Term of Award

Spring 2017

Degree Name

Master of Science in Biology (M.S.)

Document Type and Release Option

Thesis (restricted to Georgia Southern)

Copyright Statement / License for Reuse

Creative Commons License
This work is licensed under a Creative Commons Attribution 4.0 License.


Department of Biology

Committee Chair

J. Checo Colon-Gaud

Committee Member 1

Ray Chandler

Committee Member 2

Lance Durden

Committee Member 3

Oscar Flite

Committee Member 3 Email



I compared leaf breakdown and macroinvertebrate assemblages in main-channel habitats of three Coastal Plain rivers (Altamaha, Ogeechee, and Savannah) in southeastern Georgia. Over two seasons (fall 2014 and spring 2015), coarse-mesh packs of water oak (Quercus nigra) leaves were deployed across six study sites (two per basin) to assess the effects of flow regime, particularly discharge, on breakdown rates and macroinvertebrate assemblage structure. Despite significant differences in discharge between river basins during both the fall (p < 0.01) and spring (p < 0.01), each basin exhibited similar breakdown rates (fall avg. k = -0.013/d; spring avg. k = -0.011/d). Multiple regression analyses identified dissolved oxygen concentration (p < 0.01) and macroinvertebrate abundance (p = 0.04) as the best predictors of fall breakdown rates and discharge (p = 0.01) and pH (p = 0.08) as the best predictors of spring breakdown rates. To assess functional integrity, I compared breakdown rates at impacted sites to those at reference sites but did not consistently detect impact due to flow regulation. Fall assemblages were similar among basins based on abundance (p = 0.12) and biomass (p = 0.09). Spring assemblages were also similar among basins based on abundance (p = 0.06) and biomass (p = 0.07). In terms of abundance, chironomids tended to dominate across sites and seasons. In terms of functional feeding group and habit, collector-gatherers and burrowers tended to be dominant across sites and seasons. Distance-based linear models explained 29% and 27% of the overall variation in fall and spring assemblage structure, respectively, and included discharge, dissolved oxygen, specific conductance, and temperature as predictor variables. Assessments of macroinvertebrate assemblage structure did not produce evidence of impairment along the Savannah River. My results suggest that discharge is not a determining factor in leaf breakdown rates in large, coastal plain rivers but do not exclude a role for physical processing in these systems. In terms of biological processing, I posit that microbial activity is the chief contributor. Furthermore, the observed similarity in macroinvertebrate assemblage structure reinforces the usefulness of the ecoregion concept in delineating macroinvertebrate distributions in these systems.

Research Data and Supplementary Material