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Model Report


Last Revision Date: 01/18/2012 View as PDF
General Information Back to Top
Model Abbreviated Name:

Model Extended Name:

Model Overview/Abstract:
AQUATOX is a simulation model for aquatic systems. AQUATOX predicts the fate of various pollutants, such as nutrients and organic chemicals, and their effects on the ecosystem, including fish, invertebrates, and aquatic plants. This model is a valuable tool for ecologists, biologists, water quality modelers, and anyone involved in performing ecological risk assessments for aquatic ecosystems.

AQUATOX simulates the transfer of biomass, energy and chemicals from one compartment of the ecosystem to another. It does this by simultaneously computing each of the most important chemical or biological processes for each day of the simulation period. AQUATOX can predict not only the environmental fate of chemicals in aquatic ecosystems, but also their direct and indirect effects on the resident organisms. Therefore it has the potential to establish causal links between chemical water quality and biological response and aquatic life uses.

Keywords: Ecosystem modeling, Water quality modeling, Ecological risk assessment, Aquatic simulation modeling, Aquatic risk assessment, Nutrient analysis, Eutrophication, Bioaccumulation, Toxicity, Aquatic life uses, Water quality standards, Environmental fate of pollutants, Aquatic ecosystem, Organic toxicants, Suspended and bedded sediments, Contaminated sediments, Biological impairment, Ecosystem response, TMDLs, Aquatic stressors
Model Technical Contact Information:
Agency Contact
Marjorie Wellman
U.S. Environmental Protection Agency
Office of Water

Developer Contact
Richard A. Park, PhD
Eco Modeling
5522 Alakoko Place
Diamondhead MS 39525

Model Homepage: http://www.epa.gov/waterscience/models/aquatox/
Substantive Changes from Prior Version: Release 3 includes the ability to simulate:
  • linked river segments
  • estuaries
  • toxicity due to ammonia and low dissolved oxygen
  • diel oxygen
  • bioaccumulation of perfluorinated acids (PFOS, PFOA)
  • multiple sediment layers
  • biological effects of suspended and bedded sediments
  • more comprehensive representation of nutrient dynamics in sediment bed, including regeneration of P from anoxic sediments
  • incorporation of Web-ICE, a toxicity estimation tool developed by ORD-Gulf Breeze
  • an enhanced GUI with expanded analytical and graphing capabilities
  • automated nominal sensitivity analysis option
  • enhanced uncertainty analysis option, including correlations between parameters
Plans for further model development: Mostly program applications and “fine-tuning” where necessary; expansion of default data libraries

*** Release 3.0, can be found at http://www.epa.gov/waterscience/models/aquatox/download.html ***

User Information Back to Top
Technical Requirements
Computer Hardware
Pentium PC 2.0GHz or higher (or equivalent)

Minimum:512 MB RAM, 100 MB free disk space

Recommended: 2 GB RAM, 1 GB free disk space

Compatible Operating Systems
Windows 98, 2000, NT, XP or Vista
Other Software Required to Run the Model
None (operates under Windows). The Borland Database Engine is also installed as part of the installation of AQUATOX.
Download Information
The current EPA release version (currently Rel 3) can be found at HERE.
Release 3.0, available for downloand, can be found at: http://www.epa.gov/waterscience/models/aquatox/download.html
Using the Model
Basic Model Inputs
Required input data

  • Loadings to the waterbody
  • General site characteristics
  • Chemical characteristics of any organic toxicant
  • Biological characteristics of the plants and animals.

AQUATOX comes bundled with data libraries that provide default data. This is of particular importance for the biological parameters, which are probably the most difficult for a user to obtain.

Environmental loadings can be from multiple sources

  • Constant or dynamic
  • Point or nonpoint sources
  • Upstream contributions
  • Atmospheric deposition.

AQUATOX can accept input data in a wide variety of formats

Basic Model Outputs
Model output and analysis of results AQUATOX provides output in terms of time varying biomass of the various plants and animal, chemical concentrations in water, and concentrations of the organic toxicant in water, organic sediments and biota. It has numerous features to assist in display and analysis of results.

  • Graphing capability
  • Easy export to spreadsheet programs
  • Option to save and analyze time varying rates, such as consumption and photosynthesis, and limiting factors on primary productivity
  • Uncertainty and sensitivity analysis capability
User Support
User's Guide Available?
Download at: http://www.epa.gov/waterscience/models/aquatox/download.html

Release 3 also includes context-sensitive Help files and 2 tutorials.

Other User Documents
Technical Documentation. Download at:

Web site also includes model validation reports (though performed with earlier versions of the model, and a technical note on parameterization and calibration.

Availability of User Support
Yes. Users can join the AQUATOX Listserv at: http://www.epa.gov/waterscience/models/aquatox/listserv.html. There is a certain amount of one-on-one user support available by contacting the Agency contact.
User Qualifications
Knowledge of aquatic biology and ecology; moderate computer skills (no programming required)

Model Science Back to Top
Problem Identification
One of the biggest challenges to protecting or restoring our nation’s waters is to adequately understand the relationships between the chemical and physical environment and the organisms that live there. Ecosystems are complex, with seasonal and annual variations and multiple interactions among species. The biological communities in many water bodies are impaired, but the causes of the impairment may not be obvious in the face of numerous environmental stressors. It is difficult to predict how the aquatic community will respond to changes in pollutants or environmental conditions with simple methods of analysis, especially if the methods address a single stressor at a time. A complex simulation model may be required.
Summary of Model Structure and Methods
The model code is written in object-oriented Pascal. This language has a modular structure that allows for reuse of code segments; this feature increases efficiency in code writing and error correction.

AQUATOX uses a very efficient fourth- and fifth-order Runge-Kutta integration routine with adaptive step size to solve the differential equations that comprise the model. For presentation and documentation of the model constructs, and other additional information, please see the Technical Documentation.

Model Evaluation
AQUATOX Release 2 underwent external peer review during the summer of 2002. Release 3 underwent a second peer review in the fall of 2008. Both panels found that AQUATOX was consistent with current ecological theory and contained no significant scientific gaps; also that the simplifying assumptions were well documented and reasonable. They deemed AQUATOX to be essentially validated, though they recommended careful attention to calibration, especially when applying the model to new regions, or to new management issues. A summary of the Release 3 peer review is available at: http://www.epa.gov/waterscience/models/aquatox/peer.html
Key Limitations to Model Scope
Spatially simple (uniform conditions, except for thermal stratification); daily time step Several processes and significant parameters are not yet modeled, or are modeled only cursorily, including:
  • Metals fate and effects
  • Bacteria or pathogens (microbial processes are implicit in decomposition processes)

Case Studies
See validation reports, and publications (at http://www.epa.gov/waterscience/models/aquatox/pubs.html)

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