Fertilized soil may be a major source of smog near Salton Sea, researchers say

Tony Briscoe, Los Angeles Times on Dec 16, 2024

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LOS ANGELES — For decades, Southern California’s war on smog has focused on strategies to reduce pollution from tailpipes and smokestacks. But one of the main drivers of lung-aggravating smog may be right underneath our feet, according to new research.

About 100 miles east of San Diego, in the heart of the Colorado Desert, the Salton Sea air basin is one of the most polluted regions in the nation. There, at least a quarter of all nitrogen oxides — the precursors to smog — are released by the area’s irrigated green spaces, according to research from UC Davis.

From the polo grounds of Coachella Valley to the farm fields in Imperial County, vast stretches of the harsh Colorado Desert have been converted into verdant fields thanks to fertilizer and irrigation. Although the conditions are ideal for plants, the wet, heavily fertilized soil also creates a feeding frenzy for soil bacteria that release smog-forming pollution.

UC Davis researchers say the soil in the Salton Sea air basin emits more than 11 tons per day of nitrogen oxides — about 10 times more smog-forming pollution than California air regulator officials currently estimate. The findings underscore the need to better understand how the management of agricultural land and manicured lawns are contributing to regional air quality, according to Ian Faloona, a UC Davis associate professor in the Department of Land, Air and Water.

“Because it’s relatively cheap, farmers will usually apply about twice as much fertilizer as needed by the crops, just to make sure they get it,” Faloona said. “So, when you have a bunch of excess nitrogen, microbes go to town and they start using it for fuel. But some of it leaks out of their metabolism and it comes out as this air pollutant.”

In California, Imperial County ranks ninth in agricultural sales with $2 billion in revenue. However, to grow crops like iceberg lettuce and broccoli in a low-lying desert, farmers use more fertilizer than any other county. Previous studies have shown that applying excess fertilizer can produce five times as much smog-forming nitrogen oxides.

Fertilizer sales in Imperial County have more than doubled since 1991, according to estimates from the California Department of Food and Agriculture.

To withstand the extreme heat and arid conditions, crops in the Salton Sea air basin need to be watered regularly. But high temperatures and soil moisture can result in even more emissions.

When cropland is watered, it can result in “pulsing events,” where soil bacteria are reactivated and release large amounts of pollution.

These surges in pollution typically last one or two days, which may be why state air regulators hadn’t previously considered soil emissions a significant source of pollution near the Salton Sea.

“We’ve looked,” Faloona said, “but we haven’t looked carefully enough to capture these soils that are probably producing most of the [pollution].”

In a region known for growing vegetables, the findings highlight the need for more transparency on current fertilizer application and irrigation practices, which are currently not extensively tracked by government agencies.

“We don’t want to jeopardize food production, we just want to do it in a way that’s a little less harmful environmentally,” Faloona said. “The more we learn about it, the more details will be uncovered about the best steps to take.”

Air pollution near the Salton Sea has been a longstanding concern for residents. In addition to the unhealthy levels of smog over the summer, residents have had to contend with contaminated dust from the swiftly disappearing Salton Sea, California’s largest lake.

For decades, the Salton Sea was the final destination for agricultural runoff, which included toxic pesticides and fertilizer. As the lake has shrunk, more of the lake bed continues to be exposed, allowing for winds to kick up this toxic-laced dust.

In the face of perennially poor air quality, many parents limit their children’s time outside, said Daniela Flores, founder of the Imperial Valley Equity & Justice Coalition.

Still, Imperial County has had some of the highest rates of asthma-related emergency room visits for children. Compounding the issue, many of the region’s rural residents don’t live near hospitals or medical facilities.

“I don’t think that there is an environmental disaster that mirrors the Salton Sea anywhere in California,” Flores said. “How sad is it that we are living in a community where parents have to tell their toddlers that they can’t go outside and play because it’s bad outside?”

For Flores, the results of the UC Davis study confirm what many have suspected about the environmental toll and health impacts from the region’s agricultural industry.

“Allergies, asthma, missed days of school — it’s like a part of life,” she said. “People know it’s not right. People know it’s not normal. In many ways, I feel like people have been feeling the impacts of [pollution], and then the science comes a little later.”