Maura Wood, senior program manager for coastal Louisiana restoration with the National Wildlife Federation, takes a water sample in a heavily oiled marsh near Pass a Loutre, La., on Thursday.  As oil from the Deepwater Horizon spill washes up on the Louisiana coast, scientists are gearing up for a potentially massive cleanup job of the shoreline.  See graphics covering how the spill happened, what's being done to stop it, and the impact on the region.  Follow key developments since the initial explosion.  One factor that would make this task especially challenging: Wetlands, which make up a large part of Louisiana's coast, are one of the trickiest terrains to clean. On top of that, the region's ecology is already weakened by the pummeling it took from Hurricane Katrina in 2005 and and subsequent storms.  The oil has traveled across some 110 miles of water to make landfall in Louisiana; it is now threatening Florida and Cuba as well.  Nearly 50 miles of Louisiana's shoreline has been affected and Gov. Bobby Jindal said he expects the area to increase. While cleanup operations have started in some locations, they are still in the early stages.  The area threatened by oil includes seagrass beds, an important nursery habitat for various wildlife, and salt marshes, which occur in back bays and act as a buffer for the mainland against storms and hurricanes. Some 600 species of land and sea creatures are at risk from the spill, according to the Louisiana Department of Wildlife and Fisheries.  Oil cleanups on land can be notoriously inefficient. Typically, only about one-tenth of the liquid that washes ashore ever gets sopped up.  And coastal marshes, unlike beaches or rocky shores, pose special dilemmas for cleanup crews. It is easy to inadvertently stomp on and kill the vegetation. And oil sitting on the surface can get pushed into the soft ground where, in the absence of oxygen, it biodegrades much less quickly.  "With marshes, if you're not careful you can cause more harm," said Doug Helton of the National Oceanic and Atmospheric Administration, who oversees a team of scientists who respond to oil spills.  Of all the environments that can be affected by an oil spill, marshes are deemed to be the "most sensitive," according to a ranking system compiled by the NOAA.  Access thousands of business sources not available on the free web.  Various cleanup techniques could be employed, scientists familiar with past spills said. One is to use low-pressure water hoses to flush out some of the onshore oil and vacuum it off. In marshland, though, more effective high-pressure spraying would likely kill the vegetation.  A technique called in situ burning can also be applied. When the tide floods the base of marsh plants in a soiled area, their upper stalks are set on fire along with any floating oil. Since the root structure and part of the stem survive underwater, the plant can grow back, according to researchers. The approach has been used in Louisiana and Texas previously.  The cleanup effort is also affected by the state of the oil when it hits land. When a slick floats on the water's surface, its physical characteristics change as some of the oil evaporates and the rest is exposed to sunlight. Such "weathered" oil can wash ashore as gooey tar balls, usually ranging in size from a pea to a softball.  "They're distinct blobs, so they're easier to pick up on the land because they're not coating everything," said Nancy Kinner, co-director of the Coastal Response Research Center at the University of New Hampshire. Such tar balls—some eight inches across—have already washed up on the beach at Port Fourchon, La.  If the oil isn't weathered, it can come ashore as a floating mat, typically coating the marsh vegetation and making it harder to remove. Some scientists have tried "bioremediation," whereby special bacteria are sprinkled on the oil to break it down faster. But Dr. Kinner said the results have been mixed, and that naturally occurring bacteria often do the job just as well.  Write to Gautam Naik at gautam.naik@wsj.com
A potentially large amount of oil coming ashore on one of the trickiest terrains to cleanse of oil will make the task of cleaning up the Louisiana cost especially challenging.