Phytoplankton are primary producers in aquatic ecosystems, their abundance is determined by environmental changes, so phytoplankton are often used as bioindicators of waters. The aim of this research was to determine the diversity and abundance of phytoplankton in Menjer Lake, to measure the environmental factors that determine the diversity and abundance of phytoplankton, and to determine the environmental factors that most influence the diversity and abundance of phytoplankton in Menjer Lake. This research uses a survey method in 5 areas (inlet, middle of the lake, aquaculture using floating net cage, tourism, and outlet). The parameters observed were the diversity and abundance of phytoplankton as well as the concentration of water quality parameters that determine the presence of phytoplankton (temperature, light penetration, pH, DO, TSS, TDS, PO4 and NO3). To determine the environmental factors that most influence the diversity and abundance of phytoplankton were analyzed using the principal component analyses method with Past 4.10 software. The community structure of phytoplankton in Menjer Lake was dominated by Bacillariophyta (83%). The factors determining the development of phytoplankton in Menjer Lake are influenced most by light penetration and PO4 concentration. The input of PO4 concentration from the water catchment area must be controlled to prevent phytoplankton blooming in Menjer Lake.
Human activities may cause degradation of water quality. For monitoring purpose, it is necessary to know the level of pollution that occurs in water in order to sustain the function of the aquatic ecosystem. The purpose of this study was to determine the level of water pollution of Menjer Wonosobo Lake based on the physical, chemical, and biological parameters to evaluate the best function of the water to support the human activities. The study was conducted for three months (July to September 2020). Water sampling was carried out at seven stations; then, the measurement results were compared with the water quality standards based on Government Regulation No. 22 of 2021. Determination of water quality was carried out using the STORET method. The results showed that there were 7 parameters that exceeded the water quality standards, namely TSS, BOD, COD, DO, N, P and Coliform. The status of water quality was at a moderately polluted level and only functions for the needs of category 3, i.e. for freshwater fish cultivation, for irrigating plants, and or other purposes. Therefore, it was necessary to manage Menjer Lake to improve its water quality.
Phytoplankton blooms are a problem that often occurs in estuarine and coastal ecosystems. The changes in phytoplankton community species composition, diversity, biomass, and distribution were caused by the conditions of seasonal and temporal variation. The immediate location of the estuary ecosystem is near cities, where rapid economic growth and human activity tends to increase the pressure on the environment. The purposes of this research were to evaluate the seasonal and temporal variation and to determine the key species of phytoplankton in the eastern part of Segara Anakan which can cause a bloom based on season. The samples of phytoplankton were taken from 6 sites during April – September 2019 when the highest tide occurred during the dry and rainy seasons. The community structure were performed using primer software Ver 5 to find the similarity and / or differences of the phytoplankton community structure based on season. Simper analysis was used to determine key species (phytoplankton species) based on season and location. The community structure of phytoplankton in Segara chicks were composed by 5 divisions. During the dry season, Bacillariophyta was dominant (82%), whereas during the rainy season, Bacillariophyta (43%) and Chlorophyta (31%) and Cyanophyta (25%) were the dominant species. This study shows that the phytoplankton community structure in this estuary presents the environment conditions during the rainy season that increase the abundance of phytoplankton, especially of the species which may thrive into blooms. The most important species was Oscillatoria limosa that had the highest percentage of contribution.
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