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The bacterial community structure in the Changjiang estuary was studied for comparison with future changes, related to the construction of the Three Gorges Dam. Population densities of bacteria in the surface water at station C1 estimated by CFU on marine agar plates and by DAPI direct count, were 2.8 × 104 ml-1 and 4.2 × 105 ml-1, respectively. Physicochemical properties of water, such as temperature and salinity, suggested that station C1 was affected by freshwater from the Changjiang River. Cluster analysis of the PCR-RFLP patterns obtained from 9 samples showed that the bacterial community structure at station C1 was different from the structure at the other stations. Bacterial diversity in the surface water atstation C1 was studied based on the genotypes of the 250 clones of 16S rRNA, and on the phenotypes generated on Biolog GN plates for 70 isolates. Sequences of bacteria from two common marine groups, alpha- and gamma-Proteobacteria, were frequently observed. Some other divisions, including the beta-Proteobacteria, C/F/B group, low G+C gram positive, high G+C gram positive, chloroplasts, and relatives of Verrucomicrobia were also observed. The putative dominant species based on both genotype and phenotype analyses were close relatives of Alteromonas macleodii or Roseobacter spp. These results reflected the nutrient-rich environment at station C1. [ABSTRACT FROM AUTHOR]

The increasing impact of both climatic change and human activities on global river systems necessitates an increasing need to identify and quantify the various drivers and their impacts on fluvial water and sediment discharge. Here we show that mean Yangtze River water discharge of the first decade after the closing of the Three Gorges Dam (TGD) (2003-2012) was 67 km3/yr (7%) lower than that of the previous 50 years (1950-2002), and 126 km3/yr less compared to the relatively wet period of pre-TGD decade (1993-2002). Most (60-70%) of the decline can be attributed to decreased precipitation, the remainder resulting from construction of reservoirs, improved water-soil conservation and increased water consumption. Mean sediment flux decreased by 71% between 1950-1968 and the post-TGD decade, about half of which occurred prior to the pre-TGD decade. Approximately 30% of the total decline and 65% of the decline since 2003 can be attributed to the TGD, 5% and 14% of these declines to precipitation change, and the remaining to other dams and soil conservation within the drainage basin. These findings highlight the degree to which changes in riverine water and sediment discharge can be related with multiple environmental and anthropogenic factors. [ABSTRACT FROM AUTHOR]

Abstract: Using 50years of hydrologic and bathymetric data, we show that construction of ~50,000 dams throughout the Yangtze River watershed, particularly the 2003 closing of the Three Gorges Dam (TGD), has resulted in downstream channel erosion and coarsening of bottom sediment, and erosion of the Yangtze''s subaqueous delta. The downstream channel from TGD reverted from an accretion rate of ~90Mt (1Mt = 1000 000 t)/yr between the mid-1950s and mid-1980s to an erosion rate of ~60Mt/yr after closing of the TGD. The delta front has devolved from ~125Mm3 (1 Mm3 = 1000 000 m3)/yr of sediment accumulation in the 1960s and 1970s, when river sediment load exceeded 450Mt/yr, to perhaps 100Mm3/yr of erosion in recent years. As of 2007 erosion seemed to have been primarily centered at 5–8m water depths; shallower areas remained relatively stable, perhaps in part due to sediment input from eroding deltaic islands. In the coming decades the Yangtze''s sediment load will probably continue to decrease, and its middle-lower river channel and delta will continue to erode as new dams are built, and the South-to-North Water Diversion is begun. [Copyright &y& Elsevier]