/ Ecosystem analysis has been advanced by an improved understanding of how ecosystems are structured and how they function. Ecology has advanced from an eraphasis on natural history to consideration of energeiics, the relationships and connections between species, hierarchies, and systems theory. Still, we consider ecosystems as entities with a distinctive character and individual characteristics. Ecosystem maintenance and preservation form the objective of impact analysis, hazard evaluation, and other management or regulation activities. In this article we explore an approach to ecosystem analysis which identifies and quantifies factors which define the condition or state of an ecosystem in terms of health criteria. We relate ecosystem health to human/nonhuman animal health and explore the difficulties of defining ecosystem health and suggest criteria which provide a functional definition of state and condition. We suggest that, as has been found in human/nonhuman animal health studies, disease states can be recognized before disease is of clinical magnitude. Example disease states for ecosystems are functionally defined and discussed, together with test systems for their early detection.

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A stage-specific habitat classification scheme was developed emphasizing the ecological importance of habitat space as flow refugia for fish. Habitat units were based on planform and channel morphology and the resulting three-dimensional hydraulic patterns that form during floods. Fish were sampled in specific habitat patches using prepositioned areal electrofishing devices at two high-flow stages, near bankfull flow and one-half bankfull flow, during a flood. Fish were also sampled at baseflow immediately following the flood to compare changes in habitat use related to flow stage. During the bankfull stage, fish were found to use floodplain habitat units identified as vegetated point bars and concave-bank benches. During the one-half bank-full stage, fish density and biomass were greater in low-velocity habitat units identified as deflection eddies and expansion eddies than in the high-velocity habitat unit identified as the channel thalweg. Once flow returned to baseflow, fish density and biomass were greater in the main channel habitat units (pools, riffles, and glides) than in lateral habitat units identified as submerged point bars and lateral backwaters. This study provided a framework to quantify flow refugia in low-gradient streams, which is especially important in the restoration of anthropogenically disturbed watersheds that have lost habitat connectivity.

Abstract-Conventional toxicity testing has relied heavily on fixed duration continuous exposure conditions. These conditions have little relevance to the exposure conditions of many environmental pollutants, particularly the highly variable and often brief exposure regimes of episodic pollution events. This research was designed to assess the effects of brief exposures using a postexposure observation period. The common freshwater organisms Ceriodaphnia dubia, Hyalella azteca, and Pimephales promelas were exposed to a range of cadmium (Cd), zinc (Zn), and/or phenol concentrations for durations ranging from 15 to 240 min. Immobility was measured for up to 7 d after the exposure period. Results showed that organisms exposed to Cd and Zn exhibited delayed effects that resulted in increasing immobility for up to 172 h after the exposure period. Ceriodaphnia dubia, H. azteca, and P. promelas exposed to Cd for as short as 30 min exhibited 100, 95, and 85% immobility, respectively, during postexposure observation. Ceriodaphnia dubia and H. azteca exposed to Zn for as short as 30 min exhibited 100 and 30% immobility, respectively, during postexposure observation. Ceriodaphnia dubia exposed to phenol exhibited recovery of mobility after the exposure period. The presence of delayed effects or organism recovery suggests that toxicity tests used to monitor brief exposures should use environmentally relevant exposure durations and postexposure observations.

[1] This paper develops a new approach to identify hydrologic indicators related to fish community and generate a quantitative function between an ecological target index and the identified hydrologic indicators. The approach is based on genetic programming (GP), a data mining method. Using the Shannon Index (a fish community diversity index) or the number of individuals (total abundance) of a fish community, as an ecological target, the GP identified the most ecologically relevant hydrologic indicators (ERHIs) from 32 indicators of hydrologic alteration, for the case study site, the upper Illinois River. Robustness analysis showed that different GP runs found a similar set of ERHIs; each of the identified ERHI from different GP runs had a consistent relationship with the target index. By comparing the GP results with those from principal component analysis and autecology matrix, the three approaches identified a small number (six) of common ERHIs. Particularly, the timing of low flow (D min ) seems to be more relevant to the diversity of the fish community, while the magnitude of the low flow (Q b ) is more relevant to the total fish abundance; large rising rates result in a significant improvement of fish diversity, which is counterintuitive and against previous findings. The quantitative function developed by GP was further used to construct an indicator impact matrix (IIM), which was demonstrated as a potentially useful tool for streamflow restoration design.Citation: Yang, Y.-C. E., X. Cai, and E. E. Herricks (2008), Identification of hydrologic indicators related to fish diversity and abundance: A data mining approach for fish community analysis, Water Resour. Res., 44, W04412,