• Research

• Longleaf Pine Research
• Aquatics Research
• Wetlands
• Streams/Rivers
• Water Chemistry and Nutrient Dynamics in the Lower Flint River
• Coupling Source Water Chemistry to Microbiological Processes
• Annual Summary of Water Resources Conditions in Southwestern Georgia
• Effects of Flooding
• Changes in Mussel Assemblage Composition in the Lower Flint River Basin from 1999 to 2001: An Assessment of the Impacts of 2000 Drought
• Effects of Drought on Freshwater Mussels and Instream Habitat in Coastal Plain Tributaries of the Flint River, Southwest Georgia (July-October, 2000)
• Hydrologic and geomorphic controls on suspended particulate organic matter concentration and transport in Ichawaynochaway Creek, Georgia, USA
• Wood Debris Recruitment and Movement Across Differing Riparian landforms in a Coastal Plain Stream
• Groundwater
• Land-Use Impacts
• Wildlife Research
• Research Publications
• Graduate Projects

Effects of Drought on Freshwater Mussels and Instream Habitat in Coastal Plain Tributaries of the Flint River, Southwest Georgia (July-October, 2000)

Research Team: Paula M. Johnson, Anna E. Liner, Dr. Stephen W. Golladay (Associate Scientist), Dr. William K. Michener

Habitat conditions (water depth, water temperature, dissolved oxygen and flow velocity) and mussel survivorship were monitored weekly at nine locations in the lower Flint River Basin during extreme drought conditions (June-October 2000). Sites ranged in size from d-link magnitudes of 23 to 617.

Stream habitat and mussel population responses to drought were not uniform across study sites. At sites on Spring and Chickasawhatchee creeks, water flow ceased, or the stream bed dried, and dissolved oxygen concentrations were extremely low (< 5 mg/L) for extended periods. Weekly mussel mortality as high as 76% was observed at these locations. In contrast, sites on Muckalee and Ichawaynochaway creeks experienced less severe reductions in flow and dissolved oxygen, and mussel mortality was correspondingly low (i.e., weekly mussel mortality averaged 2.8% during the entire survey period).

Flow velocity and dissolved oxygen were highly correlated to mussel mortality. Unionid mortality increased when flow velocity at the substrate surface fell below 0.01 m/s or when dissolved oxygen concentrations fell below 5 mg/L. Elliptio crassidens, Lampsilis subangulata, Medionidus pencilatus and Pleurobema pyriforme experienced highest mortality under hypoxic conditions (i.e., DO<5mg/L). Elliptio complanata and Villosa vibex had lowest mortality under hypoxia and withstood long-term (>20 d) emersion. Overall, riffle-dwelling and rare mussel species experienced greater mortality in relation to drought conditions than widespread, common species.

We observed higher habitat impairment at sites with lower d-link magnitudes, i.e., generally smaller streams. Smaller streams also demonstrated a decrease in diversity, evenness and richness during the study period.

Observed mussel behavioral responses to drought (i.e., movement and mantle exposure behavior) suggest that several habitat factors might act to mediate the effects of drought on mussel mortality. Among these is the presence of large woody debris in streams, which may create small, well-shaded depressions that could serve as mussel micro-refugia during drought. In addition, instream aquifer discharge may be key to providing water, cooler stream temperatures, or increasing flow stability during drought conditions.

These results strongly underscore the need for instream flow protection that not only ensures proper water levels in stream channels, but also considers minimum dissolved oxygen and flow velocity conditions. The presence of diverse mussel assemblages observed in medium sized sites coupled with the high levels of mortality observed at these sites suggest that moderately sized stream reaches (i.e., d-link magnitudes from 80 to 130) may be priority areas for mussel conservation and protection efforts in the region.

Additional Information: pdf version of project report

Funded by: The Joseph W. Jones Ecological Research Center and The Nature Conservancy