1. National Park Service Critical Loads:
National Park Service Perspective
Ellen Porter
Air Resources Division – National Park Service
USDA Forest Service Critical Loads Meeting
February 15-18, 2005
Riverside, California
Ellen Porter
Biologist
NPS Air Resources Division, Denver

2. The Challenge
NPS administers over 270 national parks, national monuments, and other units with “significant natural resources.”
The park service administers over 270 national parks with significant natural resources, encompassing a wide variety of habitats from semi-tropical forests to arctic tundra.
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
NPS has conducted over 20 years of research at ROMO, much of it done by Jill Baron of USGS NREL with help from Heather Rueth, Koren Nydick, and others. N deposition has increased over the last 20 years in ROMO. Jill has compared ecosystem conditions on the west side of the Cont Divide in Rocky, where N deposition is relatively low (1-2 kg/ha/yr), to conditions on the east side of the park where N deposition is higher (3-5 kg/ha/yr). On the east side with higher N deposition rates she has found lower C:N ratios in foliage and soils, higher % N in soils and higher potential net N mineralization rates. In addition lake NO3 concentrations are higher on the east side of Rocky. Her group also analyzed lake sediment cores and found that in the 1950s, diatom communities in the lake shifted from oligotrophic spp to spp considered typical of more eutrophic lakes. This shift corresponds to an increase in isotopically light N in the cores, suggestive of an anthropogenic influence. Studies are underway to look at the effects of N fertilization on alpine tundra vegetation in ROMO.
We suspect that N deposition effects are also occurring in a number of other parks in the Rockies (Glacier, Grand Tetons, Yellowstone) EX: There is evidence that diatom community shifts similar to those in ROMO occurred in the Beartooth Mountains east of Yellowstone NP. In the Beartooths, the shift occurred around 1995, at a level of N deposition similar to what ROMO experienced in the 1950s.
In the Sierra NPs (Yosemite, Sequoia) high N deposition has induced a number of ecossytem effects, including increased fire fuels
In PNW, where Olympic, Mount Rainier and N Cascades are located, there is evidence of increased NO3 in lakes, vegetation and lichen effects (Linda Geiser).
Vegetation in dry arid parks like Joshua Tree and Big Bend respond to N fertilization and over time, N loving grasses and invasives may be favored over native spp.
Sulfur deposition has been elevated in the East for many years and, as a result, SHEN and GRSM are experiencing episodic and chronic acidification of streams, alteration of soil nutrient cycles, aluminum mobilization in soils, and injury to spruce-fir forests.
The park service currently consults with States and EPA on new sources of air pollution and strategies to reduce pollution. States and EPA often ask us, “how much pollution is too much?” We have recently been exploring the concept of critical loads to help us answer this question.

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
The federal land managers met to discuss the potential of using critical loads in Spring of The land managers agreed that
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

5. This diagram shows the relationship between critical loads and target loads. As deposition of N or some other pollutant increases (POINT), at some threshold a harmful effect may occur to a specific physical, chemical, or biological ecosystem component. This threshold is defined as the critical load (POINT); below the critical load, a harmful effect does not occur. The critical load is based on science, either empirical studies or modeling. Target loads could be set for political or economic reasons. This diagram shows a protective target load, target load “A” (POINT) that would be set for areas with current deposition below the critical load. This protective target load would help ensure that deposition did not reach the critical load. Because of our mandates for resource protection, federal land managers would always set a target load below the critical load.
Another type of target load, is shown as target load “B”, (POINT) which is also sometimes referred to as in interim target load. It could be set by air regulators in States or EPA in areas where current deposition is above the critical load. The interim target load could be used as a benchmark for progress towards the critical load, and adjusted periodically until the critical load or target load “A” were reached.

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
Let me re-iterate
For Critical and target loads to be useful for protecting sensitive resources on federal lands:
Federal land managers will be guided by agency policy in decisions on sensitive receptors, “specified sensitive element,” and endpoints, i.e., “harmful effect”
Ex:
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.
Conceptual diagram showing respective roles of scientists and land managers in developing critical loads

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
Modeling by Jim Galloway and others has predicted pre industrial N dep in the West to be approx 0.25 kg/ha.
Current total N dep approx 4 kg/ha/yr
In the 1950s N dep had increased enough to cause changes in diatom communities in sensitive lakes
We’ve asked Jill Baron to use some hindcasting techniques to estimate what deposition was in the 1950s when the diatom shift occurred; that level probably approximates the critical load for the diatom community in high elevation lakes diatoms.
We anticipate recommending a target load, perhaps a bit higher than the critical load; we hope to work with the State of CO to develop emissions reductions strategies to meet a variety of goals – ozone reduction, visibility improvement, and critical load attainment.

9. Episodic acidification Chronic acidification
Nitrogen Load (kg/ ha /yr)
Changes in soil chemistry
Change in diatom
species composition
Episodic acidification
Chronic acidification
I’d like to emphasize that critical loads, as envisioned by the national Park service, are defined for specific endpoints and indicators. Diatoms might be affected at far lower N loads than would cause acidification, so different critical loads would apply. If your goal is to protect the entire ecosystem, then you would want to protect the most sensitive resource, perhaps the diatom community.
Critical loads can be defined for specific indicators and endpoints

10. Critical Load Development for Rocky Mountain National Park
Science
Management
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.
Here’s the diagram you saw before, outlining CL development for ROMO

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”)
National Park Land Management Planning Goals to protect and improve resource condition
Set benchmarks for State and Regional Plans to improve air quality
EPA regulations – EPA was ordered to review the NO2 increment as a result of a court action brought by ED and others. The NO2 increment does nothing to protect AQRVs against degradation – ex., although the NO2 incremenet is met in most areas, incl across the West, NO3 levels are increasing across the West and resources are increasing harmed by N deposition. EPA was considering soliciting comments on whether CL could be used in State planning processes to protect AQRVs, and whether CL could follow inplementation of a cap and trade program or SIP program if further AQRV protection were needed. They were considering some pilot projects in select areas (ROMO) to see how CL could be developed and implemented. As they say, this was all a sweet dream. The draft proposal which finally went out of EPA did an about face, stating that “the more recent data do not provide sufficiient information from which it would be possible to conclude that the levels of the exising NO2 increments are inadequate” and said that it would not propose CL as a basis for a regulatory measure at this time.
New Source Review to assess effects of air pollutant emissions from industry, powerplants on air quality sensitive resources
In addition, Critical Loads could be used to assess the efficacy of air pollution regulatory programs (e.g., cap-and-trade programs) and broader air quality programs.
Critical loads may be a way to merge science with policy to make both science and policy more useful in protecting natural resources.

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
In order to move forward with developing and implementing critical loads in order to ultimately protect natural resources on federal lands, we believe that it’s essential to have increased communication with the scientific community.
As federal managers, we need to
communicate our resource management concerns and goals and then
collaborate with the scientific community to identify sensitive resources, identify appropriate models for both aquatic and terrestrial ecosystems, identify good indicators to use for critical loads (C:N ratio? % N in soils, etc.)
We also need to explore opportunities for using critical loads to communicate our resource concerns to States and EPA and have them consider critical loads in planning and development of regulations.