Critical Loads: National Park Service Perspective Ellen Porter

1. National Park Service Critical Loads: National Park Service Perspective Ellen Porter Air Resources Division – National Park Service Ellen_Porter@nps.gov USDA Forest Service Critical Loads Meeting February 15-18, 2005 Riverside, California

2. The Challenge NPS administers over 270 national parks, national monuments, and other units with “significant natural resources.” NPS units encompass a wide variety of resources and ecosystems, from high alpine tundra to deserts to seashores.

3. Effects on Park Resources from Atmospheric Deposition • Rocky Mountain NP – Nitrogen deposition effects • Desert parks (Joshua Tree NP and Big Bend NP) – N deposition • Studies underway on species composition shifts due to N • Shenandoah NP/Great Smoky Mountains NP – S deposition

4. Federal Land Managers Critical Loads Workshop, 2004 Federal Land Managers agree: • Critical loads should: • protect the most sensitive resources within a park or wilderness area • ensure that no unacceptable change occurs to the resource • be based on the best science available and updated with new information

6. Critical Loads as Effective Tools for Federal Land Resource Protection For critical and target loads to be useful for protecting sensitive resources on federal lands: • Federal land managers • Agency policy guides decisions on sensitive receptors, “specified sensitive element,” and endpoints, i.e., “harmful effect” • Ex: specified sensitive element = lake/stream ANC • Federal land manager would likely choose an ANC endpoint of 100 ueq/L to maintain healthy aquatic biota vs. an ANC of 0 ueq/L that would result in acidification • Scientists • Use empirical research/modeling to determine resource sensitivity • Estimate critical load for “specified sensitive element” and “harmful effect” identified by the federal land manager

7. CRITICAL LOAD DEVELOPMENT SCIENCE FEDERAL MANAGER Sensitive resources and indicators of change are selected by federal area managers for critical load development on federal lands. Federal area managers define resource protection criteria;”harmful” changes to sensitive resources based on policy goals. Empirical Studies provide evidence for specific deleterious effects on selected ecosystem components or processes. Critical Loads are derived from empirical studies and modeling analyses and identify the amount of total N and S that triggers harmful changes to sensitive resources. Policy decisions about interim or sustainable levels of N and S deposition on federal lands, also called target loads, are made by federal area managers. Consultation with air regulators and others occurs if target loads will be used for emissions control strategies.

8. Rocky Mountain National Park • Natural (pre-1850’s) deposition of N in the West ≈ 0.25 kg/ha/yr • Current deposition of N in Rocky Mountain NP ≈ 4 kg/ha/yr • Nitrogen Effects in Rocky Mountain NP: • Shift in diatom communities in high elevation lakes • Changes in C:N ratio in soils and vegetation of old-growth Engelmann spruce forests • Soil % N higher • Increase in potential net N mineralization rates • Elevated nitrate levels in runoff and lakes

9. Nitrogen Load (kg/ ha /yr) Change in diatom species composition Changes in soil chemistry Episodic acidification Chronic acidification Critical loads can be defined for specific indicators and endpoints

10. Critical Load Development for Rocky Mountain National Park Management Science Park Managers have identified park lakes, streams, vegetation, and soils as “sensitive resources”. Park managers will define resource protection criteria, ”harmful” changes to sensitive resources based on policy goals (ex. ANC>50, natural diatom communities, thresholds for % N, C:N). • Empirical Studies provide evidence of N deposition effects to: • high elevation lakes – N saturation, diatom changes • soils and vegetation - % N, C:N Critical Loads are derived from empirical studies and modeling analyses and identify the amount of total N that triggers harmful changes to sensitive resources. The State of Colorado, NPS, and EPA have agreed to pursue a collaborative process to remedy air pollution effects at the park. Park managers will select target loads to provide a margin of protection for resources. Option: the State of Colorado air regulators may use interim target loads to achieve reasonable progress towards goal (TBD) and use cap-and-trade with declining cap.

11. Use and Implementation of Critical Loads • State and Regional Plans to improve air quality • EPA regulations? • NO2 increment review • “EPA recognizes that a State may choose to utilize a critical load concept as part of its air quality management approach to meet its broader air quality goals. Thus, if a State proposes to use such a concept, considering the state of the science and its developments over time, to satisfy the State’s overall air quality goals, EPA would consider it when determining whether a State’s approach satisfies PSD requirements. The EPA believes that a State might choose to pursue this concept under a State planning option.” • Assess efficacy of cap and trade • National Park Land Management Planning (e.g., “desired future conditions”)

12. Future directions How do we move forward with developing and implementing critical loads? • Increased communication and collaboration between land managers and scientists on resource management needs, sensitive resources, relevant indicators and endpoints to meet resource protection goals. • Identify sensitive resources in many parks • Identify/refine appropriate models for estimating critical loads in both aquatic and terrestrial ecosystems • Identify new and refine existing indicators • Explore opportunities for using critical loads in air regulatory planning processes at the national, state, and local level