The California Nitrogen Assessment: Implications for the Future of Groundwater Resources
University of Colorado
Nitrogen (N) plays a vital role in sustaining the agricultural economy of California, as well as the global food supply. However, environmental losses of reactive N also have adverse impacts on other important ecosystem services by diminishing water and air quality and contributing to climate change. Despite the important benefits and tradeoffs of N in human and ecological systems, there remains a paucity of quantitative knowledge on the interrelationships between California’s N flows and the various ecosystem services that contribute to the public good. To fill this knowledge gap the Agricultural Sustainability Institute at UC Davis conducted a comprehensive integrated assessment of N in California to establish a baseline of credible information on the sources, sinks and flows of N into, out of, and within the state. This is the first comprehensive accounting of nitrogen flows, practices, and policies for California agriculture at the statewide level. We present an overview of results of a statewide N mass balance, focusing particular attention on losses of NO3 to groundwater. Leaching of NO3 to groundwater is a large flow of N within the state, accounting for roughly 16% of total N imports, with approximately 90% of the NO3 originating from crop and livestock production. Because N emissions from agricultural sources are geographically dispersed, cannot be easily observed, and are difficult to precisely control, this problem presents unique challenges for effective policy design. A suite of integrated practice and policy solutions may be needed to achieve both adequate source control and mitigation of the existing N contamination within reasonable time frames. We provide an overview of available policy instruments for nonpoint source pollution control and examine specific outcomes when these mechanisms have been implemented to control nitrogen pollution in practice. Policy characteristics are then organized into a coherent methodology for assessing candidate policies for controlling nitrogen emissions from agricultural sources in California.