[1] The history of environmental flow analysis shows a shift from an emphasis on a flat line minimum flow requirement to the development of a holistic, regime-based, approach to flow management. The ecological flow regime determines environmental flow by embracing the multitude of species within an ecosystem rather than emphasizing a single species. Moreover, this paradigm recognizes that flow magnitude, duration, frequency, timing, and predictability must be incorporated into any flow management strategy. In this study, the ecological flow regime paradigm is used to establish such comprehensive and complex management targets for operating a reservoir to satisfy a downstream aquatic ecosystem. The new paradigm incorporates the intermediate disturbance hypothesis, which holds that ecosystems are healthier under disturbances that are neither too small nor too large. The nondominated sorting genetic algorithm is used to find the Pareto set of operating rules that provides decision makers with the optimal trade-off between human needs and ecological flow regime maintenance.

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Microhabitat usage by different species of fish was studied to examine the potential for niche partitioning in riffle areas of a mountain river characterised by frequent natural disturbances. We randomly sampled 96 riffle-area plots (mostly 1 m · 1 m) in a stream in south-western Taiwan for fish abundance and microhabitat characteristics during the dry season from November 2008 to March 2009. Density and electivity values associated with microhabitat usage indicate the presence of niche partitioning among four major species of fish based largely on flow velocity and water depth. Hemimyzon formosanum, a herbivore, prefers higher velocity and shallower water but avoids sandy substrate. Onychostoma alticorpus, a herbivore, prefers lower velocity and deeper water. Rhinogobius nantaiensis, an omnivore, prefers higher velocity, shallower water and gravel-sized substrate but avoids boulder substrate. Acrossocheilus paradoxus, an omnivore, prefers lower velocity and deeper water but avoids pebble-sized substrate. The existence of differentiation of microhabitat preference and overlap of microhabitat usage suggests that interspecific competition is a factor affecting the structure of this fish assemblage, which may remain at early successional stages because of frequent disturbances in the stream. Study results also show that density and electivity detect preference differently. Density detects microhabitat preference for two herbivores while electivity detects microhabitat preference for two omnivores.

Maintaining the natural variability of a river's flow regime is one of the most critical strategies sustaining the ecological integrity of aquatic ecosystems. This research seeks to determine the ecological flow regime for management of streamflow existing reservoirs. The ecological flow regime is a human-modified flow regime that captures the natural flow variability for maintaining the structure and the functional integrity of the aquatic ecosystems. The design procedure uses regionalization analysis, the ratio method, and linear regression analysis techniques with hydrologic indicators to simulate the altered flow variability caused by humanbased annual streamflow reduction. Because it is difficult for reservoir operators to achieve the strict standard of natural flow regime, a discontinuity ratio method is used to express the reservoir's expected effect on the change in hydrologic indicator values. The final product of the ecological flow regime analysis produces a target reservoir operation and management that will provide a flow regime necessary to sustain the integrity of aquatic ecosystems.

Recent work in river restoration and water resources management has seen the need to change the focus of analysis from reach to watershed scales to better define causes of watershed impairment. However, comprehensive investigations at a watershed scale are hindered by difficulties in using reach data that was collected for analysis at small spatial and short temporal scales. This is especially true for ecological and biological data. The approach assembles assessment and monitoring data and uses an autecology matrix to identify the changes in environmental and ecological conditions that may be associated with community change over spatial and temporal scales appropriate for ecosystem analysis in watersheds. The analysis uses a weight-of-evidence approach based on the percent of the community associated with a matrix factor. We have used the autecology matrix to examine historical fish community data from the Dahan River, Taiwan. The results show that the method provides an improved understanding of historical influences on fish community structure and supports a process-based analysis of community change over watershed scales and historic time periods. Further the method helps identify habitat requirements for the fish communities at each sampling site, supporting management and ecological restoration objectives.