Zooplankter - water fleas Daphnia magna - respond to phosphorus enrichment in pond water

Abstract

Phosphorus has been pointed out as one of the limiting factors that limit freshwater bio productivity, so controlling this element at an optimum level is crucial to enhance pond water bio productivity. This study evaluates the impact of phosphorus enrichment in the pond (small lake) water on the zooplankton population development. The clear pond water of Situ Cibuntu, located in Cibinong – West Java, was fertilized up to the level of eutrophic water of Limboto Lake, in Gorontalo Province, by addition of adequate level of phosphorus in aquaria placed in a greenhouse. The phytoplankton, as well as the zooplankton, was monitored twice a week for two weeks. Phytoplankton development was represented by the chlorophyll content in the water, while the water flea Daphnia magna was introduced to observe water carrying capacity in supporting zooplankton life. The result shows that the growth rate of total phytoplankton significantly increased in response to phosphorus enrichment, indicating phosphorus limitation, followed by the development of the daphnid population. The chlorophyll-a reached the maximum concentration of 15.22 mg/m3 on day-7 of the experiment, while the maximum daphnid population of 1,272 individuals was enhanced on day-10. This experiment emphasized the importance of phosphorus control in managing lake water bio productivity.