By Saul Pa-a/PNA
TALISAY, Batangas — The Bureau of Fisheries and Aquatic Resources (BFAR) regional office in Calabarzon reported on Tuesday that the fish kill phenomenon in Taal Lake is due to an upwelling of sulfur triggered by the strong northeastern winds that accompany an extreme temperature drop in the volcanic lake.
The “sulfur upwelling” has been monitored over the weekend in the volcanic waters off Barangays Santa Maria, Buco, Caloocan and Sampaloc in this lakeshore town. It is described as the release of a lethal gas called hydrogren sulfide that takes place when the “Amihan” or northeastern wind disturbs the sediments in the lake bottom.
Nenita S. Kawit, officer-in-charge of BFAR-Batangas Inland Fisheries Technology Outreach Station (BFAR–BIFTOS) tasked to monitor the water quality of the Taal Lake, explained that sulfur upwelling is a natural phenomenon that occurs annually, usually between the months of November and February.
She reported that their monitoring station has detected an increase in the hydrogen sulfide content in the lake waters. This chemical process gives off an odor similar to rotten egg and changes the color of the water to aqua-marine or bluish-green, Kawit added.
Kawit said latest results from their water quality monitoring in Taal Lake revealed hydrogen sulfide level at 0.03 mg/L – 0.55 mg/L in the areas potentially affected by fish kills.
She also explained that they have monitored a low level of dissolved oxygen at 0.07 mg/L – 0.46 mg/L at temperatures ranging from 26.6 – 26.7°C, which could trigger the fish kill for lack of oxygen in the fish cages.
Based on laboratory test of water samples, the depletion of dissolved oxygen in the water due to cold temperature has dipped way below the normal level at 6 mg/l and above.
“Ang pagbabagong ito ng temperatura ng tubig ay nagsasanhi ng pagakakaroon ng over turn, kung saan ang tubig mula sa ilalim na may kasamang sulfur ay siyang pumaba-ibabaw (the change in water temperature results in over turn where the water from the bottom that contains sulfur surfaces),” Kawit said.
This sulfur upwelling, according to Kawit, decreases the level of dissolved oxygen in the water which could trigger the poisoning of the lake’s freshwater fishes.
