REGULATORY INFLUENCE OF WATER CURRENT ON ALGAL COLONIZATION IN AN UNSHADED STREAM AT SHILLONG (MEGHALAYA, INDIA)

Algal communities of a stream system developing on artificial substrate in a pool as well as three riffle habitats (flow rates of 10-15, 18-22 and 37-41 cm s-1) were composed of only diatoms. The stream supported scant diatom flora (9 genera and 27 species) possibly due to low pH and phosphorus-limiting conditions. In general, algal colonization was negatively related to flow rates, and was best at 10-15 cm s-1. Different diatom species assumed dominance at specific flow rates: Navicula subtenelloides Cholnoky at 10-15 cm s-1, Gomphonema parvulum (Kutz.) Kutz. and Caloneis ventricosa (Ehr.) Meist. at 18-22 cm s-1, and Synedra ulna (Nitz.) Ehr. at 37-41 cm s-1. In the pool, Eunotia pseudoparallela angstrom. Berg and Gomphonema olivaceum (Hornem.) Breb. were most abundant.