AN EASTERN PENNSYLVANIA TROUT STREAM 779 



Table 2 shows the different macroinvertebrate famihes and 

 genera dominating at the four macroinvertebrate stations. In all 

 50,305 organisms were comited and identified. The mayfly 

 Stenonema was dominant at station 28 (18% of the total macro- 

 invertebrates). The caddis fly Hydropsyche was dominant at station 

 12 (30% of the total) and also at station 10 (35% of the total). The 

 family Chironomidae dominated at station 2 (29% of total). 



DISCUSSION 



Hynes (1972) reports that downstream areas of streams are 

 usually warmer than the headwaters. The reason the temperature in 

 Bushkill Creek does not increase substantially downstream may be 

 that cool water entering the lower drainage basin from limestone 

 springs maintains lower temperatures in the lower reaches. As water 

 from the limestone springs enters the water course, carbon dioxide is 

 lost and the pH rises. The pH also rises in response to carbonates 

 entering the water from the limestone. 



The addition of carbonates also contributes to the rise in 

 alkalinity downstream. Industrial effluents in the downstream area 



TABLE 2 



DOMINANT TAXA OF BENTHIC MACROINVERTEBRATES 



BY STATION 

 (PERCENT OF TOTAL NUMBERS COLLECTED) 



