142 COVICH, SHEPARD, BERGEY, AND CARPENTER 



data for evaluating potential natural stresses in uncontaminated, 



unmanaged watersheds are lacking. Although ranges and mean 



discharge rates are usually reported in studies of managed reservoirs, 



the frequency of the fluctuations and their impacts on benthic 



macroinvertebrates in downstream waters is often not monitored. 



The concern expressed by Wolman (1971) is still unresolved: 



Many measurements of biological effects are done during low and 



summer flows where measurement is easy, organisms often 



flourish, and concentrations of various substances in the flow are 



high. The effect of winter flow . . . and the special significance to 



the flora and fauna of periodic floods are not well documented. 



Significantly, however, among the most common trends in river 



management is the progressive regulation of flow through the 



provision of storage. Conceivably regulation rather than pollution 



alone may have the most far-reaching effects on the character of 



many river systems .... 



Several investigators have called attention to some direct and 

 indirect effects of flow rates and water-level changes on benthic 

 macroinvertebrates (Baxter, 1977; Cairns et al., 1971; Trotsky and 

 Gregory, 1974; Ward, 1976). For example, Neel (1963) reported that 

 "reduction of winter stages below normal unregulated levels is 

 common and often reduces the stream's carrying capacity for many 

 forms of life .... Daily fluctuations in reservoir releases, which are 

 often occasioned by power peaking, discourage littoral stream life 

 and cause many readaptations." Minshall and Winger (1968) noted 

 that "irrigation and reservoir management practices tend to cause 

 periodic fluctuation on local stream levels, particularly during the 

 summer months, when stream flows are already minimal." Ward and 

 Short (1978) compared benthic communities from streams with 

 constant and widely fluctuating flow regimes in the Rocky Moun- 

 tains. They found that low standing-crop biomass values were 

 associated with pronounced water-level fluctuations and that streams 

 with regulated water flows had very different species compositions 

 and lower species diversities than streams with natural flow regimes. 

 In this report, we discuss the effects of varied flow rates and water 

 levels on the chironomid community downstream from a large 

 reservoir during a 7-month period. 



STUDY AREA 



Our seven sample stations (Fig. 1) were in the Grand (Neosho) 

 River drainage basin. The watershed, located in Mayes County, 

 Oklaihoma, includes two tributaries (Pryor Creek, a permanent 



