Seasonal variations of hydrographic parameters off the Chennai coast, India

Abstract

The environment plays a major role in determining the abundance of fishes in a particular region and it helps to predict the probable fishing zone. This environment variables includes temperature, salinity, pH, TSS, DO (Dissolved Oxygen), chlorophyll a, b and c, primary productivity, gross and net, nutrients, phosphate, nitrate and ammonia. These parameters were estimated using standard procedures. These parameters in a particular fishing zone varies from season to season. This seasonal variations of these parameters and its relationship with each other are studied in Ennore, (Lattitude, 80°19’31"E, and Longitude, 13°14’51"N). an industrially polluted area along Chennai coast. Factor analysis is done to remove the redundant highly correlated variables from the data, replacing the entire data with uncorrelated variables. During the post monsoon season, the 4 components extracted by factor analysis indicates that the nutrient, nitrate, chlorophyll b, TSS and dissolved oxygen are important variables deciding the photosynthetic activity, in summer season, 3 components were extracted and the variables that decide photosynthetic activity includes nutrient nitrate, temperature and nutrient ammonia. In pre-monsoon season, 5 components were extracted by factor analysis and the deciding variables include pH, chlorophyll, c, chlorophyll a, chlorophyll b and salinity. In monsoon season, 3 components were extracted and the deciding variables include TSS, DO and temperature for the photosynthetic activity to take place. The eigen values worked out in all the 4 seasons are above 1 and are reliable. The eigen value is highest in the post monsoon component tested, 4.39 and the least eigen value, 1.05 is in the pre monsoon season. Pre monsoon season among all seasons shows highest percentage of cumulative variance. In the post monsoon season, the variables N-Nitrate, chlorophyll b, TSS and DO in the components 1, 2, 3 & 4 decide the growth of phytoplankton with 12% loss of information. In the summer season, the variables, N-Nit, temp., and N-amm., in the components 1, 2 and 3 are the deciding factors for the growth of phytoplankton with 26% loss of information. In the post monsoon season, the variables, pH, chlorophyll c, chlorophyll a, chlorophyll b and salinity in the components, 1, 2, 3, 4 and 5 respectively decides the phytoplankton growth with 11% loss of information. In the monsoon season, the variables, TSS, DO and salinity in the components 1, 2 and 3 decide the growth of phytoplankton with 22% loss of information. These variables are representative of all original 11 variables and the components are not linearly correlated with each other. The size of the data from 11 variables can be reduced to three components by using factor analysis with the principal components extraction.