impacts on freshwater bodies. Both labs found that inclusion of larger organisms 

 (beyond zoo- and phytoplankton) prevented the systems from replicating nutrient 

 cycles and system stability of natural bodies of water. LRL scientists have overcome 

 troublesome features of most aquaria — the growth of dense algae mat at the 

 surface — by simply pouring or siphoning the water periodically. Stable systems that 

 are reproducible and track representative bodies from which they were derived have 

 thus been operated for up to about 60 days. '' These would be more than adequate to 

 determine short-term effects of a particular kind of wastewater treatment on 

 decomposition functions and community composition, but could not be applied 

 directly to longer term matters, such as fisheries impacts. 



Application of Laboratory Ecosystem Measurements 



The characteristics of ecosystems are expressed through processes reflecting 

 structure and composition. Measurement of process rates in the laboratory becomes 

 a significant probe of these same processes in the field. One of the most important of 

 ecosystem processes evaluated through both model systems and the real world is that 

 of bioaccumulation. We have come to regard this outcome of the various competing 

 chemodynamic and biodynamic processes as an indicator of potential threat. 

 Clearly, if even simple microcosms had been used before the introduction of DDT, 

 dieldrin, and PCBs, we would have recognized the propensity for widespread 

 contamination of biota, transfer of residues between media, and the resultant 

 ubiquity accompanying the persistence of such chemicals. 



Although a tendency to accumulate in fatty tissues can now be partially predicted 

 by simple laboratory tests (partition coefficient, solubility, etc.), only in the complete 

 system is the actual outcome of the interactions of volatility, biodegradability, 

 adsorption, and other processes realized. Before moving to the field to test a group of 

 candidate mosquito-controlling insecticides, the WHO contracted to have them 

 tested for environmental fate in model ecosystems. Bad actors were revealed in 

 advance of any threat to wildlife. ^ Even though no microcosm test is currently 

 accepted as standard, indices such as the Ecological Magnification or Biodegra- 

 dation Index may be the only experimental verification of predictions from the 

 simpler laboratory tests. Because bioaccumulation studies are so expensive, EM and 

 BI provide the substantive justification for further testing needed by either the 

 developer or regulator of a toxic substance. Employing a model ecosystem in 

 chemical mass balance studies gives us confidence in using simpler tests, or reveals 

 gaps that are unanticipated from simple relationships. 



This degree of understanding, carefully compared to field results, leads to 

 mathematical statements and models. Such efforts as EXAMS have evolved 

 considerably from microcosm studies. The useof computers can thereby bring single 

 species toxicity data into exposure assessments. By comparing anticipated exposures 

 with known toxicologic data, safety margins can be introduced as part of planning in 

 municipal water supply and wastewater treatment, permit writing for discharges, etc. 



Although microcosms are currently employed most advantageously in examining 

 chemical exposure, fate, and bioaccumulation, the success of Van Voris et at. noted 

 earlier has helped to crystallize ecological theory on the relationship of functional 

 complexity to ecosystem stability. The potential for further exploitation of ecological 

 theory is most promising. For example, benthic model ecosystems have probed 

 potential problems of community structure resulting from oil spills and ocean 

 dumping. Freshwater microcosms can suggest which treatment technology or land 

 management practice is least likely to damage nutrient cycling and decomposition 

 processes, so fundamentally important in sustained yield for fisheries. Higher order 

 interactions between species, populations, and communities may be more sensitive to 

 effects of chemicals than single species developed as bioassay standards. Conversely, 

 microcosms may be developed which demonstrate the stability of systems well within 

 the currently envisioned safety margins, thus making more precise management 



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