Wildlife Habitat and Ecological Risk Assessment
Keeping the Balance
by Lawrence Kapustka
As the modern environmental era was taking shape in the late 1960s, a famous phrase arose from the war in Vietnam: we had to burn the village to save it. The prevailing attitude about chemicals in the environment has led to a similar activity with respect to environmental management the push to remediate sites at all costs. Under the umbrella of achieving uniform compliance to environmental regulations and to minimize the number of enforcement judgments that have to be made, we have tended to focus on chemical occurrence at the expense of examining the complex array of consequences those chemicals may pose or their removal may engender.
In the early 1970s, our capacity to measure concentrations of chemicals in environmental media was exceedingly limited by todays standards. Through toxicity test methods, it was relatively easy to demonstrate that meaningful adverse effects (death, substantial impairment of growth, loss of reproductive capacity) could occur at concentrations well below analytical detection levels. For example, the addition of 40 parts per million ferulic acid (a phenolic compound present in many plants) into clean soil stopped legumes from forming nodules that allowed the plants to fix atmospheric nitrogen into organic compounds; this resulted in suppressed growth of the plants. Yet, one needed to add at least 400 ppm ferulic acid into the soil to detect its presence by the most sensitive methods available. This and similar examples led to the well-founded caution in the growing environmental movement that by the time one could detect the accumulating concentration of a chemical released into the environment, it was too late. Significant harm would have already occurred.
Advances in analytical instruments and methods in the last three decades have driven detection limits for most substances downward by several orders of magnitude, often well below the concentration required to evoke a meaningful physiological response. Yet, the lesson of caution persists if a chemical can be measured, it must be removed if we are to protect the environment.
But such removal can have great adverse consequences to ecological functions and biological resources. Instead of simply knowing that a chemical of interest is present at a site, we need to weigh the consequences of leaving the material in place (i.e., a no action decision) compared to the consequences of any number of remediation actions or other environmental management decisions. Does removal of a wetland in order to eliminate buried PCBs benefit the environment if doing so means loss of habitat for birds, mammals, and herpetofauna (amphibians and reptiles)? What are the environmental costs resulting from the loss of wetland functions including water retention and other services?
We should continually remind ourselves of the larger objectives behind our environmental management goals and objectives and apply as much understanding of ecology as we do chemistry or engineering.
Managing landscapes to enhance diverse wildlife populations, yet avoid nuisance problems, requires knowledge of habitat preferences and the needs of target species, and an understandable process to design and evaluate alternative land-use options. Can we use a less intrusive bioremediation option to mitigate risk while maintaining important habitat for wildlife? With the proper tools, the landowner/ manager could minimize adverse impacts to wildlife, maximize beneficial impacts to wildlife, and do so at minimum cost.
The practice of ecological risk assessment (EcoRA) was developed to characterize the likelihood of adverse consequences resulting from a chemical substance in the environment. Measurements of environmental concentrations, toxicity-response relationships, and likelihood of exposure are incorporated into estimates of risk.
Though much effort goes into evaluating toxicity of chemicals released to the environment, relatively little focus has been directed at the exposure component of the risk equation, and even less attention has been directed toward biological or physical conditions. Consequently, EcoRAs often miss major ecological factors that influence the status of valued wildlife species (i.e., assessment species) populations. But the same framework used to characterize risks from chemicals can be applied to assess effects of physical disturbance or biotic interactions such as occur from invasive species. The tools to expand the focus of EcoRAs and to reach more informed decisions in terms of ecological processes and biological resources are readily accessible through the sub-discipline of landscape ecology, especially if we focus on those features of the landscape that define the quality of habitat for the resources we want to protect.
Threats to ecological processes and biological resources occur on a number of fronts other than chemical, some direct and easily recognized by nearly everyone, others indirect and subject to debate even among experts. Human activities, including urbanization, the harvest of ocean fisheries, logging of forests, farming arable lands, and many more, have resulted in significant declines in many wildlife species. Other species such as white-tailed deer or Canada geese have experienced population increases to the point of being pests in agricultural areas and in adjacent suburban areas. Growth of urban areas and expansion of impermeable surfaces alter landscape diversity and modify hydrologic patterns in ways that decrease habitat quality for many desired plant, fish and wildlife species.
While most people today recognize the considerable value of wetlands, epidemics such as West Nile virus trigger anxiety and fear of what wetlands harbor. The spread of mad cow disease in domestic animals or chronic wasting disease in domesticated and wild game species promises to have major consequences on rural economies. These examples underscore a fundamental ecological tenet applicable to all species and ecological systems: Land-use management practices influence the quality of habitat, and the populations of wildlife species they support are inextricably tied to those practices.
Naturalists and wildlife managers have understood, at least in qualitative terms, the importance of critical habitat for various life history stages (e.g., nesting sites, winter range, etc.). Animals are drawn to suitable physical structure and food availability, while avoiding areas of lower quality. The term habitat, though often used loosely as an indication of environmental quality, refers to the combination of physical and biological features preferred by a particular species. What is great habitat for prairie chickens is unacceptable for barred owls. Different habitat preferences reflect evolution and adaptation of species separating from each other in n-dimensional niche space. There are differential area-use rates by different species. Animals are drawn to particular features of the landscape for foraging, loafing, nesting/birthing, etc. Some species are attracted to disturbance zones and edges, but others avoid such areas.
Using the basic framework for EcoRAs, we can incorporate the effects of habitat quality from those caused by contaminants of concern. As contaminants are distributed differentially across a landscape, behavioral preferences among wildlife species for different portions of the landscape also vary based on habitat heterogeneity. The combination of contaminant distribution patterns and habitat heterogeneity can result in minimal exposure (avoidance) or excessive exposure (attraction). Thus, conventional approaches in EcoRA, which do not factor in species-use patterns based on habitat quality, may greatly overestimate risk for some species, and greatly underestimate risk for others. A large source of uncertainty comes from the generally poor characterization of habitat requirements and poor understanding of landscape-level use patterns of the assessment species.
Assessing the quality of habitat for a given species requires an understanding of environmental conditions that afford shelter, food, nesting/ birthing, and rearing conditions. The level of detail in assessing habitat quality varies by methods from: a) simplistic qualitative binary descriptions (good, bad), b) indices such as the habitat suitability index models that capture suites of environmental indicators into algebraic expressions that scores an area from 0.0 (unsuitable) to 1.0 (ideal), or c) rigorous analyses of empirical data to generate site-specific predictive models (e.g., regression models, matrix population models). The different approaches have applications for:
Land-use management practices to achieve sustainable populations of desired species on federal and state lands;
Environmental impact assessment, where determination of the amount of wildlife habitat lost or created by a particular set of actions requires prediction and post hoc documentation; and
Ecological risk assessment, where exposure assessment is modified according to the quality of the habitat.
In April 2003, ASTM Committee E47 on Biological Effects and Environmental Fate, the American Chemistry Council and the U.S. Army Center for Health Promotion and Preventive Medicines Health Effects Research Program co-sponsored a symposium addressing issues of landscape ecology and EcoRAs. A collection of papers from the symposium will appear in the forthcoming Special Technical Publication 1458, Landscape Ecology and Wildlife Habitat Evaluation: Critical Information for Ecological Risk Assessment, Land-Use Management Activities, and Biodiversity Enhancement Practices. Currently, a draft ASTM standard guide on the use of wildlife habitat to modify exposure estimates in ecological risk assessment (WK3365) is being balloted in Subcommittee E47.02 on Terrestrial Assessment and Toxicology.
In the practice of environmental management, new applications are viewed cautiously. As this new standard and related standards are developed, we can expect to see increased application of established ecological methods in the EcoRA process. Better characterization of ecological relationships that reflect complex interactions among species in response to biological, chemical, and physical conditions will lead to more informed environmental management decisions. Capturing the relevant landscape features that determine habitat quality will provide greater ecological relevance to estimates of risk and will lead to selection of more appropirate and effective remediation strategies. //
Copyright 2004, ASTM International