Effects of Water Quality and Phytoplankton Structure and Dynamics on Fish Kill Events in Lake Buhi, Philippines

Author(s): Girlie Rueda
Email (s): ruedagirlie31@gmail.com
Institution or organization of origin: DENR-Ecosystems Research and Development Bureau (ERDB)
Country: Philippines


Fish kills are a serious global issue that have significant influence on the environment and the public. It could be an indicator of environmental stress, deteriorating aquatic ecosystems and water quality problems. Lake Buhi in the Bicol region, has been experiencing notable fish kill events since 2010 that caused huge economic loss which makes it as an ideal site for this study. By employing science-based methodologies, the plankton species present, their abundance and diversity in relation with the physico-chemical properties of Lake Buhi were investigated. The plankton species most vulnerable to changes in water quality in the advent and aftermath of fish kill were also determined. Results revealed that temperature, pH, nitrates and phosphates were within the standards for Class B waters while dissolved oxygen (DO), and ammonia failed to meet water quality standards. During the fish kill event, only DO (4.26 mg/L) was below the minimum acceptable value. In terms of water quality index (WQI), the overall state of Lake Buhi was considered “Very Poor”. Very low diversity scores were observed a month before and even during fish kill as phytoplankton community was overly dominated by a single genus of Aulacoseira, a diatom. The extremely low SDI scores (H’=<1) indicated heavy pollution which is further substantiated by high PPI values (11-16) a month before fish kill event, demonstrating a moderate to probable high organic pollution. Phytoplankton are , therefore, considered suitable indicators of the long-term health of the lake ecosystem and can be used in assessing its status.

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