Changes of soil microbial biomass and bacterial community structure in Dongting Lake: Impacts of 50,000 dams of Yangtze River

In this study, we examined possible impacts of construction of ∼50,000 dams throughout the Yangtze River watershed on the soil microbial biomass (SMB) and bacterial community structure in Dongting Lake which is the second largest fresh lake in China. Soil samples were collected from 16 study sites where the surface soil was deposited in early stage (before 1970s) or recently years. Soil properties, SMB and bacterial community structure were measured. Relationship between soil properties and bacterial community compositions was simultaneously evaluated by redundancy analysis (RDA). The results indicated that there were significant differences in soil texture and other soil properties between the early sedimentary soil samples and the recently sedimentary soil samples. As a representative for SMB, microbial biomass carbon (MBC) had a significant increase from 686 to 1324 μg C/g soil. Bacterial community structure had an obvious change, and Shannon-Weiner diversity index had a significant increase from 2.39 to 2.92. Although causes for these changes could be multiple, these 50,000 dams would be the root causes as they decreased the grain-sizes of sediment, which affected soil properties, discharged into Dongting Lake.