Pushing Wetlands to the Brink
It is hard for me to imagine how coastal Louisiana residents feel as the oil slick from a broken pipeline 50 miles and thousands of feet underwater meanders close to shore, threatening to devastate their remaining barrier islands and coastal wetlands. These are people who witnessed firsthand in 2005 during Hurricanes Katrina and Rita that unhealthy wetlands make them more vulnerable to storms.
Hurricane Katrina alone killed at least 1800 people and caused an estimated 125 billion dollars of economic damage, and it is no secret that much of this damage resulted because of the steady erosion of Louisiana’s wetlands, which provide many ecosystem services, including serving as a barrier to a hurricane’s storm surge.
Now, after decades of deteriorating health, the oil spill may drive more marshes under. If a significant amount of oil gets to land, which seems probable given the current rate, amount and movement of the spill, it could kill marshland plants and animals, leaving denuded mudlands defenseless against storm events and sea level rise.
Louisiana can’t afford to lose much more of its wetlands. Yet like a runaway train, more forces are working to erode the wetlands than to build them. And this oil spill is just the latest offender. The triple whammy of sea level rise, sinking land (known as subsidence), and tropical storms and hurricanes make it difficult to imagine how restoration, which is an expensive, long, and difficult process, will ever keep pace with the rate of loss.
I can’t help but wonder what this means to coastal Louisiana. If the wetlands keep disappearing, at what point will it become too risky to stay in certain places because of flooding? Will people even want to remain, considering that many cultural and ecological activities, such as fishing, birding, and hunting, are contingent on healthy wetlands?
After all, people settled in southeast Louisiana because it was an amazingly fertile floodplain. Around the world, floodplains are spots of incredible human culture and growth – the Nile, the Mekong, the Ganges. Deltas today, however, are incredibly burdened under the weight of high human population density, industrial agriculture, urbanization, dams, and sea level rise (see a related article about how deltas form and respond to human-use).
The land in Louisiana is sinking in large part because of a century of engineered modifications to control the movement of water on the Mississippi River. The levees built for flood protection and easy river navigation have forced the sediment and freshwater moving along the Mississippi River to bypass the coastal land and run straight out into the Gulf of Mexico. From a flood protection and transportation perspective, that makes a lot of sense, but levees are a terrible idea from the standpoint of wetland maintenance, since the movement of freshwater and deposition of its nutrient rich sediment is what built the Delta in the first place.
Essentially the Louisiana Delta has been progressively starved of sediment and nutrients, and over time it has become skinny and unhealthy. And just like an unhealthy human body, it is more vulnerable to stress. Rising seas creep further and further inland, drowning coastal marshes and salting up inland soils, causing plant death. Land without plants can’t hold soil, and when the storms come the soil erodes rapidly.
What impact the oil spill will have is completely dependent on how much of it reaches the land and for how long. A healthy coastal ecosystem could probably handle an oil spill without too much damage, but an unhealthy one, which is what exists today, is very vulnerable to long-term diebacks and erosion.
For additional information on the spill see:
- NOAA Office of Response and Restoration
- US Coast Guard Deepwater Horizon Response
- NASA MODIS Imagery
Hompage image credit: NOAA