An Investigation of the Periphyton in a Riffle of the West Gallatin River, Montana

An investigation was made of the periphyton complex in a riffle area on the Uest Gallatin River, Montana, from August 1952 through February 1954. The riffle gradient in 1954 was 1.76 feet per 100 lineal feet and average riffle depth during the study period was 12 inches. One square centimeter samples were collected from formalin-treated stones placed in the riffle. Some random stones were sampled as controls and to supplement treated stones washed from the area. . From August 1952 to March 1953 one periphyton sample was collected from each station while two samples were collected from each station from March 1953 through February 1954. Statistical analysis was made to determine the number of "count units" needed to give satisfactory precision in making estimates of organisms per ml sub-sample. Gross seasonal changes of the periphyton complex are described. Three divisions of algae representing 34 species and live phyla of animals representing 35 species were found in periphyton. Chrysophyta was the most abundant algae and Diptera was the most frequently represented animal. A sharp increase in number of organisms occurred in August-September and peaked in November. A decline occurred in Dec-ember-January and a minor peak appeared in March. Another decline occurred in May. Organisms were found at a minimum in July. Diatoms were superseded in number by a green algae in February 1953 and in July 1953 by a blue-green algae. Two peaks occurred in Tendepedidae larvae in 1952 and one in 1953. One peak in Simulium larvae was found in January 1954. The abundance of organisms in relation to temperature, ice formation, discharge, turbidity and velocity are considered. AN INVESTIGATION OF THE PERIPHYTON IN A RIFFLE OF THE VEST GALLATIN RIVER, MONTANA by . RONALD B. ODMTCW V A THESIS Submitted to the Graduate Faculty I* p a r tia l fu lfillm ent of the requirements fo r a degree of •' . 1L Master of Science in Fish and VBLldlife Management at Montana State College