Phytoplankton Community Structure and Other Related Eutrophication Indications in Lake Batur, Bali-Indonesia

Lake Batur is the largest lake in Bali and a volcanic crater lake. Local people use it to support their activities such as inland water fisheries, agriculture, recreation, etc. In order to promote its conservation and utilization management, a track record of this lake condition is necessary. This research objectives were to reveal spatial distributions of phytoplankton abundance, Total Nitrogen (TN), Total Phosphorous (TP), Suspended Solid (SS), Chlorophyll-a (Chl-a) and water conductivity respectively as eutrophication. Observation was conducted in April 2005, August 2005, October 2005, May 2006 and February 2007 at five stations. Water samples were taken at different depth and parameters were analyzed using standard methods. There were three major groups of phytoplankton, they were Chrysophyta (9 species), Chlorophyta (5 species) and Cyanophyta (2 species) respectively, with the dominant species were Synedra ulna, Navicula pupula, Cosmarium contractum and Anabaena sp. Decreasing tendency of phytoplankton abundance was observed at the end of observation, except Stations 4 and 5, the abundance was more fluctuated. Vertically, the highest abundance (107 to 2,7.107 ind/L) was found at Station 5 with the dominant Synedra ulna and Navicula. Station 5 had frequently the highest level of TN (0.430 mg/L), TP (0.044 mg/L), SS (4.662 mg/L), Chl-a (93.111 mg/m3) and conductivity (2.476 μS/cm), while the lowest values were observed at the Station 3. SS, Chl-a, and conductivity tend to be more deposited in the deepest part of the lake. During observation, conductivity and SS tend to show the increasing pattern, while Chl-a and phytoplankton abundance showed the opposite phenomenon. It seems that this lake was more loaded with mineral particles than organic matters. Oseanologi dan Limnologi di Indonesia. Vol. 39, No. 2. Hal. 179-197 ISSN 0125-9830