Fertilizers: Nitrates Ruining Our Waters

When most people think of San Diego, they think sun, surf and sand. It surprises most people to learn that the county ranks as the 12th largest farming economy among the more than 3,000 counties nationwide. With more than 6,000 farms, San Diego County is the number one producer of avocadoes and a leading producer of numerous other crops such as strawberries, pomegranates, lemons and limes.

How is all of this relevant to Coastkeeper’s mission? Well, in growing those crops, farmers fertilize, and fertilizer contains nitrates (NO3 or NO3-N). Nitrates are crops’ primary source of nitrogen, which is necessary for growth. But when the quantity of nitrates added to the soil exceeds the crops’ use, the extra nitrates can seep into the water supply, endangering the environment and human health, especially infants and pregnant women. A Coastkeeper lab experiment highlights the devastating effect that Nitrates can have on water quality.

Nitrate levels in water supply are regulated by the Safe Drinking Water Act of 1974. The Environmental Protection Agency and the California Department of Public Health have established maximum concentrations of 10 mg/L or 10ppm (parts per million) for NO3 and 45 mg/L or 45ppm for NO3-N, respectively. Unfortunately, nitrates are colorless, odorless and tasteless and cannot be detected in drinking water without laboratory analysis. Between 2008 and 2009, 137 wells in San Diego were tested for nitrates. Nitrates (as NO3) were detected in 96 of those wells, with 25 wells exceeding the 45 mg/L threshold.

Once nitrates make their way into the water supply they are notoriously difficult to remove. The predominantly agricultural communities of Central California are experiencing a water quality crisis as a result of excessive nitrate leaching, with more than 40% of tested wells exceeding legal standards and the contaminant’s stubbornness. Researchers expect remediation, if possible, to take decades.

Southern California still maintains reasonable water quality with respect to nitrates, but because prevention is easier than the cure, we must ensure that our waterways do not deteriorate – and better yet, improve!

The best way to ensure the integrity of our water supply from nitrate contamination is to limit the amount of nitrogen in the soil. Farmers should use best management practices that incorporate volume and timing considerations for fertilizer application, among other considerations, to prevent the application of excess nitrates. Organic fertilizers tend have lower concentrations of nitrates, and release them more slowly, reducing groundwater contamination. We can all encourage the use of lower-Nitrate fertilizers among San Diego farmers by buying local, organic produce whenever possible.

But it’s not just farmers who can implement best practices – the rest of us can and should as well. Property holders dedicated to maintaining beautiful lawns and gardens can also implement best practices that involve testing soil for nitrate concentration and fertilizing only when necessary and, if so, when plant growth is dormant.

On the backend, you can support the implementation and restoration of wetlands, which act as a powerful natural filtration system to eliminate nitrates from groundwater. As contaminated water flows into these marshy habitats, abundant grasses and other plants absorb nitrates, improving water quality. As a result of human development activities, including development of residential and commercial property as well as transportation and oil and gas infrastructure, statewide wetland acreage has declined from approximately 5 million in the late 1700s to just 450,000 today – a loss of more than 4.5 million acres. Restoration is thus important to preserve and enhance San Diego water quality. You can learn more about some of the efforts to improve San Diego’s wetland resources by clicking here.

If we all play our part, we can preserve and the quality of San Diego’s water supply, thereby preserving our health, the environment and the millions of taxpayer dollars that would be required to reverse nitrate contamination.