Response of phytoplankton to nutrient enrichment with high growth rates in a tropical monsoonal estuary - Zuari estuary, India

Abstract

Present study is about <span style="mso-bidi-font-style:italic">the impact of macronutrient enrichment on phytoplankton biomass and community structure in a tropical monsoonal estuary.<i style="mso-bidi-font-style:normal"> In situ</i> experiments carried out during the pre-monsoon period (February-March 2006), showed that the response time of phytoplankton to nutrient enhancement was 24-32 h. Phytoplankton biomass increased sizably, indicating nitrate and silicate limitation for phytoplankton growth. An increase in 23µg chl <i>a</i> l^-1 resulted in an uptake of 10µM nitrate, 0.6µM phosphate and 17µM silicate. Phytoplankton showed high growth rates with an average value of 1.36µg chl l^-1 d^-1.This phytoplankton community was largely dominated by diatoms (>96%), particularly chain forming species. Relative preference index (RPI) value for nitrate was >1, suggesting that, irrespective of the ambient ammonium concentration, estuarine autotrophs preferred nitrate. Few species like <i style="mso-bidi-font-style:normal">Skeletonema costatum and<span style="mso-bidi-font-style:italic"> Thalassionema nitzschioides</span></i> exhibited the ability to withstand hypoxic condition.

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