Role of ecosystem components in Cd removal process of aquatic ecosystem

An experiment was conducted using 15 glass aquariums to ascertain the pathways of removal of cadmium through numerical and compositional manipulation of ecosystem components and their role in Cd removal in different aquatic ecosystems. Each aquarium was provided with surface sediment @ 2 kg, filled with 15 L tap water and randomly distributed into five treatments having three replicates in each. Cadmium chloride (CdCl2) of analytical grade was added @ 2 mg/L to the water of each aquarium and mixed gently. Except for the first one, the other four systems received unio (Lamellidens marginalis, 55 ± 2.5 g) @ 6 pieces/aquarium. Tilapia (Oreochromis mossambicus, 35 ± 3 g) was introduced @ 6 fish/aquarium in the third and fifth systems, whereas pistia (Pistia stratiotes) was introduced @ 50 g/aquarium in the fourth and fifth systems for a 28-day observation period. The samples of water, sediment, unio, fish and pistia were collected from different systems at 7-day intervals and analyzed. Results revealed that mean substantial reduction of Cd in water varied between 1.820 and 1.994 mg/L in different simulated ecosystems. Ecosystem efficiency of Cd removal varied in the different ecosystems and showed highest (11%) value in the ecosystem carrying five components, which suggested a cumulative effect of increasing number of components employed in different simulated aquatic ecosystems significantly facilitated the reduction of the level of Cd concentration in water column. Pistia exerted (12.88–547.5 times) higher rate of Cd accumulation over the other components employed in five simulated ecosystems of various component structures. Therefore, in the present study, it may be concluded that ecosystems carrying five components exhibited the best performance for optimum minimization of Cd removal from water column. It can also be concluded that ecosystem components showed a variable performance and pistia was the efficient component from the perspective of Cd removal.