Rita, or have raised homeowners' insurance premiums to cover their risk. Environmental effects Katrina also had a profound impact on the environment. The storm surge caused substantial beach erosion, in some cases completely devastating coastal areas. In Dauphin Island (a barrier island), approximately to the east of the point where the hurricane made landfall, the sand that comprised the island was transported across the island into the Mississippi Sound, pushing the island towards land. The storm surge and waves from Katrina also severely damaged the Chandeleur Islands, which had been affected by Hurricane Ivan the previous year. The US Geological Survey has estimated of land was transformed to water by the hurricanes Katrina and Rita. Before the storm, subsidence and erosion caused loss of land in the Louisiana wetlands and bayous. This, along with the canals built in the area, let Katrina keep more of its intensity when it struck. The lands that were lost were breeding grounds for marine mammals, brown pelicans, turtles, and fish, and migratory species such as redhead ducks. Overall, about 20% of the local marshes were permanently overrun by water as a result of the storm. The damage from Katrina forced the closure of 16 National Wildlife Refuges. Breton National Wildlife Refuge lost half its area in the storm. As a result, the hurricane affected the habitats of sea turtles, Mississippi sandhill cranes, red-cockaded woodpeckers, and Alabama Beach mice. Katrina produced massive tree loss along the Gulf Coast, particularly in Louisiana's Pearl River Basin and among bottomland hardwood forests. Before the storm, the standard mortality rate for the area's trees was 1.9%, but this interval increased to 20.5% by the end of 2006. Delayed mortality as an effect of the storm continued with rates up to 5% until 2011. This significant loss in biomass caused greater decay and an increase in carbon emissions. For example, by 2006 the decreased biomass in bottomland hardwood forests contributed an amount of carbon which equated to roughly 140% of the net annual U.S. carbon sink in forest trees. The storm caused oil spills from 44 facilities throughout southeastern Louisiana, which resulted in over of oil being leaked. Some spills were only a few hundred gallons and most were contained on-site, though some oil entered the ecosystem and residential areas. After a spill at the Murphy Oil refinery, for example, 1,800 homes were oiled in the towns of Chalmette and