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Respiration Dynamics in Aquaculture Ponds

Work Plan 7, DAST Study 1

Philip Giovannini and Raul H. Piedrahita
Department of Biological and Agricultural Engineering
University of California, Davis
Davis, California, USA

Abstract

A respirometer has been developed for use in aquaculture ponds. The respirometer is designed to measure oxygen consumption rates in water samples that have been suddenly darkened. Rates of oxygen consumption are measured over 15 minute periods, and the process is repeated at 20 minute intervals, allowing for a 5 minute respirometer flushing and sample pumping period. The respirometer is connected to a data acquisition system and to a computer for automated data collection and analysis. Some results of tests carried out with the respirometer both in the laboratory and in the field are presented. The results show substantial changes in respiration rates over diel periods, with the highest rates occurring in the late afternoon. Rates decline rapidly after sunset and remain at much lower levels than during daylight hours. Limitations of the respirometer design are discussed, especially problems associated with fouling.

Stochastic Modeling of Temperature in Stratified Aquaculture Ponds

Work Plan 7, DAST Study 2

Cristiano dos Santos Neto and Raul H. Piedrahita
Department of Biological and Agricultural Engineering
University of California, Davis
Davis, California, USA

Abstract

A computer model for temperature simulations in stratified aquaculture ponds has been run with stochastic inputs. Stochastic inputs used are solar radiation, wind direction, and wind speed. Values for the stochastic inputs were obtained from synthetically generated series based on historical records obtained from the CRSP data base. The techniques used for obtaining the stochastic input values are described, as are the results of simulations carried out for Thailand ponds. Surface temperatures showed the largest fluctuations as a result of stochastic changes in the input parameters.

Calculation of pH in Fresh and Sea Water Aquaculture Systems

Raul H. Piedrahita
Department of Biological and Agricultural Engineering
University of California, Davis
Davis, California, USA

Aina Seland
SINTEF Norwegian Hydrotechnical Laboratory
Trondheim, Norway

Abstract

(Printed as submitted)

A procedure for the calculation of pH in fresh and salt waters has been developed. The method is based on a fourth-order polynomial relationship between hydrogen ion concentration and other (conservative) water quality parameters. The method avoids trial and error estimations and results in a direct calculation procedure that can be implemented in models developed in various modeling environments, such as spreadsheets, conventional programming languages (BASIC, C, FORTRAN, PASCAL, etc.), or specialized modeling languages (Extend(TM), Stella(TM)). The method developed is based on the solution of the full alkalinity-pH equation. Because of the need to simplify the equations to yield explicitly solvable polynomial equations, the accuracy of the solutions depends on the simplification made and varies with water properties. Three simplifications are tested based on a second-, a third-, and a fourth-order polynomial equation for hydrogen ion concentrations. The equations have been tested for salinities ranging from 0 to 35‰ (fresh to sea water), for temperatures ranging from 0 to 35°C, for total carbonate carbon of 0.1 and 5.0 mmol/l, and for total ammonia nitrogen of 0 and 10 mg/l. Approximations are most accurate in waters of high total carbonate carbon and low ammonia concentrations, where the fourth-order approximation yields results that are within 0.05 pH units for the full range of pH values tested (5 to 10).

Accepted for publication by Aquacultural Engineering.