Effects of Daphnia magna on the Concentration and Size Distribution of Suspended Particles

Directly or indirectly affecting the biogeochemical process of natural waters, suspended particles are an important component of aquatic ecosystems. The filter feeder Daphnia magna plays an impact on suspended particles, thus changing the habitat. However, habitat changes in the environment would be counterproductive to affect the growth and reproduction of Daphnia magna.This study aimed at determining the effects of Daphnia magna on the concentration and size distribution of suspended particles. Kaolinite, montmorillonite and natural particles were used in this experiment as three representative types of particles, and were called “KN”, “MN”, “NP” for short, respectively. As for NP, the undersize particles with diameters below 150 µm, 96 µm, and 75µm, named “<150µm” 、“<96µm” and “<75µm” samples, respectively, were used to study the effects of Daphnia magna on the concentration of suspended particles and discuss the selectivity through particle size. The results showed that Daphnia magna reduced the concentration of the particles by ingestion, especially in the more active period (the first three hours of the test time), which means that Daphnia magna shows positive significance in the reuse of wastewater. Although Daphnia magna is a kind of nonselective filter feeder, it is selective by particle size as for the same substance. Fine particles (particle size < 8µm) were easilier obtained by Daphnia magna, thus showed higher bioavailability. It was also concluded that the effects of Daphnia magna on suspended particles size distribution may be also related to the digestive process of particles, depending on the properties of suspended particles such as the composition or organic matter content and so on.