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Characterizing Ecosystem Responses to Stress
Pages 91-115

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From page 91...
... Risk assessment based on ecological science is essential to minimize these problems. In principle, ecological risk assessment is intended to illustrate and accommodate differences in stress/response relationships and to provide a basis for balancing environmental concerns with other economic and societal issues through the associated process of risk management.
From page 92...
... For example, the routine emissions from a nuclear power plant have few, if any, demonstrated adverse impacts on the health of the environment or the general public; nearby residents could receive a much greater dose of radiation from the thorium-daughter products in soils and rocks of the neighborhood, including radon in their homes, or from flying a few times across the country at high altitudes, than from a properly operated nuclear facility. In contrast, a fossil-fuel plant continuously emits a host of compounds that are known to cause adverse ecological and human health effects, including acid precipitation, greenhouse-induced global climate changes, and long-lived alpha-emitting radionuclides.
From page 93...
... There are sometimes certain issues or phrases in a law that are key to deciding which regulatory actions are to be taken by the government agency; these are often called regulatory endpoints, defined as those regulatory norms that translate fundamental legislative purposes into regulatory decisions or actions (C. Harwell, 1989; Limburg et al., 1986)
From page 94...
... ; · minimizing 'Significant adverse impacts"; · protecting '`areas of biological concern"; · preventing ``irreparable harm" to the environment; · maintaining Biological integrity"; or · not allowing actions that result in "accumulation of toxic materials in the human food chain." The remainder of this chapter focuses on such generic regulatory endpoints, because these tend to be associated with regulation based on ecological responses to human activity, as opposed to the highly specific regulatory endpoints, which tend to focus on technological capabilities or on chemical concentrations.
From page 95...
... of the Federal Water Pollution Control Act is actually interpreted in EPAs regulations to relate to maintaining a biological community that is similar to other communities in the region surrounding a local area of disturbance. Thus, the regulatory phrasing is not what was literally specified by the legislation, though it may be what was intended: EPA:s regulatory interpretation of the law refers to a community, rather than a single "population"; the biota of concern are not necessarily "indigenous" to the area; and since natural populations continuously fluctuate and experience dynamic interactions, it is not clear that "balanced" has any biological meaning at all.
From page 96...
... By focusing on such humancentered ecological endpoints, a structured way of evaluating ecological effects can be developed, and a framework can be created for incorporating non-ecological issues into environmental decision malting (Figure 1~. While regulatory endpoints are specific goals or standards stated in laws or regulations, ecological endpoints are selected characteristics of ecosystems at various levels, the examination of which can allow evaluation of societally important environmental issues.
From page 97...
... . - COMMUNITY-LEVEL ENDPOINTS · food-web structure · species diversity · biotic diversity ECOSYSTEM-LEVEL ENDPOINTS · ecologically important process · economically unportant process · water quality · habitat quality 97 because of aesthetics or other human values, e.g., dolphins, eagles, wild horses, and grizzly bears.
From page 98...
... In this case, adverse impacts on the density of krill would constitute an ecological endpoint, even though the krill population itself might have little direct concern for humans. Other bi-specific relationships include pollination (e.g., concern for a species of fruit tree might translate into concern for the insects necessary for fertilization)
From page 99...
... For instance, Section 403(c) of the Federal Water Pollution Control Act specifically calls
From page 100...
... of the Federal Water Pollution Control Act indirectly calls for maintenance of species diversity through its "balanced indigenous nnn~lntion" endnnint ns interpreted hv regulations and litigation (Harwell. rare -- —A -- -- i- -A -- me -c~9Ma)
From page 101...
... Thus, the same disturbance can have dramatically different consequences on different ecosystems, e.g., fire affecting grassland ecosystems versus tropical rain forests. In the former case, fire is a natural part of the long-term biogeochemical cycles of the ecosystem, necessary to rejuvenate a biotic community that is adapted to survival or redevelopment after fire.
From page 102...
... For example, sudden exposure to freezing temperatures in the middle of summer can severely affect a temperate forest ecosystem, whereas the same temperature decrease imposed gradually, over normal seasonal cycles, may cause no effect whatsoever (Harwell and Hutchinson, 1989~. The ability of the ecosystem to compensate or acclimate to gradual or low-level stress can lead to a fundamentally different response.
From page 103...
... If they are not, critical characteristics of population dynamics that occur out of synchrony with measurement intervals may be missed, and the response of the population thus misinterpreted. Changes within a forest ecosystem can occur gradually over long time periods and may be affected by slowly changing external factors such as climate, which can operate over centuries to millenia.
From page 104...
... If the composition and productivity of the forest trees are unchanged, does that demonstrate no effect? How does one evaluate the importance of changes in deer populations; or increased incidences of tree disease and pest outbreaks; or changes in the relative abundances in the soil invertebrate species; or alterations in the rates of nitrogen release from decomposing leaf litter; or replacement of one bacteria species by another that performs the same functions; or mortality from the toxic chemical to a breeding pair of raptors or a breeding pair of protozoans?
From page 105...
... HZJM;4N EFFECTS ON THE TERRESTRIAL ENVIRONMENT TABLE 2 Indicators of ecological effects. · PURPOSES FOR INDICATORS · intrinsic importance - key: indicator is endpoint - e.g., economic species · early warning indicator - key: rapid indication of potential effect - use when endpoint is slow or delayed in response - Animal time lag in response to stress; rapid response rate - signal-t~noise low; discrimination low - screening tool; accept false positives · sensitive indicator - key: reliability in predicting actual response - use when endpoint is relatively insensitive - stress specificity - signal-t~noise high - minimize false positives · processlfunctional indicator - key: endpoint is process - monitoring other than biota; e.g., decomposition rates - complement structural indicators · CRl l ELLA FOR SELECI ING INDICATORS · signal-to-noise ratio - sensitivity to stress - intrinsic stochasticity · rapid response - early exposure; e.g., low atrophic level - quick dynamics; e.g., short life span, short life cycle phase · reliabilitylspecifcily of response · easeleconomy of monitoring - field earning - lab identification - pre-existing data base; e.g., fisheries catch data - easy process test; e.g., decon~osition, chlorophyll · relevance to endpoint - addresses "so what?
From page 106...
... TV ~ O O x. o 0:' NV ..' 'I...,, ,,' 1~_ 0 Sp.C 1 Legend: O Species Ecosystem 3< Properties community structure physical structure processes Ecological Endpoints Ecological Indicators O (folded)
From page 107...
... For example, diversity of a forest ecosystem will increase during the early stages of ecosystem development, decline in the middle stages of succession, and increase again during the later stages (Woodwell, 1970~. In this case, the ecosystem is characterized by a moving set of values describing the trajectory of the undisturbed ecosystem.
From page 108...
... Is an ecosystem recovered when its pools of nutrients are back to the pre-stressed state; or when a specific species has reestablished its population at a particular density; or when the residues of a toxic chemical in sediments or in biological tissues have decreased to below some threshold? Just as an ecosystem functions and responds to stress at widely differing rates, hierarchical levels, and spatial extents, it also recovers differentially.
From page 109...
... . Striped bass populations became a primary indicator of ecological effects, especially through evaluations of population levels, age structures, recruitment rates, mortality rates, and migratory patterns.
From page 110...
... Consequently, the discrimination of the indicator can be rather low, i.e., it need not provide all the information needed to evaluate effects on the ecological endpoints of concern, and tight, causal relationships between the stress and the triggering of the early warning indicator are not required. Hence, this functions as a screening tool, where false positives are acceptable at a relatively high rate (i.e., having the flag go up even though further evaluation demonstrates no ecological effects of concern)
From page 111...
... Several reasons are offered for this generalization: · ecological effects are first manifest as effects on individual organisms and subsequently on populations; thus, functional responses would imply prior associated changes in biotic populations performing those functions; · there is often functional redundancy in ecosystems, so that effects on specific biota may not translate into functional effects; and · recovery of biotic structure of an ecosystem often lags behind recovery of functional attributes. However, there are instances where functional indicators respond at least as rapidly and sensitively to stress as structural indicators (Kelly et al., 1987~.
From page 112...
... A high signal-to-noise ratio is required for sensitive, stress-specific indicators; a low signal-to-noise ratio is acceptable for screening indicators, especially involving inexpensive or easily measured variables. As an example of this issue, consider the purported impacts on the striped bass population in the Hudson River ecosystem in comparison to the natural variability of that species.
From page 113...
... SUMA/L\RY Ecosystems are complex and varied, multiscaled and multitiered, and subject to continuing change and adaptation. Consequently, a sophisticated approach is needed to characterize ecological effects from human activities, relying on a suite of ecological response/recovery indicators that reflect the status of the variety of facets about the ecosystem, or endpoints, of concern to humans.
From page 114...
... 1984a. Regulatory Framework of the Federal Water Pollution Control Act, Section 301(h)
From page 115...
... Pp. 79-87 in the Proceedings of the Symposium on the Effects of Air Pollutants on Mediterranean and Temperate Forest Ecosystems.


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