Environmental Condition and Trophic Status of Lake Rawa Pening in Central Java

Abstract

Due to continuous problems of eutrophication, Lake Rawa Pening has been included into the 15 priority lakes in Indonesia to be saved from damage. This study aimed to clarify the current environmental conditions and trophic status of Lake Rawa Pening as a basis to control the eutrophication. Sediment loads, water quality, and nutrient concentrations were measured in the tributaries of lake inflow, within the lake, and at the point of lake outflow. The study was conducted in May, June, July, and August 2013. Water transparency, temperature, pH, turbidity, conductivity, and dissolved oxygen were measured in situ. Nitrogen, nitrate, total phosphorus, orthophosphate, TSS, and chlorophyll-a parameters were analyzed using standard method procedures. The Trophic State Index was used to determine the trophic state level. Hydroclimatological conditions showed that seasonally, fluctuation of water volume and discharge of lake followed the pattern of rainfall fluctuation. The sediment loads and nutrient concentration in the tributary inflow were more abundant than those in the lake  and  lake outflow. The results indicated that Lake Rawa Pening acts as sediment and nutrient sinks. Spatially and temporally, Lake Rawa Pening showed high variation of water quality. High concentration of nutrients observed during the wet and dry seasons indicated that the nutrients in the lake originated not only from external but also from internal sources. The overall results show that Lake Rawa Pening is a eutrophic lake, in which phosphorus seems to play a major role in causing eutrophication and massive growth of water hyacinth.