Effect of Freshwater Influx on Phytoplankton in the Mandovi Estuary (Goa, India) during Monsoon Season: Chemotaxonomy

Sushma G Parab,S G Prabhu Matondkar,Joaquim I Goes,Helga Do R Gomes

doi:10.4236/jwarp.2013.53a036

Abstract

The Mandovi estuary is a prominent water body that runs along the west coast of India. It forms an estuarine network with the adjacent Zuari estuary, connected via the Cumbharjua canal. The physico-chemical conditions seen in the Mandovi estuary are influenced by two factors: the fresh water runoff during the monsoon season (June-September) and the tidal influx of coastal seawater during the summer (October to May) season. However, the effects of monsoon related changes on the phytoplankton of the Mandovi estuary are not yet fully understood. An attempt to understand the same has been made here by applying the process of daily sampling at a fixed station throughout the monsoon season. It was noticed that the onset of the monsoon is responsible for an increase in nitrate levels upto 26 μM from <1 µM during pre-monsoon and enhancement of chlorophyll a (chl a) as high as 14 µg·L −1 during the same period. The phytoplankton population was observed through both chemotaxonomy and microscopy and was found to be composed mainly of diatoms. CHEMTAX analysis further uncovers the presence of several other groups of phytoplankton, the presence of which is yet to be reported in many other tropical estuaries. It includes chrysophytes, cyanobacteria, prasinophytes, prymnesiophytes and chlorophytes. The appearance of phytoplankton groups at various stages of the monsoon was recorded, and this data is discussed in relation to environmental changes in the Mandovi estuary during the monsoon season.

Highlights

Estuaries are complex ecosystems which have been proven to be interesting areas of study due to their constantly changing physico-chemical environments
During the southwest monsoon (SWM), the Mandovi estuary receives heavy freshwater discharge which results in constant alteration in the salinity
Diatoms are an important group of phytoplankton found during the pre-monsoon season

Summary

Introduction

Estuaries are complex ecosystems which have been proven to be interesting areas of study due to their constantly changing physico-chemical environments. The Mandovi estuary is located between 15 ̊25'N to 15 ̊31'N and 73 ̊45' to 73 ̊59'E along the west coast of India and is well mixed throughout the year with the exception of the monsoon months during which time vertical stratification appears [2]. The Mandovi estuary receives an annual rainfall of 250 - 300 cm·year−1 during the southwest monsoon (June-September) and less than 10 cm·year−1 during the rest of the year [3]. During the southwest monsoon (SWM), the Mandovi estuary receives heavy freshwater discharge which results in constant alteration in the salinity. The salinity varies from 0 to 22 PSU during the months from June to September [4] These variations bring changes in water turbidity and availability of solar radiation during the monsoon

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