ISSUES IN ECOLOGY Published by the Ecological Society of America Setting Limits:Using Air Pollution Thresholds to Protect and Restore U.S.Ecosystems Mark E.Fenn,Kathleen E Lambert,Tamara F.Blett,Douglas A.Burns Linda H.Pardo,Gary M.Lovett,Richard A.Haeuber,David C.Evers, Charles T.Driscoll,and Dean S.Jeffries Fall 2011 Report Number 14 esa
esa Published by the Ecological Society of America esa Setting Limits: Using Air Pollution Thresholds to Protect and Restore U.S. Ecosystems Mark E. Fenn, Kathleen F. Lambert, Tamara F. Blett, Douglas A. Burns, Linda H. Pardo, Gary M. Lovett, Richard A. Haeuber, David C. Evers, Charles T. Driscoll, and Dean S. Jeffries Fall 2011 Report Number 14 Setting Limits: Using Air Pollution Thresholds to Protect and Restore U.S. Ecosystems Issues inin Ecology Ecology
ISSUES IN ECOLOGY NUMBER FOURTEEN FALL 2011 Setting Limits:Using Air Pollution Thresholds to Protect and Restore U.S.Ecosystems SUMMARY 之o lutionvicn forubi polyUbreero restored by usinga combination of emissions-based approaches and science-based thresholds of ecosystem damage. Based on the of a comprehensive review of air pollution thresholds,we concude: and water purificati nuch nitrogen are c d include altered am ntand tion for cid d eastern United S Up to65%of lakes within sensi Mercury contamination adversely affects fish in many inland and coastal waters.Fish consumption advisories for Air quality programs,such as those stemming from the 1990 Clean Air Act Amendments,have helped decrease air A stronger ecosystem basis for air pollutant policies could be established through adoption of science-based thresh olds.Existing monitoring programs track vital information needed to measure the response to policies,and could priate ch mical and biolog r terrestrial and aquatic ecosystems and 不ehn ss for emissio The Ecological Society of America.esahq@esa.org esa 1
© The Ecological Society of America • esahq@esa.org esa 1 ISSUES IN ECOLOGY NUMBER FOURTEEN FALL 2011 Setting Limits: Using Air Pollution Thresholds to Protect and Restore U.S. Ecosystems SUMMARY More than four decades of research provide unequivocal evidence that sulfur, nitrogen, and mercury pollution have altered, and will continue to alter, our nation’s lands and waters. The emission and deposition of air pollutants harm native plants and animals, degrade water quality, affect forest productivity, and are damaging to human health. Many air quality policies limit emissions at the source but these control measures do not always consider ecosystem impacts. Air pollution thresholds at which ecological effects are observed, such as critical loads, are effective tools for assessing the impacts of air pollution on essential ecosystem services and for informing public policy. U.S. ecosystems can be more effectively protected and restored by using a combination of emissions-based approaches and science-based thresholds of ecosystem damage. Based on the results of a comprehensive review of air pollution thresholds, we conclude: l Ecosystem services such as air and water purification, decomposition and detoxification of waste materials, climate regulation, regeneration of soil fertility, production and biodiversity maintenance, as well as crop, timber and fish supplies are impacted by deposition of nitrogen, sulfur, mercury and other pollutants. The consequences of these changes may be difficult or impossible to reverse as impacts cascade throughout affected ecosystems. l The effects of too much nitrogen are common across the U.S. and include altered plant and lichen communities, enhanced growth of invasive species, eutrophication and acidification of lands and waters, and habitat deterioration for native species, including endangered species. l Lake, stream and soil acidification is widespread across the eastern United States. Up to 65% of lakes within sensitive areas receive acid deposition that exceeds critical loads. l Mercury contamination adversely affects fish in many inland and coastal waters. Fish consumption advisories for mercury exist in all 50 states and on many tribal lands. High concentrations of mercury in wildlife are also widespread and have multiple adverse effects. l Air quality programs, such as those stemming from the 1990 Clean Air Act Amendments, have helped decrease air pollution even as population and energy demand have increased. Yet, they do not adequately protect ecosystems from long-term damage. Moreover they do not address ammonia emissions. l A stronger ecosystem basis for air pollutant policies could be established through adoption of science-based thresholds. Existing monitoring programs track vital information needed to measure the response to policies, and could be expanded to include appropriate chemical and biological indicators for terrestrial and aquatic ecosystems and establishment of a national ecosystem monitoring network for mercury. The development and use of air pollution thresholds for ecosystem protection and management is increasing in the United States, yet threshold approaches remain underutilized. Ecological thresholds for air pollution, such as critical loads for nitrogen and sulfur deposition, are not currently included in the formal regulatory process for emissions controls in the United States, although they are now considered in local management decisions by the National Park Service and U.S. Forest Service. Ecological thresholds offer a scientifically sound approach to protecting and restoring U.S. ecosystems and an important tool for natural resource management and policy. Cover photo credit: Loch Vale in the Colorado Rocky Mountains. Photo by SteveB in Denver (http://www.flickr.com/people/darkdenver/) and used in this publication under a Creative Commons Attribution license
ISSUES IN ECOLOGY NUMBER FOURTEEN FALL 2011 Setting Limits:Using Air Pollution Thresholds to Protect and Restore U.S.Ecosystems Mark E.Fenn,Kathleen F.Lambert,Tamara E Blett,Douglas A.Burns,Linda H.Pardo,Gary M.Lovett, Richard A.Haeuber,David C.Evers,Charles T.Driscoll,and Dean S.Jeffries Introduction Rigncogntnoil,amdthcomsoing Natural ecosystems have been altered in vari h and to d ribe th ir use to as scientific research.scientists have documented and the vitalservices they provide.We focus how local,regional,and global sources of air here on the environmental impacts of nitro sand mercury and refer toco tion of soils and surface waters,harmful algal on thepublied rarch of hundrs lessons from and decre Air Pollution Thresholds Thresholds of air pollution in the U.S.have rations,ecosystem effects,and associated pol been widely disc ed in the scientific litera- yin py-levant s,when research estab ataffect human health and ecosystems are primarily emitted from electric ecosystems in the eastem U.S.More recently power generation, industrial, nitrogen deposition has been shown to impac of th ered in light of the often detrimental effects of specific concentration or deposition input of human health,visi. nair pollutant tha e adve the ubg rided to soc of much scientific res carch.Pollutants can accumulate with litte noticeable impacton ons ha s occur as sul cha asured by scientifically deter. generation and othe even as pop anges n many parts o restil decining due to the increase in other Air pollution thresholds can be defined 2 esa The Ecological Society of America esahq@esa.org
2 esa © The Ecological Society of America • esahq@esa.org Introduction Natural ecosystems have been altered in various ways by nitrogen, sulfur, and mercury deposited in rain, snow, or as gases and particles in the atmosphere. Through decades of scientific research, scientists have documented how local, regional, and global sources of air pollution can produce profound changes in ecosystems. These changes include acidification of soils and surface waters, harmful algal blooms and low oxygen conditions in estuaries, reduced diversity of native plants, high levels of mercury in fish and other wildlife, and decreased tolerance to other stresses, such as pests, disease, and climate change. Advancing our understanding of the linkages among pollutant deposition rates or concentrations, ecosystem effects, and associated policy decisions is a priority in policy-relevant science in the U.S. Air pollutants that affect human health and ecosystems are primarily emitted from electric power generation, industrial, transportation, and agricultural activities. The benefits and necessities of these activities must be considered in light of the often detrimental effects of atmospheric emissions on human health, visibility, ecosystems, and on the services provided to society by these ecosystems (Table 1). The 1990 Clean Air Act Amendments and other air quality regulations have led to marked declines in emissions of nitrogen, sulfur and mercury. Some emissions from power generation and other sources have decreased by over 50% since the 1970s, even as population and energy demand have increased. As the emissions and deposition of most pollutants have declined, some impacted ecosystems have started to recover. In many parts of the country, however, ecological conditions are still declining due to the increase in other forms of pollution such as ammonia (NH3), the long term accumulation of sulfur and nitrogen compounds in soils, and the ongoing biomagnification of mercury in food webs. The purpose of this report is to distill advances in the science of air pollution thresholds and to describe their use to assess, protect and manage the nation’s ecosystems and the vital services they provide. We focus here on the environmental impacts of nitrogen, sulfur, and mercury and refer to connections to climate change. The discussion draws on the published research of hundreds of scientists over the past several decades with a focus on U.S. ecosystems and lessons from Canada and Europe. Air Pollution Thresholds Thresholds of air pollution in the U.S. have been widely discussed in the scientific literature since the 1970s, when research established that sulfur deposition was above levels at which damage occurs in many sensitive ecosystems in the eastern U.S. More recently, nitrogen deposition has been shown to impact sensitive ecosystem components and processes throughout the United States. Defining the specific concentration or deposition input of an air pollutant that will cause adverse or significant ecosystem effects has been the subject of much scientific research. Pollutants can accumulate with little noticeable impact on plants or animals until major changes occur as a tipping point is reached (Box 1). These changes are measured by scientifically determined chemical or biological indicators (Box 2). Such environmental changes might eliminate a single sensitive species, or a broad shift may occur in biodiversity throughout an ecosystem. Once a species or ecosystem has passed a tipping point, a return to the previous state may not be possible. Air pollution thresholds can be defined based strictly on scientific research (ecological thresholds) or based on a balance of policy conSetting Limits: Using Air Pollution Thresholds to Protect and Restore U.S. Ecosystems Mark E. Fenn, Kathleen F. Lambert, Tamara F. Blett, Douglas A. Burns, Linda H. Pardo, Gary M. Lovett, Richard A. Haeuber, David C. Evers, Charles T. Driscoll, and Dean S. Jeffries ISSUES IN ECOLOGY NUMBER FOURTEEN FALL 2011
ISSUES IN ECOLOGY NUMBER FOURTEEN FALL 2011 ,ecologi 1.ACIDIFYING DEPOSITION sment A.Effects of Acidifying Deposition fur dix (),oe(N)n Advances in the Science of Air Pollution Thresholds to Earth in rain,snow,fog,mist and gases in Based on researchc fomsaucha5nitrcandslfrtcacidsand negative impa ts to te estrial and air pollution thre ecosystems.Ecosystems in the westemn U.S approaches (B in much of the reion and ecause in n arid or semi-arid regions the soils are relatively stre Box 1.DEFINITION OF TERMS mon sources of acidifving air pollutants ability applied to su ccurs as wet (e.g.,rainfall,fog,or snow)and dry deposition(e.g.,gaseous or parti deposition) nant in an relative to the surrounding environ ohic levels in the CRITICAL LOAD.The quantitative estimate of an exposure to one or more pollutants below which significant harmful effects on spec. ied sensitive elements vironment do not occur according neasurable change occurs in the resp se of some component of ar iety from a multitude of re ural ecosystems sof endpoints ay be adversely affected by a change i ne of effects occurring in an ec ed by an overload of nitrogen,usually from long term desired ecologic conditi olished by policy and selected basedon a balancing SENSITIVE RECEPTOR.The indicator that sthem ve to,or the ed by a tyr TIPPINGPOINT.The point at which an ecosystem shifts to a new state or condition in a rapid,often irreversible, The Ecological Society of America.esahg@esa.ord esa 3
© The Ecological Society of America • esahq@esa.org esa 3 ISSUES IN ECOLOGY NUMBER FOURTEEN FALL 2011 siderations spanning law, economics, ecological effects, human health and risk assessment (policy thresholds) (Box 1) (Figure 1). One tool increasingly used to integrate the science and policy of air pollution thresholds for ecosystem protection and management is critical loads (Box 4). Advances in the Science of Air Pollution Thresholds Based on research over the past decade, a strong scientific foundation exists for defining air pollution thresholds using critical loads approaches (Box 4). In the following sections we synthesize the state of the science related to the ecological effects, key indicators, and critical loads approaches for acidifying deposition, nitrogen pollution and mercury contamination. 1. ACIDIFYING DEPOSITION A. Effects of Acidifying Deposition Acidifying deposition (or “acid rain”) is caused by emissions to the atmosphere of sulfur dioxide (SO2), nitrogen oxides (NOx), and other acidifying compounds such as ammonia (NH3)(see Box 3 for definition of chemical names and symbols). These pollutants return to Earth in rain, snow, fog, mist and gases in forms such as nitric and sulfuric acids and ammonium (NH4 + ) and can have long-term negative impacts to terrestrial and aquatic ecosystems. Ecosystems in the western U.S. have not been greatly affected by acidification because acidifying deposition is relatively low in much of the region and because in many arid or semi-arid regions the soils are relatively insensitive to acid inputs. Some high elevation streams in the Colorado Rockies and the Box 1. DEFINITION OF TERMS ACIDIFYING DEPOSITION. Deposition of substances from the atmosphere as rain, snow, fog, or dry particles that have the potential to acidify the receptor medium, such as soil or surface waters. Emissions of sulfur and nitrogen oxides and ammonia are the most common sources of acidifying air pollutants. ACID NEUTRALIZING CAPACITY. A measure of the ability of a solution to neutralize inputs of strong acids, commonly applied to surface water or soil solution. The acronym ANC is widely used in referring to acid neutralizing capacity. ATMOSPHERIC DEPOSITION. The transfer of air pollutants from the atmosphere to the Earth’s surface. Atmospheric deposition occurs as wet (e.g., rainfall, fog, or snow) and dry deposition (e.g., gaseous or particulate deposition). BASE SATURATION. The fraction of exchangeable cations in soil which are nonacid forming cations (Ca+2, Mg+2, K+ and Na+ ), also referred to as ‘base cations’. The higher the amount of exchangeable base cations in soil, the more acidity can be neutralized. BIOACCUMULATION. The increase in concentration of a contaminant in an individual organism relative to the surrounding environment or medium (e.g., water, sediment). BIOMAGNIFICATION. The increase in concentration of a contaminant from lower trophic levels to higher trophic levels in the food chain. CRITICAL 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. ECOLOGICAL THRESHOLD. The dose of a pollutant at which a measurable change occurs in the response of some component of an ecosystem (e.g., NO3 – leaching at nitrogen deposition of 8 kg/ha/yr). ECOSYSTEM SERVICES. Benefits to society from a multitude of resources and processes that are supplied by natural ecosystems (e.g., clean drinking water). ENDPOINT. The ultimate ecological, biological or human condition or process to be protected from harm. Two examples of endpoints are human health and forest sustainability. INDICATOR. A measurable physical, chemical, or biological characteristic of a resource that may be adversely affected by a change in air quality (e.g., ANC). NITROGEN SATURATION. Syndrome of effects occurring in an ecosystem caused by an overload of nitrogen, usually from long term atmospheric nitrogen deposition. POLICY THRESHOLD. A quantitative value of desired ecological condition established by policy and selected based on a balancing of science and land management or policy goals. SENSITIVE RECEPTOR. The indicator that is the most responsive to, or the most easily affected by a type of air pollution. TARGET LOAD. The acceptable pollution load that is agreed upon by policy makers or land managers. The target load is set below the critical load to provide a reasonable margin of safety, but could be higher than the critical load at least temporarily. TIPPING POINT. The point at which an ecosystem shifts to a new state or condition in a rapid, often irreversible, transformation
ISSUES IN ECOLOGY NUMBER FOURTEEN FALL 2011 Ecological thresholds Impact EcosystemEcological Response Ecosystem Services Indicator Ecological Threshold Sulfur and Nitrogen Deposition Terrestrial 1.D wth sed fores si0hetereditotres susceptibility to diseas disturbance Foliar chemistry ppm Ca and Apytaian 3.Water quality 100eL-low risk to aquatic biota 0 ueg/L-risk of Ar leaching to eans Nitrogen Deposition Terrestrial 1.Loss of sensitive Shifts in lichen 5 ka N/hayr atmospheric deposition 1.0%6 in lichen (Let eased tree mortali Freshwater Shifts in diatom 1.5kg N/ha/yr wet deposition diat -celled low risk 2.Degraded water quaty Coastal Habitat pr Commercial oxygen 48egoum Dissolved phosphorus o1mg四 Mercury Deposition Terrestrial Wildlife health Hg in songbirds 1.3 ug/g in blood Toxicity to wildlife Freshwater 4 esa The Ecological Society of America esahq@esa.org
ISSUES IN ECOLOGY NUMBER FOURTEEN FALL 2011 4 esa © The Ecological Society of America • esahq@esa.org Table 1. Linking air pollution impacts to ecosystem services, indicators and thresholds. Ecological thresholds given are typical values that can vary depending on ecological and environmental conditions. Impact Ecosystem Ecological Response Ecosystem Services Indicator Ecological Threshold Impacted Sulfur and Nitrogen Deposition Acidification Terrestrial 1. Decreased forest 1. Timber production Ca: Al+3 ratios in soil <1 – heightened risk to trees growth 2. Climate regulation >10 – low risk 2. Increased 3. Biodiversity susceptibility to 4. Resilience to Soil percent base <10% - risk of nutritional disease disturbance saturation deficiencies in sensitive trees >30% - low risk Foliar chemistry <5000 ppm Ca and <700 ppm Mg – limiting to growth of sugar maple Freshwater 1. Reduced species 1. Recreational fishing Acid neutralizing 0 µeq/L – risk for chronic acidification richness 2. Biodiversity capacity 20-50 µeq/L – risk for episodic 2. Degraded water 3. Water quality acidification quality >100 µeq/L – low risk to aquatic biota Base cation surplus 0 µeq/L – risk of Al+3 leaching to in soil streams pH <6.0 – reduced number of fish species Inorganic Al+3 >2 µmol/L – toxic to aquatic biota Calcium <1.5 mg/L – sub-optimal for crustaceans Nitrogen Deposition Nitrogen Terrestrial 1. Loss of sensitive 1. Biodiversity Shifts in lichen 5 kg N/ha/yr atmospheric deposition Enrichment plant species 2. Soil fertility communities 2. Increase in invasive N concentration in 1.0% in lichen (Letharia vulpina) plants plant or lichen tissue 3. Increased tree mortality C:N ratio in soil <20-25 or less - elevated risk of nitrate leaching Freshwater 1. Loss of sensitive 1. Biodiversity Shifts in diatom 1.5 kg N/ha/yr wet deposition diatom (single-celled 2. Water quality communities algae) species Nitrate concentrations <2 µeq/L – low risk 2. Degraded water quality >20 µeq/L - degraded Coastal 1. Increased algal blooms 1. Habitat preservation Dissolved nitrogen High (≥1 mg/L) 2. Commercial fishing Medium (≥0.1 and <1 mg/L) 2. Decreased dissolved 3. Recreational fishing Low (≥0 and <0.1 mg/L) oxygen 4. Swimming, tourism, aesthetics Dissolved phosphorus High (≥0.1 mg/L) Medium (≥0.01 and <0.1 mg/L) Low (≥0 and <0.01 mg/L) Mercury Deposition Mercury Terrestrial 1. Toxicity to fish-eating Wildlife health Hg in songbirds 1.3 µg/g in blood toxicity wildlife 2. Toxicity to wildlife Hg in bats 10.0 µg/g in hair Freshwater 1. Mercury 1. Recreational fishing Hg in fish 0.2 - 0.3 µg/g bioaccumulation 2. Food production 3. Human health Fish and wildlife health Hg in diet 0.16 µg/g in prey fish Hg in fish-eating birds 3.0 µg/g in blood