774 BRADT 



indicate considerable water entering the stream from limestone 

 springs in the lower basin, according to Young et al. (1972). The 

 slope of the stream increases slightly 4.8 km above the mouth where 

 the stream is rocky and turbulent. The rapid flow and turbulence of 

 this area enables the stream to oxidize industrial pollutants. Two 

 sewage-treatment plants discharge effluents into tributaries. One 

 plant discharges 0.3 million gal /day (secondary treatment) into Little 

 Bushkill Creek 9.6 km above its confluence with the main stem. The 

 other plant discharges 0.5 million gal/day (secondary treatment) into 

 Shoeneck Creek 6.4 km from its entry into the main stem 0.8 km 

 below station 10 (Fig. 1). 



Daily average flow, calculated by Young et al. (1972), was 5.41 

 m^ /sec. 



MATERIALS AND METHODS 



Water chemistry and the benthic macroinvertebrate fauna were 

 sampled biweekly from March 1972 to September 1973, except 

 during December through March when sampling was monthly. Water 

 chemistry was sampled at eight stations (28, 23, 21, 13, 12.5, 12, 10, 

 and 2). The benthic macro in vertebrates were sampled at four stations 

 (28, 12, 10, and 2). Station numbers represent distance upstream 

 from the confluence of Bushkill Creek and the Delaware River at 

 Easton. 



Temperature, pH, total alkalinity, conductivity, orthophosphate, 

 nitrate, chloride, and total iron were measured 31 times at each 

 station over 17 months. Calcium was sampled six times at each 

 station (May to September, 1973). Temperature was measured in the 

 field with a 0°C stem thermometer. A Zeromatic pH meter was used. 

 Total (methyl orange) alkalinity was determined by titration with 

 0.02N sulfuric acid to a pH end point of 4.6, measured with the pH 

 meter (American Public Health Association, 1965). Conductivity was 

 measured with an Industrial Instruments conductivity meter 

 (American Public Health Association, 1965). 



Nitrate was measured by the cadmium reduction method (Hach 

 Chemical Company, 1971), and the resulting color was read with a 

 Spectronic 20 spectrophotometer (American Public Health Associa- 

 tion, 1965). 



Orthophosphate was measured by the modified stannous chloride 

 method (Hach Chemical Company, 1971) and read on the Spectronic 

 20. Chloride was determined by the Mohr method using titration with 

 silver nitrate (Hach Chemical Company, 1969). Total iron was 

 measured by the 1,10 phenanthroline method (Hach Chemical 



