Bill Finch, Director of Conservation and External Affairs with The Nature Conservancy in Alabama, explains the role that wetlands play in mitigating the effects of major storms, and how the Gulf oil spill might adversely affect those ecosystems.
Q: In coastal communities along the Gulf of Mexico and Eastern Seaboard, how do wetlands help mitigate the effects of major storms?
A: Marshes may play their most critical role in protecting shorelines day in and day out. Most shoreline erosion in the U.S. is the result of daily erosion. A three-foot high wave, for example, can easily knock down a sturdy brick wall, and even waves in the 1- to 3-foot range will clobber a bare shoreline. Thick marsh grasses bend with those waves, dissipating the energy, so that the waves have no energy left by the time they get to the hard shoreline. When you lose those marshes, on the other hand, you not only lose that dampening effect, you also effectively increase the water depth near the shoreline. And the greater the water depth, the bigger the waves can get. So big waves get closer to the shoreline, multiplying the damage. Loss of marsh grasses and oyster reefs may be a primary culprit in day-to-day shoreline losses approaching 15 feet a year (!) in places in Mobile Bay. Similar or greater rates are noted at multiple points in the Gulf and on the Atlantic Coast.
Marshes have another important effect: They collect sediment very efficiently from each wave that passes through them. So they in effect build up land, often as fast as or faster than the rate of rising sea level. That’s probably a major reason why areas that have healthy marshes have seen relatively little impact from sea level rise of about a foot over the past century.
So how do they benefit people during storms? Some of the greatest storm damage isn’t simply the result of rising water, but rather the impact of waves on top of the rising water. During Katrina, it wasn’t just the rising water that caused problems: Hundreds of houses and structures along the Mississippi Coast were bulldozed by crashing waves, and carted wholesale out into the open Gulf.
Marshes may not have a significant impact on the height of the surge, but they play a big role in determining how big those hurricane-driven waves are, and how close they come to structures.
In areas with healthy marsh, the shoreline is still stable, and the offshore area is shallow, so houses don’t sit right next to the deep water where waves can develop the most energy. And during the most common hurricanes and tropical storms, the marsh grasses themselves increase the friction in the water column, further reducing the height of waves.
Q: Are residents often aware of the role such wetlands play in protecting their communities?
A: Some coastal residents have a vague notion of the importance of marshes for shoreline and storm protection. But in areas like Louisiana, Mississippi and Alabama, there’s a growing sense that marshes can help protect coastal communities from storms.
Q: Is greater attention being paid to maintenance and protection of wetlands in areas more commonly affected by major storms?
A: Certainly, there’s a lot more lip service given to the importance of marsh … but in some areas, including here in coastal Alabama, we’re putting our marsh where our mouth is. The Nature Conservancy has been leading an effort to rebuild the marshes and reef structures that once protected shorelines, created vast areas of fish habitat and improved water quality. We’re doing that by rebuilding marshes the old-fashioned way, integrating marsh and seagrass restoration programs with oyster reef restoration. The oyster reefs, we’re discovering, once played an integral role in protecting the marshes themselves. So by combining oyster reef restoration with marsh restoration, our marsh restoration success increases dramatically.
The limitation to these efforts is money – we’re still working hard to secure enough money to restore reefs and marshes a few acres at a time. We need to be ramping this up dramatically – from a mile of new reef and marsh protected shoreline to 100 miles of reef and marsh protected shoreline.
Q: How does the oil spill in the Gulf endanger those wetlands, and what other effects might the spill have on communities’ ability to deal with the current storm season?
A: The oil spill threatens not only the creatures of the marsh, but also the marsh’s very survival. As the oil washes into the marsh, it’s quickly trapped there, like gum in your hair. There’s no good way to remove it. As it sinks down into the soils, it immediately creates a thick blanket that prevents any oxygen from entering the soil. Without that oxygen, the soil creatures that support the growth of plants die. And then the roots themselves begin to die from lack of oxygen. Soon thereafter, the toxic portions of the spill begin to have an effect, and may wipe out what’s left.
Once the roots of the marsh die, the marsh itself falls apart, soil and all, as waves quickly pick apart and cart away the fragile soils.
In the areas where some marsh vegetation survives, the soils become a toxic repository that re-contaminates creatures every time they come back to the marsh to breed and grow. Some 90 percent of our commercial seafood species use the marshes for breeding or for growing each year. Many can’t exist without the marsh. So when these creatures return each year to the marsh to produce their young, the young are wiped out again and again by contact with contaminated marsh. In Alaska’s Prince William Sound, the herring fishery didn’t recover to harvestable levels until this year – 20 years after the Valdez incident. And shrimp and many other annual reproducers still haven’t recovered there, in large part because the young are re-contaminated each year when they return to their nursery grounds near shore.
Will it be that bad on the Gulf Coast? There are reasons to hope not, in part because the marsh can grow so much faster and potentially recover more quickly here, essentially burying the most toxic elements. But where the oil comes ashore, we’ll likely see losses of contaminated young for some years.