SYMBOL 



EXPLANATION 



INPUT 



INPUT 



OUTPUT 



CONTROL FACTOR 



OUTPUT 



INPUT 



OUTPUT 



HEAT 

 S=" SINK 



INPUT 



OUTPUT 



\ HEAT 

 -±r SINK 



OUTPUT 



.HEAT 

 — SINK 



DRIVING 

 FORCE 



a. Passive Storage 



The passive storage symbol shows the location in a 

 system for passive storage such as moving potatoes into 

 a grocery store or fuel into a tank. No new potential 

 energy is generated and some work must be done in the 

 process of moving the potential energy in and out of the 

 storage by some other unit. It is used to represent the 

 storage of materials or biomass in systems. 



b. Workgate 



The workgate module indicates a flow of energy (con- 

 trol factor) which makes possible another flow of energy 

 (input-output). It is used to show the multiplier 

 inter-action of two system components. 



c. Self -maintaining consumer population 



The self-maintaining consumer population symbol re- 

 presents a combination of "active storage" and a "multi- 

 plier by which potential energy stored in one or more 

 sites in a subsystem is fed back to do work on the suc- 

 cessful processing and work of that unit. 



d. Primary producer 



The primary producer symbol is a combination of a 

 "consumer unit" and a "pure energy receptor". Energy 

 captured by a cycling receptor unit is passed to a self- 

 maintaining unit that also keeps the cycling receptor 

 machinery working, and returns necessary materials to 

 it. The green plant is an example. 



e. Energy source 



The energy source symbol represents a source of ener- 

 gy such as the sun, fossil fuel, or the water from a 

 reservoir. A full description of this source would 

 require supplementary description indicating if the 

 source were constant force, constant flux, or programmed 

 in a particular sequence. 



f. Logic Switch 



The logic switch signifies that the distribution of 

 an energy flow is controlled at some point(s) within the 

 ecosystem by a decision criteria. Where or when or how 

 much of the energy flow is taking a given output pathway 

 is determined by a logic control function. Examples 

 include the control of pumping schedules and directions 

 in response to water supply. The cost of maintaining 

 and operating the combination of control structures and 

 decision making pathways also follows the second law of 

 thermodynamics . 



INPUT - 

 OUTPUT 



INPUT - 

 OUTPUT 



T HEAT 

 — SINK 



g. Two-way workgate 



The two-way workgate or forced diffusion module 

 represents the movement of materials in two directions 

 as in the vertical movement of minerals and plankton in 

 the sea. The movement is in proportion to a concentra- 

 tion gradient or a casual force shown operating the 

 gate. The heat sink shows the action to follow the 

 second law of thermodynamics. 



Table 1. Explanation of energy circuit language symbols utilized in the 

 conceptual models (adapted from Snedaker and Lugo 1974). 



