EFFECTS OF THERMAL ALTERATION 571 



constant, unidirectional water flow. At the northern end of each 

 channel a standpipe was installed to accommodate overflow. 

 Concrete collars were poured to a depth of 61 cm around the 

 periphery of each channel to prevent waterline erosion. 



Water Supply 



Unheated and heated water was pumped directly from the steam 

 plant. Channel 1 received only unheated water; channel 2 received 

 both unheated and heated water; and channel 3 received only heated 

 water. Unheated water was pumped from the steam-plant intake 

 canal leading from the Black Warrior River. Heated water was 

 pumped from the head end of the steam-plant discharge canal to the 

 channels. Invertebrates could enter each channel through the supply 

 lines; thus organisms entering each channel depended to some extent 

 on the fauna of either the intake or discharge canal. The total design 

 capacity for each water supply was 20 liters/sec. A series of wooden 

 baffles was used to reduce surface currents, and heated water was 

 introduced at the surface of channel 2 to create a warm layer over 

 about two-thirds of this channel (Fig. 1). Motile organisms could 

 move into or out of the warm- water layer. 



Macroinvertebrate Sampling 



Ten permanent, equally spaced stations were established along 

 the length of each channel (Fig. 1). Macroin vertebrates were sampled 

 with modified Hester— Dendy multiple-plate samplers (Hester and 

 Dendy. 1962) and an Ekman dredge. The dredge samples were taken 

 at each end of the three channels between stations I and III and 

 between VIII and the drain. Each dredge sample consisted of three 

 random grabs along the middle of the channel to give a composite 

 sample of 697 cm^ . Collections were made at 4- to 6-week intervals. 

 All mud samples were screened through a U. S. Standard No. 30 sieve 

 in the field, and the residue was preserved with 5% form; i and 

 stained with rose bengal to aid in the sorting of organisms. The 

 samples were then transported to the fisheries laboratory at Auburn 

 University, where the organisms were floated from the detritus by 

 use of a saturated salt solution. The residue left in the salt solution 

 was checked for bivalves, caddis-fly cases, and other organisms. The 

 organisms in the samples were sorted into various taxa and counted. 



The plate samplers were constructed of three circular plexiglass 

 plates with two spacers between each plate to allow a total available 

 surface area of 562.3 cm^ . These samplers were suspended vertically 

 in the water column at depths of 0.6 and 1.2 m. Duplicate plate 



