Pollution Indicators based on Phytoplankton Communities in Lake Maninjau

Maninjau Lake fulfills economic, social, and ecological functions for the surrounding community and environment. However, human activities threaten the lake environment's quality and quantity, exerting additional pressure on the lake's sustainability. Phytoplankton can be used as a bioindicator for assessing environmental changes and determining the pressures on a lake's ecosystem. This study aimed to identify phytoplankton species using biological and saprobic indexes to determine pollution levels. Phytoplankton and water samples were collected 50 cm below the water surface from 5 locations in September 2022. According to the study results, Maninjau Lake had 54 phytoplankton species belonging to 26 families. The phytoplankton consists of class Bacillariophyceae, Cyanophyceae, Chlorophyceae, Zygnematophyceae, Trebouxiophyceae, Coscinodiscophyceae and Dinophyceae. The diversity index (H'), between 2.22 to 2.98, indicates moderate diversity. The evenness index (e) ranges between 0.44 and 0.56, indicating that the community is stable. Meanwhile, the dominance index (D) ranges from 0.082 to 0.156, indicating low or no species dominance. The Phytoplankton community at the Maninjau Lake station had a saprobic index ranging from -0.41 to +0.23, indicating medium pollution. Several physical, chemical, and seasonal factors could influence the phytoplankton community. The saprobic index indicates that the degree of pollution in Maninjau Lake is moderate, resulting in a moderate presence of organic and inorganic substances within the lake's waters.