Patterns of toxicological effects in ecosystems: A modeling study

Differences in patterns of response in a pelagic ecosystem due to seasonal exposure and differential sensitivities of populations and trophic levels to chemical stress were examined with a simulation model. Simulations of constant 7-d exposures initiated at different times of year demonstrated that stresses imposed during the spring reduced average producer and consumer biomass. Stresses imposed later in the year reduced grazer biomass and permitted increased phytoplankton production. Simulated exposures to phenol, naphthalene and four heavy metals (Cd, Hg, As, Pb) predicted different effects when toxic sensitivities of populations and trophic levels were ignored. Risks of increased blue-green algae production or decreased game fish production were estimated from repeated simulations that extrapolated uncertainties associated with individual toxic effects parameters. Estimates of risk that included population-specific toxicities were two or three times greater than risks estimated from trophic level toxicities alone.