Rising sea levels threaten nation’s marshes

Elkhorn Slough, along with other west coast wetlands, is better prepared to withstand rising sea levels than are east coast marshes, according to a new study published in Biological Conservation. That offers little comfort to those who manage Elkhorn Slough.

The study was conducted by the National Estuarine Research Reserve System and funded by Elkhorn Slough and 15 other sites in 13 coastal states. It evaluated the ability of tidal marshes to thrive as sea levels rise. Compared with other marshes, Elkhorn Slough was deemed “moderately resilient.”

“While the overall score of our marshes was moderate, the study highlighted real risks in the category of elevation change,” said Kerstin Wasson, research coordinator at Elkhorn Slough Reserve and a lead author of the study.

Tidal marshes provide numerous benefits to coastal communities, by protecting against storm surges and flooding, improving water quality and creating habitat for fish and wildlife.

Wetlands managers say marshes tend to keep pace naturally with rising sea levels. As sediments enter the marsh, they fall to the bottom, raising the marsh’s elevation.

That’s not happening at Elkhorn Slough.

“Since the rerouting of the Salinas River, the Elkhorn Slough no longer receives sediment on a regular basis. In the absence of a reliable source of sediment, many of our marshes may not survive sea level rise,” said Dave Feliz of the California Department of Fish and Wildlife, manager of the Elkhorn Slough Reserve.

Feliz says the state is working to reuse sediment to build a new, higher marsh.

Elkhorn Slough is the largest tidal salt marsh in California south of San Francisco Bay, and is home to sea lions, harbor seals, otters and more than 340 bird species and 102 species of fish.