The Variability of Surface Chlorophyll-a in Lake Rawa Pening within Five-Month Observations

Lake Rawa Pening is a natural lake in the Semarang Regency of Central Java Province, Indonesia, and its existence is pivotal to the surrounding communities as it provides ecological, economic, and social benefits. The ecosystem health of Rawa Pening can be represented by chlorophyll-a concentration because it indicates phytoplankton biomass, nutrient availability, and fish resources. Hence, the present study aims to disentangle the monthly variability of surface chlorophyll-a in Rawa Pening Lake by analyzing water samples that were collected once a month from nine stations within five-month observations (September 2020 to January 2021). The samples were analyzed using spectrophotometric method. Results showed that the highest surface chlorophyll-a concentration (23.33 mg/m3) took place in December, while the lowest concentration (12.64 mg/m3) occurred in October. The monthly variability of surface chlorophyll-a was likely controlled by variation of rainfall, with the highest (18.72 mm) and the lowest (12.33 mm) rainfall happened in December and October, respectively. The present study also indicates the anthropogenic activities such as agricultural activities, floating food stands, aquaculture, and tourist boats may contribute to surface chlorophyll-a variability in Rawa Pening Lake.