Bioassessments Techniques for Benthic Macroinvertebrate in the Savannah and Ogeechee River

Bioassessments are an essential surveillance tool for determining the health of streams and rivers. Benthic macroinvertebrates are commonly used for bioassessment in wadeable streams, however a standardized method for sampling in non-wadeable streams has not been developed for rivers in Georgia. This study was conducted to determine the effectiveness and potential biases of three bioassessment techniques. Mesh bags filled with leaves (leaf packs), Masonite boards (Hester-Dendy samplers), and mesh bags filled with woody debris (snag bags) were deployed during the fall of 2014 at three sites on the Savannah River (N=26) and three sites on the Ogeechee River (N=26). After 30 days, samplers were retrieved and colonizing macroinvertebrate assemblages were assessed for differences in: Richness (EPT Taxa, Diptera Taxa, Trichoptera taxa), Composition (%EPT, %Trichoptera, %Chironomidae, % Diptera), Tolerance (Hilsenhoff Biotic Index), Functional Feeding Group Structure, Habit, diversity (Shannon Wiener, Simpson) and community structure. Macroinvertebrate assemblages differed significantly in Diptera abundance (F10,34=4.6248 P=0.0004), Chironomidae abundance (F10,34=4.7010 P=0.0003) and % burrower (F10,34=2.2688 P=0.0368). Macroinvertebrate assemblages colonizing the different sampling devices also differed significantly (PERMANOVA, F12,34=1.6056 P=0.002). SIMPER analysis revealed that the samplers collected similar taxa, but the number of individuals collected from a few taxa differed between sites. There were also no significant differences when the Georgia Multi-Metric Index, a common tool used in wadeable streams, was applied to site specific data suggesting that all three samplers provide efficient means for collecting macroinvertebrates for biomonitoring purposes in larger rivers. However, Hester-Dendy samplers provide a standard sampling surface for the calculation of macroinvertebrate density and biomass and are relatively easier to process than either leaf packs or snag bags. Our study provides a comparative assessment of these three passive sampling devices for the collection of macroinvertebrates in large, non-wadeable river systems in Georgia. Therefore, our results can be used to guide future management practices for the collection of macroinvertebrates for bioassessment in large rivers of the region