MODELED IMPACT OF TSUNAMI-INDUCED SEAWATER INUNDATION ON WETLAND MICROBIAL POPULATIONS

Tsunamis can generate major disruptions in water quality and ecosystem health within coastal surface and near-surface freshwater systems, including rapid salinity changes, local flooding-related contamination, and pollution resulting from reactivation of offshore dumpsites. Microbial populations are key indicators of overall ecosystem health, since environmental stress can be reflected in their genetic diversity and abundance. To date, little is known of the particular impact of abrupt seawater inundation as an environmental stress upon bacterial communities in wetlands. This study simulates the impact of seawater upon freshwater bacteria ecosystems. We inundate samples of surface and subsurface sediments collected from two freshwater wetlands in South Bend, Indiana as a basis of comparison for surface and subsurface sediment samples from the Phuket, Thailand region that was flooded by the tsunami resulting from the M9.0 Sumatra-Andaman Islands earthquake of December 2004. The surface and subsurface sediment samples are split and flooded with seawater of low, moderate, and high salinity under conditions emulating either subsequent post-tsunami stagnant water or post-tsunami slow drainage and freshwater surface recharge. The pre- and post-tsunami microbial populations are quantified by extracting DNA from each sediment sample and using denaturing gradient gel electrophoresis (DGGE) to record relative amounts and varieties of bacteria present. This allows us to track population changes through the course of the study and determine which species are initially the most vulnerable, which are most diminished with time, and which are able to rebound and establish dominance in the microbial communities.