Reuters: A lack of oxygen and nutrients below the surface of beaches in Alaska’s Prince William Sound is slowing the dissipation of oil remaining from the 1989 Exxon Valdez spill, U.S. researchers said on Sunday. The team conducted field studies over the past three summers using geologic information and hydraulics to try to determine why patches of oil linger on the beaches 20 years after the worst oil spill in U.S. history. The supertanker Exxon Valdez spilled more than 11 million …