Air Pollution Effects on Biodiversity

Thousands of chemicals are commonly used throughout the world for industrial, agricultural, and domestic purposes with many new ones being produced yearly (Maugh 1991; Schroeder and Lane 1988). The majority of these chemicals, many of which are toxic or radiatively active, eventually enter into the atmosphere and may pose a risk to the wellbeing of plants, animals, and microorganisms. The consequences of air pollution to biota and the resulting impacts on biodiversity are not clearly known; only fragmentary information is available. The purpose of this book is to evaluate what is known, identify information gaps, explore policy issues, and provide direction for research.

The most common definitions of biological diversity focus on state variables, such as genes, species, and communities, but processes, such as gene flow, survivorship, competition, and energy flow, ultimately determine the nature of these state variables and are critical to the survival of biological diversity itself (Noss 1990). The relationship between biological diversity, ecological process, and human activities is now a critical concern for scientists and policy makers (Lubchenco et al. 1991).

This review chapter outlines the major processes influencing the transport, transformation, and deposition of the major pollutant gases and their oxidation products SO ₄ ^2— NO ₃ ^— in aerosols and cloud droplets.

Distinguishing natural successional and evolutionary changes in an ecosystem from those that occur because of subtle, anthropogenically driven processes is extremely difficult. Detailed information about ecosystem components is needed and a fundamental understanding of processes that dynamically link these components. The ecosystem components important in maintaining biodiversity are genetic variability, species composition, and the structure and function of these species in the ecosystem.

This chapter will provide some information about the effects of major air pollutants on some physiological and biochemical processes in plants. Because it is impossible to review here all past research achievements and the diverse range of current studies in a comprehensive way, we have decided to focus attention on some selected processes and mechanisms—leaf level processes, biochemical and cellular perturbations—having implications for whole plant physiology.

A complete review of solid, liquid, and gaseous air pollutants and their impacts on plant and animal species, in combination with the full range of natural stresses, is clearly outside the scope of this chapter. We focus here on plants; on the four primary phytotoxic gases, ozone (O₃), nitric oxide (NO), nitrogen dioxide (NO₂), and sulfur dioxide (SO₂); and on the principal natural stresses due to mechanical loading, shortage of water, pests and diseases, nutrient deficiency, and low temperatures. The great majority of published material on air pollution responses is of course on single species or agricultural bicultures such as grass/clover mixtures. Even for those studies in which multiple natural species have been involved, such as forest ecosystem damage caused by smelter emissions in North America (e.g., Gordon and Gorham 1963), the pollutant load has often been so high, and the damage so acute, that the results cannot be extended to chronic pollutant effects, let alone to their interactions with other stresses. Consequently, our deductions on biodiversity impacts are based primarily on the interpretation of environmental and physiological data from rather simple biological systems. Superimposed on this already complex situation of pollutant exposure we have a set of relatively new concerns brought about by increasing atmospheric carbon dioxide and UV-B radiation, and by possible changes in the distribution of global climate patterns that we have previously considered stable. If we remember, as background to this discussion, that around one-half of all known species inhabit tropical rain forests about which we have virtually no information on air pollution or its effects (Wilson 1988), then the sheer scale of the problem becomes apparent.

Biodiversity is a general term used to characterize variability in biotic resources occurring at the level of populations, species, communities, and ecosystems (see White and Nekola, Chapter 2, this volume). Biodiversity can be simplified to the issue of genetic diversity, and this manuscript addresses that diversity at the level of plant populations and the role that air pollution may play.

The important measure of Darwinian fitness is the number of offspring an individual contributes to the next generation. In higher plants, sexual reproduction provides seeds that offer the ecological advantages of dormancy and dispersal. Seeds also provide an array of individuals carrying recombinations of parental genetic material on which natural selection can operate. This chapter is concerned with the action of environmental factors, such as air pollution, on fertility through effects on pollen and stigma and their interactions at the time of pollination. Variation in the response of fertility to air pollutants within populations may change the levels of participation of individuals in the breeding systems. The effects on population genetics and population biology of such changes in fertility could have profound influences on the balance of natural ecosystems and their biological diversity.

As ecological units, biotic communities consist of aggregations of populations, interacting with other biotic and abiotic components of the ecosystem. Communities thus possess a set of emergent properties not understandable solely from inferences derived from the study of their constituent populations (O’Neill et al. 1986). Ideally then, delineating air pollution effects upon communities would involve measuring community attributes rather than attempting to infer community responses from individual plant or population measurements. However, the great body of air pollution effects literature is primarily based on individual organism responses, which provide little basis for inferring community response. Data limitations are especially acute when considering perennial plant communities, the focus of this chapter.

Air pollution has adversely affected animals since the advent of the industrial revolution (Newman 1980). Currently, the greatest threat to animal biodiversity from air pollution occurs in industrial countries where regional impacts (e.g., acid precipitation, ozone) are causing widespread direct and indirect effects to animals and their habitats. In Eastern Europe, local, regional, and transboundary air pollution is severe. Future threats will occur as underdeveloped countries that have minimal air pollution controls industrialize. Of particular concern are those areas, such as the tropical forest of the Amazon Basin, that harbor the world’s greatest biodiversity including many species yet to be described (Wilson 1988).

Regional-scale air pollution is a significant contemporary anthropogenic stress imposed on temperate forest ecosystems. Gradual and subtle change in ecosystem function and composition over wide areas of the temperate latitudes over extended time, rather than dramatic destruction of ecosystems in the immediate vicinity of point sources over short periods, must be recognized as the primary consequence of regional-scale air pollution stress. Global-scale air pollution, with its associated potential to cause rapid climate change, can dramatically alter ecosystems, especially those in the north temperate and boreal latitudes. The integrity, productivity, and sustainability of natural ecosystems are intimately linked to air quality. This chapter focuses on the ability of air contaminants to adversely affect forest ecosystem processes.

For the purposes of this paper, I define policy as the setting of a course of action, i.e., a decision in regard to choices among possible actions. We think of “policy” commonly in terms of the foreign policy considerations of many countries; we hear of it often in energy policy, and occasionally it is the subject of a public welfare concern such as the protection of biological diversity. Framework indicates concern about the scope of the problems to be considered in formulating policy—local, national, or international. In the protection of biological diversity, we are examining a relatively new aspect of public welfare, concern about the variety of species in nature, many of them important for the services they perform for direct or indirect human benefit. A policy framework for protecting biological diversity, therefore, must address the array of interests—from scientific to social, ethical, and international—that bear on decisions affecting the risk of losing or impoverishing species due to the effects of air pollution.

The subject of this chapter is the interplay between science, which spells out the effects of air pollution on biological diversity, and policy-making, which determines how society will respond. Specifically: How should scientists design their research—through the questions that they ask and the biotic quantities that they measure—so as best to inform the regulatory decision process, and so to advance the goal of conserving biological diversity?

Concerns about biological diversity or biodiversity have several origins, for example, interest in preserving pristine areas and the species therein, saving special species or threatened and endangered species, maintaining sustainable ecosystems for natural resource production, saving genetic material for future uses, and the reversal of the increased loss of species and habitat, especially but not only in the tropics (see White and Nekola, Chapter 2, this volume). The purpose of this book is to consider the topic of air pollution and its implications for local, regional, and global biodiversity.