The mathematical model WEED was derived to study the productivity of the submerged macrophyte Myriophyllum spicatum in the littoral of Lake Wingra, Madison, Wisconsin. The model coordinates four biomass compartments with selected physiological processes evaluated for a stratified meter—squared water coloumn. Light and temperature are the primary environmental forcing functions. The model considers growth form (depth distribution of biomass), total biomass/meter—squared, the depth profile of photosynthesis and macrophyte contributions to dissovled and particulate organic matter pools in the water column. The model output was tested against field data for seasonal patterns of standing crop, depth distribution of biomass and depth profile of photosynthesis for a rooting depth of 150 cm. WEED has permitted the simulation of macrophyte growth response to changes in environmental conditions and has outlined areas of needed research.

No abstract

A methodology for assessing toxic effects of chemicals on fish should be able to begin with an emission rate, an LC50, and a description of the receiving system and generate an estimate of the likelihood of reductions in fish populations. This process is a series of extrapolations, each with an associated variance. The LC50 must be extrapolated from the test species to the species of interest, to life-cycle toxicity, to long-term toxicity in the field, to changes in population size due to direct toxic effects and, finally, to the combined direct and indirect toxic effects. Similarly, the emission rate must be converted into an effective environmental concentration in an imperfectly known hydrologic, chemical, physical, and biological system. In this paper we summarize some data and methods for making these extrapolations and indicate sources of uncertainty in each stage of the analysis.

No abstract