Phytoplanton of Rawa Pening Lake and Gajahmungkur Revervoir of Central Java

Lake Rawa Pening and Gajahmungkur Reservoir represent two different types of inland water system. The first lake is a shallow semi natural lake with the maximum depth of 2.4 m, meanwhile the second lake represents a manmade lake with the maximum depth of 136 m. Like most inland water ecosystems in Indonesia, the lakes face eutrophication problems indicated by blooming of aquatic macrophytes and phytoplankton. The aim of the study is to describe the composition and abundance of phytoplankton in these two lakes as these parameters may reflect the discrepancies of the morphological condition between the lakes. Sample of phytoplankton was collected on March 2012 and thereafter was analyzed by using Modified Lackey Drop Microtransect. As complementary data, some environmental factors of the lakes were also observed. The results showed that diatoms (Chrysophyta) dominated Lake Rawa Pening; on the other hand, blue green algae (Cyanophyta) placed the position in Reservoir Gajah Mungkur. The dominant species occured in the lakes were Melosira italica for Lake Rawa Pening and Limnotrix sp for the other lake. The average abundance of phytoplankton cells in those lakes were 161,290 cell/L and 212,184 cell/L respectively. The number of identified species in Lake Rawa Pening was more that in Gajahmungkur. Meanwhile, the calculation of TN: TP ratio indicated that nitrogen acted as limiting factor for phytoplankton growth in Lake Rawa Pening and phosporous was the agent for Lake Gajahmungkur.