Predicting Early Morning Dissolved Oxygen Concentrations in Channel Catfish Ponds

Abstract

Consumption of O2 by planktonic communities of pond waters may be predicted from chemical oxygen demand (COD) and temperature (r2 = 0.85). In ponds where planktonic organisms are the major source of turbidity, Secchi disk visibility may also be used to estimate COD (r2= 0.81) or consumption of O2 by planktonic communities (r2 = 0.82). A computer simulation model for nighttime decline in dissolved oxygen (DO) concentrations was developed for channel catfish ponds. This model incorporated data on plankton respiration from the present study, data from the literature on respiration by fish, respiration by organisms in the mud, and O2 diffusion. The validity of the model was tested for two catfish ponds. Measured and calculated DO concentrations usually agreed within ±10%. Secchi disk visibility determination should be used in the computer simulation to estimate O2 consumption by plankton whenever possible. However, COD values may be used when ponds contain appreciable clay turbidity. Series of tables were prepared which give the minimum acceptable Secchi disk visibility and the maximum permissible COD which may be tolerated in a particular pond without danger of DO depletion during the night. These tables will be useful to fish pond managers. A simple, graphical technique for estimating DO concentrations at dawn from DO measurements made at dusk and 2 to 3 h later also gave good estimates of nighttime DO decline. Although this technique has several limitations, it will be useful when it is not possible to measure COD and when Secchi disk measurements cannot be used to estimate O2 consumption by plankton.