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This case study demonstrates (1) the integration of flow-ecology relationships and proposed  streamflow protection standards with existing water quality standards using a tiered Aquatic Life Use (ALU) approach and (2) the development of flow-ecology response curves using extensive habitat and biological databases.
This project is a work in progress. The process described here (Rankin et al. 2012) was carried out independently by a non-profit research institute, the Midwest Biodiversity Institute (MBI), with funding from The Nature Conservancy (TNC). A coalition of environmental groups is using the results to secure ecologically-based low flow protection in the ongoing Ohio Great Lakes Compact Implementation process.
Ohio’s development of ecological flow protection standards stems from Ohio’s commitment to comply with the Great Lakes Compact (see Michigan case study). The Ohio Legislature’s ratifying language, and allotted time of one year to develop implementation language, constrained the initial focus to low flows, which represent the most ecologically stressful period of the year. Given the time limit, water users’ resistance to new regulatory programs, and the highly altered condition of many of Ohio’s streams, the approach was designed to mesh with the Ohio Environmental Protection Agency’s existing ecological monitoring and tiered ALU framework. Because the Compact drove the process, initially it was developed only for the Ohio streams that are tributary to the Great Lakes.
The hydrologic foundation is a database of mean daily flow for the month of lowest flow (historically September) over a 20-year period.  Flow regression modeling ( Koltun and Whitehead 2002) was used to estimate this flow statistic for  ungaged sites using current conditions as the baseline.
The Ohio ALU classification stratifies on the basis of ecological condition, existing flow alteration, and thermal regime.  Ohio’s flow-ecology curves relate number of sensitive fish species to mean daily flow in September for each river type.  The habitat portion of this relationship was developed from Ohio’s Quantitative Habitat Evaluation Index (QHEI; Rankin 1989, 1995), which includes a measure of niche availability.
To comply with the Great Lakes Compact, withdrawals will need to be managed actively to prevent “adverse resource impact.” Pollution-sensitive fish species were proposed as an indicator of adverse resource impact due to their sensitivity to flow alteration and due to a correlation with the responses of other sensitive aquatic species.
The flow-ecology curves would allow the Ohio Department of Natural Resources (ODNR) to determine the cumulative amount of low-flow depletion that would cause predetermined unacceptable losses. Only withdrawals that maintain cumulative flows above threshold levels would be permitted automatically. Proposed withdrawals that trigger the permit process would be reviewed individually.
The proposed Ohio thresholds would provide the benefit of protecting ecologically sensitive freshwater ecosystems, while allowing future development in more resilient ecosystems. Because the process developed for Ohio uses existing river condition to classify river types and uses current conditions as the baseline, it “grandfathers in” existing water uses and sets no restoration goals at present. Even so, regulated interests rejected the proposal and sought alternative legislation to exempt most withdrawals from regulation. Although the legislature passed the industry-backed bill in spring 2011, Ohio’s Governor vetoed it due to technical and legal shortcomings. As of February 2012, it is not clear how the Ohio Department of Natural Resources will comply with the Great Lakes Compact. 
Read more about Ohio Thresholds for Ecological Flow Protection in A Practical Guide to Environmental Flows for Policy and Planning.