The ecological status of Lake Laguna de Bay, Philippines

Abstract

This article assesses the ecological status of Laguna de Bay using available published and unpublished information. The declining fishery productivity of the lake is the most glaring evidence of its stressed ecological state. This loss stems from numerous deleterious factors operating throughout the lake and its drainage basin. Phytoplankton community composition has drastically changed over the years and algal biomass has diminished in the presence of ample supplies of nitrogen and phosphorus. Light limitation due to high siltation rates in the perennially turbid lake whose Secchi depth is only 5 cm might be the primary limitation to photosynthesis. The problem of siltation in the lake is the result of deforestation in the watershed that heightened soil erosion rates. Trophic relationships are inadequately examined in Laguna de Bay, the biggest lake in Southeast Asia. High biological oxygen demand and high heavy metal levels in the lake water, sediments, and biota are evidence of excessive pollution. Heavy metal levels in fish are similar to those found in fish from a smaller nearby lake receiving mine tailings. Collectively, these observations show that Laguna de Bay is an extremely stressed ecosystem needing rehabilitation. The article concludes with a set of recommendations on how to deal with the problem of impairment of lake ecology, namely, the improvement of the hydrological regime, control of the internal loading of fertilizing nutrients, toxic and hazardous chemicals, control of the sources of pollution, a systematic implementation of closed and open seasons to fishing, the establishment of a system for the assessment and evaluation of environmental perturbations, and revitalization and support for local community efforts to safeguard the ecology of the lake.