastal Management in the Mississippi Delta
- Texas A&M University Press
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93 ≋ mately 60% of the estuaries and marshes in the Gulf of Mexico are located in coastal Louisiana (Lindstedt et al. 1991). During the 20th century, a massive loss of about 25% of coastal wetlands in the Mississippi Delta occurred. At present, a large-scale effort is being planned to restore the delta. An understanding of the causes of this land loss is important not only for a scientific comprehension of the mechanisms involved, but also so that effective management plans can be developed to restore the delta (for reviews see Boesch et al. 1994; Day et al. 2000; Boesch et al. 2006; Day et al. 2007). Our goal in this chapter is to describe the forces that led to the formation and maintenance of the delta, the causes of land loss, and the plans for restoration of the delta. In doing so, we put the process into a conceptual framework of deltaic functioning. A central conclusion of this discussion is that sustainable management should be based on ecosystem functioning and that ecological engineering should be used to the maximum extent possible. Development of the Mississippi Delta The Mississippi Delta, like most other deltas, is made up of several interdistributary hydrologic basins that are separated by current or abandoned river distributary channels (Roberts 1997) (Fig. 5.1). The delta consists of 2 physiographic units, the active deltaic plain to the east and the chenier plain to the west (Roberts 1997). Active deltaic The Mississippi Delta is one of the largest and most important coastal ecosystems of the Gulf of Mexico and one of the most important natural habitats in North America. It is very important, ecologically and economically , to both the state of Louisiana and to the nation. The coastal ecosystems of the delta provide habitat for fish and wildlife, produce food, regulate chemical transformations , maintain water quality, store and release water, and buffer storm energy (Day et al. 1997; Day et al. 2000; Day et al. 2007). These processes support a diversity of economic activities vital to the state and national economies. Louisiana has the largest fishery by volume in the contiguous United States. Other wetland-related activities include ecotourism, hunting, and fur and alligator harvest. Those natural resource dependent activities generate several billions of dollars in economic activity when associated goods and services are incorporated (Day et al. 1997). In addition, port activities on the lower Mississippi River are first in the nation by tonnage, and about a third of oil and natural gas used in the United States is either produced in the north-central Gulf or transshipped through the delta. The river, basin, and delta rank among the top 10 rivers in the world. Mean flow of the river is about 18,000 m3 /s. The Mississippi River has a total watershed of 3.2 million square kilometers, encompasses about 40% of the area of the lower 48 states, and accounts for about 90% of the freshwater inflow to the Gulf of Mexico. Major tributaries to the lower Mississippi River include the Ohio, upper Mississippi, Missouri, and Arkansas rivers. Approxi5 Integrated Coastal Management in the Mississippi Delta System Functioning as the Basis of Sustainable Management John W. Day, John Barras, G. Paul Kemp, Robert Lane, William J. Mitsch, and Paul H. Templet 94 ~ Day, Barras, Kemp, Lane, Mitsch, and Templet last glacial period 15,000–20,000 years ago. A number of factors enhanced the growth of the delta and retarded its deterioration. With the exception of the first delta lobe (the Maringouin lobe), significant parts of all subsequent delta lobes have been incorporated into the current delta as a system of overlapping and interwoven distributary systems. Distributary ridges, crevasse splays, and reworking of sands in barrier islands formed a skeletal framework of those natural levee ridges and barrier islands within which the delta plain has formed (Kesel 1989; Kesel et al. 1992). Ecosystem functioning and sustainability of the delta is controlled by interactions of the Mississippi River and marine processes (Day et al. 1997; Day et al. 2007). The skeletal framework modulated the interaction of those riverine and marine processes, protected wetlands on the deltaic plain from erosion and salinity intrusion, and slowed interactions between freshwater and saline parts of the delta. A number of processes were important in the formation and maintenance of the delta. Until modified by human activity, many of the distributaries continued functioning, either seasonally or year round, delivering river water to large areas of the delta plain. Fresh river water...