The US Environmental Protection Agency is faced with developing strategies to manage stressors that do not behave like traditional toxic chemicals in the environment.  Habitat change, exotic species, climate change, and nutrient over-enrichment are examples of such stressors that affect the ability of the nation’s ecosystems to deliver goods and services essential to people.  Managing the risks these stressors pose to human health and ecosystems is difficult within EPA’s existing regulatory structures because (1) the effects cross traditional regulatory media; (2) the effects are highly place-dependent; and (3) the stressors exist in many forms that interact with one another.  Further complicating the picture is the fact that some of these stressors lead to both desirable and undesirable changes.  Nitrogen (N) is one such stressor. Over the past century, human activities such as synthetic fertilizer production and fossil fuel combustion have substantially increased N inputs to the biosphere.   Ecosystem services such as food, wood, and fiber production benefit from increased N inputs, yet many ecosystem services (such as biodiversity of alpine grasslands and high altitude lakes) are negatively impacted by N at much lower input levels.  A recent survey by EPA places N in the top three causes for impairment of wadeable stream condition.  EPA is beginning the Ecosytem Services Research Program (ESRP) to develop a defensible accounting framework for ecosystem services that will illustrate these trade-offs for managers and regulators.

Results/Conclusions

An important goal of the Nitrogen research component within ESRP is to develop a framework to represent positive and negative impacts of N on important ecosystem services, across an N loading gradient. Developing a defensible framework for ecosystem services accounting would allow managers and regulators to evaluate the range of effects of N and illustrate the tradeoffs between reduction scenarios in management or policy decisions related to N. We are addressing our broad goal of connecting N to ecosystem services through a two-pronged effort, with national work where possible, and smaller scale studies tackling specific problems and ecosystem types. Recently the effects of N on ecosystems were assessed by the EPA’s Integrated Science Assessment (ISA) for NOx and SOx ambient air quality standards.  Thousands of publications on ecosystem acidification and N nutrient enrichment were reviewed and summarized.  The numerous ecological endpoints were categorized into ecosystem services categories, as an initial step to evaluate the ecological services affected by N on a national scale.