Bioindicator for environmental water quality based on saprobic and diversity indices of planktonic microalgae: a study case at Rawapening lake, Semarang district, Central Java, Indonesia

Abstract

Over the last twenty years, the aquatic environment of Rawapening Lake has been negatively impacted by increasing rates of sedimentation and rising levels of soluble organic materials. The uncontrolled growth rate of hyacinth and other aquatic plants, and the rapidly increased implementation of traditional fish cages are believed to be the main contributing factors, resulting in degraded water quality. Dynamic structure of phytoplankton can be used as a bioindicator. This study is aimed at understanding the phytoplankton community in Rawapening Lake and assessing the water quality based on saprobic and diversity indices. A purposive random sampling method was used to determine four sampling locations. The data were analyzed with the saprobic index, Shanon-Wiener diversity index, and domination index. The result of the study shows that a substantial amount of phytoplankton were dominated by the genus Melosira sp., Aulacoseria granulosa, Oscillatoria sp., and Synedra sp., with low to moderate diversity index values. The quality of the Rawapening Lake water environment based on the saprobic index value was categorized as β meso-Oligosaprobic, indicating very mild to light pollution.