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 https://www.epa.gov/exposure-assessment-models/aquatox 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

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

Conceptual Model of the Ecosystem Represented By AQUATOX

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

AQUATOX v. 3.1

Conceptual Model of the Ecosystem Represented By AQUATOX

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

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

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

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

Tool Bar Editable databases Output functions State and Driving Variables

DATABASES Chemical Library 2,4 D-Acid

2,4 D Acid Animal and Plant Toxicity Data

AQUATOX WIZARD 19 Primary Steps For Editing State Variables

AQUATOX WIZARD Step 6. Invertebrates

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.

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

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 

Model Simulation - Outputs 

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

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

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

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