RESTORATION OF A POLLUTED MARINE MARSH, SAN FRANCISCO BAY, CALIFORNIA

Much of San Francisco Bay was edged originally by marine marshes, but human activities decreased them to about 10% of their former extent. Most now are polluted by various agents; many are undergoing restoration to their assumed former conditions. An extensive restoration of a heavily polluted marsh in Richmond began in 2003, and it is still underway. The marsh was polluted 50 and more years ago by dumping of pyrite cinders, used in making sulfuric acid, onto its surface. Eventually leaching of the cinders decreased the pH to 1 and flooded the marsh with trace metal contamination exceeding recommended levels. The owner (University of California) was ordered to restore the marsh by removing the surface sediments to a depth of 2+ m and replacing them with unpolluted sediment. This new sediment was shaped to match the topography of the original marsh and various plants were placed along the margins, a great many of which died. The bare surface sediment, cracked by desiccation, was initially overgrown by microbial mats, and normal marsh plants rooted in small patches. Foraminifera did not occur in the new mud, but juvenile specimens of Milliamina fusca and later Trochammina macrescens and T. inflata appeared but failed to propagate. As the area became more overgrown by plants, foraminifera and other marsh organisms increased in numbers. The new marsh has no trace metals exceeding limits, but marsh plants and foraminifera have not yet attained their former condition nearly eight years later. Complete restoration will likely take at least another decade or so.