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Several groups of bacteria such as Dehalococcoides spp., Dehalobacter spp., Desulfomonile spp., Desulfuromonas spp., or Desulfitobacterium spp. are able to dehalogenate chlorinated pollutants such as chloroethenes, chlorobenzenes, or polychlorinated biphenyls under anaerobic conditions. In order to assess the dechlorination potential in Yangtze sediment samples, the presence and activity of the reductively dechlorinating bacteria were studied in anaerobic batch tests. Eighteen sediment samples were taken in the Three Gorges Reservoir catchment area of the Yangtze River, including the tributaries Jialing River, Daning River, and Xiangxi River. Polymerase chain reaction analysis indicated the presence of dechlorinating bacteria in most samples, with varying dechlorinating microbial community compositions at different sampling locations. Subsequently, anaerobic reductive dechlorination of tetrachloroethene (PCE) was tested after the addition of electron donors. Most cultures dechlorinated PCE completely to ethene via cis-dichloroethene ( cis-DCE) or trans-dichloroethene. Dehalogenating activity corresponded to increasing numbers of Dehalobacter spp., Desulfomonile spp., Desulfitobacterium spp., or Dehalococcoides spp. If no bacteria of the genus Dehalococcoides spp. were present in the sediment, reductive dechlorination stopped at cis-DCE. Our results demonstrate the presence of viable dechlorinating bacteria in Yangtze samples, indicating their relevance for pollutant turnover. [ABSTRACT FROM AUTHOR]

Abstract: Daning River is a deep tributary of Three Gorges Reservoir (TGR) in China, with water level fluctuations of 30m annually. It was assumed that the hydrologic regime would be the main driving force in the self-assembling of the phytoplankton community in the river. In order to test this hypothesis, limnological study was performed monthly in the estuary, midstream and upstream of this tributary from May 2008 to April 2009. We identified 17 phytoplankton functional groups among 63 genera. These phytoplankton functional groups varied significantly, both seasonally and longitudinally. During the flood season (March–September), low water level and high inflows caused a marked increase in the turbidity, especially in the estuary and upstream, allowing functional group MP (the meroplanktonic diatoms) to dominate the phytoplankton community. Meanwhile, constant water level and high temperature led to the stability and thermal stratification in the midstream. These conditions resulted in a high phytoplankton biomass and the dominance of phytoplankton functional groups Y (Cryptomonas spp.) and Lo (motile Peridiniopsis niei and Peridinium) that were adapted to water stratification. During the dry season (October–February), although the inflows were low and water retention time was long, the thermal stratification was disrupted by the disturbance due to the impoundment of TGR, and the water column was deeply mixed. The phytoplankton biomass reduced and functional groups changed: group Lo declined, and group C (small diatom Cyclotella meneghiniana) increased in the estuary and midstream. Group Y replaced group MP to dominate the phytoplankton community in the upstream with the water becoming clear and stagnant. It could be deduced that the dynamics of phytoplankton in the Daning River were mainly influenced by hydrologic regime. [Copyright &y& Elsevier]

Bioavailable water concentrations of polycyclic aromatic hydrocarbons (PAH), polychlorinated biphenyls (PCB) and organochlorine pesticides (OCP) were measured in the water column from Three Gorges Reservoir (TGR) collected in May 2008 using semipermeable membrane devices (SPMDs). The sampling sites spanned the whole reservoir from the upstream Chongqing to the great dam covering more than 600km long distance with water flow velocities ranging from <0.05 to 1.5ms−1. This is the first experience of SPMD application in the biggest reservoir in the world. The results of water sampling rates based on performance reference compounds (PRC) were tested to be significantly correlated with water flow velocities in the big river. Results of back-calculated aqueous concentrations based on PRC showed obvious regional variations of PAH, PCB and OCP levels in the reservoir. Total PAH ranged from 13.8 to 97.2ngL−1, with the higher concentrations occurring in the region of upstream and near the dam. Phenanthrene, fluoranthene, pyrene and chrysene were the predominant PAH compounds in TGR water. Total PCB ranged from 0.08 to 0.51ngL−1, with the highest one occurring in the region near the dam. PCB 28, 52, 101, 138, 153, 180, 118 were the most abundant PCB congeners in the water. The total OCP ranged from 2.33 to 3.60ngL−1 and the levels showed homogenous distribution in the whole reservoir. HCH, DDT and HCB, PeCB were the major compounds of OCP fingerprints. Based on water quality criteria, the TGR water could be designated as being polluted by HCB and PAH. Data on PAH, PCB and OCP concentrations found in this survey can be used as reference levels for future POP monitoring programmes in TGR. [Copyright &y& Elsevier]

Microplastic pollution in inland waters is receiving growing attentions. Reservoirs are suspected to be particularly vulnerable to microplastic pollution. However, very limited information is currently available on pollution characteristics of microplastics in reservoir ecosystems. This work studied the distribution and characteristics of microplastics in the backwater area of Xiangxi River, a typical tributary of the Three Gorges Reservoir. Microplastics were detected in both surface water and sediment with concentrations ranging from 0.55 × 105 to 342 × 105 items km-2 and 80 to 864 items m-2, respectively. Polyethylene, polypropylene, and polystyrene were identified in surface water, whereas polyethylene, polypropylene, and polyethylene terephthalate, and pigments were observed in sediment. In addition, microplastics were also detected in the digestion tracts of 25.7% of fish samples, and polyethylene and nylon were identified. Redundancy analysis indicates a weak correlation between microplastics and water quality variables but a negative correlation with water level of the reservoir and Secchi depth. Results from this study confirm the presence of high abundance microplastics in reservoir impacted tributaries, and suggest that water level regulated hydrodynamic condition and input of nonpoint sources are important regulators for microplastic accumulation and distribution in the backwater area of reservoir tributaries. [ABSTRACT FROM AUTHOR]