1. US Environmental Protection Agency
AQUATOX
US Environmental Protection Agency
Objective
Aquatox simulates the transfer of biomass, energy, and chemicals from one compartment of ecosystems to another by simultaneously computing each process on a daily time step for the determined simulation period. Particularly the model determines the fate of various pollutants within a aquatic environment.
Purpose
To guide how aquatic ecosystems are managed and restored by creating a better understanding of the relationship between chemicals, the physical environment and organisms.

3. Minimum Inputs
Detritus, Oxygen, Nutrients (Nitrogen, Phosphorous, Carbon Dioxide)
Additional Inputs
- Fish, algae, aquatic plants, water volume, temperature, pH, light.

4. Outputs
Concentration of State Variables i.e. nutrients and chemicals in the water
Physical characteristics of state variables.
Mass of toxicants within state variables.

5. Assumptions
You must have a strong understanding of initial ecosystems condition.
Requires significant species data.
Does not account for spatial variation in species parameters.
There is a variety of assumptions made about each of the processes.
Scale
Rivers, lakes, estuaries.
Generally the model reports in one day increments that add up to
several years

6. Uses
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 climate change.
Estimating time to recovery of contaminated fish tissues to safe levels after reducing pollutant loads.

7. Testing and Validation
Underwent two official external peer reviews.
34 published peer reviewed articles.
Issues
There are so many assumptions made by the model that not all of them are clearly documented in a way that makes them known to the user.
The model does not provide a high degree of accuracy. Should be used in conjunction with other tools.
Cannot provide casual links because several stressors could create similar results.
The model is so simplistic and user friendly that it could be misused by unskilled modelers or people without significant calibration data.

8. Results
Joyner, T. A., and R. V. Rohli Atmospheric influences on water quality: a simulation of nutrient loading for the Pearl River Basin, USA. Environmental monitoring and assessment:1-10.
- Daily dissolved oxygen is negatively correlated with daily mean air temp.
- Totally monthly P is positively correlated with monthly precip.
- Managers should anticipate climate change altering water quality.

9. Results
Lake County Water Resources Division Clear Lake Integrated Aquatic Plant Management Plan.
- Plan to use fluridone to remove hydrilla from the lake. Part of this report modeled 6 different does and attempted to measure the impact on non- target organisms.
- Direct removal of hydrilla does not impact dissolved oxygen compared with the impact of detritus created by seasonal dieoff.
- Model predicts the recovery of game fishery due to stabilizing of pH and decrease in lake temperature.