Phases of anthropogenic activities since the mid-20th century from the sediment geochemistry of Laguna de Bai (Philippines)

Metro Manila, the Philippines’ capital region, industrialized relatively recently in the mid-20th century following a long period of colonial occupation and pre-colonial settlement. Laguna de Bai (LdB) flanks the coasts of Metro Manila, and its sediments record the onset and evolution of industrialization in the country. Understanding the evolution of anthropogenic impact on LdB will direct its long-term management policies better. Major/trace element and grain size records in a sediment core from Laguna de Bai’s Western Lobe basin were examined for markers of this industrialization, and two phases of anthropogenic impact were identified: Land Reorganization and Increased Pollution. We found that the start of Phase 1 is synchronous with increased anthropogenic impact in other Southeast Asian and global records and provides a Southeast Asian perspective to the timing and records of anthropogenic activities in the geologic record. In Phase 1, Land Reorganization (CE 1953–1967) is indicated by major terrigenous elements Al, Ti, and Fe, which rapidly increased to 1.36 × Freshwater Baseline levels likely due to increased sediment generation associated with World War II recovery-, population-, and urbanization-driven changes in land use. This increased sedimentation shoaled the basin, ventilating its bottom waters. This is seen in redox-sensitive elements as an enrichment in Mn and a depletion of Mo relative to U. The additional sediment generated increased water column turbidity and reduced primary production. These changes were maintained in Phase 2, Increased Pollution (CE 1967–1998), with increased Pb pollution possibly from petrol use.