Urea as nitrogen source for phytoplankton production in coastal waters of Goa

Abstract

Annual variation of urea in coastal waters off Goa, India is 0 to 2.92 mu g-at N.1/1 and 0 to 4.69 mu g-at N.1/1 in adjacent estuarine waters of Mandovi. Peaks of phytoplankton production accompanied with the decrease in urea in June and October, when ammonia and nitrate were high, indicate that urea is utilised or decomposed by phytoplankton organisms. Seasonal fluctuation of urea is between 7 and 55% of total utilizable nitrogen, which is a large reserve of nitrogen for phytoplankton growth. Assimilation ratio (delta N: P) indicates that nitrate is in short supply. However, urea available in these waters can substitute nitrogen deficiencies for the high rate of phytoplankton production