DIATOMS OF THE MIDDLE FORK OF THE SALMON RIVER DRAINAGE, WITH NOTES ON THEIR RELATIVE ABUNDANCE AND DISTRIBUTION

A total of 145 species of diatoms was collected from 13 sites in the Middle Fork of the Salmon River drainage, Idaho, USA. Achnanthes minutissima was the prevalent species with an importance index of 19.25. Cluster analysis revealed 2 main site groupings, sites above the entrance of Loon Creek and sites below. The entrance of Loon Creek (6th order) increases the Middle Fork of the Salmon River to a 7th order stream. Shannon-Weiner diversity values were generally high. We have been characterizing the algal flora of Intermountain western North America for the past several years. At present, we are characterizing the diatom floras of several important stream systems in this area to add information to a general diatom flora of the region (Squires et al. 1973, Lawson and Rushforth 1975, Benson and Rushforth 1975, Clark and Rushforth 1977, Ross and Rushforth 1980, Rushforth et al. 1981a, Johansen and Rushforth 1981, and Cushing et al. 1983). Our studies have also extended to standing waters and other unique environments (e.g., Evenson et al. 1981, Felix and Rushforth 1979, Rushforth et al. 1981b, St. Clair and Rushforth 1976, and others). The purpose of this paper is to document the species of diatoms in the Middle Fork of the Salmon River in Idaho and several of its important tributaries (Marsh Creek, Indian Creek, East Fork of Indian Creek, Loon Creek, and Big Creek). We also determined distributional patterns within this system and performed several statistical analyses of abundance. Data also are given for one site on the main Salmon River, just below the confluence with the Middle Fork (see Fig. 1 for collection sites).