All of state’s salt marshes are at risk of vanishing. Natural protectors are threatened along coast. Blame rising seas and humans, study says. Hundreds of species would be threatened; floods would worsen.

By Rosanna Xia

On one side, there’s the rising ocean. On the other, rising buildings.

Squeezed between the two are California’s salt marshes, a unique ecosystem filled with pickleweed and cordgrass, shorebirds and many endangered species.

Coastal wetlands such as Bolinas Lagoon in Marin County, the marshes along Morro Bay and the ecological preserve in Newport Beach can purify the air, cleanse urban runoff before it flows into the sea and reduce flooding by absorbing storm surges like a sponge.

But there’s little room left for this ecosystem along the changing Pacific Coast, as the sea continues to rise and Californians continue to develop the shore. Southern California today has already lost three-quarters of its salt marshes.

The rest could be gone within 100 years. Salt marshes in California and Oregon could disappear entirely by 2110, according to a new study by a team of scientists led by the U.S. Geological Survey. Only a few might survive in Washington. The research quantifies for the first time the fate of this entire ecosystem on the West Coast, based on current projections of sea level rise.

“We’re essentially drowning the marshes,” said Glen MacDonald, a UCLA professor of geography and one of the authors of the study. “If we stay on the same carbon pathway that we are on now, and we take a look at conservative estimates of sea level rise, we would see California vegetated salt marshes we know today, Oregon vegetated salt marshes we know today, 100% gone by the first decade of the 22nd century.”

The study, published in Science Advances, examines 14 major estuaries along the West Coast, from the marshes of Port Susan Bay in northern Washington down to the Tijuana River Estuary.

Marsh by marsh, over many years, scientists measured elevation, tidal flooding, the distribution of vegetation and rates of sedimentation. Using sea level projections by the National Research Council, they designed a sophisticated model to project how each marsh would fare. By even the most conservative measures, the damage was significant — especially in California.

Coastal marshes naturally adapt to sea level rise by migrating inland through a process called transgression. But by building the Pacific Coast Highway and developing up to the edge of basically every marsh, Californians have drawn a line in the sand.

“Think about Seal Beach, think about Carpinteria,” MacDonald said. “You have expensive housing, you have commercial developments, you have our major coastal highways, the railroad, basically hemming in those marshes.”

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