Influence of Physical Raking and Biological Process in the Mud-water Exchange Dynamics of P in Fish Culture Ponds

Experiment was conducted in the laboratory using radioactive ³²P for ascertaining the dynamics and quantifying the exchangeable amount of P between sediment and water phase under the influence of physical raking and biological processes. Collected sediment (100 g) was dispensed in a glass beaker and treated with radioactive ³²P after reaction with CaCO₃. Each beaker filled with 250 ml tap water. Four different treatments: physical raking once (RO), repeated raking (RR), bacteria (Bacillus, 167 X 10² ml^-1) inoculum (BI) and bacteria inoculum (Bacillus, 167 X 10² ml^-1) plus repeated raking (BI + RR) were used in the study. Water samples were collected and tested for specific activity of radioactive ³²P, concentration of orthophosphate and count of heterotrophic bacterial (HB) population. The ³²P value of BI+RR treatment was 20, 25, 37 and 56% higher than BI, RR, RO and control, respectively. Therefore, it can be concluded that synergistic effect of bacteria inoculum plus repeated raking (BI + RR) released maximum amount of phosphorus than the rest three treatments. Critical appraisal of data clearly revealed four states of dynamic of ³²P between sediment and overlaying water: initial rapid increase of ³²P level in water - rapid desorption period (RDP) from day 0 to 12, slow increase of ³²P level of water - slow desorption period (SDP) from day >12 to 55, the ³²P moves to sediment resulting in decrease ³²P level in water - absorption period (AP) from day >55 to 90 and steady period (SP) from day >90 to 124, when ³²P concentration of water and sediment supposed to be equal indicating no movement of ³²P occurred between the water and sediment phase