Abstract: This study presents modeling of dissolved
oxygen performance in a greenhouse fishpond. A short-term Disolved Oxygen
(DO) fluctuation of a fishpond was developed by using various simple equations
and continuous measurement of DO, temperature and solar intensity. Numerical
computation has been performed for a typical winter day at the month of
January, 2007. Components considered in the DO model include the production
of DO by phytoplankton and consumption of oxygen by phytoplankton, fish,
water column and sediment. Numerical equations were solved with Excel
soft ware to predict DO in the pond. Initial slope (α) and Pmax
were calculated from DO production Vs. solar radiation curve. The amount
and distribution of oxygen production in the water column depend on solar
intensity and penetration as well as phytoplankton concentration. A parametric
study has been performed to represent the effects of pond depth, SDD,
extinction coefficient, water temperature and fish yield changes on DO
regimes in fish pond. Dissolved oxygen concentrations in the pond varied
with both pond depth and SDD. By increasing the depth of the pond and
of the SDD and maintaining phytoplankton chlorophyll-a concentration at
232 μg L-1, the overall oxygen production was increased.
The low DO values in the shallow pond (0.5 m) with a high SDD (0.5 m)
when compared to other ponds with SDD equal to their pond depths, was
the result of low overall oxygen production relative to the demand by
sediment and fish which were same for all depths of pond. Predicted and
experimental DO concentrations exhibited fair agreement with correlation
coefficient of R = 0.99 and root mean square percent deviation e = 3.73%.
Such correlation between predicted and experimental data indicates that
the assumption inherent in the computer model of the processes is valid
for the DO production and consumption in the pond. |