http://www.sciencedirect.com/science/article/pii/S1674987111001290

The Three Gorges Dam (TGD) of the Yangtze River, China, is one of the largest irrigationand hydroelectric engineering projects in the world. The effects of huge man-made projects like TGD onfauna and macrophyte are obvious, mainly through changes of water dynamics and flow pattern; however,it is less clear how microorganisms respond to such changes. This research was aimed to examine differencesin microbial diversity at different seasons and locations (in front of and behind the TGD). In addition,differences between particle-attached and free-living communities were also examined. Thecommunity structures of total and potentially active microorganisms in the water columns behind and in front of the TGD were analyzed with the DNA- and RNA-based 16S rRNA gene phylogeneticapproaches over three different seasons. Clone libraries of 16S rRNA genes were prepared after amplificationfrom extracted DNA and, for some samples, after preparing cDNA from extracted rRNA. Differenceswere observed between sites at different seasons and between free-living and particle-attachedcommunities. Both bacterial and archaeal communities were more diverse in summer than in winter,due to higher nutrient levels and warmer temperature in summer than in winter. Particle-attached microorganismswere more diverse than free-living communities, possibly because of higher nutrient levels andheterogeneous geochemical micro-environments in particles. Spatial variations in bacterial communitystructure were observed, i.e., the water reservoir behind the TGD (upstream) hosted more diverse bacterialpopulations than in front of the dam (downstream), because of diverse sources of sediments andwaters from upstream to the reservoir. These results have important implications for our understandingof responses of microbial communities to environmental changes in river ecosystems affected by damconstruction.