Kale and hearty: The salad bowl of America turns toxic

As nitrates seep into aquifers in California's Salinas Valley, local scientists are working to improve water quality

An aerial view of the three-acre experimental wetland that scientists hope can improve water quality in Calif.'s Salinas Valley

MOSS LANDING, Calif. — It has just rained, welcome respite from California’s ongoing drought, and puddles have turned a fallow farm field to squelchy mud. Artichokes will be planted here in January, to be harvested in the summer, and broccoli or cauliflower will follow. 

The Salinas Valley, with its superlative moniker “the salad bowl of America,” is where some 60 percent of the nation’s lettuce is grown, and close to half of its strawberries. It’s some of the most productive agricultural land in the world, on rich silt accumulated over centuries of flooding on wetlands. The conditions enable two to three harvests per year, like the artichoke-cauliflower rotation planned for this damp field next year. Cool air blows in off the bay, keeping greens and strawberries at their most flavorful and fueling a $4.4 billion agriculture industry. Farming is the number-one use of land in the Salinas River watershed. 

The land is fertile, but to keep producing the salad greens and vegetables that make their way to supermarkets and restaurants all over the country, farmers here apply fertilizers and pesticides to their crops. That is a widespread and not necessarily unsafe practice. All lettuce — in fact, all commercial produce — is grown with fertilizer, which is also a friend to organic farmers. But here in the Salinas Valley, where ideal climatic conditions allow for two or even three crop rotations in a single year, the amount of fertilizer that’s used goes up. When there is more fertilizer in the soil than can be absorbed by the roots of plants, that excess, high in nitrates, runs off into ditches and penetrates deep into the land. From there, it flows to the bay and seeps into aquifers, where excess nutrients such as nitrates and phosphates can regularly reach toxic levels. New regulations and lawsuits are aiming to slow pollution upstream by changing farming practices, but a group of scientists is promoting a pilot program that has the potential to improve water quality and be replicated across the country.

The nitrification in the Salinas Valley is a smaller version of the same problem that’s responsible for a dead zone larger than 5,000 square miles — about the size of Connecticut — in the Gulf of Mexico. A 2012 report by faculty members at the University of California at Davis of intensively farmed areas attributed 96 percent of nitrate sources in groundwater to agriculture

Two years prior, scientists had found the first conclusive evidence that toxic fertilizer-fueled algae were flowing into Monterey Bay, killing dozens of sea otters. And where nitrates get into groundwater, they can make the water undrinkable: In small farmworker communities near Moss Landing, public health officials have warned residents not to drink the water because the proportion of nitrates exceeds allowable state and federal levels. Even boiling water — which in most cases kills pathogens — does not remove nitrates, which in large quantities can diminish the ability of blood to carry oxygen. This is most acutely observed in babies, where the effect is called “blue baby syndrome.” Boiling, in fact, only further concentrates nitrates in the water. 

It’s emotionally wearing when you’re constantly the bearer of bad news. I got tired of it.

Fred Watson

CSU Monterey Bay professor

Regulators have taken note. A 2009 report to California’s Central Coast Regional Water Quality Control Board identified the lower Salinas River watershed as one of its two highest-priority areas: “These watersheds have multiple impairments…and the magnitude of exceedance of water quality objectives in these watersheds is great, relative to other watersheds.”

After years of political wrangling, in 2012 the Water Quality Control Board approved rules for farmers requiring them to develop plans on how to cut back on nitrates. The guidelines don’t actually require nitrate reductions, a point of contention that’s being challenged in court by the environmental nonprofit Monterey Coastkeeper, but out of the litigious muck, there’s one strategy environmentalists and farmers agree on: maintaining wetlands to detoxify the water. 

Even before the Water Quality Control Board began the yearslong hearing process to regulate farm runoff, two scientists were done fighting with farmers all the time. California State University Monterey Bay professor Fred Watson and Ross Clark, director of the Central Coast Wetlands Group, a research group at CSU’s Moss Landing Marine Laboratories, kept testing the water, finding terrible results and reporting their findings to the agriculture industry. 

“It’s emotionally wearing when you’re constantly the bearer of bad news,” Watson says. “I got tired of it.” 

In 2006, Clark and Watson tried something new: On 3 acres of poor-quality land, they planted cattails — tall, reedy plants — creating a makeshift wetland in the middle of farmland. 

It’s entirely manmade, meaning they pump water that otherwise flows through a ditch into their wetland, then out of the wetland and back onto its natural course toward the ocean. What’s they’ve found is a dramatic difference in water quality between what flows in and what flows out. 

The three-acre experimental wetland
Central Coast Wetlands Group

Rushes, sedges and grasses such as creeping wild rye fill in the mucky soil, and the muddy bottom forms an anaerobic environment. There, bacteria like Paracoccus denitrificans thrive, converting nitrates into a harmless gas that is released into the atmosphere. 

From the time that water flows into these treatment wetlands to the time it leaves, the level of nitrates is regularly slashed by upwards of 50 percent. (In waters this polluted, that’s still not enough to meet the U.S. Environmental Protection Agency drinking-water standard of 10 parts per million; after treatment, the nitrate in the outflow can drop as low as 15 ppm.) Still, that’s a big improvement over the water flowing in, which frequently reaches 45 ppm. “We think we can make a huge dent on water quality,” Clark says. 

What’s more is that this somewhat haphazard experimental wetland off California’s Highway 1 is taking out not just nitrates, but pathogens and pesticides too. Giardia, a common waterborne parasite, for example, and the pesticide diazinon decreased by more than 20 percent from the time the water was pumped into the wetland to the time it was pumped back out, according to two studies co-authored by Watson. Indeed, researchers at CSU Monterey Bay have found that local bacteria in these wetlands are actually eating pesticides in the water.

“We have no evidence to suggest what about the wetland is reducing these things,” Watson says. “Biological [factors], salinity, surface area and exposure to sunlight — there are a whole lot of processes that might be causing these beneficial effects, but we don’t know what they are yet.” What they do know is that wetlands can clean up nasty water. 

They estimate it would take 200 to 300 acres of wetlands to clean up the lower Salinas River watershed, stretching about 10 miles from the 156,000-person city of Salinas to the ocean. In a region where land can fetch up to $50,000 an acre, that’s a lot of land to take out of a multi-billion-dollar industry.

This pilot is the project that shows we can do it. It may or may not break even, but it’s helping us do better science.

Sierra Ryan

Central Coast Wetlands Group

Clark and Central Coast Wetlands Group project manager Sierra Ryan work in a small lab in a converted garage with rudimentary test kits; most of their work takes place in the field, with testing gear contained in tackle-box-sized case. They’ve got a $230,000 budget thanks to state grants, to convert another 20 acres of farmland to wetland. It’s a spot adjacent to the artichoke field, but it’s a little too soggy to plant — a good indicator it will work well as a wetland. 

“This pilot is the project that shows we can do it,” Ryan says. “It may or may not break even, but it’s helping us do better science.” 

Artichoke grower Dale Huss is working with Central Coast Wetlands Group on a plan to expand a pilot wetland on his field, but to scale up from today’s small experimental plots to 300 acres would take a lot of converted land. That’s unlikely. “There needs to be some sort of credit,” Huss says. He imagines a trade-off, perhaps something like carbon offsets; maybe a grower would be allowed to fertilize intensively by planting a wetland, Huss says. 

Besides cost and compliance, there are other worries. If geese, rats or deer move into the newly planted habitat, they might also wander into adjacent farm fields, leading to concerns for food safety. 

Geese, for instance, are particularly fond of lettuce. The solution? Design a densely vegetated wetland that doesn’t have a large enough surface area of exposed water for a goose to take off or land, say Ryan and Clark. 

In short, they are exploring ways of cutting back on the risks in a risk-averse industry. “You’ve taken a piece of dirt that had little liability associated with it, and added all these unknowns,” Clark says. 

A newly planted Salinas Valley lettuce field on April 4, 2013, near Gonzales, Calif.
George Rose / Getty Images

Before wrapping up her master’s degree in coastal and watershed science and policy last spring, Gwen Miller, who was working with Watson, collected water from the original three-acre experimental plot twice a week for two years. 

She found that both warmer temperature and higher carbon levels — which increase with more plant matter —boost the speed of denitrification, the process of bacteria consuming nitrates and transforming them into gas. 

“The wetland worked just fine in summer, but it was basically switched off in the winter,” Watson says. “There’s this unfortunate zone there where it’s warm enough to grow crops, but not quite warm enough to make the denitrifying bacteria do their thing.” 

That’s unlike places with chilly winters: In the Midwest, the winter is too cold for farming, so the nutrient load in the runoff goes down just because the farming practices change. On California’s central coast, farming go year-round. 

In response to Miller’s findings, Watson and his colleagues are exploring how to heat wetlands (solar is one option) and how to boost carbon (maybe with carbon-dense wood chips). With a warmer, higher-carbon design, he’s hoping they can become more efficient than the current cattail-lined three-acre experiment and do more with less, dropping the target of 300 acres of wetlands to something more realistic. 

With scattered wetlands on private land, it’s hard to know exactly how many acres there are today. “Nowhere near 300, that’s for sure,” Watson says.

In their expanded trial on Huss’ artichoke field, Watson’s group will try different variations of vegetation and woodchip-to-plant ratio to get more carbon, looking for that perfect system. 

It might still take years, while dozens of cycles of crops get planted and harvested. “It would be great if we were moving 10 times quicker,” Watson says. “But we’re taking the next step.”

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