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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. 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.
(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.
The Pond Dynamics/Aquaculture CRSP is funded under USAID Grant No. LAG-G-00-96-90015-00
and by
the participating US and Host Country institutions.
Questions for or about the Aquaculture CRSP? Comments about this site? Email ACRSP@oregonstate.edu.
Stochastic Modeling of Temperature in Stratified Aquaculture Ponds
Work Plan 7, DAST Study 2
Abstract
Calculation of pH in Fresh and Sea Water Aquaculture Systems
Abstract
Disclaimers
