A principal goal of pesticide science is to be able to predict the environmental impact of a pesticide before it is released into the environment. To save expense and time, we would like to be able to make such a prediction for each pesticide with as few laboratory experiments on the pesticide as possible, and even fewer field experiments. Environmental processes, however, are enormously complex and sometimes (apparently) random. The sites of most interest—agricultural fields, forests, lakes, streams, etc.—are subtle living ecosystems which are incompletely understood and subject to great variability in space and time. The very diversity and intricacy which are indicators of the health of such ecosystems makes even the definition of what constitutes a significant impact on such systems a difficult task.

The SCS/ARS/CES pesticide properties database for environmental decision-making.

Considerations involved in developing a suite of indicators to monitor regional environmental health, similar in conception to management use of ‘leading economic indicators’, are described. Linkages between human activities and well being and the state of the environment are considered essential to the evaluation of general environmental health. Biogeochemical and socioeconomic indicators are mutually affected by environmental degradation and examples of both categories of indicators are described. Desirable properties in indicators of environmental health vary with their specific management use. Different indicators are called for when collecting data to assess the adequacy of the environment, monitor trends over time, provide early warning of environmental degradation, or diagnose the cause of an existing problem. Tradeoffs between desirable characteristics, costs, and quality of information are inevitable when choosing indicators for management use. Decisions about what information to collect for which purpose can be made more rationally when available indicators are characterized and matched to management goals.

A proposed framework for developing indicators of ecosystem health

Experimental acidification of a small lake from an original pH value of 6.8 to 5.0 over an 8-year period caused a number of dramatic changes in the lake's food web. Changes in phytoplankton species, cessation of fish reproduction, disappearance of the benthic crustaceans, and appearance of filamentous algae in the littoral zone were consistent with deductions from synoptic surveys of lakes in regions of high acid deposition. Contrary to what had been expected from synoptic surveys, acidification of Lake 223 did not cause decreases in primary production, rates of decomposition, or nutrient concentrations. Key organisms in the food web leading to lake trout, including Mysis relicta and Pimephales promelas, were eliminated from the lake at pH values as high as 5.8, an indication that irreversible stresses on aquatic ecosystems occur earlier in the acidification process than was heretofore believed. These changes are caused by hydrogen ion alone, and not by the secondary effect of aluminum toxicity. Since no species of fish reproduced at pH values below 5.4, the lake would become fishless within about a decade on the basis of the natural mortalities of the most long-lived species.

Long-Term Ecosystem Stress: The Effects of Years of Experimental Acidification on a Small Lake

The removal of phosphorus during wastewater treatment: A review

SUMMARY. 1. This review considers the factors which determine the recovery of eutrophic lakes following a reduction in the external phosphorus loading.



2 The mean phosphorus content of a lake should decrease roughly in proportion to the reduction in phosphorus input. Where the lake phosphorus concentration does not decrease as predicted, then the release of phosphorus from the sediment is implicated.



3. The current understanding of the processes by which sediment phosphorus is mobilized and transported into the photic zone is described. The extent to which phosphorus release can maintain lake phosphorus concentrations following the reduction in external loading is influenced by: lake morphometry, flushing rate, sediment type, trophic state and history of enrichment.



4. A reduction in the phytoplankton biomass of a lake is dependent upon the size of the decrease in lake phosphorus concentration and the degree to which phosphorus limits primary production. The importance of phosphorus in limiting phytoplankton production tends to decrease with increasing lake trophic status.



5. Improvements in the condition of highly eutrophic lakes require very large reductions in external phosphorus loading, whereas in mildly enriched lakes moderate changes in the supply of phosphorus have noticeable effects on phytoplankton biomass.

Lake restoration by reducing external phosphorus loading: the influence of sediment phosphorus release

The assessment of the hazard associated with the introduction of chemical substances into the environment is receiving considerable attention in current ecological, political, and public forums. The purpose of this paper is to identify and evaluate the basic concepts involved in assessing the hazard of chemical substances to aquatic life. A conceptual framework for conducting a hazard assessment is elaborated. In addition, several proposed procedures for conducting aquatic hazard assessment are compared and contrasted. A discussion of the decision criteria currently utilized in hazard assessment procedures is included. The use of safety factors or ‘uncertainty factors’ as a central concept in a sequential testing approach is presented. An assessment of the ‘state-of-the-art’ in aquatic hazard assessment and recommendations for suceeding stpes in the development of procedures constitute the conclusion of the paper.

Estimating the hazard of chemical substances to aquatic life

Several experiments were designed to examine the acute toxicity of surfactants toDaphnia. Specific tests were designed to develop comparisons between existing acute toxicity data for fish and similar data forDaphnia, and to provide data on the effects of various environmental factors on resultant toxicity of surfactants toDaphnia.
 Acute toxicity data for a series of homologous linear alkyl benzene sulfonates (LAS) demonstrate increases of up to one order of magnitude in toxicity for each increase of two alkyl carbons. LC 50's obtained withDaphnia magna are similar to those obtained with bluegills,L. Macrochirus. Comparative tests withD. magna andD. pulex indicate no statistical differences in 48-hr LC 50 values for three anionic and two nonionic surfactants. A 50 mg/L concentration of suspended, naturally-occurring kaolin significantly reduced the toxicity of longer chain length LAS homologs and had no effect on nonionic surfactant toxicity. In tests with variable hardness concentrations, the acute toxicity of LAS toD. magna is a combined function of both culture and test water hardness. The toxicity of a nonionic surfactant toD. magna was higher in soft water and was not affected by culture water hardness levels. Unlike previously published data for fish, the results of acute toxicity tests withD. magna cultures previously exposed to 0.4 mg/L LAS for periods up to seven generations indicated no significant difference in LAS susceptibility compared to simultaneously tested unexposed controls.

Acute toxicity studies of surfactants to Daphnia magna and Daphnia pulex.

The impact of detergent phosphorus bans on receiving water quality

Modeling the fate of chemicals in the aquatic environment

The effects of diet and water hardness, alone and in combination, on life history characteristics of Daphnia magna were determined in two laboratory tests. Number of young on the first day of reproduction, total young and the number of generations were greater with increasing hardness. At the maximum test hardness of 350 mg/l (as CaC03), approximately 65% more young were produced than at the lowest hardness of 50 mg/l (as CaCO3). Furthermore, time to sexual maturity was about one day shorter in the harder culture water. Daphnids fed the combination of a green alga, trout chow and dehydrated alfalfa were over three times more productive than daphnids fed only the alga or only trout chow and alfalfa. The combination of the algae-reinforced diet with hard culture water provided for optimal productivity.

Alan W. Maki

Papers

Estimating the hazard of chemical substances to aquatic life

Acute toxicity studies of surfactants to Daphnia magna and Daphnia pulex.

The impact of detergent phosphorus bans on receiving water quality

Modeling the fate of chemicals in the aquatic environment

Effects of water hardness and diet on productivity of Daphnia magna Straus. in laboratory culture