144 COVICH, SHEPARD, BERGEY, AND CARPENTER 



stream, and Chouteau Creek, an intermittent stream) of the Grand 

 River, which flows south into the Arkansas River. Upstream from the 

 study area, the Grand River is impounded by Lake Hudson and, 

 downstream, by Fort Gibson Reservoir. Because the reservoir system 

 is used to produce hydroelectric power (Lake Hudson generates 

 100 MW, and Fort Gibson produces 45 MW), a large amount of 

 storage capacity is needed. The major river flow occurs in winter and 

 spring, whereas the peak power demand occurs during the summer 

 months (Fredrich and Beard, 1975). 



Most of the drainage area is used for pasture (~50%) and 

 rangeland (~10%). Forest covers less than 25%; cropland is ~10%, 

 and the remaining 5% is urbanized. Heavy rainfall is followed by 

 rapid runoff because natural vegetative cover is sparse. 



The U. S. Geological Survey collects data on mean daily 

 discharge 4.0 km downstream from Lake Hudson (Fig. 1, point A) 

 and 1.8 km downstream from Fort Gibson Reservoir (Fig. 1. point 

 B). From March through August 1977, the maximum discharge 

 occurred in late June below Lake Hudson and in early July below 

 Fort Gibson Reservoir (Fig. 2). During periods when releases from 

 Fort Gibson did not match those from Lake Hudson and other 

 inflows, we observed upstream flow in Pryor and Chouteau creeks. 

 Although we made no attempt to measure flow rate, we did note 

 rapid increases in water level (up to 2 m at station G-1) after 

 managed releases from upstream and downstream reservoirs. 



METHODS 



Beginning in February 1977, three prelabeled Hester— Dendy 

 samplers (Hester and Dendy, 1962) were placed at each of the seven 

 sample stations. Samplers were suspended ~1 m below floats tied to 

 emergent trees and stumps. After a period of approximately 1 

 month, allowed for colonization by invertebrates, the samplers were 

 removed, and another set was exposed. The Hester— Dendy samplers 

 were carefully raised, placed immediately into plastic bags, and 

 washed with 70% isopropyl alcohol to preserve the specimens. 



Organisms were sorted under a dissecting microscope and 

 identified to the generic level. The techniques described by Mason 

 (1973), Bryce and Hobart (1972), and Beck (1975) were used for 

 mounting head capsules for microscopic identification. Specimens 

 were deposited in the permanent collection of the Stovall Museum of 

 Science and History, University of Oklahoma. 



Results were expressed as density (number of individuals per 

 square meter of sampler), biomass (total weight of each taxon 



