Design,management, and key accomplishments of a coordinated environmental research program on acidic deposition

The present and potential adverse effects of the atmospheric input of acidic and acidifying substances on the environment have been of significant public and scientific concern for the past several decades. This article describes the background, design, implementation, and major accomplishments of a 6-yr integrated multidisciplinary environmental research program designed to address the issue of the regional scale consequences of acidic deposition on the environment and human health in Alberta. The research program was called the Acid Deposition Research Program (ADRP) and was a cooperative undertaking between industry, the Energy Resources Conservation Board, and the government of Alberta, Canada. The research effort was designed and guided by two external science advisory boards, biophysical and human health, to maintain objectivity and continuity from beginning to end. Public input was sought, encouraged, and ensured by a public advisory board. The major conclusions of the ADRP are presented as well as observations on the needs of future integrated multidisciplinary research programs.     

The effects of sulphur gas and elemental sulphur dust deposition on Pinus contorta x Pinus banksiana: cell walls and water relations

The bulk modulus of elasticity (E) for Pinus contorta (lodgepole pine) x Pinus banksiana (jack pine) hybrids was compared between a site (AI) close to a sour gas processing plant and a control site (AV). The mean bulk modulus of elasticity for branches from AI was 47.5 MPa vs 18.5 MPa for the control site (AV). Site AI had been exposed to S-gas emissions and large amounts of elemental S deposition and had an acidic soil (pH 4.0 at 10 cm depth). During 1981 the needles at AI had more aluminum and iron compared to those at AV (900 ppm vs 390 ppm AI in the 3-year-old needles). Mean leader growth was measured over a 3-year period and was observed to be greater at AI than AV (46+/-7 cm vs 29+/-9 cm for 1988). Histochemically, the needles at AI had higher phenol and lignin content than AV. These results suggest that the S-gas fumigation, S-dust deposition, plus increased concentrations of soluble aluminum and iron had altered the cell wall elastic properties resulting in altered water relations. The implications of this on leaf diffusive resistance and photosynthesis are discussed.     

Air quality and its possible impacts on the terrestrial ecosystems of the North American Great Plains: an overview

Over the past several decades, numerous studies have been conducted on the impacts of air pollutants (air quality) on terrestrial ecosystems (crops and forests). Although ambient air is always composed of pollutant mixtures, in determining the relative air quality and its ecosystem impacts at a given geographic location and time, a predominant number of studies have shown that at the present time surface-level O(3) is the most important phytotoxic air pollutant. Within the North American Great Plains, the precursors for surface-level O(3) are mainly anthropogenic NO(x) and VOCs (volatile organic compounds). Texas and Alberta are the top regions of such emissions in the United States and Canada, respectively. This appears to be due mainly to the prevalence of natural gas and/or oil industry in the two regions and the consequent urbanization. Nevertheless, the total emissions of NO(x) and VOCs within the North American Great Plains represent only about 25-36% of the corresponding total emissions within the contiguous United States and the whole of Canada. Within the Great Plains many major crop and tree species are known to be sensitive to O(3). This sensitivity assessment, however, is based mainly on our knowledge from univariate (O(3) only) exposure-plant response studies. In the context of global climate change, in almost all similar univariate studies, elevated CO(2) concentrations have produced increases in plant biomass (both crop and tree species). The question remains as to whether this stimulation will offset any adverse effects of elevated surface O(3) concentrations. Future research must address this important issue both for the Great Plains and for all other geographic locations, taking into consideration spatial and temporal variabilities in the ambient concentrations of the two trace gases.     

New exposure-based metric approach for evaluating O(3) risk to North American aspen forests

The United States and Canada currently use exposure-based metrics to protect vegetation from O(3). Using 5 years (1999-2003) of co-measured O(3), meteorology and growth response, we have developed exposure-based regression models that predict Populus tremuloides growth change within the North American ambient air quality context. The models comprised growing season fourth-highest daily maximum 8-h average O(3) concentration, growing degree days, and wind speed. They had high statistical significance, high goodness of fit, include 95% confidence intervals for tree growth change, and are simple to use. Averaged across a wide range of clonal sensitivity, historical 2001-2003 growth change over most of the 26 Mha P. tremuloides distribution was estimated to have ranged from no impact (0%) to strong negative impacts (-31%). With four aspen clones responding negatively (one responded positively) to O(3), the growing season fourth-highest daily maximum 8-h average O(3) concentration performed much better than growing season SUM06, AOT40 or maximum 1h average O(3) concentration metrics as a single indicator of aspen stem cross-sectional area growth.     

Foliar sulphur species in pine: a new indicator of a forest ecosystem under air pollution stress

An eleven-year foliar sulphur (S) monitoring program was carried out from 1976 to 1986 near a sulphur recovery-gas plant in west-central Alberta, Canada, as part of a case study designed to determine the effects of chronic, low concentration sulphur gas emissions on the forest ecosystem surrounding the gas plant. Measurements of both foliar total sulphur (ST) and foliar inorganic sulphur (SO4-S) concentration in lodgepole x jack pine trees at the end of each of the 11 growing seasons were taken to provide an indication of S loading of the forest from industrial sulphur emissions. To measure the state of the forest ecosystem, foliar ST was separated into foliar accumulated sulphur (inorganic sulphur or SO4-S) and foliar assimilated sulphur (organic sulphur or S0) and the ratio of SO4-S/S0 taken. Foliar S0 was calculated as the difference between foliar ST and foliar SO4-S. The median SO4-S/S0 ratio, with all three years of needles considered, varied from 0.29 at a reference location (AV) to 0.88 at the location with the highest stress (AI). The corresponding mean values ranged from 0.3 at the reference location to 2.2 at the location of highest stress. The mean seasonal photosynthetic rate of current year's foliage of the pine trees and soil pH were reduced at a stressed location (AI) compared to the reference location (AV), between 1976 and 1981. Over this same time period the mean foliar SO4-S/S0 ratio increased from 0.4 +/- 0.1 to 1.0 +/- 0.3 at the stressed location (AI) and remained nearly the same at the reference location (AV) at 0.3 +/- 0.1. This research suggests that the foliar SO4-S/S0 ratio is a useful indicator of the state of forest ecosystems under S air pollution stress. It is concluded that foliar S separated into various fractions has potential as an early warning environmental management tool.     

Modeling mammal response to fire based on species’ traits

Fire has shaped ecological communities worldwide for millennia, but impacts of fire on individual species are often poorly understood. We performed a meta-analysis to predict which traits, habitat, or study variables and fire characteristics affect how mammal species respond to fire. We modeled effect sizes of measures of population abundance or occupancy as a function of various combinations of these traits and variables with phylogenetic least squares regression. Nine of 115 modeled species (7.83%) returned statistically significant effect sizes, suggesting most mammals are resilient to fire. The top-ranked model predicted a negative impact of fire on species with lower reproductive rates, regardless of fire type (estimate = –0.68), a positive impact of burrowing in prescribed fires (estimate = 1.46) but not wildfires, and a positive impact of average fire return interval for wildfires (estimate = 0.93) but not prescribed fires. If a species’ International Union for Conservation of Nature Red List assessment includes fire as a known or possible threat, the species was predicted to respond negatively to wildfire relative to prescribed fire (estimate = –2.84). These findings provide evidence of experts’ abilities to predict whether fire is a threat to a mammal species and the ability of managers to meet the needs of fire-threatened species through prescribed fire. Where empirical data are lacking, our methods provide a basis for predicting mammal responses to fire and thus can guide conservation actions or interventions in species or communities.