Decomposition of lizard (Iguana iguana, Ctenosaura similis) and toad (Bufo marinus) carrion open to arthropods was studied in a tropical dry and a tropical wet forest in Costa Rica. Carcass fates, feeding interactions of necrophagous animals and their predators, temporal succession patterns, and species compositions differed between sites. More than 170 species representing 49 families were associated with the carrion baits; calliphorid and sarcophagid larvae and adults and adult Formicidae and Scarabaeidae were most important in reducing carcasses to the dry skin stage. The significance of these results is discussed in relation to nutrient cycles and the decomposition submodel of a tropical forest ecosystem.

Human health and ecological risks must be balanced at hazardous waste sites in order to ensure that remedial actions prevent unacceptable risks of either type. Actions that are designed to protect humans may fail to protect nonhuman populations and ecosystems or may damage ecosystems. However, there is no common scale of health and ecological risk that would allow comparisons to be performed. This paper presents an approach to addressing this problem based on classifying all risks (i.e., health and ecological risks due contaminants and remediation) as insignificant (de minimis), highly significant (de manifestis), or intermediate. For health risks the classification is based on standard criteria. However, in the absence of national guidance concerning the acceptability of ecological risks, new ecological criteria are proposed based on an analysis of regulatory precedents. Matrices and flow charts are presented to guide the use of these risk categories in remedial decision making. The assessment of mercury contamination of the East Fork Poplar Creek is presented as an example of the implementation of the approach.

Nitrogen fixation is shown to occur in decaying logs of American chestnut, Castanea dentata (Marsh.) Borkh., by acetylene reduction techniques, and its significance is considered in relation to log decomposition in forest ecosystems. F o u n d a t i o n under Interagency Agreement with the Atomic Energy Commission-Oak Ridge National Laboratory, and in part b y the D e p a r t m e n t of Microbiology, University of Georgia, Athens. J. ]3. W. held a N S F Predoctoral Fellowship during the study period.

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