EFFECTS OF FLUCTUATING FLOW RATES 

 AND WATER LEVELS ON CHIRONOMIDS: 

 DIRECT AND INDIRECT ALTERATIONS 

 OF HABITAT STABILITY 



ALAN P. COVICH, WILLIAM D. SHEPARD, ELIZABETH A. BERGEY, 



and CARYN S. CARPENTER 



Department of Zoology, University of Oklalioma, Norman, Oklahoma 



ABSTRACT 



Regulation of stream flow-through water storage by hydroelectric dams and 

 flood-control impoundments may alter benthic macroinvertebrate communities 

 that are adapted to distinct seasonal shifts in water levels. Isolating these changes 

 in community structure from changes caused by alterations in water quality is 

 not possible currently, because data on effects of fluctuating flow in 

 uncontaminated streams are infrequently reported. Studies from February 

 through August 1977 on the Grand River and two of its tributaries in Oklahoma 

 were conducted at seven stations. Of the 122 taxa of macroinvertebrates 

 collected, 24 were genera of chironomids. Glyptotendipes dominated most 

 locations in terms of density and biomass. Fluctuations in water level and water 

 flow resulting from reservoir discharges were found to influence chironomid 

 populations in both the discharge-receiving river and its two tributaries. 

 Decreased density, biomass, and numbers of genera characterized the most 

 intensely fluctuating sites. Indirect effects on substrate size, composition, and 

 movement, as well as direct washing out of organisms from the substrate, may 

 have caused the relative declines in abundance. 



Many studies of macroinvertebrate community structure emphasize 

 analyses of changing population densities and species diversities 

 because these biological changes are known to reflect long-term 

 changes in many physical and chemical parameters (Cummins, 1975; 

 Edwards, Hughes, and Read, 1975; Gaufin, 1973; Goodnight, 1973; 

 Hynes, 1970; Isom, 1971). Despite the recognized importance of 

 fluctuations in flow rates and water levels for "catastrophic drift" 

 (Waters, 1972) of aquatic invertebrates, data on fluctuations of 

 natural lakes and streams are infrequently reported. Thus base-line 



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