Spatio-temporal distribution of chlorophyll-a in relation to physico-chemical parameters in coastal waters of the northwestern Bay of Bengal

Abstract

The present study focuses on understanding the long-term distribution of physico-chemical parameters and their influence on the distribution of chlorophyll-a (chl-a) at a coastal site in the northwestern Bay of Bengal. Chl-a showed large variability (0.12 to 10.05 mg m(-3)) on a spatio-temporal scale during the study period. However, the distribution showed a similar pattern with marginal variability from March 2010 to February 2011 and March 2011 to February 2012. The vertical distribution of salinity, pH, total suspended matter (TSM) and chl-a showed systematic temporal variability. However, dissolved oxygen (DO) and nutrients (nitrite + nitrate, phosphate, silicate) did not show any significant spatio-temporal trend. Chl-a showed bimodal distribution on an annual scale, with the first peak appearing during the pre-monsoon period in March due to a seasonal phytoplankton bloom, whereas the second peak occurring during September as a result of nutrient loading from river influx due to monsoonal precipitation. Factor analysis revealed the association of low salinity and high nutrients with chl-a. This infers that the nutrients brought by the influx of river into the study area were fuelling the growth and abundance of phytoplankton. Cluster analysis resulted in two distinct clusters among all physico-chemical datasets, indicating the presence of two distinct areas separated by the 30 m isobath that were strongly influenced by physico-chemical characteristics associated with the seasonal monsoon.

Phytoplankton community structure in local water types at a coastal site in north-western Bay of Bengal

“…The circulation pattern of the study area is governed by the effects of seasonal East India Coastal Current (EICC) and surface current driven by monsoon winds, cyclonic circulation, and river discharge (Shetye et al 1991;Vinayachandran and Yamagata 1998). Contrasting water quality properties on either side of 30 m bathymetry with the formation of two local water types is an important environmental characteristic of this region (Baliarsingh et al 2015).…”

“…In a recent study, the existence of the two local water types (type 1 < 30 m isobath and type 2 > 30 m isobath) in coastal waters of north-western BoB has been described based on water column physicochemical properties (Baliarsingh et al 2015). Hence, the physicochemical and biological datasets of surface water were spatially averaged over near-coastal stations (R1, R2, and R3) representing type 1 and far-coastal stations (R4 and R5) as type 2.…”

“…Recurrence of phytoplankton bloom caused by diatom (Asterionellopsis glacialis) and dinoflagellate (Noctiluca scintillans) found to influence coastal water quality of north-western BoB (Sasamal et al 2005;Mohanty et al 2007). Phytoplankton biomass in coastal waters off Rushikulya estuary, northwestern BoB, found to be largely controlled by nutrients entrained from estuary and bottom waters leading to the formation of two local water types (Baliarsingh et al 2015). Each phytoplankton species has a specific water quality preference and introduction of any non-native species, of high reproduction efficiency, may cause significant adverse impact on existing biodiversity as well as water quality (Pysek et al 2009;Carlton 2009).…”

Seasonal variation in optically active substances at a coastal site along western Bay of Bengal

“…Differential distribution and variability of hydro-biological parameters in coastal waters off Gopalpur deciphered two local water types on either side of 30 m isobath. The effect of estuarine and terrigenous influx reaching up to 30 m bathymetry is the important factor responsible for formation of contrasting hydro-biological local water types [3].…”

“…[5]. Although many of studies have been carried out to understand the variability of chl-a, TSM and nutrients in this region, no comprehensive monitoring study carried out on the OAS including CDOM [1][2][3][4][5][6][7]. The present study is focused on understanding the temporal variability of OAS off Goplapur, a coastal site along the north-western Bay of Bengal.…”