The first complete map of tidal wetlands that once made up vast portions of the Pacific coast’s estuaries shows 85 percent of the areas from California to Washington have been lost to development and farmland, and also confirmed the Columbia River’s tidal wetlands are only a quarter of the size they once were.
This means salmon and steelhead born in the Columbia Basin once used an estuary twice as large as what they have now, and used tidal wetlands four times their current size.
This loss of half of Columbia’s estuarine habitat—more than 114,000 acres—has been known for at least a decade to people working on its preservation and restoration. But new mapping of tidal wetlands along the entire West Coast of the U.S. focuses attention on the vast shoreline areas that have been lost with development of the coastline into cities, farmland and industrial areas.
The map comes from research described in a journal article titled “Insights into estuary habitat loss in the western United States using a new method for mapping maximum extent of tidal wetlands.”
In the research, scientists used LIDAR—Light Detection and Ranging, a method using pulsed lasers with GPS to get precise elevation mapping—to determine the historical extent of tides that once defined 444 estuary habitats.
Tidal wetlands are the portions of an estuary with permanent vegetation. Estuaries also include open water, mud flats, sand flats and other habitat types.
Coastwide, 85 percent of estuarine tidal wetlands have been lost, largely to agriculture but also to coastal development; the Columbia River has experienced a loss of 74 percent.
While the Columbia’s estuary was already well mapped, many others were not. Laura Brophy, a lead author of the new analysis, said she has been studying estuaries for more than 20 years and knew from the beginning existing maps were inadequate.
“I was finding that a third to a half of the former tidal wetlands were not shown as ever having been part of the estuary,” Brophy told NW Fishletter.
All along the West Coast, estuaries cover a fraction of their former area. Tidal wetlands, Brophy said, have largely been converted to agricultural land. “It happened early and at tremendous labor, for which I have huge respect,” she said, noting that people worked hard to convert wetlands into productive agricultural fields.
As director of the Institute for Applied Ecology’s estuary technical group, Brophy said having accurate maps—both current and historical—is important when trying to plan and prioritize preservation and restoration work.
In addition, that work is gaining new importance in the face of climate change. Researchers are now studying the possibility of restoring some of those agricultural lands into wetlands as one method for helping to slow the impacts of climate change. Wetlands are proving highly important in sequestering carbon dioxide—pulling CO2 from the atmosphere and storing it in soils.
Scientists have long known the vital role estuaries and estuary wetlands play in the life cycles of salmon and steelhead—and many other species—as nurseries and rearing areas for migratory fish on their way to the ocean, serving as feeding areas for young salmon making the transition to saltwater. According to NOAA Fisheries, lost estuary habitat results in limited foraging success, impeded growth and reduced survival.
Catherine Corbett, chief scientist for Lower Columbia Estuary Partnership, said restoring estuarine habitat for salmon and steelhead is a main purpose of the partnership’s work. Since 2000, the nonprofit organization has restored or protected more than 4,183 acres of estuary and improved more than 82 miles of streams. Combined with projects completed by others, the region has restored or protected more than 28,000 acres along the lower Columbia River, Corbett told NW Fishletter.
The Columbia’s estuary was designated as an Estuary of National Significance in 1995, and is one of 28 nationwide operating under a national estuary program with EPA. That’s one reason why—unlike many other estuaries on the West Coast—the Columbia’s estuary was already accurately mapped. The partnership’s analysis in 2009 found that since 1870, the Columbia’s estuary has been affected from “direct modifications, including diking and draining wetlands for agricultural, residential and industrial development, disposal of dredged material, and deforestation.” Indirect modifications include upstream water withdrawal, dam construction, flow regulation and flow control.
Since 1870, agriculture increased from 1 percent to 24.4 percent of the estuary’s total land area, increasing from 2,267 acres to 61,849 acres. Development went from 0.8 percent to 26 percent of the total land area, jumping from 1,724 to 65,751 acres.
Using maps that compare the current estuary with the habitat in 1870, the partnership recently developed new restoration targets, prioritizing those that have sustained the most loss. Those goals include allowing no net loss of native habitats from a 2009 baseline; recovering 30 percent of priority native habitats by 2030; and restoring 40 percent of those lands by 2050. That translates to 10,382 acres and 22,480 acres, respectively.
To help prioritize lands targeted for restoration, the partnership considered which estuary habitat types were most severely impacted, and found 68 to 70 percent of the Columbia’s vegetated tidal wetlands and 55 percent of its forested uplands have been lost.
The largest losses of wetland classes include herbaceous tidal wetlands, which decreased from 15.4 percent of the estuary to 4.5 percent, losing more than 24,000 acres; and wooded tidal wetlands, which decreased from 17.2 percent to 4.9 percent of the estuary, losing more than 26,000 acres.
The partnership will also target locations along the 146 miles between Bonneville Dam and the Pacific Ocean that have lost the most habitat, such as the area between Portland and Longview, Wash.
Corbett said a big challenge to restoring the Columbia’s estuary is whether the restoration work is keeping pace with development.
Brophy noted that despite strong regulations for protecting estuaries and wetlands, those lands can still be developed if agencies are using outdated maps that inaccurately reflect current or historical tidal wetlands. Now, with better maps available, planners still must adopt them before those areas are protected, she added.
Whether salmon populations can recover to some semblance of their former populations without providing estuarine habitats they once had is not something Brophy felt qualified to answer. But, she said, “I can say that restoration can make a big difference.”
She said estuaries are dynamic places. Water is constantly rising and falling, and nutrient-rich sediments—and a wide array of creatures—are constantly flowing in and out again. Because of that, organisms that use estuaries respond quickly to changes, including restoration.
“Trying to work toward better fish populations and resilience and recovery is a big motivation for doing this work,” she said, adding, “I think we definitely can make a difference. It’s not hopeless at all. It’s really pretty exciting.”