Samantha Wohlfeil photo
While the amount of toxic metal pouring into Lake Coeur d'Alene is decreasing over time, scientists say more research is needed to monitor the health of the lake and further address some of the contamination.
Lake Coeur d'Alene received good news this week as a report from the National Academies of Sciences, Engineering and Medicine found that the amount of toxic metals being deposited in the lake is declining.
In a 428-page water quality report released Friday, Sept. 30, a committee of scientists found that cleanup work in the Bunker Hill Superfund site in the Silver Valley has helped reduce the amount of metals going into the lake over the last 10 years. That's a change from previous decades that saw increasing deposits of lead, zinc, cadmium and arsenic flowing into the lake after a century of mining in North Idaho.
Significantly, the committee found that the lake isn't currently at risk of low oxygen levels, which could pull those toxic metals out of lake bottom sediments and suspend them in the water column. If that were to happen, it could create health risks for people, plants and wildlife.
However, there is little data on the shallowest parts of the lake, which may serve as early warning signs of worsening conditions as those areas may be the first to experience the low oxygen effect known as eutrophication. Because of that, the scientists said ongoing and expanded research efforts on the lake are necessary.
There's also little known about the potential human health risks in the shallow areas where people recreate and the sediment may contain high levels of lead, as the "Future of Water Quality in Coeur d'Alene Lake" report states. Because the lake was intentionally not included in the Bunker Hill Superfund site, little research has been done to show how high lead levels might be impacting drinking water and fish that people eat, or directly exposing people to the toxin that can impact brain development.
"A spatial assessment of lakeside soils is also essential to evaluate if there are human health risks in the shoreline area, especially associated with areas where flooding might have occurred in the past," the report states. "Given the extreme concentrations of lead in the particulate material in flood waters from the CDA River, soil monitoring of lakeside areas that can be flooded would also fill an important gap."
The scientists also said that more data is needed to understand which types of phosphorus are entering the lake, as the element can play a significant role in lake health. The levels of that contaminant have increased in some parts of the basin and decreased in others.
In a news conference call Friday, members of the committee said they frankly don't know what exactly is impacting the phosphorus levels, but hypothesized that they could be influenced by changes in forest practices, the climate, and even the elimination of air pollution that used to be present when smelting operations were ongoing in the region. There's also been significant population growth around the lake, and developments can contribute phosphorus from fertilizers and wastewater systems.
"There's still a tremendous amount of uncertainty about why these things are happening," said committee member Robert Hirsch, a retired hydrologist who worked for the U.S. Geological Survey. "Any efforts to control phosphorus into the future are really going to depend on a much improved understanding of what's driving phosphorus into the system."
Even though deposits of toxic metals are declining, the lake still has significantly higher levels of cadmium, zinc and lead than other large lakes around the country, even in industrialized areas. For example, lead can be toxic to organisms at 110 to 530 micrograms per gram, and Lake Coeur d’Alene has lead concentrations of 1,800 to 3,850 micrograms per gram, according to the report.
Climate change could also slow or reverse some of the progress that's been made. Warming temperatures could impact how metals flow from rivers into the lake as the area sees changes to snowpack, precipitation and flooding.
“Overall, the water quality of the lake is improving, but it is possible for this progress to be reversed,” said Samuel Luoma, the committee chair and a research ecologist at the University of California, Davis. “Our report details improvements that should be made to lake and watershed monitoring, so that researchers and those managing the lake have more information to work with as the uncertainties of the future unfold.”
Because of the uncertainties ahead, looking to the past to forecast the future is difficult to do, Luoma said.
"There's no question, progress has been made, but there's still a long ways to go in terms of recovery of the lake," Luoma said. "There will be surprises."
