Dissolved organic nutrients and phytoplankton production in the Mandovi estuary and coastal waters of Goa

Abstract

Total organic nitrogen (TON) and dissolved organic phosphorus (DOP) in the coastal and estuarine waters of Goa, India varied from 0.6 to 47.1 mu g-at N 1-1 and 0.12 to 3.49 mu g-at P l-1 respectively. The chlorophyll content of these waters fluctuated from 0.3 to 11.3 mg m-3. The increase in TON and DOP in June and October coincided with the chlorophyll peak, there-by suggesting that these two are derived from planktonic activity. The low values of concentration ratio and assimilation ratio (NO3 -: PO4 3-) suggested that inorganic nutrients were deficient in these waters. However, the percentage of TON and DOP in total nitrogen and total dissolved phosphorus varied from 50.7 to 96.6% and 15.3 to 74.6% respectively, during the post and premonsoon months, when the production remained high. A large portion of TON and DON in the coastal and estuarine waters of Goa might serve as an efficient nutrient supplement for the phytoplankton at times of nitrate deficiency