"In this study, a three-dimensional (3D) hydrodynamic model was developed to investigate the Water
circulation characteristics of a shallow tropical lake environment (Laguna Lake, Philippines) under
varying wind stress, watershed river discharge, and sea interaction (Manila Bay, Philippines) to
elucidate hydrodynamic implications to eutrophic vulnerability. The analyses were based on field
observations and numerical simulations covering longterm periods (dry and wet season) and
intensive field measurements. The results demonstrated different circulation pattems and vertical
current regimes in time and space that accentuated a thermally stratified lake environment in spite
of a shallow water depth (2.5 meter average). In the wet season, current movement is generally
toward Pasig River, the lake’s only outlet, with embayment water mass moving in the clockwise
direction. The dry season lake flow pattern was characterized by counter-clockwise gyre
circulations, Pasig River backflow, and salinity intrusion. Wind forces showed strong influence on
lake hydrodynamics due to the complex surrounding topography, steep land-ake thermal
difference, regular passage of tropical storms and typhoons, and shifts in the monsoon wind
direction. The resulting mixed layer hydrodynamics revealed important implications to the
planktonic movement, nutrient recycling, and primary production of the lake. Long term
continuous observations and numerical analyses also demonstrated the intrusion of seawater to
Laguna Lake that potentially adds to its eutrophic vulnerability with the associated entry of nutrient
and microorganism-rich polluted waters from Metro Manila."
