Phytoplankton and Chlorophyll-a: Distribution, Abundance, and Trophic State Index (TSI) in the Transitional Season in Limboto Lake

Limboto Lake is one of the strategic lakes in Gorontalo Province but has experienced damage to the ecosystem, which has resulted in decreased water productivity. The existence of phytoplankton is fundamental because it is the primary producer in aquatic systems including lakes. In the tropic level system, the presence of phytoplankton is the primary food source for fish larvae and other animal organisms. This study aimed to analyze the distribution of phytoplankton abundance, chlorophyll-a distribution and the relationship between nutrients and phytoplankton abundance. This research was conducted on Limboto Lake, Gorontalo Province, Indonesia. The variables analyzed in this study were the analysis of the abundance of phytoplankton. The results showed that the analysis of the abundance of phytoplankton in water conditions had a phytoplankton diversity index (H') in the waters of limboto Lake, which was in the range of values ​​of 0.515-1.611, indicating that the lake was in the categories of moderately polluted and heavily polluted. Phytoplankton that contributes much chlorophyll-a is class Cyanophyceae, with a total distribution of 238900 Cells/L. The research results showed that Limboto Lake is classified as very productive with a tropical index status; namely, hyper eutropic.