California's coastal marshes could be washed out to sea by 2110

Pass by the Carpinteria Salt Marsh Reserve on your way up the 101, and you'd be forgiven for thinking nothing of it. From afar, it looks like a giant piece of brown, barren land sitting idle between you and the Pacific ocean. 

Approach it on foot, and you'll see that it's actually a dynamic ecological hotspot, teeming with life. Migrating and endangered birds call it home, feeding on crabs, clams and mussels rooted deep in the silt. Its brown hue comes from knee-high pickleweed that's actively filtering salt out of the seawater, so that it can stay hydrated. Life is sustained by the sea, which carries in nutrients twice a day, as rising tides flood the area.

A bird takes off from the pickleweed that covers the Carpinteria salt marsh.

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Jacob Margolis

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The marshes along California's coast have been around for the last 5,000 to 6,000 years, but they'll likely disappear by the next century if we continue emitting greenhouse gases at current levels. That's according to a new study from the U.S. Geological Survey and the University of California Los Angeles. 

While tidal forces keep the marshes alive, rising sea levels due to climate change are also likely to destroy them if we don't take steps to curb fossil fuel consumption.

"Essentially, 100 percent of these vegetated marshes in the state would disappear," said Glen MacDonald, geologist at UCLA and co-author of the paper, standing on a dirt berm above the Carpinteria marsh. 

The marshes along California's coast are dynamic systems able to maintain equilibrium along with the sea. Saltwater pushes in during high tide, carrying with it sediment and nutrients. As it pulls back during low tide, the nutrients and sediment are left behind. 

But as sea levels rise, so does the amount of sediment that's deposited on the marshes. Plants for now are managing to grow their way through, MacDonald said.

Pickleweed survives by separated salt from the water that engulfs it on a daily basis.

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Jacob Margolis

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But MacDonald said that heretofore slow process is speeding up. Throughout most of the 20th century sea levels rose about 1.5 mm per year. Now, the rate is closer to 3 mm. That rate is expected to increase substantially through the end of the century. That means low-lying marshes will likely be completely submerged while those on higher ground will flood and will be unable to adapt. In either case, large areas of ecologically significant habitat will disappear, as plants die off and animals disperse.

MacDonald said some marshes could survive if allowed to migrate inland, but those would be the exception. 

"When we looked at the California marshes ... for most of them there's very low potential for that to happen," he said.

Stand in the middle of the Carpinteria marsh, turn a full 360 degrees and you'll see development on all sides. Houses are built on a sand bar that's been maintained to create a channel that limits the water that flows in and out.

The channels of water that wind their way through the Carpinteria salt marsh reserve run towards the ocean.

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Jacob Margolis

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The rear of the marsh presses right up against a business park and train tracks that carry the Pacific Surfliner.

A business park development prevents the Carpinteria salt marsh from moving towards the hills as rising sea levels threaten its survival.

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Jacob Margolis

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There's nowhere for the marsh to go. It's a scene, MacDonald said, that's true for the majority of the marshes throughout the state.

As the marshes disappear, so will key habitats that've been relied on by plants and animals for millennia. The marshes are rich stopovers for migratory birds making their way down the length of North America, and for near-shore fish that rely on them for food. The endangered light-footed Ridgway's Rail and Belding's Savannah Sparrow both risk extinction if the habitats disappear, as does the endangered salt marsh harvest mouse, which seeks refuge in the high plants to protect itself from both the water and predators. 

In addition, marshes also serve key functions related to the health of the planet. They store carbon, which will be released as they begin to die off. They are barriers to storm surges that protect against erosion. They act as catches for debris that make their way down from the hills after wildfires. And they filter polluted water and sediment that flows from our cities towards the ocean, keeping our seas a bit cleaner.

This is not the first time California marshes have faced trouble. 

"90 percent of our wetlands have been lost in California because of coastal development," said Karen Thorne, research ecologist with the USGS and co-author of the paper.

There's a small possibility that marshes can be saved. Humans could curb greenhouse gas emissions and hope for a minimal rise in sea levels, scenarios that might save a few of California's remaining marshes, according to authors of the study. But, assuming that doesn't work, there are some other potential options.

One is that we could deposit sediment manually to raise the levels of the marshes faster than they would rise on their own. That's what the U.S. Fish and Wildlife Service has been doing at the Seal Beach National Wildlife Refuge in Orange County over the past year. The marsh there is particularly low lying, and thus one of California's most threatened. So, while dredging Anaheim Bay, they decided to spread the sediment across the top of the marsh to see if they could help it recover.

https://www.youtube.com/watch?annotation_id=annotation_3569411329&feature=iv&src_vid=grfOtnTuVMY&v=cftiZ5ENguo

"It seems to have worked, it just depends on if people want to contribute the time and money," said Thorne. "Ecosystems are resilient if we let them do what they're made to do."

Pickleweed and spartina, both plants that thrive in coastal marshes, have begun to recover in the area. The problem is the cost, which according to MacDonald is about $200,000 per acre. That raises questions about the financial feasibility of the solution. 

There are other possibilities, like regulating the amount of ocean water that reaches the marshes by installing dikes and pumping stations. Or, adjusting our communities to allow the marshes to migrate further inland. 

Standing between the winding channels of the Carpinteria salt marsh, it's peaceful. Birds pick through the mud, seawater trickles in along with the rising tide, and the horn of the Pacific Surfliner blares somewhere off in the distance.

"The fact that basically, your grandchildren, my grandchildren, they might not be able to stand here and see this," said MacDonald, "that kind of hits home."

The Carpinteria Salt Marsh Reserve.

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Jacob Margolis

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The study was published in Science Advances.

This story is part of Elemental: Covering Sustainability, a new multimedia collaboration between Cronkite News, Arizona PBS, KJZZ, KPCC, Rocky Mountain PBS and PBS SoCal.