Development of an Effective Fish Index of Biotic Integrity for the Sandhills Region of North Carolina

Abstract

We describe a process for developing an index of biotic integrity (IBI) for resident fish assemblages in an ecoregion that exhibits low natural productivity and biodiversity. From 1990 to 2006, 55 fish community samples were collected by the North Carolina Division of Water Quality (NCDWQ) in the Cape Fear, Lumber, and Yadkin river basins within the Sandhills US EPA level IV ecoregion. Initial analyses of these data, using the 12 IBI metrics employed by the NCDWQ in other regions of the state, failed to distinguish significant differences between reference and non-reference streams. To develop a more robust method of measuring responses to anthropogenic disturbance, we delineated contributing watersheds for each of the 36 sample sites using GIS, hydrologic modeling, and 20-foot resolution Digital Elevation Models (DEM) derived from Light Detection and Ranging (LiDAR) data. The 2001 National Land Cover Database (NLCD) and in situ habitat data were used to determine various land use/land cover and hydrologic variables within each watershed. These variables were then used to select the sample sites with absolute minimal anthropogenic impacts. We used the Kruskal-Wallis test to identify eleven fish community metrics, two chemical metrics, and nine individual species that were significantly different in reference and non-reference sites. Of these fifteen metrics, only three exhibited higher values in reference streams. Our results demonstrate that the abundance and diversity of the Sandhills fish fauna are greater in area more highly impacted by anthropogenic activities. By automating the process by which reference sites are chosen, we were able to produce a multi-metric IBI that reflects the varying levels of anthropogenic impacts on wadeable streams in the Sandhills ecoregion.