AQUATOX Fact Sheet  (EPA-820-F-12-023) August 2012

AQUATOX Release 3.1 Plus includes the following enhancements:

• Option to model nutrient limitation in plants based on internal rather than external nutrients.  This allows for luxury uptake of nutrients during high-nutrient periods and expenditure of nutrient stores during lower-nutrient periods.  Concentrations and derivative rates may be output from these new internal-nutrient state variables as well as the nutrient-to-organism ratio for each plant.  This option should improve the prediction of the timing and duration of algal blooms.       
• Sinking of plants and suspended detritus is now affected by the salinity & therefore the density of water in non-estuary segments.
• New outputs for net primary productivity, pelagic invertebrate biomass, benthic invertebrate biomass, and fish biomass.     
• Capability to load and save observed data to a file to move from one study to another.      
• Significantly optimized loading and saving of very large aps or als files.
• For moving water (streams and rivers), the average water temperature must drop below 0 deg. C before ice cover is assumed.

AQUATOX Release 3.1 includes numerous significant enhancements over previous versions that increase the realism and utility of the model. The most important enhancements include:

• Addition of sediment-diagenesis "steady-state" mode to significantly increase model speed;
• Modification of denitrification code in order to simplify calibration and to achieve alignment with other models;
• Enabled importation of equilibrium CO2 concentrations to enable linkage to CO2SYS and similar models;
• New BOD to organic matter conversion relying on percent-refractory detritus input; input and output BOD is clarified to be "carbonaceous" BOD.
• Refinements for floating plants:
  • Added floating option for plants other than cyanobacteria (formerly labeled "blue-green algae”)
  • Converted the averaging depth for floating plants to the top three meters to more closely correspond to monitoring data
  • Floating plants now explicitly move from the hypolimnion to the epilimnion when a system is stratified.

• Modifications to PFA (perfluoroalkylated surfactants) model to increase flexibility:
  • Uptake rates (K1s) and elimination rates (K2s) are visible and editable for animals and plants
  • New interface to estimate animal K1s and K2s as a function of chain length
  • Improved gill-uptake equation for invertebrates.

• Bioaccumulation and toxicity modeling improvements:
  • Optional alternative elimination-rate estimation for animals based on Barber (2003) ; works best with PCBs;
  • Updated ICE (toxicity regressions), based on new EPA models released in February 2010 and improved AQUATOX ICE interface;
  • Addition of output of K1, K2, and BCF estimates.

• Improved sensitivity and uncertainty analyses:
  • "Output to CSV" option for uncertainty runs so that complete results for every iteration may be saved and examined;
  • Option for non-random sampling for "statistical sensitivity analyses";
  • A "reverse tornado" diagram (effects diagram) that shows the effects of each parameter change on the overall simulation;
  • Nominal range sensitivity analysis has been added for linked- segment applications.

• Database Improvements:
  • AQUATOX database search functions dramatically improved;
  • "Scientific Name" field added to Animal and Plant databases.

• Interface and Data Input Improvements:
  • Software and software installer is 64-bit OS compatible;
  • Added an option in the "Setup" screen to trigger nitrogen fixation based on the N to P ratio;
  • Addition of output variables to clarify whether photosynthesis is sub-optimal due to high-light or low-light conditions;
  • Time-varying evaporation option in the "Site" screen has linkage from the "Water Volume" screen;
  • Grid mode within a study so that all animal, plant, and chemical parameters in a study can be tabulated, examined, edited, and exported to Excel;
  • Added capability to input time-series loads of fish based on fish stocking;
  • Updated HSPF WDM file linkage to be more generally applicable (does not require use of WinHSPF, the version of HSPF contained in BASINS);
  • Enabled hourly loadings for the following variables: all nutrients, CO2, Oxygen, Inorganic suspended sediments (sand/silt/clay), TSS, Light, Organic Matter;
  • "Graph Setup" window now enabled for linked-mode graphics;
  • Other minor interface improvements.

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