The Threats to the Value of Ecosystem Goods and Services of the Mississippi Delta

Abstract

The Mississippi delta, North America's largest river delta, is also one of the continent's most important coastal ecosystems, both in ecological and economic value. Over the past half century, however, the delta has deteriorated dramatically losing about 1.2 million acres (1900 km2) or about 25{\thinspace}% of the coastal wetlands that existed in the early twentieth century. Much of this loss is due to how the Mississippi River was transformed and managed in the twentieth century. Major dams, primarily on the Missouri River, trapped sediments and reduced sediment delivery to the Gulf by about 50{\thinspace}%. Flood controlFlood controllevees eliminated almost all riverine input to the deltaic plain. In addition, there was pervasive hydrologic alteration of the deltaic plain including oil and navigation canals, induced subsidence, and impoundment. We carried out an analysis of the valuation of ecosystem goods and services of the delta, including three scenarios for continued degradation, stabilization, and rebuilding of the delta. The goods and ecosystem services valued in this study include hurricane and flood protection, water supply, water quality, recreation and fisheries. Presently, the Mississippi River Delta ecosystems provide at least $ 12--47 billion in benefits annually. If this natural capital were treated as an economic asset, the delta's minimum capital asset value would be $ 330 billion to $ 1.3 trillion (3.5{\thinspace}% discount rate). We examined three restoration scenarios. Scenario 1 is a ``business as usual'' scenario where the delta continues to deteriorate. Estimated losses associated with this option are an additional $ 41 billion not including estimates of damage from major future hurricanes (which could top $ 100 billion in costs for a single event). Scenario 2 is a ``hold the line'' scenario that with a suite of projects that aim to maintain the current amount of land across the delta and prevent net land loss. This option assumes prevention of further collapse of the delta and the loss of at least $ 41 billion in ecosystem services. Scenario 3 is a ``sustainable restoration'' scenario, which implements large-scale, controlled diversions of river water and sediment to reconnect the river to the delta and would result in a net increase of wetlands. This scenario will avoid the $ 41 billion in damage under scenario 1 and produce benefits with an estimated present value of at least $ 21 billion, bringing in an annual net increased benefit of $ 62 billion. These values are very conservative figures since they include only partial values of 11 ecosystem services and do not include the value of increased protection for levees, avoided catastrophic impacts such as levee breaching, the benefit of reduced displacement of residents, reduced FEMA relief and recovery costs, lower insurance rates, lower national oil and gas prices, less litigation, or the benefits of an expanding coastal economy, greater employment, and stability gained for existing communities and residents.