California Forum

With sea level rise, a major California ecosystem faces extinction if we don’t act

The Bolinas Lagoon and other Pacific coastal marshes protect coastal developments from storm surges and erosion and filter pollution from contaminated surface waters. With rising sea levels, they could vanish by the end of the century.
The Bolinas Lagoon and other Pacific coastal marshes protect coastal developments from storm surges and erosion and filter pollution from contaminated surface waters. With rising sea levels, they could vanish by the end of the century. mcrisostomo@sacbee.com

It is increasingly clear that climate change will touch every corner of California. For the state’s coastal marshes – a major ecosystem from San Diego to Humboldt counties – the toll may be complete annihilation.

New research from UCLA, the United States Geological Survey and several other institutions reveals the stark vulnerability of state coastal marshes to rising sea levels. By the end of the century, chances are good that these places will disappear without drastic emissions-reducing measures on a global scale.

Once dismissed as unproductive “swamplands” to be dredged, filled-in or otherwise obliterated, coastal marshes – vegetated intertidal zones where freshwaters meet ocean waters – are now recognized as having immense value in the form of ecosystem services.

They provide irreplaceable habitat for birds, fish and other animals. As green infrastructure, they protect coastal developments from storm surges and erosion. They filter pollution from contaminated surface waters, protecting oceans and coastal areas. One recent study concluded the annual value of these services in the United States ranges from $5,000 to $70,000 per hectare.

After years of intensive surveying and modeling of topography, vegetation and sedimentology of marshes from the Tijuana Estuary in California to the Port Susan Bay Estuary in northern Washington, my colleagues and I reached a sobering conclusion: The entire ecosystem faces extinction.

Marshes are not helpless, but their defenses are rendered moot by human activity and the increasing pace of sea level rise. Marshes typically survive by growing upward or moving inland. For now, they’ve kept up by accumulation of mineral sediments and growth of marsh plants, but these mechanisms will be overwhelmed under current rates of greenhouse gas emissions.

Complicating matters, migration inland will not be an option in many cases. Coastal development surrounds many marshes with valuable infrastructure such as housing, commercial facilities and major highways. Seawalls and other protective measures built around these places will preclude landward expansion, sentencing marshes to death by drowning.

The threats are particularly acute in California, where we estimate that by 2110, all current productive vegetated marshes will be replaced by mudflats. Oregon’s marshes face a similar fate. In Washington, perhaps 32 percent of current vegetated marshlands may survive.

Our conclusions are based on an estimated maximum increase in sea level of 5.25 feet by 2100. Based on new satellite data and projections of glacial melt in Greenland and Antarctica, that estimate may be conservative.

Recent measurements of greenhouse gas concentrations also counsel against optimism. Globally, we remain stuck on the highest emissions pathway projected by the International Panel on Climate Change.

So what can California do to save coastal marshes? Hard engineering solutions are impractical at this scale.

In a field experiment at Seal Beach Marsh, we enhanced vertical growth by adding thin layers of additional sediment, but the project is proving incredibly expensive and difficult. Per-acre costs exceed $ 275,000. Sophisticated dykes and gates to manipulate water levels would be similarly cost-prohibitive.

As seas rise and flood developed areas, the smartest approach economically might be land use planning that accounts for the value of ecosystem services and allows wetlands’ landward migration. This would require forfeiting some current developments, but it is not unprecedented. In 2015, a levee was breached so coastal marsh could reclaim 1,500 acres in the San Pablo Bay National Wildlife Refuge.

But maybe we’re putting the cart before the horse. Go take a good, long look at one of California’s marshes. See the subtle play of the sun on chord-grass and pickleweed, listen to the call of the birds, smell the rich fecundity of this special ecosystem.

Savor the moment, because you may be part of the last generation to see a California coastal marsh unless we begin confronting climate change much more urgently.

Glen M. MacDonald is the John Muir Memorial Chair and distinguished professor of geography at the Institute of the Environment and Sustainability, and Ecology and Evolutionary Biology at UCLA.; mcdonal@geog.ucla.edu.

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