Hidden wetlands of Alameda Point

In the southwestern corner of Alameda Point – on the wildlife refuge – are 30 acres of wetlands.  They lie within the cleanup area known as Site 2.  The wetlands themselves are not contaminated, but due to protracted cleanup efforts and studies elsewhere on the site, the entire area has been off limits since the base was closed in 1997.

In May 2012, the Navy released a draft plan for covering the old underground waste disposal area on Site 2 with clean soil and seeding it with native grasses.The plan also includes a study of the wetlands on the site.  Here are some highlights from the wetlands report, and also some photos taken by a Navy contractor a few years ago during investigative work.

The wetland delineation report prepared for the Navy identified three distinct wetland and water features:

Open Water/Mudflat – Open water/mudflat is found in two large ponds, the North Pond and the South Pond.

The North Pond is connected to San Francisco Bay by a 36-inch-diameter culvert that penetrates the perimeter berm and seawall.  “The culvert appears to be appropriately sized to allow full tidal exchange on a diurnal basis, as the tidal wetland drains and fills completely twice a day,” according to the report.

Of the South Pond, the report said, “Most of this pond is either shallow standing water or mudflats, with a fringe of pickleweed (Salicornia virginica) forming the transitional plant community between the mudflats and nearby uplands.  Freshwater seasonal pond and transitional mudflat habitats such as this have been identified in the Baylands Ecosystem Habitat Goals Project (SFEI 2001) as rare and important habitat components.”

The Navy’s summary of the wetlands report goes on to say, “The South Pond and mudflat matrix is high-value habitat in that it offers high tide refugia for wading shorebirds, and low tide refugia for ducks and geese. Because pond water surface elevations in this area are maintained by groundwater and precipitation, they do not fluctuate on a diurnal basis as they do in the northern (tidal) pond. Since this area normally has both mudflats and open water, it is available as foraging habitat year-round. At the time of the reconnaissance survey in late October [2011], an estimated 500 birds representing at least eight species were observed foraging in this pond and mudflat.”

Seasonal wetlands – One area on the north side of the site is considered low quality and will be covered by the soil cap.  The lost wetland acreage will be replaced at other locations on the site.  At the south end of the site is another seasonal wetland.

Tidal wetlands are found surrounding the North Pond that is connected to San Francisco Bay.