United States
                 Environmental Protection Agency
Office of Water
   4305T
EPA-823-F06-015
    October 2006
             I  AQUATOX (RELEASE 2.2): MODELING
                ENVIRONMENTAL FATE AND ECOLOGICAL EFFECTS
                IN AQUATIC ECOSYSTEMS
AQUATOX is a freshwater ecosystem simulation model that predicts the fate of various pollutants,
such as nutrients and organic chemicals, and their effects on the ecosystem, including fish,
invertebrates, and aquatic plants. AQUATOX is a valuable tool for ecologists, biologists, water
quality modelers, and anyone who performs ecological risk assessments for aquatic ecosystems.
Background
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.
About AQUATOX
AQUATOX is a PC-based ecosystem model that predicts the fate of nutrients and organic chemicals
in water bodies as well as their direct and indirect effects on the resident organisms.
AQUATOX simulates the transfer of biomass and chemicals from one compartment of the
ecosystem to another. It does this by simultaneously computing important chemical and biological
processes over time. AQUATOX simulates multiple environmental stressors (including nutrients,
organic loadings, toxic chemicals, and temperature) and their effects on the algal, macrophyte,
invertebrate, and fish communities. AQUATOX can help identify and understand the cause and
effect relationships between chemical water quality, the physical environment, and aquatic life. It
can represent a variety of aquatic ecosystems, including vertically stratified lakes, reservoirs and
ponds, and rivers and streams.

AQUATOX Applications
AQUATOX can be used to address a wide variety of issues requiring a better understanding of the
processes relating the chemical and physical environment to the biological community. Possible
applications of AQUATOX include:

-------
       Developing numeric nutrient targets based on desired biological endpoints.
       Evaluating which of several stressors is causing observed biological impairment.
       Predicting effects of pesticides and other toxic substances on aquatic life.
       Evaluating potential ecosystem responses to invasive species.
       Determining effects of land use changes on aquatic life by using the linkage with BASINS.
       Estimating time to recovery offish or invertebrate communities after reducing pollutant
       loads.
            AQUATOX Simulates Ecological Processes & Effects
                      within a Volume of Water Over Time
                                                         Suspended sediment
                                                           (TSS, Sand/silt/clay)
                                                                Light extinction
                                                              Plants
                                                            Phytoplankton
                                                            Attached algae
                                                             Macrophytes
                                                                    Ingestion
Detritus
(suspended, paniculate,
dissolved, sedimented)
Death
Ingestion
A
• Settlina. resusoension
                                                               Animals
                                                             Invertebrates (spp)
                                                                Fish (spp)
                                    Inorganic Sediment
About Release 2.2
AQUATOX Release 2.2 includes several minor updates to Release 2.1. These updates include:
•  The model will now calculate reservoir retention time.
•  The calculation for light extinction due to blue-green algae was refined, and the model now
   calculates blue-green algae as a percentage of total algae.
•  There were minor corrections made related to the effects of excess temperature in plants, and
   calculation of initial conditions
•  There is an improved algal parameter set and updated example applications.
•  There is an improved graphical user interface for more easily assigning toxicity data, and
   graphing model results

Additional information
Additional information on AQUATOX is available at
http://www.epa.gov/waterscience/models/aquatox/. You may also contact Marjorie Coombs
Wellman at 202-566-0407 (phone) or wellman.marjorie@epa.gov.

-------