In an effort to increase oxygen levels in Taal Lake, the government will lay out several oxygen pumps around the affected areas in Batangas in order to counter the natural processes that caused the massive fish kill in the province in late May. In an interview with GMA News TV's "Balitanghali" on Monday, Bureau of Fisheries and Aquatic Resources (BFAR) director Asis Perez said some 17 oxygen pumps will be deployed around the lake. According to BFAR data, oxygen levels in the lake remain at a fatal 2.8 parts per million since Saturday, a far cry from the 6 parts per million required to keep fish alive. This, despite the government's efforts to dismantle more than 1,300 illegal fish cages in Batangas to address issues of overcrowding in the area. On Monday, it was reported that new incidents of "unusual" fish behavior have been observed in around four villages in Batangas over the weekend. Batangas Vice Governor Mark Leviste, however, denied speculations that this could eventually lead into another fish kill, saying the number of reported incidents is too low for it to be called such. "Bagaman meron po tayong sightings ng mga isdang nalutang at namatay, ang fishkill ay termino para sa isang malakihan o malawakang pagkamatay ng mga isda," Leviste said in a separate interview with GMA News TVs' "News to Go."
Oxygen depletion Leviste said authorities have already started preparing oxygen aerators for deployment in the area, in hopes of salvaging the remaining fish that are still alive and can eventually be harvested. "Ito po ay para makapagbomba ng oxygen sa mga fish cages para po sa mga isda, at umaasa tayo na maisasalba natin yung mga tila naghihingalo o hindi pangkaraniwan na pagkilos ng mga isda sa mga fish cages sa lawa ng Taal," he explained. Leviste said that according to experts, oxygen depletion in the lake occurred due to the continuous rains in the past week, which changed the temperature of the water in the lake. "They call this an overturn of temperature and oxygen in the waters of Taal Lake, kung kaya't 'yung mga isda ay tila naghahanap ng safer ground for oxygen," he added. In the same interview on "Balitanghali," Asis said the overfeeding of fish inside the cages also compounded the problem. "Medyo mataas ang temperature ng tubig sa baba ng (Bgy.) Sampaloc, dahil nandun yung maraming feeds. Eh naiwan, so pag yun ang umakyat, low oxygen content iyon, 'yon ang palagay naming dahilan kung bakit bumababa ang oxygen content ng lawa," he explained.
Increasing saturation Asis referred to a natural process called water turnover (or upwelling), which causes the bottom part of the lake's water to rise above the surface. The
US State of Virginia Department of Game and Inland Fisheries said heat and relatively calm weather during the summer causes the water in the lake to stratify into layers. "There is a less dense, warm, upper layer that is exposed to the sun and atmospheric oxygen (epilimnion), a very thin layer where temperature and density changes rapidly (metalimnion), and a cold, denser, lower layer that receives little sunlight and does not mix with the upper layers (hypolimnion)," it explained. When a sudden torrent of cold rain causes the water to "turn over" or suddenly mix—similar to what happened in the past week—the bottom layer of the water with low dissolved oxygen can reduce oxygen level in the lake "enough to cause a fish kill," it added. According to the
Illinois Environmental Protection Agency's Lake Notes, artificial circulation (through the use of oxygen aerators and destratifiers) can increase a lake's oxygen level "by forcefully circulating the water to expose more of it into the atmosphere." Aerators are placed on the bottom of the lake and push air bubbles up the water surface, causing the lower layer of water to rise and mix with the surface water layer. "[If] enough air is injected, this process continues and the transition zone between the upper and lower layer of water is broken down," it explained, adding that this will eventually cause the entire lake to be of nearly equal temperature with oxygen distributed throughout.
Stricter implementation Aside from aerating the water, Asis said a stricter implementation of policies governing fish cages will ensure that a similar spell of fish kills will not happen again in the future. "Meron pong tinatawag tayo na stocking density, kung saan mula po 20-50 piraso lang bawat cubic meter po ang dapat laman po ng mga fish cages," he said. He also reiterated the need to cut down the number of fish cages in the lake, which can only accommodate about 6,000 cages. "Pati po yung sukat halimbawa ng fish cage, yan po ay may sukat na 10 x 10 x 6, yan po ay hindi sinusunod, kaya nga po nagbabaklas na rin tay (ng mga lumalabag diyan)," he added.
— JM Tuazon/RSJ, GMA News 
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