1. AQUATOX v. 3.1 Host Institution/URL
Erin Sexton
Ecosystem Model Evaluation # 2
AQUATOX v. 3.1
Host Institution/URL
United States Environmental Protection Agency
Domain/Objective – AQUATOX is an ecosystem model that simulates the fate of nutrients, sediments and organic chemicals in aquatic systems, and their effects on aquatic life, including fish, invertebrates and aquatic plants.
Key Assumptions –
Average daily conditions for a well-mixed aquatic system
Model is run with a daily or hourly maximum time-step

2. AQUATOX v. 3.1 Temporal/Spatial Scale Temporal
Default is daily reporting time step, but can use hourly time-step and reporting
Results are integrated over a specific time period
2) Spatial
Simple unless linked to a hydrodynamic model
Thermal stratification
Salinity stratification
Modular and flexible
Written in object-oriented Pascal (Delphi)
Model only what is necessary
Multi-threaded, multiple document interface
Control Vs. Perturbed Simulations

3. Conceptual Model of the Ecosystem Represented By AQUATOX

4. AQUATOX v. 3.1
Model Inputs
1) State variables - components of the modeling system, such as animal biomasses, that are tracked (uses differential equations to represent changing values)
2) Driving variables - Time series inputs that are not changed by the model (temperature, light and nutrient loadings)
3) Parameters – constant model inputs that are used to calculate the modeled state variables (uses process equations)
4) Boundary conditions – information about state variables from outside the model domain (upstream loadings, or point-source loadings)
5) Physical characteristics – constant model parameters or time series such as mean depth, that describe the site being modeled

5. AQUATOX v. 3.1

6. Conceptual Model of the Ecosystem Represented By AQUATOX

8. Key Outputs = Regulatory Endpoints Modeled
Nutrient and toxicant concentrations
Biomass
plant, invertebrate, fish
Chlorophyll a
phytoplankton, periphyton, moss
Biological metrics
TSS, Secchi depth
Dissolved oxygen
Biochemical oxygen demand
Bioaccumulation factors
Half-lives of organic toxicants

9. AQUATOX Applications Screening-level Model Nutrients
TMDL’s
Site-specific Water Quality Criteria
Invasive Species
Risk Assessments for new or Existing Chemicals
Impacts of Contaminated Sites on Aquatic ES
Sewer /Stormwater Discharge
Nutrients
Developing targets, identifying cause and effect
Toxic Substances
Ecological risk assessment of chemicals impacts to non-target organisms
Aquatic Life Support
Evaluate proposed water quality criteria
Estimate recovery time after pollutant reduction
Evaluate responses to invasive species and mitigation measures
Climate Change
Can link to climate and/or watershed models

10. Park, R. A. , J. S. Clough, and M. C. Wellman. 2008
Park, R.A., J.S. Clough, and M.C. Wellman AQUATOX: Modeling environmental fate and ecologicaleffects in aquatic ecosystems. Ecological Modelling 213: 1-15 (24 April 2008)

11. Running a Simulation AQUATOX 3.1 is delivered with 39 example studies
single segment, multi-segment and examples for rivers, streams, ponds, lakes, reservoirs and estuaries

12. Tool Bar
Editable databases
Output functions
State and Driving Variables

13. DATABASES
Chemical Library
2,4 D-Acid

14. 2,4 D Acid
Animal and Plant Toxicity Data

15. AQUATOX WIZARD
19 Primary Steps For Editing State Variables

16. AQUATOX WIZARD
Step 6. Invertebrates

17. Model Simulation Onandaga Lake, New York
Described as the most polluted lake in the United States (Effler, 1996)
The lake has significant nutrient inputs from a wastewater treatment plant, combined sewers, successive algal blooms, hypoxia in the hyplimnion, high mercury levels and salinity.

18. Model Simulation Onandaga Lake, New York
Well-calibrated Nutrient Analysis - assumes a small aerobic layer above a larger anaroebic layer (assumes anoxic sediments)
One dimensional with vertical stratification
The simulation time is two years
10 additional State Variables
Ammonia
Nitrate
Orthophosphate
Methane
Sulfide
Bioavailable silica
Non Biogenic Silica
Particulate Organic Carbon (POC)
Particulate Organic Phosphate (POP)
Particulate Organic Nitrate (PON)
Chemical Oxygen Demand

19. Model Calibration and Validation
Onandaga Lake, New York
Observed vs Predicted data for Dissolved Oxygen in the hyplimnion
Two levels of validation analysis using loadings data
Monthly
Daily
Predicted anoxic conditions in the summer 

20. Model Simulation - Outputs

21. Model Simulation Onandaga Lake, New York Particulate Organic
Phosphate (POP)
Dissolved Oxygen

22. Model Simulation – Technical Documentation
Process and Differential Equations
Example – Nutrient Loading Variable Equations

23. Processes Simulated Capabilities Bioenergenetics Environmental fate
Feeding, assimilation
Growth, promotion, emergence
Reproduction
Mortality
Trophic relations
Toxicity (acute and chronic)
Environmental fate
Nutrient cycling
Oxygen dynamics
Partitioning to water, biota and sediments
Bioaccumulation
Chemical transformations
Capabilities
Ponds, lakes, reservoirs, streams, rivers, estuaries
Riffle, run, and pool habitats for streams
Completely mixed thermal stratification or salinity stratification
Linked segments, tributary inputs
Multiple sediment layers with pore waters
Sediment Diagenesis Model
Diel oxygen and low oxygen effects, ammonia toxicity
Interspecies correlation estimation
Variable stoichiometry, nutrient mass balance, TN and TP
Dynamic pH

24. Limitations of AQUATOX
Does not model metals
Hg was attempted but was not successful
Does not model bacteria or pathogens
Microbial processes are implicit in decomposition
Does not model temperature regime and hydrodynamics
Can be easily linked with a hydrodynamic model