Distribution of diatoms in spring in the Julian Alps (NW Slovenia)

DISTRIBUTION OF DIATOMS IN SPRINGS IN THE JULIAN ALPS (NW SLOVENIA) - In the Julian Alps (Slovenia), the diatom communities of 16 mountain springs were studied between May and October 1999. Four of them were sampled monthly for a more detailed investigation of seasonal changes in community structure. The sampling was performed by scraping of the rock surface. In all sampling stations, physical and chemical parameters were measured. The purpose of the work was qualitative assessment of the diatom communities. The diatom flora of these springs consisted of 60 diatom taxa and showed similarities with springs and headwater stream diatom communities from different geographic areas. Achnanthes minuttisima reached the highest relative abundance in most of the samples. Characteristic spring taxa (crenophiles) were present, but also included subdominant and rare taxa. Five different spring types were identified, with respect to diatom assemblages, using cluster analysis. Current velocity and periodical dryness in a spring appeared to be the dominant environmental factor affecting diatom distribution in selecting karst springs. In some springs, however, peculiar environmental factors (dim light, ionic strength) affected the structure of diatom assamblages. The Shannon-Wiener diversity index was the highest in permanent springs