Sugandha Shankar

Education

B.Sc (H) University of Delhi, India, 2008 ; M.Sc Madurai Kamaraj University, India 2010

Research interests

My work is based on the hypothesis that ammonium is the more important form of dissolved inorganic nitrogen supporting annual summertime blooms of Alexandrium fundyense in the Gulf of Maine -- Georges Bank region. It is already known that as compared to nitrate and nitrite, ammonium is the more preferred nutrient for phytoplankton because of its reduced state. Previous oceanographic surveys have shown that nitrate injections in upstream regions (Eastern Gulf of Maine and Northern Flank of Georges Bank) lead to diatom blooms downstream followed by dinoflagellate blooms, including populations of Alexandrium. These populations of Alexandrium continue to bloom even after nitrate is exhausted from the surface waters. Phytoplankton in general have been shown to rapidly utilize even very small nitrogen micro-patches like the ones formed by zooplankton excretion. Rapid remineralization of nitrogen to ammonium and strong coupling of ammonium regeneration and uptake makes sure that even very low ambient ammonium concentration can be enough to sustain phytoplankton production. It is suggested that in the absence of nitrate, heterotrophic regeneration of ammonium occurs at rates sufficient to sustain continued growth of Alexandrium. Therefore, it is important to quantify the kinetics of that uptake. During my stay here I expect to elucidate the role ammonium plays in these Alexandrium fundyense blooms, describing the half saturation constant for ammonium and, based on field surveys, examine the correlation between nitrate concentration, ammonium concentration and Alexandrium cell densities present in the Gulf of Maine.

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