AN EASTERN PENNSYLVANIA TROUT STREAM 781 



spinner which passively feeds in water rich in organic particulate 

 matter (Hynes, 1970). The Chironomidae are also tolerant of a wide 

 range of environmental conditions (Robach, 1974). When a factor 

 becomes limiting, the most sensitive species disappear, the more 

 tolerant species increase to occupy the vacated niches, and the 

 diversity of the community decreases (Reid, 1961). An increase in 

 the nutrient supply can decrease diversity just as an increase in the 

 intensity of any factor can decrease diversity (Hooper, 1969). 

 Increasing development in the drainage basin has put stress on the 

 lower reaches of the stream. Station 28 is in a rural area with some 

 agricultural lands nearby, but the diversity at station 28 was the 

 highest in the study. Station 12 had diversity (x = 2.89) similar to 

 station 2 (x = 2.87). Station 12 is located in an agricultural area. The 

 effluent from the sewage plant on the Little Bushkill may be 

 responsible for the lowered diversity at station 12. The members of 

 the Trichopteran family. Hydropsy chidea (Hy dropsy che and 

 Cheumatopsyche), which comprise 55% of the total macro- 

 invertebrate population at station 12 and 42% of the total 

 population at station 10, show preference for open areas with high 

 periphyton density (Hynes, 1972), fast current (Macan, 1962), and 

 high organic loading (Roback, 1974). Station 12 is immediately 

 downstream of a short (183 m) section of rechanneled stream where 

 shading trees were removed and several gabions installed. 



Station 10 had the highest total numbers, total taxa, and wet 

 weight. This station is immediately downstream of the 2.0 km of 

 rechanneled streambed and the gabion installation. The stream banks 

 above station 10 were stripped of ground cover, shrubs, and trees 

 during the rechanneling process. The banks were replanted following 

 the rechanneling, but the trees are not yet large enough to shade the 

 stream effectively. Station 10 is the most productive station in terms 

 of biomass (x = 1.87 g) and has the second highest alkalinity 

 (x = 87.2 ppm). Armitage (1958) reported that the yearly standing 

 crop of macroinvertebrates and the number of Trichopterans were 

 both correlated with alkalinity. Beyerle and Cooper (1960) found 

 that moderately alkaline streams were more productive than soft- 

 water streams. 



Station 2 is influenced by nutrients from the urban area and 

 industrial effluents. The fact that station 2 has a diversity just below 

 3.0 attests to the effectiveness of rapidly flowing water in maintain- 

 ing good water quality in the urban area. The mean dissolved-oxygen 

 level at station 2 was 8.9 mg/liter, ranging from 6.0 to 11.8 mg/liter 

 (Bradt, 1974). 



