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Canada - United States Air Quality Agreement

2002 Progress Report

SECTION IV  Scientific Cooperation

AQUATIC EFFECTS RESEARCH AND MONITORING

Water Chemistry Trend Analyses

A study of the 1989–1999 water chemistry trends observed at sites included in the International Cooperative Programme on Assessment and Monitoring of Acidification of Rivers and Lakes²⁷ confirmed the results of previous analyses that used data up until 1995.²⁸ The new study showed that in midwestern North America (northwestern Ontario, Michigan, Wisconsin, and Minnesota) and in eastern North America (central Ontario, Quebec, Atlantic Canada, and New York) declining sulphate and base cation (calcium + magnesium + sodium + potassium) concentrations were the predominant trends, i.e., they occurred in more than 50% of the monitored sites. These trends were both spatially widespread in occurrence and highly statistically significant. The fact that base cation declines appear to be a primary ionic compensation for sulphate declines is at least part of the reason why increases in pH and/or alkalinity (considered by many the "real" measure of acidification recovery) were not so predominant (see following paragraph). Nitrate concentrations also remain mostly unchanged in both regions, but concentrations of dissolved organic carbon (DOC) are increasing in some lakes. Increasing DOC may be important since, like increasing base cations, it can offset the pH and/or alkalinity improvements expected to accompany declining sulphate. On the other hand, increasing DOC may have the beneficial effect of reducing aluminum toxicity. Acidic waters typically have elevated concentrations of inorganic forms of aluminum that are toxic to aquatic biota. In the presence of DOC, inorganic aluminum combines with organic molecules, which renders it much less harmful.

Analyses of recent water chemistry trends observed in long-term monitoring networks from some eastern Canadian provinces confirm the foregoing generalities; however, they also show that differences exist both between provinces and between lake types. Declining sulphate was the predominant trend in long-term monitoring networks from Newfoundland and Nova Scotia, ²⁹ Quebec,³⁰ and Ontario³¹ but declining base cation concentrations was the most important compensatory response for only the latter two. Another Ontario network with a sample population composed of small lakes in wetland landscapes gave an entirely different result:³² For this network, "no significant change" was the dominant sulphate response, probably reflecting mobilization (oxidation) and export of sulphur from wetland soils during periods of drought.³³ The effect of this climatic stressor is to counteract the chemical signal expected from declining sulphate deposition. Increasing lake pH or alkalinity was observed in 10%, 14%, 49%, 15%, and 41% of the lakes from Newfoundland, Nova Scotia, Quebec, Ontario (with wetland lakes), and Ontario (without wetland lakes), respectively. Continued monitoring is required to understand the complex chemical responses that are occurring in the face of multiple and sometimes competing ecosystem stressors.

FOREST EFFECTS

Several factors affect forest health: biotic, climatic, soil-related as well as management intervention. Eastern forests are routinely exposed to acid deposition (as sulphur and nitrogen), as well as to ground-level ozone, in levels that are known to cause damage to sensitive components of ecosystems.

The NEG/ECP Forest Mapping Project

As reported, the Acid Rain Action plan, endorsed by the Conference of New England Governors and Eastern Canadian premiers (NEG/ECP), includes a component called The Forest Mapping Project. The project recognizes that in the presence of triggering stresses acid precipitation reduces soil fertility in some forests and is the underlying cause of decline of forest health and dieback. The goal of The Forest Mapping Project is to determine sustainable levels of acid deposition for forest soils in northeastern United States and eastern Canada using a calculation and mapping system inspired by a model developed and implemented in Europe for estimating 'critical loads' and their 'exceedances'.

The project receives funding and in-kind resources from a number of organizations and involves scientists from both countries.

In 1991, a Protocol for Assessing and Mapping Forest Sensitivity to Atmospheric Sulphur and Nitrogen Deposition was developed and published. The protocol lays out the methodology for estimating the 'sustainable' acid deposition rate, i.e., the rate that maintains or enhances the current level of soil base saturation such that soil reserves of plant nutrients can be maintained under given forest management practices and/or natural disturbance regimes for the foreseeable future (i.e., several forest rotations). The assessment of sustainable deposition is based on the long-term equilibrium between the provision and removal of nutrients (calcium, magnesium, potassium, and nitrogen) from forest ecosystems. The protocol takes the following into account: atmospheric deposition, mineral nutrients freed from weathering of soil minerals, nutrients removed from a site through forest harvesting, and nutrients leached out of the soils by acidic deposition.

During phase 1 of the project, maps of sustainable deposition and actual exceedances were prepared for Vermont and Newfoundland. Preliminary results were presented and discussed with some foresters in both jurisdictions, and as a result, additional data and further improvements were incorporated in the calculations. During the next three years, maps will be produced for all of the New England states and eastern provinces.

Documenting Effects of Ozone on Forests

The North American Forestry Commission (NAFC; Mexico, United States, Canada) has developed a proposal outlining research and field activity to carry out an integrated assessment of the effects of air pollution on forest ecosystems of North America. Monitoring protocols are being developed as a first step toward implementation of the proposal. Examples of pollutants of concern to forest health that can be sampled with passive samplers are O₃, SO₂, NH₃, NO₂, and HNO₃.

NAFC is also producing a pamphlet, aimed at a general audience, looking at impacts of ground-level ozone on sensitive forest ecosystems in North America. This pamphlet will concentrate on four sensitive forest ecosystems: one in Canada, two in the United States, and one in Mexico. The tentative date of publication is early 2003.

The Forest Indicators of Global Change (FIGC) project completed its third year of activity since the establishment of plots in 1998. The project comprises 26 eastern Canadian, forested, permanent sample plots arranged across four zones of acidic deposition critical load exceedence and four of ozone critical level exceedence. The 1,800 km transect features a 2-7°C variation of mean annual temperature and a 700-1,500 millimetre (mm) variation of mean annual precipitation. The most westerly plot is located at Turkey Lakes in northern Ontario and the most easterly near the Bay of Fundy, New Brunswick.

Sugar maple is contiguous as a dominant species across the gradient; white pine dominates as the coniferous species in Ontario; and red spruce is the predominant species in Quebec/New Brunswick. Sugar maple and red spruce have been the most prominent northeastern species suffering decline since the 1960s. The gradient includes CFS Acid Rain National Early Warning System (ARNEWS), Canada–U.S. North American Maple Project (NAMP), and new plots selected to fill geographical gaps. Nested within the whole are two sub-gradient studies focusing on high-elevation cloud/fog impacts and the 1998 ice storm. ARNEWS plots have been intensively monitored for up to 15 years, while NAMP plots have been monitored for more than 10 years. With respect to the 11 Ontario plots, 0% to 83.3% of trees per plot were classed in 2001 as moderately damaged and 0% to 35.5% classed as healthy.

Outputs planned for in the FIGC include new indicators for early detection of changes in forest health as a result of global change, enhanced global change risk assessment, and linkage of indicator responses with monitoring trends.

The USDA Forest Service initiated the Forest Health Monitoring (FHM) program in 1991 as a multi-agency, cooperative effort to determine the status, changes, and trends of health indicators in all forest ecosystems in the United States. The FHM program comprises four interrelated components:

• Detection Monitoring – field plot and aerial survey activities for national and regional monitoring
• Evaluation Monitoring – intensified monitoring or analysis in problem areas
• Intensive Site Ecosystem Monitoring – monitoring to understand processes and improve predictive capabilities
• Research on Monitoring Techniques – research to improve monitoring

The FHM program uses the Santiago Declaration and accompanying Criteria and Indicators as a framework for forest sustainability assessment and reporting.³⁴ Periodic assessments and reports are issued by the FHM program evaluating the status and changes of forest health indicators and stressors such as land use and forest fragmentation, air pollution, drought, storms, insects and pathogens, alteration of fire cycles, and invasive species.³⁵ The forest health indicators are analyzed in another report by ecoregion section.³⁶ More information on the FHM program is available on the FHM national Web site at http://www.na.fs.fed.us/spfo/fhm/index.htm. In 1999, the ground plot activities of FHM's Detection Monitoring component were integrated with the Forest Inventory and Analysis (FIA) program to maximize the strengths of both programs. More information about the enhanced FIA program can be found on the FIA national Web site at http://www.fia.fs.fed.us.

Current Forest Conditions

The FHM program produces annual summaries of forest health indicators, including species diversity, bioindicator species (lichens and plants sensitive to ozone), changes in trees (crown condition, damage, and mortality), soil physical and chemical characteristics, and above- and below-ground carbon pools. The program tracks several tree health variables that relate to amount and fullness of foliage and the vigour of the apical growing points of the crown. Two of these variables are the mortality of the terminal twigs in the sun-exposed portions of tree crowns (dieback) and the transparency of the foliage of the whole tree crown to sunlight (i.e., sparseness of the crown foliage). Hardwood transparency has been increasing in portions of the United States over the period of FHM data collection (1991-1999), particularly in the Upper Midwest and portions of northern Idaho and eastern Washington. Hardwood dieback was highest in northeastern Maine and moderately high in New England. Softwood transparency was found to be increasing in the Appalachian Mountain area as well as in portions of Minnesota and Wisconsin. Softwood dieback was increasing in north-central Wyoming, eastern Maine, and lower New England in the Hudson Valley.

Tree mortality was analyzed by comparing the volume of mortality to the volume of growth for specific sections of ecoregions. Areas of highest mortality relative to growth were Central Till Plains and Beech-Maple in Illinois, Shawnee Hills in Indiana, and northern California Coast Ranges.

Air pollution

The FHM program has analyzed average exposure and trends in exposure of forests to air pollution for wet deposition of nitrate (NO₃^-) and sulphate (SO₄^2-) and ozone (SUM60)³⁷ from 1994 to 2000. A biomonitoring approach based on ozone-sensitive plants and lichens is also used to assess air pollution effects on forest environments. More than 900 biomonitoring sites in 33 states were evaluated in 2000. Data and field documentation are available online at http://www.na.fs.fed.us/.

Average wet sulphate deposition rates were highest in the north and south forest regions from 1994 to 2000, with approximately half of the forest areas exposed to more than 23 kg/ha/yr. Significant decreasing trends in wet sulphate deposition rates were detected in north and south regions. The rates in Pacific Coast and Rocky Mountain forests were about one-sixth of the deposition rates for the North and South.

Wet nitrate deposition was highest in the North, with approximately half of the forest exposed to more than 18 kg/ha/yr. The only region with a significant decreasing trend in nitrate deposition was the South. Relatively low wet nitrate deposition rates occurred in the Pacific Coast and Rocky Mountain regions, with 50% of the forests receiving less than 6 kg/ha/yr.

  [D]

Growing season ozone concentrations were generally highest in the South, with 90% of the forests exposed to SUM60 ozone concentrations of more than 25 ppm-hours. High ozone exposure also occurred in forested areas in California. A plot level index calculated for ozone biomonitoring plots was based on amount and severity rating for each plant and the number of species evaluated at each site. Index values between 0 and 4.9 indicated little or no foliar injury; values between 5 and 24.9 indicated low to moderate injury ; and values greater than 25 indicated severe foliar injury. Little or no ozone injury to plants was recorded on most biomonitoring plots. In the North and South, approximately 77% of the plots had little or no injury from ambient levels of ozone. Only a small portion of plots had severe foliar injury. These were clustered in the airsheds surrounding the more industrialized portions of Illinois, Indiana, and Ohio, and all along the eastern corridor from Georgia, north through Virginia and up into southern New England had severe foliar injury. Severe foliar injury was also recorded on approximately 1% of the plots in the Pacific Coast region.

The relative exposure of forest types to air pollution was analyzed via cluster analysis of six air pollution indicators (ozone biosite index, average SUM60, average NO₃^-, NO₃^- change, average SO₄^2-, and SO₄^2- change). Higher relative air pollution exposure scores indicate higher exposure to air pollution. Forest types in the eastern United States had higher relative air pollution exposure scores than western forest types (figure 20). The oak-hickory forest type, which covers much of north and south forest regions, had the highest relative air pollution exposure score. Other eastern forest types with high relative air pollution exposure scores were oak-gum-cypress, loblolly-shortleaf pine, and oak-pine. Western forest types with the highest relative air pollution exposure score were the western hardwoods, pinyon-juniper, and chaparral types.

EFFECTS ON MATERIALS

The U.S. National Center for the Preservation of Technology and Training (NCPTT) and the Canadian Conservation Institute are continuing studies begun in 2000 on using lasers for conservation of cultural materials and on the potential benefits of laser technology, in general.

The effects of sulphur dioxide and other pollutants on cultural resources such as monuments, buildings, and sculpture are being studied by NCPTT, an office of the U.S. National Park Service. NCPTT operates an Environmental and Materials Research Program that focuses on determining the effects of air pollution on cultural resources and on developing treatments to mitigate those effects. The research focuses on air pollution interactions with limestone, marble, and bronze materials. Recently published work includes the effects of stone surface morphology on pollution deposition; studies on pollution-caused soiling to limestone buildings; a review of acid deposition and stone deterioration; and the interaction of pollutants and microorganisms on stone decay. NCPTT funds research on new treatments to prevent deterioration caused by air pollution, including development and testing of organic coatings for the protection of outdoor bronze. Finally, NCPTT funds the development of particle-modified material to consolidate deteriorating stone caused by pollution damage.

NCPTT operates a one-of-a-kind environmental exposure facility, including an environmental exposure chamber constructed in 1987 by the National Oceanic and Atmospheric Administration and the U.S. Geological Survey in conjunction with the National Park Service. The chamber is used to test the uptake of pollution onto materials.

One recent NCPTT laboratory study focused on effects of stone surface morphology and stone porosity on SO₂ deposition.³⁸ The study focused on four high-calcium limestones: Salem, Cordova Cream, Cottonwood Top Ledge, and Monks Park.

The results of this work show that porosity emerged as the dominant factor influencing dry deposition of SO₂ onto limestone. A secondary factor influencing deposition was surface roughness. Findings showed that the valleys on a stone surface enhanced deposition while the protruding "peaks" limited deposition.

NCPTT-funded research with Carnegie Mellon University concluded in 2001 with the culmination of 10 years of study of the effects of air pollution on tall limestone buildings.³⁹ This project encompassed a series of graduate and undergraduate projects designed to document the soiling patterns and characterize the conditions that led to the soiling of the Cathedral of Learning in Pittsburgh, Pennsylvania. The overall goals of this project were to better understand why and how soiling occurs and to develop models that link soiling to pollution types and concentrations. Results show that soiling at the Cathedral occurred somewhat uniformly over the building surface and that the building became soiled relatively quickly (within a few years) after construction. The main pollutants responsible are sulphur oxides, elemental carbon, and fly ash, all from coal combustion. Since pollutant levels have decreased since construction from the 1920s to the 1930s, the soiling patterns now seen are the result of rain eroding the soiled surfaces of the building. Computational fluid dynamics modelling results are consistent with soiling patterns observed on the building. Furthermore, measurements of rain fluxes to the building walls are in reasonable agreement with the fluid dynamics modelling.

In other studies, a review of the field of scientific literature on stone deterioration due to "acid rain" was conducted.⁴⁰ The reviewed articles indicate that dry deposition, mainly influenced by short-range transport of pollutants from local sources, is the main source of damage. A secondary source is wet deposition that is responsible for long-range transport of pollutants. However, in areas where buildings and monuments remain wet for long periods of time, and in rural areas, wet deposition can be a major source of damage. If pollution is very low, this phenomenon becomes indistinguishable from the "normal" weathering of stone by "clean" rain.

Other NCPTT-funded research studies concluded in 2000 on interactions between air pollutants and microorganisms on the deterioration of stone.⁴¹ This three-year project resulted in the development of a new analytic technique called micro-computer-assisted-tomography (mCT), which investigates the processes involved in microbial interactions with these pollutants on limestone. The data showed that stone treated with products of acid rain increased in volume and gypsum crusts were formed. When researchers exposed this stone to other microbial acids, they detected no loss in volume or voids within the stone and concluded that the minerals formed by the interaction of sulphates with the limestone provided protection from the action of microbial acids. Therefore, while pollutants do affect the microbial ecology found on limestone, the microorganisms do not enhance the chemical deterioration of limestone.

In other studies, a team of researchers at North Dakota State University is developing new coating systems for the protection of outdoor bronze from air pollution.⁴² Pollutants such as SO₂, NO_x, CO₂, and chlorides affect various materials including bronze and lead to greater atmospheric corrosion. The team focuses on exploration of new coating technologies that would be appropriate for outdoor bronze sculpture.

Another NCPTT-funded project is developing new treatments to strengthen degraded stone.⁴³ Calcareous stone, such as limestone and marble, is susceptible to attack by sulphur dioxide in air pollution, a chemical interaction that leads to the formation of calcium sulphate, also known as gypsum. Since calcium sulphate is relatively water soluble, rain can dissolve and remove material, including the cementitious materials that bind the grains of stone together. The result is a weak, sugaring stone. Ethyl silicate-based consolidants are used to restore strength to degraded stones; however, one of the limitations of strength development using these products is cracking during drying. The research team is using particle modified consolidants (PMC), which consist of a silicate matrix plus colloidal oxide particles, to consolidate degraded stone. The presence of particles physically limits the silicate network from shrinking under capillary pressures and thereby reduces the loss of strength during drying. In addition, the network maintains a higher permeability because the dried consolidants remain porous.