A warming climate and rising ocean will push seawater farther upstream in the Columbia River estuary.
By the year 2100, the estuary will see enormous changes in the type and amount of habitat that is now used for salmon and, in the worst-case scenario, it becomes what one researcher calls an “inland sea.”
Those are some of the conclusions of a draft study by Antonio Baptista and Mojgan Rostaminia of the Center for Coastal Margin Observation & Prediction at Oregon Health & Science University.
“While uncertainties remain on the strength and timing of sea level rise off the Oregon coast, should sea level rise reach values of about 1 meter (well within current predictions), the Columbia River estuary will be deeply affected,” Baptista said. “Salinity and other ocean influences could reach as far as the Willamette River under low to moderate river discharges, altering residence times and ecological function, and affecting salmon habitat.”
“There will likely be winners and losers among species and estuarine functions,” he continued, “and planning ahead (even in the face of uncertainty) for a potentially very different system will be critical when making long-term regional decisions.”
Baptista spoke to over 300 people Tuesday, Oct. 18, at the 2016 Future of Our Salmon Conference in Portland. The conference was sponsored by the Columbia River Inter-Tribal Fish Commission. Baptista and other conference speakers challenged the region to combat climate change by restoring the critical connection between floods, floodplain habitat and a healthy river system.
Baptista is professor and director of the Science and Technology Center at CMOP. Rostaminia is a Ph.D. student and Baptista is her advisor. The results presented are a part of Rostaminia’s thesis. CMPO is a multi-institutional center headquartered at OHSU, with Oregon State University and University of Washington among other key partners (www.stccmop.org).
“Sea level rise matters to the estuary,” Baptista said, as he described the uncertainty of predicting what actually will happen over the remainder of this century.
Using a modeling system for collaborative science and management called Virtual Columbia River, Baptista reviewed a number of climate change scenarios that impact sea level rise in the Columbia River estuary.
The scenarios were developed by the U.S. Army Corps of Engineers and National Oceanic and Atmospheric Administration and include low, medium and high estimates of sea level rise in the estuary. The scenarios run the gamut from nearly no change in sea level to a rise of 1.77 meters, the NOAA high estimate for the year 2100.
“There are certain thresholds and one meter grabs our attention,” Baptista said. “If crossed, the estuary is vastly transformed with deeper salinity intrusion, smaller plumes and gains and losses of habitat.”
In months when the Columbia River is at its lowest flows — generally fall, winter and summer — salinity will intrude as far up the river as 170 kilometers (about 106 miles), all the way to the Willamette River in the worst case scenario (1.77 meter sea level rise).
“At 1.27 meters of sea level rise and at low flow, we are seeing salinity where we’ve never seen it before,” Baptista said. “At 1.77 meters it is no longer an estuary, now it is an inland sea.”
Plume could disappear
In addition to salt water intruding farther up into the estuary than ever seen, the river’s plume volume at low to moderate water will decline significantly.
“The plume is important to salmon survival,” Baptista said. “Essentially, one of the geographic features of the Northwest Coast will disappear.”
Declining plume size, he said, will affect ocean entry conditions for juvenile salmon, and (within some uncertainty, and with appropriate context) is believed to negatively affect smolt-to-adult ratios.
And, there will be “enormous” changes in juvenile salmon habitat, he said. However, each reach will be impacted differently. “There will be some gains and some losses.”
There will be as much as a 375 percent to 500 percent change in the amount of shallow water habitat in areas between Longview and the Willamette River, for example. The lower estuary and upper estuary will see the fewest changes.
“These changes will have deep implications on ecosystem functions and salmon populations,” Baptista said.
Salmon habitat within the estuary is characterized in the model by the physical properties of water depth, velocity, temperature and salinity.
“Both nursery and migratory habitats are considered, but the focus is on the former,” he added. “Favorable nursery habitat calls for shallow water and velocity thresholds specific to fish size, and is negatively affected outside certain temperature and salinity ranges.”
Still being refined
The Baptista and Rostaminia study is still being refined and has yet to go through peer review, something he expected would begin within a couple of months.
“But the results show a potential for drastic change that is too clear to ignore, and that should be incorporated into regional thinking now,” he concluded.
Baptista has studied the Columbia River coastal margin for a quarter century. He provides scientific leadership for an innovative “collaboratory” (SATURN, the Science and Technology University Research Network; www.stccmop.org/saturn), where sensors, models, information flows and communities of practice come together to advance the scientific and practical knowledge of the estuary and plume.
The Baptista and Rostaminia presentation can be found at tinyurl.com/Estuary-Changes.