SAVANNAH — Land once used to bury garbage near the Port of Savannah has been converted to a man-made ecosystem of marsh grasses and microbes, bugs and birds aimed at cleaning pollutants from rainwater before it reaches the Savannah River. Georgia Ports Authority officials said Monday that they spent $4 million installing 14 acres of artificial wetlands that meander for about a mile along the busy highway trucks travel to carry cargo to and from Savannah's docks. The work was finished about six months ago, but the port authority put off any public announcement until Earth Day.