Effect of current velocity on diatom colonization on glass slides in unpolluted headwater creek

Sa？etak Abstract Background and Purpose: The goal of this study was to determine the effect of current velocity on diatom colonization rate during the first 30 days of artificial substrate (glass slides) exposure. Materials and Methods: From autumn 1990 to summer 1993 artificial substrates were submerged in an unpolluted mountain stream. The parallel oriented glass slides (against the surface) were placed 10 cm beneath thewater surface (protected from debris) and exposed to different current velocities (10–30 cm s–1, 40–60 cm s–1 and 80–100 cm s–1). The samples were collected seasonally. To define diatom colonization, a nonlinear regressive analysis of empirical data was performed. Results: A total of 71 diatom species were found. Species Cocconeis placentula, Surirella ovata, Gomphonema olivaceum, and Navicula gracilis were the most abundant, depending on different current velocity. Conclusions: The time needed for reaching the equilibrium progressively increased with the current velocity (F= 16.7; P< 0.01). In the summer and autumn, the time needed for the stabilization of diatom flora was longer than in spring and winter. Concerning species abundance, Cocconeis placentula, and Navicula gracilis were independent of the current velocity, while Surirella ovata was abundant at lower (≤30 cm s–1) and Gomphonema olivaceum at higher (≤60 cm s–1) current velocities