ORDINATION OF MACROI NVE RTEBRATE COMMUNITIES 749 



macroinvertebrates of the Clinch River. Using an ordination proce- 

 dure (Bray and Curtis, 1957), I have examined the pattern of 

 affinities among a river system's macroin vertebrate communities over 

 a gradient from clean water to multistressed communities. The 

 stressors of significance in this study, municipal and industrial 

 wastew^ater and power-plant effluents, are fairly common to the large 

 rivers found in the highly populated areas of the United States. 



I used 14 stations over three time periods to investigate changes 

 in biotic composition on both a longitudinal and a temporal basis. 

 Modifications in the pattern of relationships between communities 

 owing to changes in river discharge and other physicEil— chemical 

 parameters were also studied. 



METHODS 



Study Area 



The Great Miami River basin is located in southwestern Ohio. 

 The Miami River flows 257 km in a southwesterly direction from its 

 headwaters in central Ohio, finally entering the Ohio River in the 

 extreme southwestern comer of Ohio. Two major tributaries, the 

 Mad and Stillwater rivers, join the Miami River at Dayton to form 

 the Great Miami River, 129 km above its confluence with the Ohio 

 River. The average Great Miami River discharge is approximately 

 5100 m-^/min. The population of the Great Miami River basin is 

 approximately 1.5 million; about one-half of this population is 

 concentrated in the Dayton area (Weston, 1967; Little, 1964). 



The study area (Fig. 1) consisted of a 53-km section of the Great 

 Miami River and a station on each of the major tributaries, the Mad 

 and Stillwater rivers (for exact station locations see Beckett, 1977). 

 Three upstream stations were established: one each on the Mad 

 River, the Stillwater River, and the Miami River. These upstream 

 stations were in woodland areas. Although there are some small 

 municipal sewage-treatment plants far upstream of these stations, 

 there are no major municipal or industrial discharges near these 

 upstream sample sites. 



Eleven stations were established along the Great Miami River 

 within the study area (making a total of 14 stations). A station was 

 established at both the intake and the discharge of the two power 

 plants (the F. M. Tait and the O. H. Hutchings). Each of the power 

 plants has a low-level dam located between the plant's intake and 

 discharge. Station 13 was established below a fairly large dam 

 (Chautauqua Dam). The entire study area on the Great Miami River 

 (stations 4 through 14) underwent some modification for 



