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.