Abstract

Asha Udayamali Meegolle Lokuhewage

Nitrogen and phosphorous are essential elements to aquatic biota. Different types of humic substances (HS), such as humic acid (HA) and fulvic acid (FA) have impact on the freshwater nutrients. The aim of the study was to examine how the presence of humic substances may affect nutrient availability to the growth of ULOTHRIX ZONATA (Weber and Mohr) Kutz. Samples were incubated on different nutrient treatments: nutrient sufficient (+NP), nitrogen deficient without HA or FA (-N) and with HA or FA (-NH/-NF) and phosphorous deficient without HA or FA (N) and with HA or FA (NH/NF). The results demonstrated that addition of HA or FA increased the production of Chlorophyll A and cell density as compared with the cultures exposed to nutrients only at the same concentration. U. ZONATA represented the highest growth efficiency (cell density 14.5 x107 cells/ml, determined by counting number of cells per milliliter in suspension of filamentous green alga) under N deficient with HA or FA treatment. During the experiment, whereas the N deficient treatments had the lowest cell numbers (2.2 to 2.5 x 107 cells /ml). It is suggested that HA and FA could be of great importance in the growth of green alga U.