natural process of sediment deposition has been blocked by an extensive levee system that directs flood water past wetlands. The western coastline is marshy, but the marshes only extend inland by at the most, then the elevation begins to increase and the marshes fade into solid grounded prairies. Therefore, rising sea levels due to global warming and coastal erosion, may not affect the western coastline as profoundly as it will the eastern half, which may be replaced in open water over substantial areas. Loss of the wetlands The wide range of benefits provided by the wetlands of this region were not recognized by a majority of policy makers in the early 20th century. Wetlands provide vital ecological services including flood control, fisheries production, carbon storage, water filtration and enhanced disagreement over the relative importance of these factors, although it is probably safe to say that the two major factors now acting are subsidence, mostly from lack of sediment, and salt water intrusion from canals dredged to service oil and gas wells and facilitate oil and gas exploration. Further wetland loss is attributed to the construction of the now-closed Mississippi River Gulf Outlet, which introduced salt water into freshwater and intermediate marshes and facilitated significant erosion. A brief explanation of various causes follows. Subsidence of the coast is certainly occurring. Some people blame the direct effects of oil and gas extraction. The logic is that as billions of barrels of oil and saltwater and as trillions of cubic feet of gas were removed from the reservoirs in which they had accumulated over millions of years, these reservoirs lost their ability to support the weight of the rocks above. As these structures slowly collapsed, the soil above gradually subsided. The wetlands on the surface began to sink into the gulf waters. Others argue that subsidence is a natural process in deltas, as sediments compress, and that the real problem is the lack of flood waters that would normally deposit new layers of sediment. The role of hurricanes is also a matter of disagreement; some studies show that hurricanes actually build elevation in marshes. Another factor is rising sea levels estimated to be about 2mm per year associated with global warming. Sediment compaction is also a significant source of wetland loss. Compaction rates have been conservatively estimated at 5mm to 10mm or more per year for the organic-rich Holocene sediment (peat) that predominates