Coastal Wetlands Trends
Coastal wetlands currently make up about 30% of the wetlands in the lower 48 states, or approximately 27 million acres. Since the 1700s, more than half of all of the wetlands in the lower 48 states have been lost, and although there are no reliable statistics that deal solely with coastal wetlands, several factors point to the loss of coastal wetlands as being at least as severe as the loss of wetlands overall. A U.S. Fish and Wildlife Service report estimates that by the mid 1970s, over half of all salt marshes and mangrove forests present in pre-colonial times had been destroyed. California, a large coastal state, has lost over 90% of its wetlands. Florida and Louisiana, two coastal states with the greatest acreage of wetlands, have lost about half of their original wetland area. Louisiana alone is losing between 16,000 and 25,000 acres of wetlands a year, which is the highest sustained wetland loss rate in the country. Most of that loss is occurring in coastal areas.
Why are coastal wetlands disappearing? Many factors are responsible for coastal wetland loss. In the early part of this century, coastal wetlands were drained and used for farming or grazing. More recently, coastal wetlands have been filled or dredged for roads, houses, golf courses, marinas, and other development. In Louisiana, where most of the country's coastal wetland loss is occurring, wetlands are being lost to open water due to a combination of factors including canals dredged through the marshes, dams on the Mississippi River reducing sediment to the marshes, land subsidence, and sea level rise. Even wetlands that are not actually filled or dredged are becoming degraded due to pollution, changes in water flows, and invasion by weeds or other non-native plants and animals.
Coastal wetland losses can be directly traced to population pressures and other human changes occurring along the coast. Coastal populations have increased steadily since 1970. Currently, over half the population of the United States lives in coastal counties, at densities about five times greater than those of non-coastal counties. This trend of people moving to coastal areas is expected to continue in the coming decades. Expanding populations place enormous pressures on existing natural resources, particularly wetlands, which are very vulnerable to changes in water flow, pollution, and habitat fragmentation. As existing population trends continue, coastal managers will be faced with maintaining a delicate balance between ecological considerations and economic development.
The difficulty of maintaining this balance is magnified by global considerations such as sea level rise. Along most of this country's coast, sea level is rising at a rate of between a few inches to a foot or more per century. Although that may not seem like much, if the land is fairly flat a few inches of rise in sea level can mean that the coastline moves hundreds of feet inland. Coastal wetlands can and do move inland with rising sea level, but in developed areas roads, houses, parking lots, and other human structures interfere with this natural migration of coastal habitats. In many places, artificial seawalls keep rising water levels back for a time and coastal wetlands become submerged, eventually dying and eroding away.
The good news is that the rate of coastal wetland loss has declined over the past decades, particularly for tidal coastal wetlands such as salt marshes. In the 1950s, the rate of tidal coastal wetland loss was about 46,000 acres a year, but today it is around 20,000 to 25,000 acres a year. Federal and state regulations governing the destruction of wetlands are partly responsible, as are community efforts to preserve existing coastal wetlands and restore damaged ones. The bad news is that coastal wetland loss continues, and the economic pressures for development in coastal areas are unlikely to lessen. Efforts are needed at all levels of government, in the private sector, by non-profit groups, and by the general public to promote the conservation and restoration of coastal wetlands.
