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Little information about biodiversity patterns in high‐elevation aquatic systems has been gathered, even though these patterns are important for understanding the impacts of human activities. The source region of the Yangtze River, a typical alpine zone with vulnerable and sensitive ecosystems, was selected. Phytoplankton, which play a critical functional role as freshwater primary producers, serve as an important ecological indicator of aquatic systems. Here, systematic surveys on the water environment and phytoplankton were carried out to examine how the phytoplankton community varies with elevation based on hypothesized structural equation models (SEMs) in 10 typical rivers of the Yangtze River source region in March and October 2018. In total, 58 species of phytoplankton belonging to 28 genera were identified. The relationship between species abundance and elevation for phytoplankton showed unimodal elevational patterns. The results of the SEMs showed that all studied aspects affecting the phytoplankton community were directly or indirectly associated with elevation. The synergistic effects of human activities and basic environmental factors (terrestrial productivity and slope gradient) were the drivers affecting the phytoplankton community in the Yangtze River source region. Climate, topography, human activities and other factors are significantly different with changes in elevation, resulting in significant differences in the structure of aquatic communities at different elevations. Human activities were the major drivers affecting the phytoplankton community along the elevational gradient. As the elevation decreased, the disturbances to aquatic ecosystems caused by human activities intensified in the study area. [ABSTRACT FROM AUTHOR]

Sediment transport simulations are important in practical engineering. In this study, a graphics processing unit (GPU)-based numerical model coupling hydrodynamical and morphological processes was developed to simulate water flow, sediment transport, and morphological changes. Aiming at accurately predicting the sediment transport and sediment scouring processes, the model resolved the realistic features of sediment transport and used a GPU-based parallel computing technique to the accelerate calculation. This model was created in the framework of a Godunov-type finite volume scheme to solve the shallow water equations (SWEs). The SWEs were discretized into algebraic equations by the finite volume method. The fluxes of mass and momentum were computed by the Harten, Lax, and van Leer Contact (HLLC) approximate Riemann solver, and the friction source terms were calculated by the proposed a splitting point-implicit method. These values were evaluated using a novel 2D edge-based MUSCL scheme. The code was programmed using C++ and CUDA, which could run on GPUs to substantially accelerate the computation. The aim of the work was to develop a GPU-based numerical model to simulate hydrodynamical and morphological processes. The novelty is the application of the GPU techniques in the numerical model, making it possible to simulate the sediment transport and bed evolution in a high-resolution but efficient manner. The model was applied to two cases to evaluate bed evolution and the effects of the morphological changes on the flood patterns with high resolution. This indicated that the GPU-based high-resolution hydro-geomorphological model was capable of reproducing morphological processes. The computational times for this test case on the GPU and CPU were 298.1 and 4531.2 s, respectively, indicating that the GPU could accelerate the computation 15.2 times. Compared with the traditional CPU high-grid resolution, the proposed GPU-based high-resolution numerical model improved the reconstruction speed more than 2.0–12.83 times for different grid resolutions while remaining computationally efficient. • The aim of the work is to develop a GPU-based numerical model to simulate hydrodynamical and morphological processes. • The novelty is the application of the GPU techniques in the numerical model. • Making it possible to simulate the sediment transport and bed evolution in a high-resolution and efficient manner. [ABSTRACT FROM AUTHOR]

This study quantified the temporal properties of precipitation and actual evapotranspiration (ETa) in the Zoige basin of the Yellow River source region, China during the 1967–2011 period, as well as their influence to the area reduction of peatland. We extracted areas of different land-use and land-cover (LULC) types and obtained daily precipitation data. Then, we calculated annual precipitation (AP) and specific cumulative precipitation (SCP), which is the sum of precipitation to the date when an image was taken, and showed that the peatland areas were strongly affected by SCP. Using a modified Penman–Monteith equation, we calculated ETa for each LULC type and the area-weighted ones to show that the area-weighted total ETa was mainly contributed from grassland and peatland, which was between 450 and 550 mm. Temporal trends of the ratio of SCP to evapotranspiration showed that precipitation was generally greater than evapotranspiration rate not only during the summer but also over the 1967–2011 period. This trend failed to completely explain the continuous decrease of peatland area in the Zoige basin in decades. The draining effect of artificial ditches and natural gullies might play an additional role in causing peatland degradation but requires further process-based studies. [ABSTRACT FROM AUTHOR]

The Dongting Lake, a river-connected lake, plays a vital role in people's living, agricultural production, and ecological security of the Yangtze River basin. A systematic investigation of macroinvertebrates was conducted in the Dongting Lake during May 2004 - January 2005. Altogether 65 taxa belonging to 27 families and 53 genera were identified. The annual average density and biomass of total macroinvertebrates were 265 ind/m2 and 2.40 g dry mass/m2, respectively. It is demonstrated that seasonal variation existed in environmental factors structuring macroinvertebrate assemblages of the Dongting Lake. Hydrological parameters (i.e., flow velocity, water depth) were the driving factors for macroinvertebrate assemblages in spring and summer, whereas the concentrations of water nutrients (i.e., phytoplankton chlorophyll a, total dissolved phosphorus) played the leading role in governing macroinvertebrate assemblages in autumn and winter. After operation of the Three Gorges Dam in 2009, the Dongting Lake may be confronted with the threat of species diversity declining and assemblage structure changing. Thus, ecological restoration measures shall be put forward. © 2016 American Institute of Chemical Engineers Environ Prog, 36: 914-920, 2017 [ABSTRACT FROM AUTHOR]

The disturbance of the water-sediment interface by wind-driven currents and waves plays a critical role in sediment resuspension and internal nutrient release in large, shallow lakes. This study analyzed the effects of the interactions between wind-induced currents an1d waves on the driving mechanism of sediment resuspension in Lake Taihu, the third largest freshwater lake in China, using acoustic and optic techniques to collect long-term, high-frequency, synchronous in situ measurements of wind, currents, waves, and suspended solid concentrations (SSCs). The results suggested that water turbidity started to increase at wind speeds of approximately 4 m/s and significantly increased when wind speeds exceeded 6 m/s. In most cases, wind-induced waves were the main energy source for changes in turbidity. Wave-generated shear stress contributed more than 95% to sediment resuspension and that only in weak wind conditions (<4 m/s) did the lake bottom shear stresses generated by currents and waves contributed equally. The relationship between SSC and bottom shear stress generated by wave was established by fitting the observed results. The processes of sediment dynamics were divided into four stages (A through D) according to three shear-stress thresholds. In stage A, SSC remained stable (about 45 mg/L) and τ was less than 0.02 N/m. In stage B, the sediment bed was starting to be activated (SSC 45∼60 mg/L) and τ was in the range of 0.02∼0.07 N/m. In stage C, a medium amount of sediment was suspended (SSC 60∼150 mg/L) and τ ranged from 0.07 to 0.3 N/m. In stage D, large amount of sediment was suspended (SSC 150∼300 mg/L) and τ was larger than 0.3 N/m. The findings of this paper reveal the driving mechanism of sediment resuspension, which may further help to evaluate internal nutrient release in large shallow Lake Taihu. [ABSTRACT FROM AUTHOR]

Sediment resuspension plays an important role to provide nutrient release for algal growth in large shallow lakes. The settling velocity ( w ) is the key parameter for understanding the suspended sediment transport. In this paper, acoustic Doppler velocimeter (ADV) and optical backscatter sensor (OBS) instruments were used to measure in situ velocities and suspended sediment concentration (SSC) simultaneously without affecting the ambient turbulence in the bottom layer of Lake Taihu. The results showed that (1) ADV echo intensity (EI) could be transferred into SSC successfully by using a simple logarithmic relationship with a strong correlation of 0.87. (2) Three methods from a balance of settling and diffusive flux gradients for calculating settling velocities were applied, including Reynolds concentration flux, estimation of eddy diffusivity using the von-Karman Prandtl equation, and Kwon's power equation. The average settling velocity during the observation period was 0.11 mm/s for Lake Taihu. (3) The fitted power function, w = 1.85 × 10 C , could be used to estimate w according to SSC. (4) Settling velocity changes with SSC, vertical velocities, and wind speed, which describes suspended sediment instantaneous and continuous motions. This paper provides an effective approach for estimating the settling velocity, provides a reference value of settling velocity for hydrodynamic model, and supports a better understanding of sediment transport process and nutrient release in large shallow lakes. [ABSTRACT FROM AUTHOR]

Trace metals and metalloids in aquatic ecosystems may lead to adverse effects on the survival of fish, especially in the sensitive life stages of vulnerable species. It is still unknown whether threatened fish species in the heavily sediment-laden Yellow River are exposed to toxicity risks associated with multiple trace metals. Herein, we analyzed the concentrations of trace metals in aquatic environmental media and fish tissues across the Yellow River mainstream and assessed the level of metal toxicity to threatened fish. Significantly different concentrations of trace metals in fish tissues were measured between at least two categories among near-threatened, vulnerable, endangered, and critically endangered fish. No metal showed a higher concentration in demersal fish than in pelagic fish. Substantially low metal toxicity was observed for the gill of Rhinogobio nasutus (near-threatened) in the upper reaches, as well as for the gill and liver of Silurus lanzhouensis (endangered) in the middle reaches. High contents of suspended sediment in water and high metal concentrations in sediment and suspended matter could influence the survival and reproduction of fish, especially those already with threatened status. [Display omitted] • Toxicity risks of trace metals in threatened fish were studied in the Yellow River. • Metal concentrations in fish tissues significantly differed with threatened status. • No metal had a higher concentration in demersal fish than in pelagic fish. • Fish tissues of some species were exposed to very low toxicity of multiple metals. • Threatened fish in sediment-laden rivers require more attention due to metal toxicity. [ABSTRACT FROM AUTHOR]

The health risk caused by metal pollution is a global concern due to potential metal bioaccumulation, toxicity, and carcinogenicity with multiple sources and pathways. Here, the factors influencing metal bioaccumulation in more than a thousand fish individuals were investigated along a 5464 km continuum of the heavily sediment-laden Yellow River and the health risks to humans were evaluated. The average concentrations of Cr, Zn, As, Cu, Cd, and Pb were below the permissible limits established by domestic and foreign organizations. The fish showed biomagnification of Se and Sn through trophic transfer and a growth dilution effect for V, Mn, Co, Ni, Cu, Zn, As, Cd, and Ba. The concentrations and distributions of most metals in fish were mainly influenced by the trophic levels (δ15N) of fish and the content of the metals in the aquatic environment. The consumption of fish from the Yellow River does not pose a noncarcinogenic risk to the health of adults and juveniles. Cr and As could cause carcinogenic risks, and Cd and Pb also have carcinogenic risks, but these were within an acceptable range. The carcinogenic risks of fish consumption were relatively low in regions with low levels of metal pollution, such as the source region, while the risks were high in regions with heavy pollution and carnivorous fish at high trophic levels. In response to this threat, people can minimize these risks by adjusting their diet and appropriately reducing their consumption of aquatic products from the Yellow River. [Display omitted] • Concentration of metals was investigated in the sediment-laden Yellow River. • Fish showed a clear growth dilution effect for most metals such as Mn, Co, and Cu. • Biomagnification of Se and Sn was confirmed in fish through trophic transfer. • Significant correlations between most metals concentration in fish and habitat • Cr and As could cause carcinogenic risks to the health of adults and juveniles. [ABSTRACT FROM AUTHOR]