Abstract:
The Bioaccumulation and Aquatic System Simulator (BASS) is a Fortran 90 simulation model that predicts the population and bioaccumulation dynamics of age-structured fish assemblages which are exposed to hydrophobic organic pollutants and class B and borderline metals that complex with sulfhydryl groups (e.g., cadmium, copper, lead, mercury, nickel, silver, and zinc). BASS's bioaccumulation ... algorithms are based on diffusion kinetics and are coupled to a process-based model for the growth of individual fish. The model's exchange algorithms consider both biological attributes of fishes and physico-chemical properties of the chemicals of concern that determine diffusive exchange across gill membranes and intestinal mucosa. Biological characteristics used by the model include the fish's gill morphometry, feeding and growth rate, and proximate composition (i.e., its fractional aqueous, lipid, and structural organic content). Relevant physico-chemical properties are the chemical's aqueous diffusivity, n-octanol/water partition coefficient (K_{ow}), and, for metals, binding coefficients to proteins and other organic matter. bass simulates the growth of individual fish using a standard mass balance, bioenergetic model (i.e., growth = ingestion - egestion - respiration - specific dynamic action - excretion). A fish's realized ingestion is calculated from its maximum consumption rate adjusted for the availability of prey of the appropriate size and taxonomy. The community's food web is specified by defining one or more foraging classes for each fish species based on either its body weight, body length, or age. The dietary composition of each of these feeding classes is specified as a combination of benthos, incidental terrestrial insects, periphyton/attached algae, phytoplankton, zooplankton, and one or more fish species. Population dynamics are generated by predatory mortalities defined by community's food web and standing stocks, size dependent physiological mortality rates, the maximum longevity of species, and toxicological responses to chemical exposures. The model's temporal and spatial scales of resolution are a day and a hectare, respectively. Currently, BASS ignores the migration of fish into and out of the simulated hectare.
Input variables are broadly classified into three categories: simulation control parameters, chemical parameters, and fish parameters.
Simulation control parameters provide information that is applicable to the simulation as a whole, e.g., length of the simulation, the ambient water temperature, nonfish standing stocks, and user output options.
Chemical parameters specify the chemical's physico-chemical properties (e.g., the chemical's molecular weight, molecular volume, n-octanol/water partition coefficient, etc.) and exposure concentrations in the environment (i.e., in water, sediment, benthos, insects, etc.).
Fish parameters identify the fish's taxonomy (i.e., genus and species), feeding and metabolic demands, dietary composition, predator-prey relationships, gill morphometrics, body composition, initial weight, initial whole body concentrations for each chemical, and initial population sizes.
The model's output includes:
1) Summaries of all model input parameters and simulation controls.
2) Tabulated annual summaries for the bioenergetics of individual fish by species and age class.
3) Tabulated annual summaries for the chemical bioaccumulation within individual fish by species and age class.
4) Tabulated annual summaries for the community level consumption, production, and mortality of each fish species by age class.
5) Plotted annual dynamics of selected model variables as requested by the user.
Quality
Numerical integration of BASS's differential equations can be performed using either an Euler or Runge-Kutta integrator. These methods offer users two distinctly different options with respect to software performance and execution. Although Euler methods may often allow for fast model execution, they cannot assess the accuracy ... of their integration. Runge-Kutta methods, on the other hand, can monitor the accuracy of their integration but at the cost of increased execution time. Fortunately, however, this additional computational burden can often be significantly reduced by employing adaptive step sizing. BASS's Runge-Kutta integrator, which is the model's default integrator, is patterned on the fifth-order Cash-Karp Runge-Kutta algorithm outlined by Press et. al. (1992).
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City:
Greenbelt
Province or State:
MD
Postal Code:
20771
Country:
USA
Publications/References
Barber, M.C., L.A. Su�rez, and R.R. Lassiter. 1991. Modelling bioaccumulation of organic pollutants in fish with an application to PCBs in Lake Ontario salmonids. Can. J. Fish. Aquat. Sci. 48:318-337.
Barber, M.C. 2001. Bioaccumulation and Aquatic System Simulator (BASS) User's Manual Beta Test Version 2.1. U.S. Environmental Protection Agency, National Exposure Research Laboratory, Ecosystems Research Division, Athens, GA. EPA 600/R-01/035.
Press, W.H., S.A. Teukolsky, W.T. Vetterling, and B.P. Flannery. 1992. Numerical Recipes in FORTRAN. Cambridge Univ. Press. pp 963.
