Air Resources Division – National Park Service Critical Loads for Atmospheric Deposition: Assessing, Evaluating and Protecting Natural Resources Tamara Blett Air Resources Division – National Park Service CANS Workshop Feb 2006 Discuss in more detail about model outputs, and how we think we should develop and use them CL= The deposition loading at which something significant happens in an ecosystem

Development/Use of Critical Loads IMPLEMENTATION (how can the CL be used to protect parks & wilderness areas? DEVELOPMENT (what is the CL?) Spend a little time on the right side of the graph, to think through how to produce something meaningful on the left side. CLs cannot be used effectively in policy/management or regulation unless they are developed to do so. For example-expressing loading in equivalents/ha rather than kgN/ha and kgS/ha can’t be dealt with very well in U.S. regulatory systems. If developed and reported in the same way as in Europe, then will likely not be useful here. Need to be strategic. Scientists Regulators Land Managers, (NPS/FS), EPA

Definitions…

Critical load/Target load “The quantitative estimate of an exposure to one or more pollutants below which significant harmful effects on specified sensitive elements of the environment do not occur according to present knowledge.” (Nilsson and Grennfelt 1988) Target load: The level of exposure to one or more pollutants that results in an acceptable level of resource protection; may be based on political, economic, or temporal considerations. Critical loads and target loads can be developed for any pollutants. This is the definition we are exclusively using now… internationally accepted. When you talk to policy folks/regulators about CL, please be clear on these differences –otherwise they will want to set CL based on what is economically feasible… Critical loads- science based: the loading at which some type of effect on the ecosystems occurs. Target load- policy decision (acceptable loading over any number of years, time frame to recovery, could incorporate NPS protection goals, or Air Reg Agency emissions reduction goals, or any number or things.

Preserve and Protect “…conserve [natural and cultural resources]…as will leave them unimpaired for the enjoyment of future generations.” (NPS Organic Act) “Wilderness areas…shall be administered…in such a manner as will leave them unimpaired for future use and enjoyment as wilderness…” (Wilderness Act of 1964) “…preserve, protect and enhance the air quality in national parks, national wilderness areas, national monuments, national seashores…” (Clean Air Act as amended in 1977) The park service is guided by a number of mandates, including National Park Service Organic Act Wilderness Act – both direct us to manage resources in such a way to leave them unimpaired for future generations Clean Air Act tells us to preserve, protect, and enhance air quality in national parks Congress further directed the park service and other federal land managerment agencies to proactively protect air quality sensitive resources on federal lands and, in cases of doubt, err on the side of protecting these resources for future generations. “In cases of doubt the land manager should err on the side of protecting the air quality-related values for future generations.” (Senate Report No. 95-127, 95th Congress, 1977) [Rocky Mountain NP should be managed for] “…preservation of the natural conditions and the scenic beauties thereof.” (1915 park enabling legislation)

Defining the critical load ”The maximum amount of pollution into an ecosystem that does not cause significant damage to system resources, survival, structure or function” “The quantitative estimate of an exposure to one or more pollutants below which significant harmful effects on specified sensitive elements of the environment do not occur according to present knowledge.” (Nilsson and Grennfelt 1988) This first CL definition used in some European approaches… request that we use the *second definition for sensitive U.S. systems and this modeling effort

Indicators and Thresholds….

Ecosystem endpoints for CL: Conceptual Diagram Rocky Mountain National Park: Continuum of Impacts to Ecological Health Ecosystem endpoints for CL: Conceptual Diagram N Load (kg/ ha /yr) FLMs want CL for the most sensitive systems. “Significant harmful effects” are those that alter natural structure or function, not “dead trees” or “dead fish”. Sometime seems like what is “significant” is what is “easy to measure” and what is “harmful” is what is “dead” Land managers more interested in “healthy natural ecosystems” and the CL that preserves or restores them. Effects on aquatic animals (episodic acidification) Forest decline (acidification effects on trees) Changes in soil & water chemistry Surface water N saturation Changes in tree chemistry Change in aquatic plant species composition Change in alpine plant species Lethal effects on fish, other aquatic animals (chronic acidification) Critical loads are defined for specific indicators and endpoints

CRITICAL LOAD DEVELOPMENT SCIENCE FEDERAL MANAGER Federal manager is guided by agency policy in selecting sensitive resources and indicators of change; defines ”harmful” changes to sensitive resources based on policy goals. Scientists conduct empirical studies to identify resources sensitive to deposition Scientists derive critical loads from empirical studies and modeling analyses. Conceptual diagram \ Scientists Use empirical research/modeling to determine resource sensitivity Federal land managers will be guided by agency policy in decisions on sensitive receptors, “specified sensitive element,” and endpoints, i.e., “harmful effect” (e.g. may be trees and tree growth on timber harvest lands; and may be understory plants and mycorhyzae viability or lichen or diatoms, or surface waters ability to support healthy biota on park and wilderness lands) 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 Don’t intend to tell scientists how to conduct science – only what questions to ask if the intent is for CL to be used or useful. Also may inadvertantly be used as license to harm resources if carelessly done. Decisions about interim or sustainable levels of N and S deposition on federal lands are made by federal manager, with consultation with air regulators and others if target loads will be used for emissions control strategies.

Science/Policy Integration Recommendation- March 2004 FLM CL Workshop 4 box model is useful conceptual framework for considering S and N Critical Loads Acidif. Nutrient Can develop CL for any one or ALL of these variable on a given piece of land Aquatic Terrestrial

“Sensitive Elements” and “Effects” “Specified sensitive elements”: ecosystems sensitive to nitrogen and/or sulfur deposition, e.g., Poorly buffered lakes, streams, soils Ecosystems that evolved under low nutrient conditions and/or with short growing season (e.g. deserts or alpine areas) “Harmful effects”: changes in the natural functioning of an ecosystem, e.g., Loss of acid-neutralizing capacity affecting biota (growth, viability, condition, etc) Unwanted enrichment by nitrogen resulting in changes in natural vegetative community Different people will define these differently. Critical that NPS defines these for resources on our lands. – Scientists often define ‘harmful’ as “dead” and “sensitive” as “easy to measure” Important that NPS staff talk about our definition of “sensitive elements” and “harmful effect” with scientists BEFORE they so critical loads work in the field