Rising bay water could drown marshlands
Mike Taugher
Contra Costa Times
11/16/2011
Rapidly rising seas could wipe out nearly all of San Francisco Bay's remaining tidal marshes, the most important wetlands on the West Coast for shorebirds and a buffer against flooding of highways and property.
More than 80 percent of bay shoreline marshes have been lost since 1850, and a new study reveals the possibility that if sea level rise speeds up, more than 90 percent of what is left could disappear in the next 100 years, researchers say in a new study.
Even newly restored wetlands could go under, perhaps including portions of a South Bay salt ponds restoration that is expected to cost $1 billion over several decades and smaller projects in Marin County and along the northern rim of San Pablo Bay.
The study confirms a long-standing fear, said Peter Gleick, president of the Pacific Institute, an Oakland-based environmental research group and the author of two papers on sea level rise in the bay. He was not involved in the study released Wednesday. "The remaining wetlands in the bay are extremely vulnerable to rapid sea level rise."
The study was done by scientists at PRBO Conservation Science, a Petaluma-based organization that advocates for conservation, along with researchers at the University of California, the University of San Francisco, San Francisco State and a private consulting firm, ESA PWA.
"Tidal marshes are incredibly resilient to changes in sea level, depending on how fast seas rise and how much
sediment is available," the study's lead author, Diana Stralberg, said in a news release. Stralberg is a biologist at the University of Alberta who is also affiliated with PRBO Conservation Science.
Unfortunately, she said, marshes cannot keep up with rapid sea level rise. "They will need our help."
Researchers recommend preparing now by opening more levees to create new marshes and limiting development in slightly higher shoreline areas marshlands might shift to.
Despite the threat to newly restored marshes, researchers said their results show such projects are critical if the bay is to have any marshes at all.
Restored and maintained wetlands have a better chance of replenishing themselves with sediment or by shifting to higher ground.
Two factors will determine what happens, researchers say. One is how rapidly the water rises, and the other is how much sediment rivers bring into the bay. Sediment has been declining in recent years.
This is the first time researchers coupled sea level rise projections with detailed estimates of sediment buildup. That enabled them to predict when rising seas would swallow up wetlands and when sediment deposits would replenish them.
The results ranged from startling to reassuring.
In the worst case -- the sea rising 5½ feet in 100 years and sediment continuing to decline -- 93 percent of remaining tidal marshes would be destroyed.
At the other extreme -- a 1½ foot rise with more sediment deposited -- the tidal marshes would build up faster than the rising water.
The projections for sea level rise were based on an intermediate and a high rate of sea level rise.
The seas have risen gradually since the last ice age, and tide gauges at the Golden Gate show about 7 inches of rise since the mid-1800s, which scientists have attributed largely to ice melt and expansion caused by warming.
