Most of the West Coast’s estuary habitat has vanished, according to a new study, the most thorough of its kind. The mapping project found that, today, less than 15% of historic estuaries remain along the Washington, Oregon and California coastlines.
Estuaries form where fresh water from rivers and streams meets the salt water of the ocean. They take the form of salt marshes, tidal forests, beaches and steep river mouths. They are among the most productive and diverse ecosystems on Earth. Estuaries are also among the most endangered habitats on the planet. The study found that, at one point, salt marshes covered roughly 2,800 square miles of the West Coast. That's an area larger than the state of Delaware. But today, that number has been reduced by more than 85%. Other research indicates rising seas caused by climate change could soon drown much of the little estuary habitat that remains.
Laura Brophy, an estuary ecologist at the Institute for Applied Ecology in Corvallis, Oregon, is one of the study's authors. She said humans are responsible for the disappearing ecosystem.
“When Europeans arrived in this area they began doing the alterations that have caused the loss of the wetlands,” Brophy said.
White settlers built dikes and levees. They filled in some wetlands and drained others. Fertile salt marshes were converted into valuable agricultural lands. And houses were built on tidal flats.
Some stretches of the Columbia River in Oregon, for example, have lost more than 90% of their historic wetland habitat. More than 98% of the estuarine land in Samish Bay on the north shore of Washington's Puget Sound were converted to farmland. Large quantities of Tillamook Bay’s estuaries (78%) were converted to agricultural land, which today produce hay for dairy cows.
Other areas were filled in to make way for urban development.
“Especially in bigger cities along the southern California coast, estuaries have been filled,” Brophy said.
That actually made the research harder to do because Brophy and her collaborators from the Pacific Marine and Estuarine Fish Habitat Partnership created maps using lidar and digital elevation models to estimate the historic extent of tidal wetlands. Since the maps were created using the maximum reach of tides, and many urban areas have been built up from lower elevation levels, those no-longer-tidal areas weren't detected.
That means Brophy’s maps likely underestimate the extent of wetland lost in urban areas like Los Angeles.
This is the first study of its kind to look at the historic extent of wetlands across the entire West Coast and not just at individual wetlands. That’s important, Brophy said, because those new maps can serve as a standardized baseline for future research. If scientists know where wetlands once were, they know what areas to target for habitat restoration.
The maps can also help scientists know how wetlands might shift and move as sea levels rise, and which ones might be drowned forever. The shape of the mountains and river mouths that border some estuaries might prevent the wetlands from moving farther inland as the shoreline recedes.
“The biggest threat to estuaries today is sea level rise, in my opinion,” said Karen Thorne, a research ecologist at the United States Geological Survey Western Ecological Research Center who was not involved in the study. “U.S. Wetlands are no longer being drained to the same extent, but sea levels are rising around the world, and in some areas they’re rising faster than wetlands can keep up.”
Salt marshes and estuaries naturally rise in elevation. The winding channels and reeds capture sediment and biological matter as it flows downstream, and the plants and trees in a salt marsh also build up soil when they eventually die and decay.
So far, the West Coast’s estuaries have grown at a rate that has protected them from with sea level rise, Thorne said. But climate change is continuing to warm the oceans and warm water is taking up more space than cold water. Combined with melting glaciers and ice sheets, this is causing sea levels to rise at unprecedented rates. Many marshes and estuaries won't be able to keep up.
Restoring and preserving wetlands is extremely important, Thorne said, because they provide a number of benefits for the surrounding ecosystem and the humans who live near them.
Estuaries serve as natural filters, cleaning water as it winds its way to the sea. They serve as barriers, absorbing storm surges and high tides and protecting inland houses from pounding waves.
"When you take out a wetland and put in a sea wall, it can be more prone to flooding from both sea level rise and storms,” Thorne said. “We removed the natural, green protection for people who lived there.”
Estuaries provide habitat for dozens of fish species and invertebrates. They’re where clams and oysters grow best. Tiny wetlands, scattered up and down the coast, also provide important resting grounds for migrating shorebirds and marine mammals.
Even larger game fish like endangered Northwest salmon can spend a large part of their developmental phase growing and hiding from predators in sheltered, food-filled estuaries.
“We’ve learned more and more recently how important these estuaries and wetlands are for salmon,” Thorne said.
Even animals like orcas, which rarely enter estuaries, rely on the food these areas produce.
Thorne said estuaries can support so much life because they’re at the interface between land and sea, and that means they’re full of nutrients. “They’re some of the most productive ecosystems on earth.”
Although they’re vanishing, there is some good news. Thorne’s past research shows that the more untouched an estuary is, the longer it can hold up to sea level rise. Netarts Bay in Oregon, for example, has only lost about 2% of its total estuary habitat. By focusing on habitat restoration, Thorne believes other estuaries can be preserved for future generations, or at least, a little bit longer.