Monday, March 20, 2023

The fate of the big blue lake

Staff Writer | May 7, 2021 1:08 AM

As the Future of Water Quality in Coeur d’Alene Lake committee closed its second set of meetings, members raised questions and discussed next steps for the National Academies of Sciences study.

Talk of phosphorus, climate change, forest fires, and known lake data filled the last two days of presentations by national, regional, state and local officials.

Sponsored by the U.S. Environmental Protection Agency, Idaho Department of Environmental Quality and Kootenai County, the $770,000 NAS study aims to assess whether Lake Coeur d’Alene is at risk of going anoxic — a low concentration of dissolved oxygen — and releasing toxic metals into the water system.

By reviewing water quality data and modeling in the 2009 Lake Management Plan and other credible sources, the committee’s goal over the next two years is to determine what the future of Lake Coeur d’Alene could be.

As one of the first in-depth studies on Lake Coeur d’Alene in several years, the committee does not intend to provide remedial recommendations. However, sponsors of the study have said that another investigation could be organized if action is needed.

Samuel Luoma, chairman of the committee, opened a group discussion during the Wednesday climate change presentation by Guillamaue Mauger, calling for the group to focus on one of its goals: Looking to the future of Lake Coeur d’Alene.

One of the implications of climate change on the lake, Luoma noted, is stratification — when water with different properties forms layers that inhibit water mixing, leading to anoxia.

“We’ve seen in the river that stratification, anoxia, and release of nutrients and dissolved metals coincides with cooling in the basin and then lake drawdown and mixing,” said Dale Chess, water quality specialist for the Coeur d’Alene Tribe. “We found at the Harrison site high dissolved lead and high dissolved arsenic in the river in late November early December — months after the water column has been aerobic, and it’s still suspended.”

The whole flood plain of the Coeur d’Alene River acts almost like a sponge of metals that is saturated throughout the summer, Chess said, overloaded by the Post Falls dam like a “stew” of warm anoxic water.

Drawing from the Tuesday discussion, NAS committee member Michael Brett asked about the particulate phosphorus levels in Lake Coeur d’Alene and the compilation of nutrient data collected by agencies throughout the water system.

Phosphorus can be a powerful player in anoxia, as high concentrations of the mineral can cause increased algae or aquatic plant growth. That growth can cause eutrophication, or decreased levels of oxygen, and anoxia, which the EPA says negatively impacts water quality, food resources and aquatic habitats.

Craig Cooper, a limnologist with the Idaho Department of Environmental Quality, led the phosphorus inventory conversation on Tuesday, noting that the mineral levels had increased by 200% from 1991 to 2013.

While it changes regularly, Cooper said about 80% of the phosphorus is sediment-bound, traveling from the Coeur d’Alene River, St. Joe River, and — to a lesser degree — the lake tributaries. He noted that there are strongly seasonal and geographical factors that influence phosphorus deposits, making short studies less reflective of possible trends.

“If 80% of it is particulate bound, then we really want to know a lot more about the composition of that particulate bound traction because that is going to have a tremendous impact on whether the phosphorus that is coming to the lake is actually bioavailable and contributing to production or not,” Michael Brett said.

Chess said a significant hole in the current data is that the potential bioavailability of phosphorus in the lake is unknown.

“We don’t have an estimate of how much of that phosphorus is really getting settled, at what rate it is settling in the lake, how it’s being moved from the rivers through the lake, and really what the fate of that phosphorus is,” Chess said.

The Coeur d’Alene Tribe has tried to collect long-term data on phosphorus trends, Chess said, but has been inhibited by the mass of resources and money extensive studies require. The other agencies with projects throughout the basin have also shared that burden, said Lauren Zinsser from USGS and Ed Moreen from EPA.

“It’s largely dependent on budget, and we’ve actually had to scale back on the frequency of sampling in our basinwide monitoring program because it is such a beast, and we have so many moving parts on this cleanup site,” Moreen said. “I agree it would always be great to have more data, but as you know, as scientists, we always have to use the budget and make the hard decisions so that we can push forward with our programs.”

Information about the committee is available at under “The Future of Water Quality in Coeur d’Alene Lake.”

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