Nitrogen fixation and carbon uptake in a tropical estuarine system of Goa, western India
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Biological production in aquatic systems is often nitrogen limited. Nitrogen (N2) fixation is an important contributor to nitrogen requirement of phytoplankton not only in oligotrophic but also in nutrient-replete waters. However, the importance of N2 fixation in meso-polyhaline estuaries is not well known. Here we report significant N2 fixation rates, ranging between 0.1 and 34--mol-N-m-3-d-1 from the Mandovi and Zuari estuaries, two typical tropical monsoon-affected estuaries located along the Indian west coast. The estuarine waters were moderately rich in nutrients with nitrate concentration up to 5--M in the Mandovi and 6--M in the Zuari and PO4- up to 1--M. Chlorophyll a concentration varied between 0.1 and 8-mg-m-3 with moderate primary production (up to 262-mg C m-3-d-1). The organisms responsible for the observed diazotrophic activity in the estuaries still remain to be identified.
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