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Despite major efforts, the reduction of reactive nitrogen (Nr) using traditional metrics and policy tools for the Chesapeake Bay has slowed in recent years. In this article, we apply the concept of the Nitrogen Cascade to the chemically dynamic nature and multiple sources of Nr to examine the temporal and spatial movement of different forms of Nr through multiple ecosystems and media. We also demonstrate the benefit of using more than the traditional mass fluxes to set criteria for action. The use of multiple metrics provides additional information about where the most effective intervention point might be. Utilizing damage costs or mortality metrics demonstrates that even though the mass fluxes to the atmosphere are lower than direct releases to terrestrial and aquatic ecosystems, total damage costs to all ecosystems and health are higher because of the cascade of Nr and the associated damages, and because they exact a higher human health cost. Abatement costs for reducing Nr releases into the air are also lower. These findings have major implications for the use of multiple metrics and the additional benefits of expanding the scope of concern beyond the Bay itself and support improved coordination between the Clean Air and Clean Water Acts while restoring the Chesapeake Bay. [ABSTRACT FROM AUTHOR]

The chemical nitrogen cycle is becoming better characterized in terms of fluxes and reservoirs on a variety of scales. Galloway has demonstrated that reactive nitrogen can cascade through multiple ecosystems causing environmental damage at each stage before being denitrified to N(2). We propose to construct a parallel economic nitrogen cascade (ENC) in which economic impacts of nitrogen fluxes can be estimated by the costs associated with each stage of the chemical cascade. Using economic data for the benefits of damage avoided and costs of mitigation in the Chesapeake Bay basin, we have constructed an economic nitrogen cascade for the region. Since a single ton of nitrogen can cascade through the system, the costs also cascade. Therefore evaluating the benefits of mitigating a ton of reactive nitrogen released needs to consider the damage avoided in all of the ecosystems through which that ton would cascade. The analysis reveals that it is most cost effective to remove a ton of nitrogen coming from combustion since it has the greatest impact on human health and creates cascading damage through the atmospheric, terrestrial, aquatic and coastal ecosystems. We will discuss the implications of this analysis for determining the most cost effective policy option for achieving environmental quality goals.