Major Types of Ecosystem Perturbation 



The major types of ecosystem perturbations include nutrient enrichment, 

 acidification, addition of toxic substances, nutrient depletion, surface mining, 

 habitat modification (such as stream flow alteration), destruction of native species 

 (such as impingement and entrainment), and introduction of alien species. Under- 

 standing how each of these perturbation types affects each ecosystem type is impor- 

 tant. The nature and severity of the effect will also depend on the intensity, duration, 

 and seasonal occurrence of the perturbation. 



Mode of Perturbation Activity 



The characteristic mode of response of an ecosystem to a given type of perturba- 

 tion depends upon whether the primary effect of disturbance is upon the system's 

 structural components or upon its functional processes. Some effects are stimula- 

 tory; others are inhibitory; and yet others affect the system's structural characteris- 

 tics. These effects are illustrated in the Figure I (from Cairns et al.-*). The relationship 

 of the major types of perturbations to the modes of activity is shown in Figure 2. 



Recent Phases in Perception of Problem 



The academic community's or society's perception of its relationship to the 

 environment presumably will go through a third and fourth phase beyond the two 

 already experienced. The first was an awareness phase which most people in the 

 United States associate with the "earth days" of the late sixties and seventies. 

 Although Aldo Leopold, Rachael Carson, and many others were fully aware of 

 assaults on the environment at a much earlier time, society as a whole paid little 

 attention to their warnings at first. Nevertheless, these early warnings ultimately 

 resulted in a general awareness of environmental problems. The second phase was 

 one in which biological effects of chlorinated hydrocarbons and other materials 

 released into the environment were documented and quantified. 



The third phase is now beginning. This phase involves the development of predic- 

 tion models for estimating the probability of harm that will result from various 

 courses of action (e.g., use of new chemical) before that action is taken. In short, 

 phase three involves the development of a predictive capability. 



A logical next step is the development of a regional (e.g., drainage basin, etc.) 

 management plan incorporating both predictive and reactive methods (e.g., quality 

 control methods) to maintain desirable ecosystem quality and to restore that quality 

 when it has been degraded. '' Additionally, society undoubtedly will wish to restore 

 certain damaged ecosystems to original condition or to conditions more acceptable 



Stimulatory Perturbations 

 (e.g., Nutrient Enrichment) 



1 



Ecosystem Boundary 



Inhibitory Perturbations 

 (e.g.. Addition of Toxic Substances) 



Structural Removal 

 (e.g., Clear-Cutting) 



Figure 1. Modes of action of perturbants on ecosystems. 



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