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In this study, a three-dimensional (3D) hydrodynamic model was developed to investigate the Watercirculation characteristics of a shallow tropical lake environment (Laguna Lake, Philippines) undervarying wind stress, watershed river discharge, and sea interaction (Manila Bay, Philippines) toelucidate hydrodynamic implications to eutrophic vulnerability. The analyses were based on fieldobservations and numerical simulations covering longterm periods (dry and wet season) andintensive field measurements. The results demonstrated different circulation pattems and verticalcurrent regimes in time and space that accentuated a thermally stratified lake environment in spiteof a shallow water depth (2.5 meter average). In the wet season, current movement is generallytoward Pasig River, the lake’s only outlet, with embayment water mass moving in the clockwisedirection. The dry season lake flow pattern was characterized by counter-clockwise gyrecirculations, Pasig River backflow, and salinity intrusion. Wind forces showed strong influence onlake hydrodynamics due to the complex surrounding topography, steep land-ake thermaldifference, regular passage of tropical storms and typhoons, and shifts in the monsoon winddirection. The resulting mixed layer hydrodynamics revealed important implications to theplanktonic movement, nutrient recycling, and primary production of the lake. Long termcontinuous observations and numerical analyses also demonstrated the intrusion of seawater toLaguna Lake that potentially adds to its eutrophic vulnerability with the associated entry of nutrientand microorganism-rich polluted waters from Metro Manila. |
