Consumption of O2by planktonic communities of pond waters may be predicted from chemical oxygen demand (COD) and temperature (r 2 -0.85). In ponds where planktonic organisms are the major source of turbidity, Secchi disk visibility may also be used to estimate COD (r 2 -0.81) or consumption of O2 by planktonic communities (r 2 = 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. Can. 32:1283-1288. BOYD. C. E. 1973. The chemical oxygen demand of' waters and biological materials from ponds. Trans. Am. Fish. Soc. 102:606•511. ß 1976. Evaluation of a water analysis kit. Auburn Univ. Agric. Exp. Sta., Auburn, Ala. Leaflet 92.3 pp. ß 1977. Evaluation of a water analysis kit. J. Environ. Qual. 6:381-384. --, E. E. PRATHER, AND R. W. PAaI½S. 1975. Sudden mortality of a massive phytoplankton bloom. Weed Sci. 23:61•57.

A number of water quality variables were measured at 1‐ to 2‐week intervals in five channel catfish (Ictalurus punctatus L.) production ponds at Auburn, Alabama, during the 1978 growing season. Concentrations of most variables increased with time since feeding rates were progressively increased as fish grew. The DO concentration at dawn was often lower than 2.0 mg/liter during August and September. Emergency aeration was used one or more times in each pond to minimize the danger of fish kills because of low DO. In addition, unionized ammonia (NH3) and carbon dioxide concentrations were occasionally high enough to possibly have had adverse effects on fish. A computer simulation model for predicting the early morning DO concentration in ponds proved efficient. The average difference between measured and predicted DO concentration, disregarding sign, was 0.47 mg/liter for 30 trials. Spillway discharge from channel catfish ponds was more concentrated in pollutants than streams near Auburn, Alabama.

No abstract

The detergent industry uses about $2 billion of inorganic chemicals a year. Two products-sodium tripolyphosphate, with almost $

No abstract