Diatom index of Galela Lake, Halmahera, Indonesia in relation to human activities

Diatoms, silicious microalgae, have been used successfully as bioindicators of water quality assessment in aquatic ecosystems. Diatoms have a degree of tolerance to the water quality and some diatoms are a good indicator for several water quality variables. Diatom indices have been developed to assess river water quality, mostly in Europe. This study aims to apply diatom indices developed in Europe for the tropical lake of Galela adjacent to residential areas influenced by human activities. Galela Lake is one of the biggest lakes in Halmahera Utara, Indonesia with its main functions being domestic water supply, irrigation, fisheries, and tourism. Human activities have impacted the area around the lake. The 90-cm and 85-cm long sediment cores were collected using a piston corer from Site 1 and 2, respectively. Sediment samples were sliced every 5 cm, separated from sediment by adding HCl and H 2 O 2 . The diatom valves were identified under a microscope with 1,000 × magnification. The water quality status of each layer was inferred with diatom indices performed using OMNIDIA software version 6.0. Forty-nine and 63 diatoms species were identified from Site 1 and Site 2, respectively. The number of species and diversity of diatoms was higher in the lower layers than those in the upper layers. The preserved diatom assemblages reflect past physical and chemical water quality. Generic Diatom Index and Specific Pollution Sensitivity Index provided the best evidence for change in Galela Lake—they integrated 70–100% of the diatom taxa from the sediment core samples.