by Tom Moorman, Ph.D.
Hurricanes Katrina and Rita have been devastating for residents along the Gulf Coast. As vital recovery work for people and their homes and businesses proceeds, biologists are assessing the impacts the storms had on Louisiana’s coastal marshes that provide vital waterfowl wintering habitat for several million ducks and geese and untold numbers of other wetland birds and wildlife.
Historically, hurricanes—along with fire—played an important role in the complex ecology of coastal wetlands. Healthy marshes consist of dense stands of grasses and other emergent wetland vegetation interspersed with small ponds, lakes, and bayous. If unchecked, however, marsh vegetation can choke out open-water areas over time. This natural process, known as succession, eventually forms “closed marsh” with little value for waterfowl and other wildlife. In the past, hurricanes periodically set back succession in Louisiana’s coastal marshes by breaking up dense stands of vegetation and scouring new ponds and lakes. Additionally, accompanying storm surges pushed salt water inland into fresh and intermediate-salinity marshes where plants are intolerant of high salinity levels. Lengthy exposure to salt water kills salt-intolerant vegetation, creating more open-water areas. Whether caused by wind and wave action or changes in salinity, the new ponds and lakes created by hurricanes were prime habitat for waterfowl, as wild celery, widgeon grass, delta duck potato, and other prime duck foods flourished in the shallow, open water.
Unfortunately, people have dramatically altered the hydrology of Louisiana’s coastal marshes, increasing the vulnerability of both coastal communities and waterfowl habitats to the effects of intense storms such as Katrina and Rita. Robbed of nourishing sediments from the Mississippi River and fragmented by numerous shipping canals, much of Louisiana’s remaining coastal marsh is rapidly eroding. Consisting of large expanses of open water interspersed with small islands of vegetation, this “broken marsh” is the opposite condition of healthy coastal wetlands.