Primary productivity, chlorophyll, phytoplankton and the development to eutrophic state of Taal Lake, southern Luzon, Philippines

Physico-chemical properties and biological components such as primary productivity, chlorophyll-a and phytoplankton were measured from January to October of 2008. This study aimed to determine the present trophic state and to provide information needed by policy makers for the management, conservation and sustainable use of Taal Lake. Primary productivity was measured using the Light and Dark Bottle Method, chlorophyll-a by fluorescence using SD204 Instrument, phytoplankton using Haemacytometer Method, and identification keys. All the parameters except pH have no significant differences on the type (cage or open water areas). However, all the parameters except net primary productivity and chlorophyll had significant differences between cages and open water areas. There are significant differences with respect to water temperature, water transparency, and dissolved oxygen among stations and months. Dissolved oxygen, nitrate and net primary productivity in the cages and open water areas displayed interaction effects on the months. Moreover, all parameters except Gross Primary Productivity (GPP) and chlorophyll-a in the stations had significant interaction effects also on the months. Nitrate is positively correlated with primary productivity, dissolved oxygen and pH, while total phosphorus has direct association with chlorophyll. Based on transparency readings, Taal Lake is mesotrophic. Both nitrates and total phosphorus exceeded the prescription of USEPA 1976a and UNEP-IETC-ILEC 2001 of 0.30 mg/L and 84.4 mg/L, respectively. On the other hand, chlorophyll-a peak concentration obtained in the study was fivefolds higher than the standard set by USEPA (1974) as cited by Novotny and Olem (1994) and UNEP-IETC-ILEC (2001). The cyanobacterial dominance and high chlorophyll, reduced transparency, off-flavor, and odor problems are symptoms of eutrophication, indicating that Taal Lake has developed into eutrophic status. It is recommended that continuous monitoring of water quality be carried out to determine if there is improvement or conditions remain the same or further deterioration occurs. Likewise, the carrying capacity of the lake and the causes of off-flavor must also be determined.