A New Method to Establish Scoring Criteria of the Index of Biotic Integrity
Shih-Hsiung Liang and Bruce W. Menzel (1997) A new method to establish scoring criteria of the Index of Biotic Integrity. Zoological Studies 36(3): 240-250. Karr's Index of Biotic Integrity (IBI) was applied in north central Iowa streams to examine the technique's utility for measuring environmental quality in agriculturally influenced streams and to develop methodological improvement. During 1988 and 1989, fish were collected in the Boone River and Lizard Creek systems, and physical and chemical measurements of stream environ mental conditions were taken. A modified two-step procedure was proposed for establishing the scoring standard of the 12 IBI metrics. First, a simple linear regression relationship of the metric variable on log drainage area was calculated(p = 0.1). If a significant correlation was found, a Maximum-Species-Richness Line (MSRL) was determined by calculating the 95% Y-intercept as its intercept, and then plotted by the original regression slope. If a nonsignificant relationship was obtained, the upper and lower 5% data points were deleted to define the upper and lower boundaries of the remaining points with horizontal lines. Final ly, the area below the calculated 95% MSRL and the area between the two horizontal lines were equally trisected into above average (5 point), average (3 point), and below average (1 point) categories. After the scoring criteria were established, the IBI value of each sampling site in Boone River and Lizard Creek systems was calculated.
The new scoring procedure resolved the problem of the commonly adopted "eye-fit" method through generating only a single MSRL for a given data set. In Lizard Creek, IBI results were generally consistent with evaluations of physical and chemical environmental quality. During the drought period, variations of IBI scores reflected the dynamics of environmental conditions in the sampling sites. Additionally, the IBI showed greater temporal consistency than another commonly used analytical tool, the Shannon-Weiner Diversity Index. Thus, the new scoring procedure seems to advance the effectiveness of IBI in assessing the environment quality of lotic waters. Numerical species metrics associated with species diversity were more important than proportional ones in contributing to the IBI. Drought conditions throughout the study period influenced some of the data and analytical results.
The new scoring procedure resolved the problem of the commonly adopted "eye-fit" method through generating only a single MSRL for a given data set. In Lizard Creek, IBI results were generally consistent with evaluations of physical and chemical environmental quality. During the drought period, variations of IBI scores reflected the dynamics of environmental conditions in the sampling sites. Additionally, the IBI showed greater temporal consistency than another commonly used analytical tool, the Shannon-Weiner Diversity Index. Thus, the new scoring procedure seems to advance the effectiveness of IBI in assessing the environment quality of lotic waters. Numerical species metrics associated with species diversity were more important than proportional ones in contributing to the IBI. Drought conditions throughout the study period influenced some of the data and analytical results.
Keywords
Biological indicator, Index of Biotic Integrity, Environmental assessment, Stream fishes, Community ecology.
