Main Messages by Chapter
To understand the stocks and flows of nitrogen in California, we first identify important underlying drivers—the economic, political, and technological processes that influence human decision-making in such a way as to affect nitrogen’s presence in and passage through California ecosystems.
The release of nitrogen the environment is in part a consequence of the inherent properties of the N cycle but is greatly affected by human decisions. This chapter assesses those human and natural processes that directly alter N cycling (hereafter referred to as ‘direct drivers’). The chapter considers trends in these on-the-ground actions that influence N use, leakages, and emissions, following on our examination of underlying drivers and leading to calculations of the relative magnitude of N flows in the state.
A mass balance of nitrogen inputs and outputs for California was calculated for the year 2005. This scientifically rigorous accounting method tracks the size of nitrogen flows which allows us to understand which sectors are the major users of nitrogen and which contribute most to the nitrogen in the air, water, and ecosystems of California.
Changes in nitrogen levels in soils, air, and water affect the benefits people derive from ecosystems. These benefits, known as ecosystem services, fall into the four categories of provisioning, regulating, cultural, and supporting services. In this chapter we examined ecosystem services that are known to be affected by nitrogen levels and management activities, with a focus on those that are relevant to California.
Scenarios can help stakeholders deal with controversy and complexity, and they are particularly useful in cases where there is a large amount of uncertainty, as is the case in this assessment. This chapter describes the process and results of a scenarios development workshop involving a diverse group of stakeholders who were asked to creatively think about the following question: How will we manage nitrogen in California agriculture over the next 20 years?
Management practices, and their underlying technologies, together with land-use decisions, have a dramatic influence on the total amount and ultimate fate of nitrogen (N) in the environment. Based on the California nitrogen mass balance (Chapter 4), nine critical areas for intervention in the nitrogen cascade were identified. This chapter reviews these critical control points and evaluates related mitigative strategies and technological options to reduce emissions of nitrogen. This chapter also evaluates the potential for synergies and trade-offs that may occur from adopting these strategies.
Because nitrogen 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 stock within reasonable time-frames. This chapter provides an overview of available policy instruments for non-point source pollution control and examines specific outcomes when these mechanisms have been implemented to control N pollution in practice. Policy characteristics are then organized into a coherent methodology for assessing candidate policies for controlling N emissions from agricultural sources in California.