146 COVICH, SHEPARD, BERGEY, AND CARPENTER 



per sampler), and diversity. Diversity was measured by the 

 Shannon— Weaver index (d) as described by Wilhm (1972) and Weber 

 (1973). Pupae were not used in diversity calculations because of 

 difficulties in identification. Biomass was determined by weighing 

 ovendried (4 hr at 100°C) specimens on an electrobalance (Cahn 

 Instruments, model G). Measured biomass was an underestimation 

 because head capsules were removed for identification before drying 

 and weighing. 



RESULTS 



Of the 122 taxa of macroinvertebrates collected, 64 were insects. 

 Twenty-four genera in three subfamilies of the Chironomidae were 

 collected. The most represented subfamily was the Chironominae, 

 with 15 genera. Of these 15, ten were very widespread, being found 

 at all seven sample stations. In contrast, five genera were found at 

 only one station (Table 1). Station C-2 had the highest number of 

 genera; rarer genera were restricted to one or two stations on Pryor 

 and Chouteau creeks. 



The dominant chironomid, in terms of both density and biomass, 

 was Glyptotendipes, which comprised over half the chironomids 

 collected throughout the sampling period, except at station G-1 

 (Fig. 3). Dicrotendipes was the second most abundant genus at five 

 of the sampling stations, but Ablabesmyia was more common at the 

 Pryor Creek stations. Glyptotendipes and Dicrotendipes are both in 

 the subfamily Chironominae, and Ablabesmyia is in the subfamily 

 Tanypodiriae. 



Station G-1 showed the greatest increase in water level and flow 

 rate when water was released from Lake Hudson because a low-water 

 dam is located immediately below this station and the river channel 

 is constricted. The density and biomass values were consistently low 

 at station G-1 (Figs. 4 and 5) in comparison with other stations on 

 the Grand River, especially during May and June, when discharge 

 rates and water-level fluctuations were maximal. Station G-2, which 

 was somewhat sheltered, being located near an island among 

 emergent dead trees, frequently showed a higher chironomid density 

 than did the more exposed stations, G-1 and G-3. Station G-2 also 

 had the highest biomass values of any Grand River station in early 

 June before maximal discharge (Fig. 4). 



Although the chironomid densities of the Chouteau Creek 

 stations (C-1 and C-2) were higher than those of Pryor Creek stations 

 (P-1 and P-2), the patterns of chironomid density throughout the 

 sampling period were quite similar for the two tributaries (Figs. 6 



