Efforts Underway to Reduce Mercury, Improve
Faced with a combination hazardous levels of mercury and high water temperatures, Idaho Power is taking a watershed approach to improve the quality of the Snake River as it runs through the Hells Canyon Complex of three hydroelectric dams.
Through decades of work to relicense the Hells Canyon, Oxbow and Brownlee dams, water temperature was determined one of the biggest risks to cold water fish downstream, particularly federally endangered chinook salmon. Ralph Myers of Idaho Power said in the heat of the summer water flowing into Brownlee Reservoir was reaching 25 degrees Celsius or 80 degrees Fahrenheit. To spawn, chinook salmon below the three-dam complex look for water in the 13 degree Celsius range or around 56 degrees Fahrenheit.
“The temperature of the water coming out of Hells Canyon during the summer months doesn’t meet spawning standards,” Myers said.
The Hells Canyon Complex license with the Federal Energy Regulatory Commission expired in 2003. Idaho Power’s been given extensions as it works through myriad issues related to recreation, water quality and fish and wildlife habitat.
Myers said as members of Idaho Power’s environmental team were looking at ways to tackle the warm water concerns a stakeholder suggested using a temperature control structure that would release water from deep in the reservoir where the water is colder than it is on the surface.
“If there is cold water deep in Brownlee we had the option to pull selectively cool water to release downstream,” Meyers said.
As Idaho Power’s environmental team wrestled with water temperature Myers said it was also annually applying and reapplying for Clean Water Act Section 401 Certification from Oregon and Idaho. At one point Oregon’s Department of Environmental Quality asked Idaho Power to analyze toxins from Brownlee Reservoir.
According to a U.S. Geological Survey report the agency was asked to conduct the water quality research and methyl mercury was discovered in 198 similar-sized smallmouth bass collected between the inflow to Brownlee Reservoir and the Salmon River confluence. The study found 31 percent of the fish exceeded Idaho’s human health fish-tissue criterion for mercury of 0.3 milligram per kilogram and 96 percent exceeded the more stringent State of Oregon criterion of 0.04 mg/kg.
Austin Baldwin of the Boise USGS office said his agency has been asked to look at all aspects of the mercury cycle – where and how it’s distributed in water, plankton, fish and sediment and how the levels of methyl mercury changes seasonally.
“Previous studies looked at a lot of different contaminants in the Snake River and 500 different chemicals and metals were found,” Baldwin said. “Mercury was the problem contaminant; nothing else was at such a high level.”
The source of mercury comes from the atmosphere - from volcanic eruptions to forest fires and coal-fired power plants. Baldwin said inorganic mercury falls to the ground, either into the water or on land where it eventually washes into a stream. When mercury particles get into Brownlee Reservoir they either go into the sediment or move downstream.
“The concentrations of methyl mercury increases as you move through the system of dams,” Baldwin said.
He said as nutrients from agriculture come into Brownlee Reservoir, plankton eat them. When the plankton die they sink to the bottom and are decomposed by bacteria. In so doing the bacteria use up the available oxygen in the deeper parts of the reservoir, Baldwin said. Depleting the oxygen creates anoxic conditions. In this environment mercury is converted to methyl mercury – the highly toxic variety.
“In moving water there aren’t anoxic conditions because the water is circulating more,” Baldwin said.
Methyl mercury both bio-accumulates – the more fish one eats with mercury the higher the levels increase – and also biomagnifies, Baldwin said. When big fish eat smaller fish they are ingesting the mercury in their prey.
“As humans we eat a whole bunch of fish and it magnifies as it goes up the food chain,” Baldwin said.
The mercury research will continue for the next several years, but Chris Randolph of Idaho Power said based on what they know about the heavy metal’s risk to downstream fish and wildlife and the entire food web, they scrapped building the temperature control structure and are looking upstream for solutions to high water temperatures and contaminants.
Along with The Freshwater Trust, a nonprofit that designs and implements river restoration projects, Idaho Power came up with the Snake River Stewardship Program to improve habitat through stream bank restoration and riparian planting on two of the Snake’s tributaries, as well as improving irrigation efficiency and instream channel reconstruction along the middle section of the river.
Myers said, “We partnered with Freshwater Trust - we got to give them the credit, they came up with that idea.”
The Freshwater Trust has worked with tribes and interested groups to reconfigure the Kootenai River near Bonners Ferry, Idaho in an effort to improve habitat for the endangered white sturgeon, Myers said. Based on that experience, Idaho Power and Freshwater Trust designed a pilot project at Bayha Island south of Nampa near Walters Ferry.
Myers said the Snake River’s channel was formed 15,000 years ago by the Lake Bonneville Flood. Upstream federally managed storage projects built 100 years ago capped off high flows that carved the river’s channel. Coupled with the low gradient where it flows through southern Idaho, the river is now shallower and warmer.
Danielle Dumont of Freshwater Trust’s Portland office said, “Flows are managed so much by the dams and the water bed is so shallow it moves slowly in certain areas - this has impacts on the overall health of the river.”
While they continue to grind through the relicensing process that could take another five years, Idaho Power started an instream river restoration project that is wrapping at the end of October. Dumont said they are deepening and narrowing the river channel to change its flow.
“It should help with some of the sediment and temperature issues,” Dumont said. “If is successful, based on what we learn, we could do the same in 40 to 50 more spots.”
Bayha Island will be built up from five acres to ten. Dumont said adding land will help narrow the river and deepen the remaining river channel.
The sides of the channel will be “roughened” or slowed by submerged logs and boulders, Dumont said, because deepening and narrowing the channel will increase flow velocity.
Christy Meyer Boise is Freshwater Trust’s Idaho program manager overseeing the Bayha Island project.
She said one of the real benefits of the watershed approach is it not only addresses temperature and pollutants, but creates habitat as well. Besides the habitat improvement associated with the instream work, the stewardship program identifies the Powder River and the Weiser River as tributaries in need of riparian plantings. The third piece of the stewardship program is working with irrigators to upgrade to center pivot sprinklers that conserve water.
“The real ecological benefits of the program go beyond temperature - the reason we like it so much,” Meyer said.
Despite initial skepticism, the environmental team at Idaho Power is on board.
Randolph said, “We think we have the opportunity to do a more holistic, sustainable program as mitigation.”
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