Modules for Analysis 



Starting with an incremental water allocation perspective, the IFG approach to 

 developing an analytical procedure sensitive to both macro- and microhabitat 

 quantification recognized that: 



1. Physical processes drive biological processes, i.e., biological species evolve 

 (respond) to fill niches in the physical habitat. 



2. There are four components that are interrelated and must be evaluated: 



a. Watershed 



b. Water quality 



c. Channel structure 



d. Flow regime 



Consistent with a philosophy of incrementalism(the examination of alternatives), 

 it is necessary to first determine the characteristics of each of the components, 

 determine the relationship among components, and be able to carry a change in one 

 of the components through the entire system. This process should then allow the 

 evaluation of the consequences of a small change anywhere in the system. 



Such an approach starts with a hierarchical and modular setting. Figure 2 

 diagrams a structured thought process with a series of decision points, feedback 

 loops, and cross-checking procedures needed to examine the component modules. 

 The modules and state-of-the-art models constitute the "building blocks" of this 

 procedure. 



Watershed. The nature of the watershed governs the delivery of water to the 

 stream, which in turn governs the nature of the flow regime and the size and shape of 

 the channel. The decomposition of parent materials and input of allochthonous 

 organic material determines the nutrient input to the stream, and its influence within 

 the watershed by longitudinal changes in elevation, vegetation, geology, and climate. 

 The substrate characteristics of a stream are dominated by the parent material 

 present at various points along the longitudinal profile, i.e., streams flowing through 

 resistant igneous or metamorphic parent materials tend to be coarse-bedded. 



It would be convenient if longitudinal changes in watershed characteristics 

 proceeded in a regular manner. Although many watersheds do exhibit smooth 

 gradations, many others are typified by abrupt changes and occasionally by 

 inversions. Consistent with the macrohabitat concept, the fauna of these streams also 

 reflect these abrupt changes. 



Most riverine habitat evaluation techniques presented earlier automatically 

 assume that the conditions of the watershed are held constant. This assumption is 

 often made as a convenience; it is easier to assume the problem away than to attempt 

 to predict changes to the system imparted by the watershed. Where land use changes 

 are not anticipated, climatic and geologic factors can be safely assumed as constant, 

 and consequently a steady state watershed is a safe assumption. Conversely, a steady 

 state assumption in an altered watershed would be totally inappropriate. 



In an undisturbed watershed, both the terrestrial and aquatic environments are in a 

 dynamic equilibrium. Perturbations on the watershed such as timbering, agriculture, 

 grazing, mining, and urban development may drastically change the input rates to the 

 stream system. Such watershed activities affect the stream system in three major 

 ways: (1) through variations in water quantity input (either ground water or surface 

 runofO which affect the streamflow regime and in turn the physical structure of the 

 channel; (2) through changes in heat, sediment, inorganic nutrients, and toxicants 

 which all affect water quality and thus, the physiological responses of target 

 organisms; and (3) through changes in the quantity of organic substances which 

 influence the source of energy for utilization within the food web. 



The initial question to be answered in this module is whether the watershed is in 

 equilibrium with its drainage system, or whether it is changing. For a great many 

 watersheds the question of watershed equilibrium can be answered with a simple 



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