Title: Development of an ecosystem model MARSHDO for assessing oxygen demand in a recirculating shrimp aqua
1Development of an ecosystem model (MARSHDO) for
assessing oxygen demand in a recirculating shrimp
aquaculture treatment wetland
- David R. Tilley
- Biological Resources Engineering University of
Maryland - College Park
Harish Badrinarayanan, Ji Ho Son
Environmental Engineering Texas AM
UniversityKingsville
Paper given at American Society of Agricultural
Engineers 2004, Ottawa, Ontario
2Motivation
- Shrimp Farming Increasing in Popularity
- Needs to be Ecologically Sustainable
- Treatment Wetlands used as Recirculation Filters
- Wetlands remove Suspended Solids and Nutrients
- OXYGEN levels drop!
3Objectives
- Evaluate how a Treatment Wetland altered the
dissolved oxygen levels of process water
discharged from a full-scale shrimp farm (8 ha) - Develop a simulation model of the long-term
temporal dynamics of dissolved oxygen (D.O.)
discharged from the Treatment Wetland - Test affects of organic and nutrient loading and
management on Treatment Wetland D.O.
4Plan of Study
- Monitor D.O. along flow transect of shrimp farm
treatment marsh - H.T. Odums Energy Systems Language used to
diagram oxygen cycle of treatment marsh. - Develop computer simulation model using STELLA
software. - Model calibration based on literature values and
validated with field observations. - Test sensitivity of D.O. to changes in inputs and
management of live and dead organic matter.
5Loma Alta Shrimp Farm Marsh Recirculation
Filter
Flow Rate 13,600 m3 d-1 (3.6 MGD) Hydraulic
Residence Time 24 h Depth 15 to 45 cm Study
period July 24 - Oct. 9, 2000
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12Roseate Spoonbills
13Drop in D.O. across Wetland
14D.O. change along Marsh Transect
15BOD change along Marsh Transect
16pH change along Marsh Transect
17D.O. to BOD ratio lower in Highly Organic
Sections of Marsh
18Model Development
19Systems diagram Marsh-DO simulation model
J. Son
20Systems diagram for Marsh-DO modelnumerical
values for sources, storages and pathways
J. Son
21Determination of MARSHDO coefficients
22STELLA Diagram of MARSH-DO
23Long-term Dynamics of Key State Variables in
Marsh-DO
Biomass
Phosphorus
Org. Matter
D.O.
2410-year Simulation of Sensitivity of D.O. to
Organic Loading
½X Present Load
2X Present Load
2510-year Simulation of Sensitivity of D.O. to
Nutrient Load
½X Present Load
2X Present Load
26Sensitivity of DO to changes in Organic and
Nutrient Loading
27Management Effects
Biomass
Phosphorus Removal
Unmanaged
g/m2
Managed
Dead Organic Matter
Dissolved Oxygen
Unmanaged
Managed
g/m2
ppm
Managed
Unmanaged
Weeks
Weeks
28Model Deficiencies/Improvements
- Separate Organic Matter into suspended and soil
compartments. - Be careful in zeal of removing Organic Matter to
increase Oxygen because - O.M. supports removal of other pollutants (heavy
metals, pathogens, nitrogen)
29Conclusions
- An ecosystems model of Dissolved Oxygen levels in
a Treatment Marsh operated as the Recirculation
Filter on a Full-scale Shrimp Farm was developed
with energy systems language and simulated with
STELLA software. - Soil oxygen demand is at least as important as
water column oxygen demand. - Doubling of Organic Loading decreased long-term
Dissolved Oxygen levels more than doubling
Nutrient Loading. - Annual removal of Biomass and Dead Organic Matter
increased mean Dissolved Oxygen levels. -
30the end