Date of Award





Earth and Space Science - Environmental Science Track


Earth & Space Science

First Advisor

James A. Gore


The rapid bioassessment method for stream bio monitoring generally uses a fixed count of 200 macro invertebrates as the standard subsample size. This number has been argued to be too small to provide accurate estimates on the richness of macro invertebrate communities and is believed to give misleading information pertaining to stream health. In this study, I used data collected from multiple habitats from 29 streams located in several subecoregions of Georgia to examine how the rapid bioassessment scores perform across subsample sizes of 100, 200, and 300 organisms. Subsample sizes of 100 and 200 organisms were found to underestimate richness, functional feeding group, habit, HBI and NCBI for macroinvertebrate communities. As a result, the overall bioassessment scores were significantly altered. Stream health was estimated better when subsample sizes of 300 organisms were used. However, subsample sizes did not affect the ability of reference sites to differentiate from impaired sites. A longitudinal trend was observed which indicated that 300 organisms were required by streams in north Georgia. Three- hundred organisms were not always required by streams in middle and south Georgia. Stream gradient was an important factor in subsample size determination - fast flowing streams required larger subsample sizes while slow moving streams did fairly well with smaller subsamples. Using different subsample sizes for different subecoregions have been recommended in this study.