Lake Ulu Mahmud lake is located at coordinates of ± 0?55’44”, 102?46’11”, 90?. Administratively, it is in Meranti Regency, Tebing Tinggi Island, Riau. The lake has unique environmental conditions because it is in the middle of a forest and is natural, indicating by relatively large plants growing and protected tropical pitcher plant (Nepenthes). This study aimed to determine the biodiversity and abundance of plankton in Lake Ulu Mahmud. This research sampled nine sampling points with three replicates. The results showed several types of planktons, both phytoplankton (Chlorophyta, Bacillariophyta, Cyanophyta) and zooplankton (Cladocera, Copepoda). The lake's water was probably influenced by fresh and marine waters although it was not directly visible (salinity: 0). This condition was demonstrated by abrupt changes in water temperatures. The average acidity level there was quite low (pH = 5).

Diah Etika Maharatih Setiarina

Peatland, Plankton, Tebing Tinggi Island, Ulumahmud Lake