rate-controlling pathway over the flow through the workgate. The "x" indicates 

 that as the magnitude of the rate-controlling element increases, the flow 

 through the workgate increases. The "-" indicates that as the magnitude of the 

 rate-controlling element increases, the flow decreases. 



The symbol with concave sides (Figure 3-lg) is a switch. It may be similar 

 to a workgate, except that it does not control flow by varying continuously - 

 it is either on or off. Several types of switches exist: some are simple on 

 and off switches; others are on when two or more energy flows occur simultan- 

 eously or are at proper levels. 



The pipe or tube symbol (Figure 3-lh) is a sensor. Sensors indicate 

 passive effects of particular material flows. Another symbol indicating 

 sensor-like functions is the cap, which is attached to primary producers 

 (bullet symbol) or storages (tank symbol) and represents a passive function. 

 For example, plants produce shade as a result of their growth. 



Solid lines (Figure 3-li) represent the flow of energy or materials into 

 the system, out of the system, and within the system. The direction of the 

 flow is indicated by arrowheads on the lines. 



The ecosystems diagrammatic approach makes sense only when the diagram 

 (and thus the ecosystem) is viewed as a whole. The model should be considered 

 as an entire functioning system. Then by quick inspection of the diagram, the 

 idea of "what affects what" may be summarized. This idea is particularly useful 

 in predicting impacts as was pointed out by Odum (1972b). He noted that a good 

 impact statement (one that accurately predicts impactsT is by definition a good 

 model. 



Known changes in inputs or internal organization can be entered into the 

 diagram, and affected components can be identified. Usually the direction of 

 change in the affected components may be discerned, and with careful use of 

 logic and judgment, predictions of ecosystem change may be made. Such is the 

 sort of tool necessary to assess the effects of oil and gas development and to 

 determine the success of protective and mitigative measures. 



MODELING THE SYSTEMS 



The basic design of the ecosystems diagram and its utility in modeling 

 natural systems is fully described in the preceding section. This section 

 analyzes the dynamics of the six coastal ecosystems. It describes the ecological 

 function of each community within each ecosystem and the links within and between 

 the ecosystems. 



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