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.

"There was an old horse stable on the lands that we've used, there was a lot of residential and industrial garbage, and we've created this area that captures water and effectively cleanses it," Curtis Foltz, the executive director of Georgia's ports, told reporters at the site Monday.

The artificial wetlands are sandwiched between the docks and the port terminal's rail yard. Drainage pipes route stormwater running off paved services into the wetlands, where microbes living at the roots of sawgrass and rushes essentially eat pollutants in the rainwater before it trickles another 2 miles to the river. Those microbes help support other wildlife such as crawfish and brim, egrets and dragonflies.

The man-made ecosystem is capable of filtering about 100 million gallons of rainwater a year, said Natalie Dawn, the port's chief environmental officer. She said that keeps pollutants from reaching the river and reducing the amount of dissolved oxygen in the water, which fish need to breathe.

Ensuring the Savannah harbor contains enough dissolved oxygen for wildlife has been a major issue for environmentalists as the port authority seeks to deepen the 30-mile shipping channel to make room for supersized cargo ships. Deeper water makes it harder for oxygen from the water's surface to mix all the way to the river bottom.

The Army Corps of Engineers plans to spend $70 million installing a dozen machines in the harbor that essentially work like giant versions of the bubblers in home aquariums. They suck up river water, swirl it with oxygen from a generator and then inject it back into the river. Even if the machines work as promised, the government will have to pay an estimated $1.2 million a year to keep the oxygen injectors running.