Earth
What Lies Beneath
At the bottom of the Salton Sea sits an ecosystem run amok.
By Sarah Nightingale
If nature were allowed to take its course, the Colorado River would flow freely from its source in the Rocky Mountains, through deserts and canyons of the Southwestern states, and across the vast wetlands that stretch into the Gulf of California.
But when it comes to the Salton Sea, nature has not been allowed to take its course.
From its birth in 1905 when Colorado River floodwater escaped an irrigation channel to its gradual demise over the past century as the river’s coveted supply has been tapped again and again, the Salton Sea is a patchwork of human interventions.
“When people hear the Salton Sea was filled by a dam breach, they assume it is there by accident, so they don’t see the problem with letting it dry up,” said Marilyn Fogel, the Wilbur W. Mayhew Endowed Professor of Geoecology and director of UCR’s Environmental Dynamics and GeoEcology Institute, or EDGE. “But the reality is that we have created an environmental crisis affecting not just the wildlife that now relies on the lake, but also the people who live and work in the surrounding communities.”
The crisis at the Salton Sea is not just the fact that it’s shrinking, although that’s bad news for birds traversing a state where many other natural watersheds have dried up or been paved over. It’s also what’s left behind.
“The Salton Sea is in a closed basin, so it has no outflow,” said Tim Lyons, a distinguished professor of biogeochemistry. “For the past 100 years, it has been filling up with salts, metals, fertilizers, and pesticides — things that come naturally from the river as well as from agricultural and municipal runoff. As the water evaporates, everything else becomes more and more concentrated.”
At a salinity approaching 7%, the Salton Sea is twice as salty as seawater. Heavy metals like selenium — essential for life but toxic in high doses — are approaching or have already exceeded dangerous levels. An overabundance of nutrients that percolate through the surrounding farmland and pour into the lake is wreaking havoc on its ecosystem.
“These chemicals have nowhere to go but the mud at the bottom of the lake,” Lyons said. “As the lake loses volume, the sediments are becoming exposed, drying out, and turning into dust that will then be eroded and transported by the wind into surrounding regions. This is already happening.”
Fogel and Lyons, both professors in UCR’s Department of Earth and Planetary Sciences, are examining the lake’s major chemical ingredients — including carbon, nitrogen, hydrogen, sulfur, and metals. Most of these elements exist in two or more forms, called isotopes, that differ in their masses and act differently when processed chemically, physically, and biologically. By measuring the ratios of these different isotopes in microbes and animal bones of varying ages, Fogel and Lyons can determine how the lake has changed over time and how these changes have affected its ecosystem.
“Our work goes beyond collecting data,” Fogel said. “It establishes predictive models that will help policymakers evaluate which of the various wetland restoration plans under consideration will protect not only the endangered bird species, but also the health of people in the area.”
A Rotten Story
Launching a Boston Whaler boat onto the southern end of the lake’s shrinking footprint has become an increasingly hard task, but that’s how Lyons and Kingsley Odigie, a postdoctoral researcher, sample water and mud from its depths.
Fogel sticks to dry land. Working in collaboration with the California Fish and Wildlife Department, she combs the shoreline for dead fish and bird feathers. Back in her lab, she measures their isotope ratios to determine how these top organisms are coping with environmental changes.
For a lake drenched in contaminants, plenty of life survives beneath the surface — but the ecosystem is suffering.
“You can say that life in the Salton Sea is thriving, but it is just a few species that are choking everything else,” Lyons said.
Among the microbes capitalizing on this unusual environment are algae, tiny aquatic plants powered by the glut of nitrogen and phosphorous carried in by agricultural runoff. The algae bloom in massive amounts and then die and decompose.
“The algae are photosynthetic, which means they produce oxygen at the surface of the lake as they grow. But when they rot at the bottom, the bacteria that eat them consume oxygen,” Lyons said. “These occurrences, which we call anoxic events, are becoming larger and more frequent. In summer there are now vast swaths of the lake that have no oxygen.”
Fogel’s analyses of tissues from fish and fish-eating birds underscore how damaging such algal blooms have been to wildlife. More importantly, they enable her to predict how much worse they’ll be in the future.
“We are able to see the effects of low oxygen using the nitrogen isotopes in the tilapia remains. With new samples coming in from California Fish and Wildlife, we’ll have an even better opportunity to connect food web structures with biogeochemical data from Tim Lyons and Kingsley Odigie.”
Lyons is concerned for two other reasons.
First, a decrease in dissolved oxygen means a rise in bacteria that produce hydrogen sulfide, a toxic gas characterized by a rotten egg smell.
“In the summer months, the lower portions of the lake are loaded with hydrogen sulfide. On windy days, those deeper waters are stirred up, releasing the smelly gas into the air, which can be detected as far away as Los Angeles and is strong enough in the surrounding regions to cause health concerns,” Lyons said. “That is a quality of life issue, but it also shows how far material released from the Salton Sea can spread.”
Second, oxygen levels dictate whether heavy metals, such as selenium, lead, and mercury, remain trapped in the water or are deposited as sediments. In oxygen-rich waters, metals are generally more likely to remain in solution. But in waters lacking oxygen, they are more likely to settle in the muds.
“Understanding how oxygen and hydrogen sulfide have varied in the waters over time is central to understanding how and where the muds have been contaminated and will be in the future,” Lyons said.
Either way, it’s a problem. Most of the mitigation plans for the Salton Sea will result in vast portions of the lakebed being exposed, allowing these metal-rich sediments to be blown into the atmosphere as dust, Lyons said.
“On the other hand, if the metals remain in the water, they could make their way up the food chain and poison the wildlife,” he added. “It all depends on how the chemistry of the lake changes as the lake shrinks and how much of the lakebed is exposed.”
A potential silver lining could come in the form of a thick salt crust forming at the lake’s shoreline, which may offer a protective cap over the toxic sediments, Lyons said. The crust, which is 1–4 inches thick, is made of gypsum, which has been crystalizing out of the salt-saturated lake.
With support from the Coachella Valley Mountains Conservancy, Lyons and Odigie are studying whether this crust extends from the shoreline into the lake’s deeper center.
“In regions that we are able to find this crust, we are interested in whether it can prevent toxic sediments in the mud from being released back into the water, or in areas where the lakebed is exposed, from being blown into the air as dust.”
If the crust doesn’t offer this protection, this loaded gun of toxic mud would become airborne dust when exposed if the lake’s water level drop as expected over the coming years.
“As researchers and California residents, we worry deeply about the present and potential impacts on wildlife and humans throughout the region,” Lyons said.
California has lost more than 90% of its natural wetlands over the past century. As a result, the Salton Sea has become an important refueling stop for more than 400 species of birds on the Pacific Flyway, the major north-to-south flight path for migratory birds in America, and a popular destination for birdwatchers.
Due to declining sea levels and the increasing salinity of the sea, many fish can no longer tolerate living in it. This is especially problematic for migratory birds, who face a diminished food supply as well as outbreaks of deadly diseases such as avian botulism and avian cholera. Toxic levels of the mineral selenium have also been found in the systems of Salton Sea fish and birds.
Two state-funded projects, the Torres Martinez Wetlands and Red Hill Bay, seek to benefit fish and migratory birds and reduce airborne dust through the construction of habitats fueled by groundwater (Torres Martinez Wetlands) and a blend of Salton Sea and Alamo River water (Red Hill Bay). In 2018, the Torres Martinez Wetlands made history as the first state-funded Salton Sea project to reach completion, with Red Hill Bay now under construction.
