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The construction of multi-function reservoirs is important to guaranteeing the development and utilization of water and hydropower resources, but the construction of any hydrologic projects will inevitably affect the downstream flow regime that provides the driving force for riverine ecosystems. This paper therefore aims to propose a framework for assessing multi-objective reservoir operation models based on flow regime using the middle and lower Yangtze River as a case study. Using indicators of hydrologic alteration (IHA) and the histogram matching approach (HMA), critical influential factors for flow were investigated at the Yichang and Datong gauges, which are typical of the middle and lower Yangtze River. This found the magnitude of annual extreme minimum water flow rates to be the most dramatically changed indicator, with an overall degree of hydrologic alteration at the Yichang and Datong gauges of 41.98% and 34.58%, respectively. The monthly mean discharges of February and October at Yichang have been significantly changed as a result of the Three Gorges Reservoir (TGR) operation. Meanwhile, an improved range of variability approach (IRVA) was developed to obtain ideal target ranges for monthly average flow. A multi-objective ecological reservoir operations model was created for the TGR; the Non-dominated Sorting Genetic Algorithm II (NSGA-II) was applied to the model. Three typical years of wet, normal and dry years were selected, and the operation results with corresponding ideal target ranges were analyzed for the downstream Yichang and Datong cross sections. The results showed that there should be a reduction by 23.57%, 28.10% and 39.92% in the monthly mean flow of February and an increase by 34.48%, 112.36% and 52.12% in the monthly mean flow of October at Yichang cross section in wet, normal and dry years, respectively. Close attention therefore needs to be given to integrating ecological objectives with appropriate flow regimes into multi-objective operation models. [ABSTRACT FROM AUTHOR]

Surface sediments were collected from the Yangtze River Estuary (YRE) in May 2012, August 2012, November 2012 and February 2013 to analyse the seasonal and spatial distributions of acid-volatile sulphide (AVS), simultaneously extracted metals (SEM) and the sediment toxicity. An optimised method was used for the AVS and SEM analysis and the results showed that the seasonal variations of AVS were positively correlated with changes in water temperature and the position of higher AVS was relatively fixed. The average of SEM was gradually increased from May 2012 to February 2013 and there were abnormally high values of SEMCuand SEMNiin the YRE. Concentrations of the five SEM components were in the following order: Cd < Pb < Cu ≈ Ni < Zn. The correlations among the concentrations of the five metals suggested that these metals in the sediments of the YRE did not have stable anthropogenic and/or natural origin. The mean values of AVS and SEM in the YRE were closer to those in the Huanghe Estuary and were lower than those in the Pearl River Estuary. The results of two sediment toxicity assessments showed that the sediments of most areas in the YRE had potential sediment toxicities, especially the Ni and Cu contamination. [ABSTRACT FROM PUBLISHER]

The Yangtze Estuary is heavily influenced by coast-continent geochemical processes and anthropogenic activity; thus, the source and distribution of chromophoric dissolved organic matter (CDOM) in the estuary are strongly impacted by these processes. Here, a series of samples were collected from across the Yangtze Estuary to investigate the source and spatial dynamics of CDOM and its components throughout the system. Three indices ( a(355), spectral slope, and fluorescence) were then calculated and interpreted. The results indicated that the distribution of CDOM was dominated by allochthonous input, conservative mixing, and phase transfer. The contribution of biogenic CDOM to total CDOM increased with salinity, and three individual CDOM components were identified upon fluorescence excitation emission matrix spectroscopy and parallel factor analysis of the water samples: C1, corresponding to humic substance-like CDOM, C2, corresponding to tryptophan-like CDOM, and C3, corresponding to tyrosine-like CDOM. C1 primarily originated from a terrestrial source, C2 had widespread origins, none of which played a dominant role, and C3 mainly originated from allochthonous input in the medium salinity area. Unexpectedly, no marine humic-like component was found in the surface water of the Yangtze Estuary, possibly because turbidity decreased the depth of sunlight penetration, limiting production of this component. [ABSTRACT FROM AUTHOR]

Construction of water conservation projects may change the transport of water and sediment, and nutrient and food web dynamics in river systems, thus impacting the ecological systems downstream, especially fish habitats. This study proposed an improved habitat model that consider both habitat quality and quantity and applied it to evaluate the impact of water conservancy projects on fish habitats. The indices of fragmentation, which emphasize the core habitat patch, and connectivity, based on the minimum spanning tree, appeared to be the most suitable indicators of fish habitat quality. Chinese Sturgeon ( Acipenser sinensis ) was used as an indicator species and spawning sites between the Gezhouba Dam and Yichang Station were selected as study areas. The relationships between habitat quality and water temperature and discharge were established in these areas. The results indicated that discharges from 13,100 m 3 /s to 24,200 m 3 /s and water temperatures from 17.1 °C to 20.0 °C are recommended for Chinese sturgeon spawning and hatching. The improved habitat model showed that the impoundment and operation of the Three Gorges Dam and the construction of the separation levee project both caused a decrease in the habitat quality of Chinese sturgeon spawning sites. Compared to previous studies, the improved habitat model provides a promising intermediate step to reduce the uncertainty in evaluating and quantifying the impact of water conservation projects on fish habitats. [ABSTRACT FROM AUTHOR]