ABSTRACT
This chapter utilizes an existing method of deriving such threshold relationships: compare lines derived from this method to lines drawn by eye for Index of Biotic Integrity (IBI) metrics, describes threshold relationships for several different environmental datasets and examines the problems, limitations, and concerns when deriving and interpreting such threshold associations. The maximum number of sensitive fish species in Ohio streams and rivers is strongly and clearly limited by physical habitat quality, as measured by the IBI. Dissolved oxygen (DO) is a well-known limiting parameter for fish in streams and rivers, and is one of the primary causes of aquatic life impairment in Ohio streams. DO criteria in Ohio’s water quality standards criteria differ and are stratified by aquatic life use. A major consideration when calculating a 95th percentile regression is choosing the range of the independent variable. The 95th percentile line is considered an empirical estimate of an upper threshold effect of an independent parameter on some dependent parameter.
