High nitrate levels found in some regions

New water quality results for surface water and ground water on the Central Coast offered good and bad news for growers at the Sustainable Ag Expo, held in San Luis Obispo, Calif., in late November.

In the most extensive release of surface water findings to date, Sarah Lopez, technical program manager of Central Coast Water Quality Preservation Inc., reported that detections of two organophosphate insecticides had declined dramatically from 2005 to 2013. The insecticides were chlorpyrifos and diazinon, neurotoxicants once widely applied to an array of crops, including vineyard, vegetables and berries.

In the same presentation, however, Steve Deverel, hydrologist working for the Central Coast Groundwater Coalition (CCGC), reported that tests of hundreds of Central Coast domestic wells in 2013-14 revealed high nitrate concentrations throughout the Salinas Valley, and in farming regions in the Pajaro, Gilroy, Hollister and Santa Maria groundwater basins.

The first findings relate to surface waters at the bottom of watersheds, and reflect a significant drop in insecticides that can be damaging to human health and aquatic organisms. The second findings characterize nitrates in domestic wells that are a source of drinking water, a supply generally within 400 feet of the surface. Nitrate at unsafe levels has been linked to infant death, cancer, and thyroid and reproductive disorders.

The data came from two grower coalitions, both formed in response to requirements by the Region 3 Central Coast Regional Water Quality Control Board. When that board renewed the agriculture waiver in 2012 for a five-year period, it called for increased monitoring, management and reporting by growers.

Preservation Inc. has performed surface water monitoring since 2005, but monitoring of groundwater is relatively recent, an outcome of the agricultural waiver of 2012. Growers formed CCGC in 2013 to perform that monitoring. Growers not in CCGC are required to test their own wells.

Deverel noted, “Nitrate levels in groundwater exceed the maximum contaminant level, the EPA’s safe drinking water standard, in 58% of the domestic wells in Salinas Valley. In general, nitrate concentrations decreased with increasing depth.”

He said preliminary results from studies he is completing this winter seem to indicate that much of the accumulation of nitrate has occurred in recent decades, primarily since the 1980s.

Deverel and his team at Hydrofocus Inc., based in Davis, are using radioisotope testing to determine the age and source of nitrate contamination. They are analyzing findings from 830 wells in all, 588 of which the coalition sampled directly. They also obtained recent data from local and state government agencies.

“The main source of nitrate in this region is synthetic fertilizer,” Deverel added. “Very little comes from septic systems, dairies or pharmaceuticals. In addition, data show higher effects in the last 10 to 20 years.”

While previous studies have shown nitrate contamination in California groundwater and wells, this is the most extensive study in the Central Coast to date, and the first in this region to provide extensive data on age and source of nitrate.

Parry Klassen, director of the CCGC, observed, “Our growers, in every case where there was nitrate contamination, responded by notifying employees and others using the wells for drinking water. They all voluntarily offered them either bottled water or reverse-osmosis treatment. Many had already been doing so for years.”

Kevin Merrill, vineyard manager at Mesa Vineyard Management in Santa Maria, said, “Close to 100% of irrigation on the Central Coast relies on well water. We know that nitrate accumulates over time, and so growers are now testing well water to see what nitrogen is available and then using that as part of their nitrogen budget. Also, a very high percentage of growers now rely on drip irrigation, allowing more precise application of water and fertilizer. There is almost no surface runoff.”

Surface water readings from 2005 to the present taken by Lopez and her team show declining trends in surface water nitrate concentrations in many watersheds, but some other water bodies show increasing trends. Surface water readings reflect a combination of past and present practices. For instance, some nitrate in surface water is from recent applications, but since much irrigation water is drawn from wells, irrigation runoff can also reflect nitrate that has accumulated in groundwater over decades.

“Decreasing trends currently outweigh increasing trends in nitrate,” she said. “While this is encouraging, we have to wait to see if this pattern continues in order to confirm that it is the result of changed practices.”

While vineyard owners apply nitrogen fertilizer, in general they apply less than growers of other crops because too much nitrogen leads to excessive vegetative growth and poor-tasting wine.

However, vineyards, along with row crops and tree crops, can be significant sources of sediment from soil erosion. Pesticides and applied nutrients can adhere to soil particles and, through erosion, be washed into surface waters in runoff.

Randy Krag, vineyard manager for Beckstoffer Vineyards in Lake County, noted, “If we maintain cover on soil and employ smart design and management of roads, we can greatly reduce erosion, which is a major concern in water quality in our region.”

Agricultural waivers were initially established as part of the Clean Water Act of 1972, but subsequent California legislation called for them to sunset in 2001. Since then, all nine regional water control boards have required growers to renew waivers every five years, and wastewater discharge requirements for growers have increased steadily in each version.

Many growers address these monitoring and management requirements through coalitions. Owners of 95% of the Central Coast’s irrigated farmland have joined Preservation Inc., the surface water monitoring group established in 2005. Growers representing 50% of the acres in the Central Coast region have joined the more recently formed Central Coast Groundwater Coalition, starting in 2013.

When nitrate is not used by plants, volatilized or otherwise metabolized by soil organisms, it can run off in field drainage or percolate through soil from the surface to the groundwater. Movement to groundwater is sometimes more rapid but usually occurs over decades. Even if nitrogen fertilization stopped tomorrow, it would take decades before a discernible effect appeared in groundwater, Deverel said. Grower concerns include how to show improvement in nitrate concentrations in the five-year period before the current agricultural waiver expires in 2017.

“One of the things missing in these five-year waivers is a recognition of what is possible in that time,” said Merrill of Mesa Vineyard Management. “Five years isn’t long enough to understand what’s going on and how to fix it. We need to get out of the regulatory frame of mind and ask ‘How do we work together to fix these things?’ We already know there’s a problem.”

Another concern of researchers and growers alike is the unintended effects of chasing one pollutant after the other, forcing growers to switch to other materials.

“It’s true that organophosphates have gone out of use because the water board said we couldn’t use those. But as a result, the use of pyrethroids and neonicotinoids has continued the same or gone up. These are the unintended effects, and we have to be careful how we look at it,” and Merrill.

Lopez noted, “My concern is that in regulating pollutant by pollutant, we lose the ability to look at overall trends and the whole picture. It is more in the interest of water quality to focus on controlling off-site movement of all applied products, rather than targeting this one or that one for elimination, and then moving on to the next one.”

Krag noted that growers across the state are watching what happens in other regions and subregions. “Here in Region 5 we’re especially watching San Joaquin County,” he said. “New regulations have already been rolled out there, and based on that experience, will be extended to all of Region 5 over a few years. We expect new rules by 2017. Nutrient management plans will probably be part of the new regulations regionwide.”