As I mentioned the other day, there is a lot of frustration and denial on the part of farmers when it comes to nitrate pollution in the Central Valley. Recently, the UC Davis researchers who wrote the massive report on nitrates in groundwater held a public workshop to formally present their results. When pressed on the 96% figure for nitrate coming from agricultural sources, one of the scientists acknowledged that the figure may not be “precise”. Oh dear, you just admitted uncertainty – surely it only went downhill from there. Where were the error bars in the original study? If you admit uncertainty, then error bars at least constrain the uncertainty. An admission of imprecision suggests to the public that it all might be crap.
Turns out that the farmers may have some reasonable issues with the study methodology, partly because the study had to estimate nitrogen fertilizer application rates over the past ~60 years. Nitrogen prices have gone up significantly, which already presses farmers to be highly efficient in their applications. Plus there is more and more use of low-water irrigation (e.g., drip irrigation), which further decreases the rate of nitrogen leaching into the groundwater. The scale of the UC Davis study simply did not permit inclusion of these trends, which suggest that farmers are already mitigating the nitrogen issue as much as they can. Based on the above article, I doubt that the researchers satisfactorily explained why they conducted the study in the way that they did.
That said, legacy contamination is still an issue, and I don’t think there’s any way that fertilizer application was not the cause of the groundwater nitrate contamination. So who should pay to clean it up? I would still argue that nitrogen fertilizers and irrigation water are the easiest things to target, even if it is a burden on the farmers. The fees would provide a cost-benefit incentive for all farmers to engage low-water irrigation and efficient nitrogen use, plus there is some talk of using contaminated groundwater as irrigation water, letting the nitrates be consumed by crops. Think that’s unfair, farmers? Talk to the chemical industry about joint and several liability for Superfund sites under CERCLA…
Recently the California State Water Board hired UC Davis to perform a $2 million independent study of groundwater nitrate contamination in the Central Valley, specifically the Tulare Lake Basin and Salinas Valley. Surprisingly for a government project, the study was completed on time, but not surprisingly the results have already generated some controversy. UC Davis estimates that 96% of the nitrate in groundwater comes from agricultural sources, with sources like wastewater treatment plants, septic systems, and manure lagoons minor on the basin scale but potentially significant on a local scale. Since no one measures basin-wide nitrogen inputs to croplands, the UC Davis researchers had to derive the agricultural data from historical land use per crop, plus a crop-specific nitrogen mass balance. The approach looks pretty sound to me.
Two months after the release of data, Tulare County Supervisors are about to strike back. They voted last week to send a letter of concern to the State Water Resources Control Board, which is coming up with what to do about the nitrate contamination. The UC Davis report suggests that nitrogen fertilizers should be taxed to cover groundwater remediation for drinking water sources. This scares the Tulare County agricultural interests, and the Tulare County Supervisors will claim in their letter of concern that the UC Davis report did not consider sources of nitrogen, but rather assumed that the source was agricultural. Further study is necessary!
I find this very confusing. In looking at the UC Davis approach, they did consider the source of nitrogen contamination, and in fact Figure 1 of the Executive Summary shows their breakdown of the nitrogen sources. So what gives? I think this is a last-ditch effort of agricultural interests to resist the reality of numbers staring them in the face. After all, these are some of the most productive agricultural lands in the world (including 10% of US milk production), so anything that might decrease productivity is a threat. But the number of drinking water wells with elevated nitrate in these basins is only increasing with time, and for agriculture to refuse to acknowledge complicity in the problem is to live with their heads in the sand.