At the Great Salt Lake, record salinity and low water endanger millions of birds | Science

Utah’s Great Salt Lake is smaller and saltier than ever in history. In July, the US Geological Survey (USGS) reported that the world’s third-largest saline lake had fallen to its lowest level ever documented. And last week, researchers measured the highest salt concentrations ever seen in the southern arm of the lake, an important habitat for birds. Salinity has risen to 18%, crossing a threshold at which essential microorganisms begin to die.

The trends, driven by drought and water diversion, have warned scientists that a critical breeding ground for millions of migratory birds is at risk of collapse.

“We’re in uncharted waters,” says Westminster College biochemist Bonnie Baxter, who has documented the lake’s alarming changes. “For a week the birds are away from a place where we normally see them. The next week we see dead flies along the coast. And every week we have to walk further to get to the water.”

After years of inactivity, the prospect of a dying lake, plus the risk of harmful dust blowing from the lake’s dry bottom, is prompting policymakers to find ways to restore water from the shrinking lake.

The Great Salt Lake is actually two lakes, separated in 1959 by a railroad. Over time, the northern arm, which has few freshwater sources, became saltier than the southern arm, which is fed by three rivers. Historically, salinity in the northern arm has fluctuated around 32% – too salty to support more than microorganisms – and about 14% in the southern arm.

Although the southern part is about four times saltier than seawater, it supports a vibrant ecosystem characterized by billions of brine shrimp and brine flies, which feed on photosynthetic cyanobacteria and other microorganisms. Birds, in turn, devour huge numbers of flies and shrimp when they arrive at the lake to nest, molt or rest during migrations. For example, a diving water bird called the eared grebe needs 28,000 adult brine shrimp each day to survive.

The low water and rising salinity threaten to destroy the foundation of this food web, researchers say. The receding shoreline has already dried out many reef-like mats of cyanobacteria, known as microbialites, that lie at the bottom of the lake. Baxter fears that the salt water now threatens even the microbial communities that remain submerged. “In lab tests, when the salinity level exceeds 17%, we see the cyanobacteria begin to die,” she says.

NASA satellite images from June 1985 and July 2022 show Utah’s Great Salt Lake shrunk to the lowest level recorded since the records began in the 1840s. Use the slider to view the two images.NASA Earth Observatory images by Joshua Stevens, using Landsat data from the US Geological Survey and data from the National Water Information System

Loss of the mats can harm brine fly populations, Baxter says. The flies lay eggs on the surface of the lake, producing larvae that swim to the microbialites, where they pupate before reaching adulthood. Some bird species feed on the larvae or adults, while others eat the pupae — which turned up dead on the lakeshore by the billions during this fall’s migratory season.

The brine shrimp was soon also able to dwindle. “The fear is that in the next year, [the lake] will become so salty that populations … will collapse,” a pair of state ecologists wrote recently.

Meanwhile, researchers are mobilizing to monitor the unfolding crisis. Baxter calls in a brine fly expert to assess the situation. Conservation groups monitor shorebird populations across the intermountain West. And USGS has established a program to monitor hydrology and ecology in other saline lakes in Oregon, California, Nevada and Utah, which face similar stresses.

The shrinkage of the lake threatens both humans and wildlife. In a 2019 state-funded report, University of Utah atmospheric scientist Kevin Perry estimated that 9% of exposed sediments in the lake bottom contain problematic levels of arsenic or metals, believed to be from industry. , wastewater treatment or agriculture. Winds are likely to erode the crust that holds the sediment in place and transport dust far and wide. With more than 1 million residents living near the lake, in Salt Lake City and its suburbs, the worst-case scenario would be an air pollution disaster, similar to that of communities in Iran near other salty lakes. Even Utah’s famous ski slopes are threatened by the dust; scientists have documented how storms already dump lake particles onto the snow, darkening it and hastening melting.

For years, conservationists have urged policymakers to reduce the water that farmers and other users divert from streams that flow into the lake. But “the conventional wisdom is that it’s just a salty lake — we should use the water upstream,” said Utah State Representative Tim Hawkes. “For many in Utah, the lake has been a little bit out of sight, out of mind.”

This year, however, policymakers took action. In April, Utah Governor Spencer Cox signed a series of important bills to save the lake and address the drought. They include new rules that allow farmers to sell water rights they don’t use to groups that allow the water to flow to the lake. The state has set aside $450 million for water infrastructure and conservation projects, including a $40 million fund that could acquire water for the lake in the future.

It could take years for such policies to have a noticeable impact, especially if the current drought continues. For example, Baxter wonders, “Is this enough?” But Marcelle Shoop, chief of the Saline Lakes program for the National Audubon Society, says she is “optimistic because there are so many people trying to develop solutions.”

In the meantime, the lake can be temporarily relieved from another source: the upcoming wet winter season. If it produces good snow cover in nearby mountains, the runoff can help fill the region’s parched streams.