Assessment and management of surface waters has evolved from a system of primarily simple chemical criteria to one that includes complex chemical criteria and standards for whole effluent toxicity and biological community performance (Yoder, 1991; Water Quality Standards for the 21st Century). Biological criteria are narrative or numerical expressions that describe the reference condition of an aquatic community inhabiting waters of a given designated use.
The objective of this study was to determine whether biological indices are sufficiently sensitive measures of surface water resource integrity. Using a spatial modeling methodology developed previously (White and others, 1992; Computers and Geosciences), we explored the relationships between two measures of biological criteria for the Black River watershed in northeastern Ohio. Values for the index of biotic integrity (IBI) and the invertebrate community index (ICI), taken from the Ohio EPA ECOS database for 1982 and 1992, were used as response variables in an ordinary least-squares (OLS) regression model. Explanatory variables in the OLS regression model represented point-source and nonpoint-source impacts in the watershed. Point-source predictor variables were extracted from the Ohio EPA LEAPS (Liquid Effluent Analysis and Processing System) database using the median and ninety-fifth percentile for such parameters as water temperature, five-day BOD, and TKN measured at facility outfalls. Nonpoint-source attributes were characterized from land use/land cover classification of a March 1991 Landsat Thematic Mapper satellite scene.
The spatial modeling methodology depends on the topologic relationships among point and areal entities, to aggregate pollution sources from upstream drainage areas for landscapes having point-source and nonpoint-source water-pollution effects. The spatial model relies on an infrastructure of stream networks and drainage basin divides to define the hydrologic system. The basin divide and reach network was derived using morphometric extraction routines on digital elevation models and the U.S. EPA Reach File 3. The spatial relationships between point and nonpoint pollution sources and measurement locations were referenced to the hydrologic infrastructure using network analysis and relational database management techniques within the geographic information system ArcInfo.
Implementation of this spatial model over statewide domains would benefit the preparation of statewide water quality summaries like those required under Section 305(b) of the U.S. Clean Water Act (P.L. 95-217) by increasing the total numbers or lengths of "evaluated waters." Presentation of these statewide summaries still are beset by problems of inconsistent reporting of total stream length and number of assessed waters in each state.
Dale A. White
Ohio Environmental Protection Agency
Division of Surface Water
1800 Watermark Drive
Columbus, OH 43216-3669
Telephone: 614-644-2138
Fax: 614-644-2329
Email: dawhite@cfm.ohio-state.edu
Edward T. Rankin
Ohio Environmental Protection Agency
Division of Surface Water
1800 Watermark Drive
Columbus, OH 43216-3669