A partnership for sustainable lake environment: collaborative monitoring and research on Laguna de Bay, Philippines, for management of resource use and ecosystem conservation

摘要

Laguna de Bay is the second largest inland waterbody in South-east Asia. Considering its large size, its competing and conflicting water resource users, and increasing threats to its ecological integrity, coherent and participative relationship between and among its stakeholders is crucial for its sustainable management. This study discusses the foundation and framework, and the research results, of an ongoing joint monitoring and research collaboration between an academic institution and a government agency directed to the Laguna de Bay environment. Spatial and temporal monitoring of climatic, hydrodynamic and water quality lake variables were carried out collaboratively through field surveys and laboratory analyses. The lake's temporal and spatial dynamics under changing atmospheric conditions were investigated through field monitoring efforts, coupled with three-dimensional hydrodynamic and water quality modelling. Contrary to common perception, these study results indicated significant vertical and diurnal variations in lake variables, in spite of a shallow average water depth of 2.5 m. Intense atmospheric heating («800 W m~2), accentuated by the lake's high turbidity (16-32 FTU), generated density differences along the vertical axis and caused stratification. Higher biological activity, with significantly correlated pH, dissolved oxygen and chlorophyll-a variations during the dry season, is strongly related to the stable solar irradiance, reduced lake water volume and inflow of nutrient-rich seawater from Manila Bay and Metro Manila sewage. The observed bottom hypoxic conditions (2-4 mg L~(-1)), concurrent with the absence of thermal overturn, are suggestive of the importance of diel wind-induced mixing and attest to the eutrophic condition of the lake. Numerical modelling analysis indicated that lake water quality was significantly affected by aquaculture operations and polluted seawater intrusions. Scenario simulations on bathymetric evolution demonstrated morphological changes that contributed to the eutrophic vulnerability of Laguna de Bay, in addition to anthropogenic-based stressors. Given the natural inclination of tropical lakes to eutrophic conditions, actions across boundary, resource and responsibility sharing, and expansion of intellectual horizon through partnership, are vital for the rational and systematic resolution of lake water resource allocations and ecological preservation.