A Quinquennial Multivariate Monitoring of the Brackish Water Zone of Hooghly Estuary, Northern Bay of Bengal, India

Abstract

A quinquennial study (Mar'2010-Feb'2015) was undertaken to comprehend the interrelationship of the selected ecological variables in the lower Hooghly estuarine complex. The yielded data pointed out that there was a paradigm shift after in the year 2013 as the real time data revealed considerable changes in mean before and after that period. A total of 19 variables were considered for the study among which 4 were ecological indices derived. From the extensive study it was evident that variables such as dissolved nutrients, pH, water temperature, air temperature, turbidity, wind speed, relative humidity and precipitation etc were all influential on the population density of phytoplankton [r-values ranging from -0.99 to +0.95 @ 95% confidence level; p-values of upto +0.99]. A 'single factor ANOVA' was performed on the normalized data sets, the 'Null hypothesis' was rejected. To detect the set(s) where the differences in variances of means lie, two sets of t-tests were performed (assuming equal and unequal variances) where in both the cases the 'Null hypothesis' was rejected. A multivariable regression analysis was also performed [Multiple R:+0.9004; R Square: 0.8107; Adjusted R Square: 0.7519; Standard Error: 3.1117; Observations (n): 60, at 0.05 level of significance] and the generated equation is as follows: NPP = [+47.0402] + (-0.1054) Rh + (-0.0056) Precpn. + (+0.4871) WS + (0.4080) pH + (+0.2870) Sal + (+0.2006) D. O. + (-0.9625) aT + (+0.7120) wT + (-0.0340) Turb + (+0.0068) NO3 -N + (+0.4755) PO4 -P + (+0.0109) SiO4 -Si + (-0.6815) Chl a + (+0.0005) Den.