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

National Park Service

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.

The Challenge

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

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

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

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.

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.

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.

CRITICAL LOAD DEVELOPMENT

SCIENCE FEDERAL MANAGER

• 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

Rocky Mountain National Park

Nitrogen Load (kg/ ha /yr)

Changes in soil chemistry

Change in diatomspecies composition

Episodic acidification

Chronic acidification

Critical loads can be defined for specific indicators and endpoints

Critical Load Development for Rocky Mountain National Park

Empirical Studies provide evidence of N deposition effects to:•high elevation lakes – N saturation, diatom changes•soils and vegetation - % N, C:N

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).

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.

Science Management

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”)

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

Future directions