Stratigrafi diatom Danau Rawapening: kajian paleolimnologi sebagai landasan pengelolaan danau

The potential use of diatom as bioindicator of water quality had been studied in many countries. Recently, many researches focus on using diatom for paleolimnological analysis, but still limited in Indonesia. Rawapening Lake is one out of 15 Indonesian lakes that stated as Priority Lake 2010-2014 for conservation followed Bali Agreement 2009. This research was conducted in order to determine environmental changes of the lake based on the stratigraphical record from Rawapening Lake sediment. Sediment samples had been taken from 4 sites in Rawapening Lake using hand auger. Diatoms analysis were analyzed every 0.5 cm slice sediment sample by 3 processes: the extraction to separate the diatoms from sediment, by 2 treatments of 10% chloride acid followed by 10% peroxide; the preparation to mount residual diatom on slide; and identification-enumeration of diatom until the minimal number of 300 valves found. Stratigraphic diagram shows the changes on diatom assemblages in different layers. Rawapening Lake had in the eutrophic condition with relatively high organic content, indicated by a high assemblage of Synedra ulna almost in all layers. Aulacoseira granulata dominance at upper layer, indicates hypereutrophic condition with pH more than 9. The dominance of Aulacoseira ambigua, A. distans, A. granulata and Discostella stelligera in the upper layers in all sites, Eunotioid and small diatoms in the midle and lower layers, particularly in Dk site indicate that pH tend to increase over time. This is supported by by transfer function with Weighted Averaging on diatom and pH.