The impacts of hurricane winds and storm surges on broken, unhealthy marshes can be devastating. Early estimates from the USGS National Wetlands Research Center suggest that Katrina converted nearly 30 square miles of marsh east and southeast of New Orleans to open water. It’s unclear at this time whether these losses will be permanent, or if flooding in these areas will eventually subside. However, it is very likely that substantial marsh vegetation was swept away as the storm struck some of the most vulnerable broken marsh areas in coastal Louisiana.
Another area where long-term impacts from Katrina are apparent is in the Chandeleur Islands located east and southeast of New Orleans. Aerial photographs taken by USGS personnel clearly show these barrier islands have been reduced in size by almost 50 percent. Important nesting habitat and rookeries used by brown pelicans, black skimmers, and several other species of waterbirds on the islands were severely eroded and likely destroyed by Katrina. In addition, the hurricane appears to have devastated extensive shoalgrass beds surrounding the islands, which were a critical food source for as many as 25,000 redheads and smaller numbers of lesser scaup. With the loss of protection once provided by the islands, a substantial portion of these shoalgrass beds will probably never recover.
Hurricanes Katrina and Rita will also have significant short-term consequences as saltwater storm surges from the hurricanes affected interior marshes far inland. Some of the largest concentrations of wintering waterfowl in North America gather on these marshes, where the birds feed on submersed aquatic vegetation and seeds of emergent plants. But storm surges likely uprooted and destroyed much of this beneficial vegetation, and most of the rest was likely killed by high salinity in the days and weeks following the storms.