RATES OF ORGANIC-CARBON AND NITROGEN DEGRADATION IN INTENSIVE FISH PONDS

Water quality in intensive aquaculture systems is to a large extent controlled by the microbial biodegradation of organic residues, The ability to simulate processes in such systems depends on the availability of data on the rates of these processes. The first order kinetic rate constants for both organic carbon and organic nitrogen degradation in fish ponds were evaluated. The rate constants were computed by either relating the measured rate of disappearance of the substrate concentration or by the comparison of the measured with a theoretically derived evolution pattern of organic carbon or nitrogen concentrations in model ponds. The organic carbon degradation rate constant was found to be 0.15/day. The organic nitrogen degradation rate constant was expected, theoretically to be about 0.06/day and was found experimentally to be in the range of 0.05-0.09/day. These values seem to be reasonable approximations for constantly aerated-mixed ponds, at a temperature range of 20-30 degrees C. Organic matter previously metabolized in anoxic sites at the pond (e.g. resuspended sediments), has a degradation rate of ca. 0.6/day, and can thus consume large amounts of oxygen in the water body.