Seasonal and Tidal Dynamics of Nutrients and Chlorophyll a Concentration in Water at the Sundarbans Mangrove Ecosystems of Bangladesh

The seasonal and tidal variations of physicochemical parameters, nutrient concentrations and chlorophyll a concentration from the water of Passur river and Koromjol canal in the Sundarbans mangrove ecosystems were investigated during March 2018 to February 2019. Samples were collected from five sampling stations during March, August and November where these months were considered as pre-monsoon, monsoon and post-monsoon seasons, respectively. The nutrients NH3-N, NO3-N, PO4-P, SO4 and Chlorophyll a concentrations were found 0.001 to 0.09, 3.5 to 50, 0.06 to 5.4, 30 to 272 and 0.18 to 1.75 mg/L, respectively, during high tides, and 0.001 to 0.39, 4.2 to 47, 0.1 to 2.75, 20 to 179 and 0.218 to 1.88 mg/L, respectively, during low tides. The NO3-N was very high than suitable limit during both tides at monsoon and post-monsoon season. The PO4-P was found moderately high during both tides at all stations. The SO4 was found to be 187.8 and 76.87 mg/L during high tide, and 135.4 and 95.73 mg/L during low tides in pre-monsoon and post-monsoon, respectively, that were very high than water quality standards. The Passur river and the Koromjol canal were fluctuating seasonally and tidally in some magnitude and their variations can alter the water quality as well as the density and distribution of living organisms.