Laguna Lake in the Philippines is the biggest inland water source for domestic supply, with average depth of 2.5 meters, can significantly support water supply demand in the metropolis. However, the presence of cyanobacteria, known as blue-green algae, is a major threat to the lake water quality which directly affects nearby communities. Aiming to provide information for mitigation strategies to improve the water quality, the objective of this study is to quantitatively assess and monitor the harmful cyanobacteria in the water and sediment. The first ever 2-methylisoborneol (2-MIB) detection was recorded in Laguna Lake in August 2016. Collection of secondary qualitative data for the period 2012-2016 and quantitative detection and analysis of primary data from 2016 were considered for this study. To grab sampling on board, a boat was conducted with Ekman dredge and stainless water sampler for sediments and water column, respectively. Using the real time quantitative polymerase chain reaction, enzyme-linked immunosorbent assay, and gas chromatography, several species of harmful cyanobacteria were detected at various stations among the lake. The assessment of the 2012 data revealed the dominance of microcystis at cell density of 1,181,700 per liter at one of the major stations of the lake. Succeeding results from the 2016 monitored data uncovered abundance of toxigenic cyanobacteria species, high concentration of toxins such as microcystins and cylindrospermopsins, and high number of gene copies that produced taste and odor problems in the water. The cell density of microcystis monitored at the Central Bay area of the lake was 16,000,000 cells/mL while that of cylindrospermopsis was 220 cells/mL at the South Bay side. The abundance of 2-MIB in water column range from 210 to 100,000 copies/mL, while the concentrations range from 5.0 ng/L to 774.7 ng/L. This record suggests high activity of cyanobacterial bloom during the same period. The detection and quantitative analysis of the harmful blue-green algae in the lake provides a clearer picture of its water quality and implications to human health if not addressed properly. Such information may prove crucial in developing remediation strategy, appropriate water treatment system, research direction, as well as developmental cooperation among primary stakeholders within the Philippines. Concerned regulatory agencies can also benefit from the detection technology to implement measures and direct policy enhancement towards sustainable management of the lake.
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