The objective of this research was to identify the materials and methods necessary to study the attached algal community on a river bottom in deep water. The study site was the Susquehanna River near Falls, Pennsylvania . Artificial substrates of smooth glass, frosted glass, Vermont slate, `sandy slate' (flagstone) and acrylic plate were placed on the stream bottom in detritus free sample holders by scuba divers. Both monthly and long-term cumulative samples were collected from the plates employing scuba and a Bar-Clamp sampler . River stones (natural substrates) were collected for comparison . Samples were analyzed in a Palmer Cell under a Bausch and Lomb research microscope .
Diatoms were the most important colonizers of river stones, with the genera Nitzschia and Navicula most abundant . Highest
periphyton densities occurred on natural substrates in winter
with a maximum of 2 .2 x 10° units/ mm 2 . Artificial substrates
with one month exposure periods accumulated maximum
periphyton density from May through October with relatively
low densities in winter . Cumulative artificial substrates were
most like river stones in patterns of colonization . Frosted acrylic
is recommended for future studies employing benthic artificial
periphyton substrates .