Using the above data, pollution transport functions convert injections of 

 pollutants at the nodal points to concentrations of pollutants at and between 

 the nodes. Initial injections of pollutants at a node are mixed with quantities 

 of pollutants arriving from upstream nodes; the mixture is diluted by the flow 

 at the node; and the mixture is transported to the next node while on the way 

 certain constituents are removed by natural processes. Dissolved oxygen 

 concentrations are estimated with Streeter-Phelps relationships. (The decay 

 rates for all the modeled pollutants were provided by Ken Young of GKY and 

 Associates, Inc. A detailed discussion of the parameters and equations may be 

 found in Gianessi, Pes kin, and Young 1981.) It should be noted that the model 

 assumes that point source pollutants are inserted at specific nodal points. 

 However, agricultural nonpoint pollutants are assumed evenly inserted along the 

 reach between the nodal points. 



Translating Ambient Water Quality into Dominant Fish Populations (Fishery Types) 



Predictions of values of classical water quality parameters still leave us 

 one large step from the desired goal of a water-quality-related measure connected 

 directly to recreational fishing. In making that step we commissioned a survey 

 of the fishery biology and management literature on which was based a set of 

 rules (an informal model) that appeared to capture whatever consensus existed 

 on the water quality conditions, in terms of DO, pH, TSS, and water temperature, 

 necessary for the survival and reproduction of fish populations of various types. 

 (Recall the assumption that managers will make sure that if upgrading is possible 

 it will occur.) 



These rules for determining type of fishing supportable are summarized as 

 logical if-then statements in table 1. From the logical statements see that if 

 dissolved oxygen is very low or temperature very high the water will be unsuitable 

 for recreational fishing. At higher DO levels, the fishery type depends on 

 both temperature and suspended solids loadings. But, because temperature is 

 usually a function of natural factors, and suspended solids loadings are 

 exogeneously specified in our water quality model and do not change in response 

 to FWPCA/CWA implementation, policy-related water quality improvement as reflected 

 in changing species class is a function of changing dissolved oxygen 

 concentrations.^ The improvement chains are shown schematically in table 2. 



* Other, similarly rough, rules for translating physical chemical water 

 quality parameters into measures of fishing quality may be found elsewhere. 

 For example, U.S. EPA in "The Red Book" (1976) asserts that "a minimum 

 concentration of dissolved oxygen to maintain good fish population is 5.0 mg/ 1 . 

 The criterion for salmonid spawning beds is a minimum of 5.0 mg/1 in the 

 interstitial water of the gravel." (p. 123) Alabaster (1969) summarizes the 

 then current state of knowledge about differential sensitivity of fish species 

 to pollution and concludes: 



It seems that there is already sufficient information 

 from laboratory and field observations to conclude that 

 coarse fish are generally somewhat less sensitive to 

 pollution than trout, though differences between species 

 are not always the same for all poisons. 



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