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.