Experimental Studies on Silicate as the Limiting Nutrient in Altering Phytoplankton Community Structure

Abstract

In the present study, nutrient enrichment experiments were carried out to understand the role and importance of silicate in the phytoplankton blooming. Water temperature (26.6 – 29.8ºC), salinity (33 - 37‰), pH (8.01 – 8.64), and DO (4.26 – 6.38mgl^-1) not showed significant variation and not play important role in the phytoplankton growth. At the first day of the experiment, nutrient concentrations (NO₃ - 9.44µM, NO₂ – 1.51µM, PO₄ – 24.40µM and SiO₃ – 45.60µM) were at its maximum concentration in enrichment tanks and it gradually decreased (PO₄ – 14.19µM and SiO₃ – 6.11µM) at the end of experiment period, suggested uptake of nutrients by the experimental microalgal species. The pronounced maximum chlorophyll concentration (8.90µgl^-1) in tank5 corresponding with addition of highest concentration of silicate (25µM), clearly pointed out that silicate addition has influenced the diatom dominated microalgal growth evidenced by the increased chlorophyll concentration. Increased utilization of SiO₃ supported by PO₄ indicates the nutrient preference by the diatom. The regression trend recorded in the present study could be used as the positive signal in mapping silicate using remote sensing techniques. The regression analysis between silicate and chlorophyll showed significant correlation coefficient (R² = 0.609) and increased phytoplankton growth rate (0.277 d^-1) at tank 5 when compared to control substantially proved the uptake of silicate by phytoplankton community dominated by diatoms.