It has become increasingly apparent that methods and tools are needed to analyze the combined fate and effects of all stressors on aquatic ecosystems from all sources. Stressors may include nutrients, organic loading, toxic organic compounds, sediments and habitat alteration; sources include point and non point source loadings and atmospheric deposition. Stressors may affect water clarity, algae populations, dissolved oxygen levels, fish and invertebrate communities, levels of contaminants in fish tissue, and many other important environmental conditions. Management approaches that focus on one stressor at a time may miss important interactions that could determine whether overall environmental goals, such as restoration of a more natural aquatic ecosystem, are met. Environmental management programs and activities that could benefit from additional tools for an integrated approach include water quality criteria and standards, Total Maximum Daily Loads (TMDLs), identification of the cause(s) of biological impairment where there are multiple stressors, and ecological risk assessments. AQUATOX is a time-variable ecological risk assessment model that simulates the fate and effects of various environmental stressors in aquatic ecosystems. It simulates the fate and transfer of pollutants from loads to the water, sediments, and biotic components, and transfer throughout the food web. Simultaneously it predicts the effects of the stressors on the ecosystem, by simulating the chemical, physical and biological processes that bind the ecosystem together. AQUATOX can predict the fate and ecological effects of nutrients, organic toxicants, and bioaccumulative compounds, as well as the expected ecosystem responses to pollution reductions. It considers several trophic levels, including attached and planktonic algae and submerged aquatic vegetation, invertebrates, and forage, bottom-feeding, and game fish; it also represents associated organic toxicants. BASINS (Better Assessment
Integrating Point and Nonpoint Sources) is a combined GIS/water quality modeling system that includes numerous national level environmental and cartographic data layers, analytical tools, watershed loading models, and instream water quality models. One of the main advantages of an integrated system such as BASINS is that the time consuming task of developing input data files for the various models is reduced: watershed characteristics necessary for the watershed models can be developed from the landscape data layers, and data can be converted into the proper formats for model input files. BASINS Version 3 changed the system architecture to a modularized system, and converted the models and many other functions to ArcView 'extensions.' The modular setup allows the models to run either as part of BASINS or stand alone. The modularity also makes it easier to add components, and for users to customize BASINS for their own purposes. This new software extension links the AQUATOX ecosystem model to the BASINS modeling system.