Nitrogen Sources and Potential Nitrogen Leaching to Groundwater in the Central Valley and Salinas Valley, California



Nitrate‐nitrogen is the most common pollutant found in the Central Valley and Salinas Valley aquifer systems of California. This project provides a long‐term assessment of past and current potential nitrogen loading to groundwater on irrigated and natural lands across the Central Valley and Salinas Valley of California (study area) using a nitrogen mass balance approach, mapping, and an extensive literature review of nitrogen sources; assesses the long‐term implications for groundwater quality in the study area; evaluates potential best management practices to reduce groundwater nitrogen loading from irrigated lands; and provides a planning tool to better understand local and regional groundwater quality response to specific best management practices and policy/regulatory actions. The project complements other work to assess the vulnerability of Central Valley and Salinas Valley groundwater to nitrate contamination, sources of nitrate in groundwater, and how to reduce source loading.

The maps on this website include data from Harter et al. (CDFA-FREP, 2017) and - for the Salinas Valley - from Harter, Lund et al. (SBX2 1, 2012).

Methods and Citations

More information about how these data were compiled can be found at and

Central Valley data is from:

Harter, T., K. Dzurella, G. Kourakos, A. Hollander, A. Bell, N. Santos, Q. Hart, A.King, J. Quinn, G. Lampinen, D. Liptzin, T. Rosenstock, M. Zhang, G.S. Pettygrove, and T. Tomich, 2017. Nitrogen Fertilizer Loading to Groundwater in the Central Valley. Final Report to the Fertilizer Research Education Program, Projects 11-0301 and 15-0454, California Department of Food and Agriculture and University of California Davis, 333p.,

Salinas data is from:

Harter, T., J. R. Lund, J. Darby, G. E. Fogg, R. Howitt, K. K. Jessoe, G. S. Pettygrove, J. F. Quinn, J. H. Viers, D. B. Boyle, H. E. Canada, N. DeLaMora, K. N. Dzurella, A. Fryjoff-Hung, A. D. Hollander, K. L. Honeycutt, M. W. Jenkins, V. B. Jensen, A. M. King, G. Kourakos, D. Liptzin, E. M. Lopez, M. M. Mayzelle, A. McNally, J. Medellin-Azuara, and T. S. Rosenstock. 2012. Addressing Nitrate in California's Drinking Water with a Focus on Tulare Lake Basin and Salinas Valley Groundwater. Report for the State Water Resources Control Board Report to the Legislature. Center for Watershed Sciences, University of California, Davis. 78 p.


Thomas Harter (
Nick Santos (