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NW Fishletter #370, June 5, 2017

[4] Warming Climate Complicates Cold-Water Species Management

New data show Columbia Basin rivers are warming, which can create a lethal environment for salmon and steelhead, as happened in 2015.

Overall, water temperatures in the basin are increasing slowly, but the largest mainstem rivers are heating up much faster.

That's what USDA Forest Service researcher Dan Isaak and colleagues determined after examining 40 years of stream temperature data from nearly 400 sites in the basin.

Isaak gave a presentation on the study at the May 16 Northwest Power and Conservation Council meeting.

In 40 years--the period over which river temperature data has been available in the basin--the trend is 0.01 degrees C per decade in June; 0.27 degrees C per decade in July; 0.14 degrees C per decade in August; and 0.15 degrees C per decade in September.

While those increases may, at first glance, seem small, Isaak said, "Obviously cold water fishes will end in immolation."

But the rate at which streams are warming, called climate velocity, depends not only on the time of year but also the slope of the river. Steeply sloped streams, generally at higher elevations, have slower climate velocities, he said.

Trout and other species at higher elevations will be buffered from the extreme changes and can find cold-water refuges, but salmon and steelhead returning to natal homes in steep-sloped areas have to get there by traversing lower elevation mainstem rivers on their way.

Isaak said these larger mainstem rivers are on wide, flat plains, where geomorphic processes have been a work for millennia, and are warming at higher rates.

For example, he said the temperature of the Snake River as measured at the Anatone, Wash. recording station is increasing in the summer by 0.3 degrees C per decade (or 0.54 degrees F per decade). The Willamette, Yakima and Entiat are other examples of mainstem rivers where temperatures are rising.

Earlier presentations at the Council have reported on numerous studies underway to identify cold-water refuges in lower river reaches and to understand both the processes that form and maintain these refuges and how fish use them.

Beaver dams contribute to hyporheic cooling. Credit: Weber et al., 2017

What we know is cold-water habitats are created by cooler water plumes from tributaries, groundwater seeps and springs, colder side channels and floodplain alcoves, and hyporheic upwelling, staff hydrologist Leslie Bach told Council members April 17.

Though not as well known, hyporheic (literally, "underneath flow") upwelling is a very significant process that contributes cold water to rivers, Bach said.

Hyporheic upwelling is the exchange of water through gravel and soils under and beside side channels and floodplains. Because hyporheic flow occurs below the surface, it is protected from solar radiation.

Where are these various cold-water habitats located? Surveying 190 tributaries between the Columbia River mouth and the confluence of the Columbia and Snake rivers, the EPA identified some 150 tributaries that were at least 2 degrees C colder than the two mainstem rivers.

Groundwater and hyporheic exchange were found to be the primary sources of cooler water in the Willamette River, according to research by retired Oregon State University professor Stan Gregory and his team.

Of the floodplain alcoves surveyed in the Willamette, 56 percent were more than 2 degrees C colder than the mainstem, while only 25 percent of the side channels surveyed were 1 or 2 degrees C colder than the mainstem.

In the Yakima River, another of the basin's larger mainstem rivers, researchers with U.S. Geological Survey found groundwater was a major source of cold water.

In the basin's smaller streams, intermittent and ephemeral streams as well as groundwater are providing cold water, Bach told the Council.

The thermal profiles for most rivers and streams in the basin are incomplete.

Other gaps in information include understanding how habitat restoration and hydro system operations can modify groundwater-surface water interactions and floodplain habitats to provide refuges for salmon, steelhead and other cold-water species.

Beyond that, fish managers and ratepayers need to know, among the many options, where to make investments to protect and restore cold-water processes and places.

"This would include," wrote John Harrison, the Council's information officer, "planting more streamside vegetation that shades the water in spawning and rearing areas, and perhaps providing fish passage into areas of cold-water habitat that currently are blocked by dams or natural barriers.

"Other approaches could include taking steps to reduce the risk of wildfires in places where streamside vegetation could be destroyed, and purchasing water rights from willing sellers to leave more water in streams and rivers."

Forest Service scientist Isaak said the best preservation and enhancement approach will incorporate species distribution--where and when fish spawn, rear and migrate--into stream temperature models.

Both Isaak and Bach emphasized that the tools and resources needed to get the job done are mostly available, may be as never before.

Using thermal infrared cameras and optical imaging mounted on drones are relatively easy ways to collect data.

In-channel temperature monitoring with handheld devices can be used by individuals, including citizen volunteers. eDNA sampling, to identify the presence of cold water species, can also be collected from a stream by single individuals.

This and other valuable crowd-sourced information is becoming more common, Isaak said.

However, what's needed is a real-time weather system for 30,000 river kilometers in the U.S. portion of the Columbia Basin, and it's going to take time to develop, Isaak said.

While some of the data and technology are there, he said, the space-time network models needed to integrate data and forecast river conditions will require "new statistical theory and big computers." -Laura Berg

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