Decline in the Index of Biotic Integrity of Delaware Run, Ohio, over 50 Years

The purpose of this study was to compare the present biotic integrity of a central Ohio headwater stream with the conditions in 1940. Major changes in fish faunal composition occurred in Delaware Run over this time period. Only 33% (11 of 33) of the totalspecies collected were present in both years. Indices of biotic integrity (IBI) estimated for the 1940 data indicated that the stream was in good condition then, whereas it is in fair to poor condition now. The primary differences are as follows: 1) an increase in abundance of tolerant species suggesting an increase in general pollution, 2) a decrease in percentage of insectivores together with an increase in percentage of generalists suggesting a reduction of the insect food base, 3) a decrease in the number of simple lithophilic spawners suggesting degradation of reproductive habitat through siltation, and 4) an increase in percentage of pioneering fishes suggesting increased temporal stresses in the stream. Although the stream was not in pristine condition in 1940, it has been degraded further in the past half century. OHIO J. SCI. 93 (4): 95-100, 1993 INTRODUCTION The Federal Water Pollution Control Act of 1972 started the nation on a policy to "... restore and maintain the chemical, physical and biological integrity of the Nation's water" (Hocutt 1981). Because fishes are dependent throughout their lives on suitable water conditions, it should be possible to assess both present and recent past conditions in a watershed by examining the fish fauna. In recognition of this, Karr (1981) proposed an initial version of the index of biotic integrity (IBI) calculated by totaling the scores on each of 12 metrics (Table 1). The score on each metric is set at one of three values: five for conditions showing minimal human impact, three for evidence of moderate impact, or one for severe impact. Modifications of the index have been developed for various parts of the United States (e.g., Fausch et al. 1984, Leonard and Orth 1986, Miller et al. 1988, Bramblett and Fausch 199D, including Ohio (Ohio EPA 1988; Table 1), as well as for Ontario (Steedman 1988) and France (Oberdorff and Hughes 1992). Karr et al. (1987) and Fausch et al. (1990) report that the IBI is superior to any current alternative in assessing stream degradation, and Karr (1991) both summarizes the rationale used in the development of the index and presents the presumed ranges of sensitivity for each metric. In the present paper, the IBI is used to compare the ichthyofauna in Delaware Run in 1940 with that present in 1992 as a means of determining if there has been environmental degradation over the 50-year span. MATERIALS AND METHODS Delaware Run is a low gradient (2.4 m'knr), 10-km tributary of the Olentangy River in central Ohio with a watershed of about 25 km. At normal water levels, most of the stream consists of glides with occasional pools and 'Manuscript received 26 January 1993 and in revised form 22 June 1993 (#92-23). Present Address: New York Cooperative Fish and Wildlife Research Unit, Department of Natural Resources, Cornell University, Ithaca, NY 14853 TABLE 1 Karr's (1981) original IBI metrics compared to those used by the Ohio EPA (1988) to assess headwater sites. Karr (1981) Ohio EPA (1988) Number of: 1. fish species