ORDINATION OF MACROINVERTEBRATE COMMUNITIES 757 



The five municipal sewage-treatment plant discharges and the 

 numerous industrial discharges located between stations 6 and 14 

 probably precluded recovery to Tait intake H' and S levels. Scott 

 (1969) and Conn (1973) surveyed the macroinvertebrates of the 

 Great Miami River using Beck's (1954) index as a measure of water 

 quality. Although they used a clean- water form index rather than a 

 diversity index, their results were similar to mine. In historical 

 perspective, then, evaluation of river conditions over a number of 

 years seems to give a fairly similar picture. 



Physical— chemical parameters measured in this study are pre- 

 sented in Table 2. Alkalinity and pH were within natural limits for 

 rivers such as the Great Miami on all sample dates at all stations. No 

 consistent upstream— downstream pattern was observed for pH and 

 alkalinity. The current was generally greater in June than in August 

 or October owing to greater stream discharge. Because of the 

 channelization of the Great Miami River and the use of low-level 

 dams, current was undetectable at a number of stations. 



Observed change in temperature (AT) on June 21 across the Tait 

 plant (intake to discharge) was +3.0°C, +4.7° C on August 16, and 

 +6.3°C on October 14. The AT for the Hutchings plant was +5.0°C 

 for June 21, +5.2°C on August 16, and +5.5°C for October 14. The 

 greater AT values in August and October were due to a decrease in 

 stream discharge in these months, which enhanced plant effects. A 

 summary of stream-discharge data for the Great Miami River over the 

 macroinvertebrate collection periods (Table 3) indicates this steady 

 decrease in stream discharge over the study period. 



Observed oxygen concentrations were fairly high at all stations 

 on June 21. However, fairly low O2 levels were observed at stations 9 

 through 14 on August 16. Oxygen concentrations at stations 10 and 

 11 were critically low, less than 1.5 mg/liter on this date. Oxygen 

 levels were higher in October than in August; however, depressed 

 levels at stations 10 and 11 were still apparent. 



Conductivity, a measure of the total concentration of dissolved 

 ionic matter in the water, showed a consistent pattern throughout 

 the study. Marked conductivity increases were observed below 

 sewage-treatment plants and below known industrial-wastewater 

 outfalls, resulting in a general pattern of increasing conductivity from 

 upstream to downstream stations. Temperature and conductivity 

 both showed linear negative correlations with total taxa per station 

 (S) (rtemp. ^ —0.51, rcond. ^ — 0.35). A multiple stepvidse regression 

 (computer package BMD02R, Dixon, 1973) showed that tempera- 

 ture, conductivity, and oxygen were all significantly correlated with 

 S [observed Ftemp. = 36.95, Fcond. = 25.39, Foxy. = 10-07 > criti- 

 cal F0.95 (1,3 8) ^ 4.10] . These three variables explained 56.7% of 



