By Katie Frankowicz / The Daily Astorian
ASTORIA, Oregon — A new survey reveals the West Coast has lost about 85% of its historical estuary habitat, but the mapping could also help identify restoration opportunities and provide a baseline for predicting future changes.
Though large estuaries like the Columbia River have been mapped and surveyed extensively, the recent survey is the first time researchers have applied consistent mapping methods for estuaries along the contiguous West Coast, The Daily Astorian reported.
Marshlands and tidal wetlands that form where rivers transition to the ocean provide rich, dynamic habitat for plants and wildlife, and serve as crucial nurseries for young salmon and steelhead.
Research in the lower Columbia River shows some salmon species linger in the estuary even longer than scientists had realized, putting on the size and weight that will help them thrive in the ocean.
“Given how valuable estuaries are to so many different species, it’s important to understand how much they have changed and what that means for fish and wildlife that depend on them,” Correigh Greene, a co-author of the new study and a research biologist at the National Oceanic and Atmospheric Administration, said in a statement.
The new information accomplishes two goals, said Laura Brophy, lead author of the study and director of the Estuary Technical Group at the Institute for Applied Ecology in Corvallis.
By combining past research with elevation mapping called LIDAR and water level modeling available from NOAA, they establish the extent of estuary habitat and uncover the reach of the historic habitat.
Brophy and the other researchers estimate West Coast estuaries once covered nearly 2 million acres — about three times the size of Rhode Island. Now, following European settlement and development, only a fraction remain. The Columbia River has lost about 74% of its estuary.
In the past, wetland mapping relied heavily on the interpretation of aerial photos and data like soil surveys. Researchers would work with landowners to understand changes in the habitat because of past and current development.
More often than not, they spent a lot of time peering through blackberry bushes trying to find out why some areas that had likely once been wetlands might be disconnected from the estuary.
“We still need people to go peer through blackberries,” Brophy said.
Coordination with landowners and the layering of historic information remains crucial to understanding how and why estuaries have shifted over time and what can be done to restore them.
But there was a recognition that past mapping efforts had fallen short.
The new surveys and estuary mapping technique were possible thanks to an influx of new data — including accurate elevation data and the federal water models — in combination with an accumulation of field experience among researchers and a widely recognized urgency to understand loss in the estuaries, Brophy said.
Taken together, the new information about estuary loss, what the estuaries used to encompass and what remains today provide an important baseline for understanding what the future holds when it comes to climate change-related shifts like rising sea levels.
“We have a better ability to determine what future tidal wetland extent might look like,” Brophy said, adding, “You can’t estimate future change if you don’t have a good handle on current conditions.”
“There’s a big question about sea level rise and how that’s going to be influencing the landscape,” Greene agreed. “This work is really a first step in making good predictions for that.”
While similar work has already been undertaken by local and regional groups on the Columbia River, Catherine Corbett, chief scientist for the Lower Columbia Estuary Partnership, said the new maps provide an important context.
“We can compare what we have in the Columbia to the rest of the West Coast,” she said.
Given what the surveys reveal about where estuaries and associated wetlands once existed, Greene, who works at NOAA’s Northwest Fisheries Science Center in Seattle, hopes the new maps will help agencies and groups that work on restoration prioritize projects and identify new sites.
The areas where much of the current restoration occurs are low in the estuaries, Greene said. At these sites, the economic cost of maintaining the land for agriculture might be relatively high compared to the benefit and landowners might be more open to giving it back to the tides.
But these are also sites that are more vulnerable to sea level rise. The historic information opens up an entirely new landscape of possibilities when it comes to restoration.
The surveys have their limits, however. In highly urbanized areas like Portland, LIDAR can only reveal so much. Greene thinks it is likely researchers are underestimating the amount of estuary loss in these places.