Nutrients are substances that are used by living organisms in the growth and survival of organisms. On the basis of this background, the aim of this study was to assess the concentration of nutrients (macro and micronutrients) and chlorophyll in the Menjer lake and to examine the relationship between nutrient concentration and algal biomass to identify the determinants of algal development in tropical lakes (Menjer Lake Wonosobo, Indonesia). The research was conducted using a survey method at Menjer Lake Wonosobo. Observations and sampling were carried out 3 times with intervals of 1 month at 7 locations in the photic zone. The concentrations of macronutrients and micronutrients in the Menjer Lake were spatially even in all locations and the temporally slightly increased concentrations were relatively the same during the measurement period. The Cu, NO2, Si, and Na macronutrients are the determining factors for algal blooming in Menjer Lake Wonosobo. The effect of Cu, NO2 and Si concentrations was inversely related to the algal abundance, while the Ca, Na and Mo concentrations were in line with the abundance of algae.
The use of phytoplankton as an indicator of water pollution is a promising tool for assessment of water quality. The purpose of this study was to determine whether diversity indices, including the species richness and diversity of phyto-plankton, could be used for reliable assessment of water quality in the Wadaslintang Reservoir in Indonesia. Surveys were conducted monthly at eight sites, from July 2019 to October 2019. Phytoplankton was collected during the day at 10:00 until approximately 15:00 in the euphotic zone. The parameters investigated were species richness and the abundance of phytoplankton, as well as water quality parameters listed in Government Regulation Number 82 of 2001. The level of pollution was represented biologically by the Shannon–Wiener diversity index and physicochemically by the STORET (storage and retrieval of water quality data) index. Moreover, the two indices were compared to determine whether a particular diversity index was more effective for assessment of this reservoir. The results showed that during the dry season, 22 taxa of phytoplankton were present, belonging to Cyanophyta, Chlorophyta, Chrysophyta, and Euglenophyta. During the wet season, 29 taxa were found, belonging to Cyanophyta, Chlorophyta, and Chrysophyta. Based on the Shannon-Wiener index and STORET index, water quality was better during the wet season than during the dry season. The results of water quality assessment using both indices were consistent, but the diversity index was a more sensitive indicator of pollution levels. Therefore, the Shannon–Wiener index is a useful tool for assessment of water quality in the Wadaslintang Reservoir.
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