A method is presented for extrapolating laboratory toxicity data to aquatic ecosystem effects such as decreased productivity or reduction in game fish biomass. The extrapolation requires translating laboratory data into changes in the parameters of an ecosystem model, the Standard WAter COlumn Model (SWACOM). The translation is effected through knowledge of toxicological modes of action. The uncertainties associated with both laboratory measurements and extrapolations are explicitly retained, and risk estimates are given in the form of probabilities that an effect could occur. The approach is illustrated by scenarios in which effects of toxic substances are distributed across different trophic levels. Each scenario affects population interactions in different ways and alters both the level and the nature of the risks to ecosystem processes. Particular attention is paid to analyzing the interaction between toxicity and the uncertainties associated with extrapolation.

The population parameters have been characterized for the generations that developed during a complete reproduction year of a population of the calanoid copepod Diaptomus calvipes Schacht. A model is presented to calculate the numbers of each of the various instars of a copepod produced during any previous interval of time. Life tables were constructed from laboratory data and for the five generations of the 1971 field population as an aid in studying the population dynamics. Successful reproduction in the field population occurred from mid—March until mid—October. Development time increased for successive instars of the same generation. All generations had similarly shaped survivorship curves and there was a progressively lower rate of survival in successive generations. This lower survival rate was related to decreasing survival during the early naupliar stages. Survivorship of adults was characterized by a rectangular curve. Greatest mortality rates occurred during the egg to fourth naupliar interval (N—IV) and in the sixth naupliar stage (N—VI). Critical controlling factors in this population appear to be those which affect either survivorship in the interval between egg and N—IV or reproductive activity of adults.

A direct positive relationship was demonstrated between egg size and naupliar size in the calanoid copepod Diaptomus clavipes Schacht. Number of eggs per clutch and total clutch volume were inversely associated with measures of egg and naupliar size (egg volume, maximum egg length, naupliar volume, and maximum naupliar length). Thus, small clutches with large eggs give rise to large nauplii.

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Acute toxicity tests were performed on adult males and females of a freshwater calanoid copepod, Diaptomus clavipes Schacht, using the azaarene acridine as the test compound. Tests were performed at three temperatures (16, 21 and 26°C) and over a range of nutritional states (fed, starved and stock). Observations on mortality were made at 24‐h intervals for 96 h. Analysis of the data was based on comparisons (using different treatment combinations) of the parameters in a logistic survival function used to describe the mortality data. Median lethal concentrations (using 96‐h LC50 values) were estimated from the logistic survival function as well as from the probit function, for comparative purposes. The LC50 values ranged from 1.64 to 6.70 mg/L, depending on temperature, nutritional state of the animals and sex. The LC50 values were highest for animals (fed before testing) at 16°C. As food availability decreased and temperature increased, toxicity of acridine increased up to fourfold. No significant differences in LC50 values were found between the sexes except in starved animals at 26°C, when males were more sensitive than females. This difference in toxicity between the sexes at 26°C may be due to differences in nutritional stress between the sexes (at this temperature), since control mortality at this temperature was also higher in males than in females.