152 COVICH, SHEPARD, BERGEY, AND CARPENTER 



genus (Beck, 1977; Weber, 1973). Paine and Gaufin (1956) found 

 Glyptotendipes to be typical of organically enriched streams, whereas 

 Kimerle and Anderson (1970) reported that G. barbipes was the 

 dominant species on waste-stabilization lagoons. In Oklahoma this 

 genus occurs where summer oxygen levels are lowered by high rates 

 of organic productivity, e.g., in Arbuckle Lake, as reported by 

 Parrish and Wilhm (1978). Thus the genus appears to be well adapted 

 to the relatively nutrient-rich slow-flowing water found in most of 

 our sampling area. In contrast to four of our seven stations, Harrold 

 (1978) found approximately equal numbers of Glyptotendipes and 

 Ablabesmyia in his Hester— Dendy samplers in the Knife River in 

 North Dakota. 



Although the species of Glyptotendipes from the Grand River are 

 not yet identified, at least three species (G. libiferous, G. merid- 

 ionalis, and G. barbipes) are known to be opportunistic in their rapid 

 invasion of new reservoirs (Aggus, 1971; Patterson and Fernando, 

 1969; 1970). Presumably the species that dominate the Grand River 

 share this trait and are readily able to colonize samplers placed in 

 habitats with fluctuating flow rates and water levels. 



A general pattern emerges when the chironomid populations are 

 compared with the relative degree of water-flow and water-level 

 fluctuations at each of the seven sampling sites. First, under 

 conditions of extreme fluctuation (i.e., at station G-1, where the 

 Grand River is constricted), chironomid density, biomass, and 

 numbers of genera present were all low and were relatively constant 

 throughout our study period. A smaller degree of fluctuation occurs 

 in a second group of stations. Stations G-3, which is on a relatively 

 exposed, straight section of the Grand River, and C-1 and P-1, where 

 the relative narrowness and shallowness of the two upstream 

 tributaries make them more susceptible to water-level fluctuations 

 than the downstream stations, have an intermediate level of 

 chironomid densities. These densities also showed a successive series 

 of changes (increasing in the tributaries and decreasing at G-3) during 

 the sampling period. In addition, stations P-1 and C-1 have fewer 

 genera than the downstream stations on the same streams. 



The remaining stations (G-2, P-2, and C-2), which comprise the 

 third group, have a smaller degree of water-flow and water-level 

 fluctuations. The two downstream tributary stations (P-2 and C-2) 

 are located where the streams meet the Grand River. Both areas are 

 wide and fairly deep. Each of these stations has a high chironomid 

 biomass and the highest densities and largest number of genera in 

 each of their respective river or stream systems. Also, each has a June 

 peak in chironomid density, indicating a possible minimal effect of 



