EFFECTS OF THERMAL ALTERATION 573 



Macroinvertebrate Dominance 



To aid in processing the data, we divided the 27-month sampHng 

 interval into 9 equal periods. During most periods oligochaetes and 

 chironomids (Diptera) were the dominant organisms found in both 

 the plate and dredge samples. Other major groups were the caddis 

 flies (Trichoptera), ceratopogonids (Diptera), gastropods (Mollusca), 

 mayflies (Ephemeroptera), and water boatmen (Hemiptera). 



Macroinvertebrate Totals 



The estimated total numbers of larger fish-food organisms and 

 taxa collected by the plates and dredge samples are indicated for 

 each period in Tables 1 and 2. Plate samplers in channel 3 collected 

 the greatest total number of organisms (130,000) but had fewer taxa 

 in each period than did the other channels. Dredge samples collected 

 in channel 2 yielded the greatest number of organisms (55,000), with 

 channel 3 again having the fewest taxa. Totaling the organisms found 

 for all the periods for each channel for both the dredge and plate 

 samplers, we find that channels 2 and 3 each had ^160,000organisms, 

 and channel 1 had ~1 30,000. 



Macroinvertebrate Diversity Index 



Diversity indexes (d) were calculated for the larger fish-food 

 organisms (oligochaetes, amphipods, snails, clams, and insects) for 

 each station in each channel, and the values were averaged to obtain 

 a mean diversity index (D) for each period for each channel. Means 

 were compared using Duncan's new multiple range test (P = 0.05) 

 (Tables 1 and 2). 



Winter 



Even_though it was not statistically significant, channel 1 had the 

 highest D for both winter periods (1975 and 1976) for the plate 

 samplers. Dredge samples from channel 1 (D = 1.78) were not 

 significantly different from either channel 2 or 3 even though the 

 heated-water channel (3) had a D of only 0.67 during the winter of 

 1976. 



Spring 



The plate-sampler data indicated no significant differences duriiig 

 the spring periods even though channel 1 maintained the highest D 

 for both periods. During the first spring (1975), the D for channel 1 

 was significantly higher than that for channel 3 for the dredge 

 samples. A year later (spring 1976), the D's had dropped in all three 



