Simulating the Effects of Tidal Dynamics on the Biogeochemistry of the Hooghly Estuary

A three-dimensional coupled hydrodynamic biogeochemical sediment transport model is proposed to simulate the response of plankton dynamics in the Hooghly estuary to freshwater discharge under the presence and absence of tide, and in-depth understanding the significant processes involved in estuarine biogeochemistry based on Regional Ocean Modeling System (ROMS). Riverine-estuarine circulations are used to evaluate the tidal consequence on wavering of biogeochemical properties in the Hooghly estuary. Therefore, three numerical experiments are performed: 1) model run with tidal forcing, river discharge, and applied biogeochemical and sediment properties along with coastal current; 2) model run with tidal forcing along with coastal current plus applied biogeochemical and sediment properties; and 3) model run with river discharge along with coastal current plus applied biogeochemical and sediment properties to determine the chief role of this physical parameters on the transport of bloom in a well-mixed estuary using this coupled model for the first time in Hooghly estuary. The model divulges its capability in imitating observed temporal variability in tidal oscillation representing skill coefficients more than 0.80. The satellite remotely sensed Ocean Color Monitor Data is assimilated using an SOR algorithm to incorporate in the model as the initial field for chlorophyll-a concentration (chla) to retrieve the productivity of the estuary. Productivity is found maximum in the area of soaring suspended sediment implying maximum bottom stress contributed by tidal currents along with coastal currents evident from the realistic case. The RMSE calculated is less than 0.6, which implies that the model can perform reasonably well.