Middle Yangtze River Research Articles

Using the health index of the environmental microbiota to predict the health status of aquatic wildlife

In aquatic animals, the gut microbiota has a significant function in host health and is impacted by the environmental microbiota. To conveniently monitor, assess and predict aquatic animals’ health, a general and effective microbiota health index (microHI) would be helpful, and the correlation between the aquatic environmental microHI and wildlife gut microHI could be expected. Here, we proposed a general microHI based on the microbial phenotypes of mobile element content, potential pathogenicity and oxidative stress tolerance, and then tested the reliability of the fish gut microHI and its correlation with the environmental microHI in the middle Yangtze River. The results showed that there were positive correlations among the abundance ratios of microbes with the microbial phenotypes of mobile element content, potential pathogenicity and oxidative stress tolerance, suggesting that defining the microHI using the average abundance ratios of microbes without these microbial phenotypes is suitable. Fish gut samples with a lower microHI were more likely to have been obtained from specimens with a disordered microbiota (always means unhealthy host), indicating that the gut microHI has the potential to be used to evaluate the health status of aquatic animals. In the middle Yangtze River, the aquatic environmental microHI had hundred-kilometers-scale high spatial heterogeneity but month-scale low temporal heterogeneity from June to September 2020, and in the section with a low aquatic environmental microHI, the fish gut samples were more likely to have relatively low gut microHIs, indicating that the environmental microHI has the potential to be used to predict the health status of aquatic animals at the community level. The current work initially showed the possibility of using environmental microHI to predict aquatic animals’ health although it was not very exact and precise. We encourage more researches to assess the quantitative relationship between the aquatic environmental microHI and aquatic animal gut microHI.

River Bars and Vegetation Dynamics in Response to Upstream Damming: A Case Study of the Middle Yangtze River

Investigating river bars and their vegetation dynamics in response to upstream damming is important for riverine flood management and ecological assessment. However, our mechanical understanding of the damming-induced changes in river bar and vegetation, such as bar area, morphology, and leaf area index (LAI), remains limited for large river systems. Leveraging satellite images and in situ observed hydrogeomorphic data from, we improve a machine learning-based LAI inversion model to quantify variations in river bar morphology, vegetation distribution, and LAI in the Middle Yangtze River (MYR) following the operation of the Three Gorges Dam (TGD). Then we analyze the mechanisms controlling the bar and vegetation dynamics based on high-resolution river cross-sectional profiles as well as daily discharge, water levels, and sediment in both the pre- and post-TGD periods. Our results indicate that the river bar area decreased by approximately 10% from 2003 to 2020, while the vegetation area and average LAI of these bars increased by >50% and >20%, respectively. Moreover, the plant community on most river bars tended to expand from the bar tail to the bar head and from the edge to the center. The main factor driving vegetation expansion in the MYR after the TGD’s operation was the reduction in bar submergence frequency (by 55%), along with a slight bar erosion. Further analysis revealed that the standard deviation of annual discharge decreased by approximately 37%, and the frequency of vegetation-erosive flow decreased by approximately 74%. Our data highlight the potential impact of large dams downstream flow regimes and vegetation encroachement. Such findings further the understanding of the biogeomorphological impacts of large dams on the river bar vegetation and have important implications for riverine plant flux estimatin, flood management and ecological restoration in dammed river systems.

Main Flow Migration in the Middle Yangtze River Influenced by Cascade Reservoirs: Characteristics, Controlling Factors, Trends, and Ecological Impact

The main flow migration in the middle Yangtze River occurs in most river sections and is affected by factors such as incoming water and sediment, riverbed boundaries, and channel shapes, leading to a complex riverbed evolution. Revealing the controlling factors and analyzing the developmental trends are important for addressing the adverse ecological impacts caused by these changes. Based on a large amount of observational data since the impoundment of the Three Gorges Reservoir, the characteristics of the main flow migration in the middle Yangtze River under different flow conditions were analyzed, and its correlation with the nodes and bars at the inlet, the plane shape of the river, and riverbed morphology were determined to identify the key controlling factors. The results showed that it is characterized by the displacement of the main flow zone during the middle-flow period. The key factors controlling the main flow migration include the deflecting action of the nodes and sidebars at the inlet, relaxation of the channel plane shape, and resistance difference caused by the riverbed morphology between the branches. The trend analysis suggests that the main flow migration in the middle Yangtze River may become more frequent after the operation of the cascade reservoirs in the future and may threaten the ecological environment.

Effect of Froude similitude deviation on curved channel simulations: A case study in the Middle Yangtze River

Froude similitude and friction similitude are the two crucial similarity conditions that are often used in physical-scale modeling of rivers. However, models often deviate from Froude similitude when dealing with real-world situations. This study developed several fixed-bed river models with various curvatures to determine the effect of Froude similitude deviation on curved channel modeling. Models were constructed according to the characteristics of the Middle Yangtze River. Differences in longitudinal slope, transverse slope, and main stream line location were measured by varying Froude similitude deviation. The deviations of longitudinal slope and velocity were negligible because friction similitude was accounted for. The transverse slope varied significantly with the Froude similitude deviation, and the main stream line varied with the curvature and Froude similitude deviation. Formulae were derived to estimate the slope deviation. These analyses helped to clarify the feasibility of the method of Froude similitude deviation for curved channels.

Factors affecting the stability of soil aggregates of plinthosols in the middle reaches of the Yangtze River

Soil aggregate stability is a key factor that affects soil erosion and ecological restoration. In this study, three typical plinthosol profiles in Wuhan (W), Yueyang (Y), and Jiujiang (J) were selected, and the mean weight diameter (MWD), geometric mean diameter (GMD), and fractal dimension were used as indicators of soil aggregate stability, as well as the erodibility factor (K value). Based on the end-member analysis, it appears that the plinthosols in the three profiles were wind-formed deposits, which greatly affected particle size and erodibility. There was a greater resistance to erosion among the plinthosols developed from finer grains than among those developed from coarse grains. The stability of aggregates in profiles W and Y decreased gradually with depth, while it varied little in profile J. The initial moisture content had a significant effect on the anti-erodibility of the plinthosols, and there were some differences between the profiles: in profile W, the anti-erodibility increased with the increase in initial moisture and reached its maximum value at the initial moisture content of 20%; in profiles Y and J, when the initial moisture content was 15%, the anti-erodibility was the highest. Reddishmatrixhadahigher anti-erodibility than white veins.ProfileJhadthelargeststability gap between white veins and reddishmatrix,followed by profileY and W. These results provide a theoretical basis for the conservation of soil and water in the Yangtze River middle reaches by revealing the stability characteristics of plinthosols.

Living environment shaped residents’ willingness to pay for ecosystem services in Yangtze River Middle Reaches Megalopolis, China

Profound understanding on the diversity of local residents’ willingness to pay (WTP) for ecosystem services (ESs) may aid evaluation of policy impacts by uncovering trade-offs and synergies for achieving sustainable environmental resource management. However, the reasons for the spatial preference heterogeneity of WTP are still unclear. In this study, an extensive survey with 4,580 residents in the Yangtze River Middle Reaches Megalopolis (YRMRM), central China, was carried out to investigate the public’s WTP to maintain and improve ESs. We identified key influencing factors and explored how they shaped the preference heterogeneity in WTP by random forest model and surface fitting method. Our results showed that 81.4% of residents reported WTP for ESs greater than zero. Water supply, waste treatment, food supply and raw material supply were the preferred ESs for residents. Living environment factors (i.e., extent of farmland, water and forest near the residence) were found as the key drivers of WTP. Proximity to farmland, water and forests resulted in high WTP values for a series of specific ESs. The reasons for the heterogeneity of WTP are (1) the difference in proximity to farmland, water and forest (i.e., the contributor to ESs), (2) the divergence of local residents’ preferences for ESs. This study disclosed the heterogeneity and causes of public preferences in YRMRM, which could help policy and decision makers to develop eco-compensation initiatives towards conservative and sustainable use of the environmental resources.

Riverine antibiotic occurrence and potential ecological risks in a low-urbanized and rural basin of the middle Yangtze River: Socioeconomic, land use, and seasonal effects

This study firstly investigated the effects of season, land use, and socioeconomic on the spatiotemporal changes of riverine antibiotic concentrations in a low urbanized and rural watershed. In the dry and wet seasons, water samples were collected and analyzed for 15 antibiotics. The results indicated that 14 antibiotics, excluding leucomycin, were detected. Monsoon led to significantly lower total antibiotic concentrations in the wet season (22.0ngL−1) than in the dry season (51.2ngL−1). Total antibiotic concentrations were dominated by amoxicillin (below limit of detection (<LOD)-34.7ngL−1)), erythromycin-H2O (<LOD-14.7ngL−1), roxithromycin (<LOD-27.9ngL−1), and trimethoprim (<LOD-6.34ngL−1). The total antibiotic concentrations were usually higher in the downstream areas of urban land than in the river reaches of forest land and agricultural land. At county or city scales, total antibiotic concentrations in the dry season were significantly correlated with the rural population, public budget, husbandry product and output, effluent volume, fishery product and output, and hospital number, which generally depend on land use in the basin. Amoxicillin poses a high ecological risk to aquatic algae, whereas erythromycin-H2O, ofloxacin, and norfloxacin pose medium ecological risks. However, trimethoprim poses a medium ecological risk to mollusks. These results provide improved insights into the characteristics of antibiotic occurrence and ecological risks in the waters of low-urbanized and rural areas in China and can be extrapolated worldwide.

Construction of hybrid constructed wetlands for phosphorus chemical industry tailwater treatment in the middle Yangtze river basin: Responses of plant growth and root-associated microbial communities

Constructed wetlands are commonly utilized to treat industrial wastewater due to their effectiveness, affordability, and environmental benefits. Many phosphorus chemical enterprises in the middle Yangtze River basin are facing high pollution load challenges and efforts are needed to improve removal efficiency of pollutants. This work was the first to use constructed wetlands for phosphorus chemical industry tailwater (PCITW) treatment. The new hybrid constructed wetlands (CWs) proposed were the aeration horizontal subsurface flow constructed wetland (AHSCW) and the integrated vertical flow constructed wetland (IVCW), which were constructed on a pilot scale. Here, the effectiveness of pollutant removal along hybrid CWs, wetland plant growth, and root-associated microbial community responses to the PCITW were investigated. The results showed that there was spatial variation in removal of carbon, nitrogen, and phosphorus in the hybrid CWs, and that the AHSCW and the IVCW played synergistic roles in the removal of pollutants. Compared with influent, the toxic effect of effluent to embryos of a rare minnow (Gobiocypris rarus) was alleviated. Exposure to the effluent resulted in no malformation or death for embryos. Plants and microorganisms in the wetland system of the phosphate chemical tailwater were then compared with the control system of municipal tailwater. Plants in the former system had lower root density, and higher average root diameter, root shoot ratio, specific root length, and specific surface area. Plant roots also had decreased NH4+ uptake ability but increased Ca2+ uptake to adapt to the high load and complex pollution stress. Unlike the control system, stochastic mechanisms had a more important role than deterministic processes in shaping the microbial community assembly associated with the PCITW. Meanwhile, analysis of microbial network-level topological characteristics demonstrated substantial reduction in network interactions complexity and microbiome stability in the treatment system. Findings from this study suggest wetlands will be helpful for efficient purification of phosphorus chemical industry wastewater in the Yangtze River basin.

Phylogeographic analysis revealed allopatric distribution pattern and biogeographic processes of the widespread pale chub Opsariichthys acutipinnis-evolans complex (Teleostei: Cyprinidae) in southeastern China

Understanding phylogeographic patterns of widespread species can provide insights into their speciation processes and guide the conservation and management measures. In the present study, Cyt b sequences were used to investigate the phylogeographic structure of the Opsariichthys acutipinnis-evolans complex in southeastern China. The gene tree revealed six major lineages (lineage A-F) which were distributed allopatrically, with lineage B distributed in the western part (middle Yangtze and Pearl River) and the other lineages in the eastern part (lower Yangtze and coastal waters of southeastern China). Dating of the lineage diversification revealed the early eastward-westward divergence separating lineage A, B, and C during the late Pliocene and early Pleistocene (3.00, 2.61, and 2.12 Ma, respectively), possibly due to the uplift of the Qinghai-Tibetan Plateau and subsequent orogenies in southeastern China. The following northward-southward diversification resulted in the separation of lineage D, E, and F in the early-middle Pleistocene (1.33 and 0.95 Ma), likely associated with the enhanced succession of glacial cycles during the Early-Middle Pleistocene transition. Although the genetic divergence of 0.017–0.070 among lineages indicated possible different species, morphological characters failed to separate them. Therefore, they were treated as a species complex. Given the distinct genetic divergence of the various lineages, they were suggested as different evolutionary significant units.

The evolution and determinants of Chinese inter-provincial green development efficiency: an MCSE-DEA-Tobit-based perspective.

Continuous and rapid economic development has brought about excessive resource consumption and environmental pollution. Therefore, it is particularly essential to coordinate economic, resource, and environmental factors to achieve sustainable development. This paper develops a new data envelopment analysis (DEA) method that can be used for multi-level complex system evaluation (MCSE-DEA) to reveal the inter-provincial green development efficiency (GDE) in China from 2010 to 2018. Moreover, the Tobit model is applied to explore the influencing factors of GDE. We found that (i) the MCSE-DEA model tends to have lower efficiency scores than the traditional P-DEA (panel data envelopment analysis) model, and the top three provinces are Shanghai, Tianjin, and Fujian; (ii) the efficiency shows an increasing trend during the whole study period. The southeast region and the Middle Yangtze River region have the highest efficiency values, reaching 1.09, while the northwest region ranks last with an average efficiency value of 0.66. Shanghai performs the best, while Ningxia performs the worst, with efficiency values of 1.43 and 0.58, respectively; (iii) the provinces with lower efficiency values mainly come from economically underdeveloped remote regions, which can be attributed to issues of water consumption (WC) and energy consumption (EC). Moreover, there are much room for improvement in solid waste emissions (SW) and soot and industrial dust emissions (SD); (iv) the environmental investment, R&D investment, and economic development level can significantly improve GDE, while industrial structure, urbanization level, and energy consumption have inhibiting effects.

A computational study of 3D flow structure in two consecutive bends subject to the influence of tributary inflow in the middle Yangtze River

Enhanced understanding of turbulent flow structure in bends in natural rivers is essential for waterway regulation, navigation safety and environmental and ecological wellbeing. However, the flow structure in consecutive bends has so far remained poorly understood, especially when it is subject to the influence of tributary inflow. Here, the 3D flow structure in two consecutive bends, namely Qigongling (upstream bend) and Guanyinzhou (downstream bend), subject to the influence of tributary inflow from the Dongting Lake, in the middle Yangtze River, is numerically investigated. The RNG k-ϵ turbulence model is applied under the FLOW-3D software platform. The results show that: (1) the high-velocity zones shift from inner to outer banks in both consecutive bends. (2) No secondary current cells are spotted at the entrance of either bend. At the bend apex, multiple cells of secondary currents appear in Qigongling, but not in Guanyinzhou under certain discharges. (3) Recirculation vortices occur mainly on the inner bank (small-scale) in Qigongling, but on both the inner (small-scale) and outer (large-scale) banks in Guanyinzhou. (4) With increasing mainstem (tributary) discharge, the velocity and turbulent kinetic energy enlarge (reduce). However, a decrease of the secondary current strength in Qigongling and an increase in Guanyinzhou (all increase in both bends).

Shoreline hardening affects species composition and condition of larval fishes in the Yangtze River: Implications for conservation and inshore habitat restoration

AbstractInshore habitats play a crucial role in the downstream drift of larval fish in large rivers. Natural inshore habitats of most of the world's large rivers have been heavily degraded by shoreline stabilization measures, but the knowledge about consequences for the condition and distribution of larval fishes is extremely limited. Investigations during the peak season of larval drift into species composition as well as into feeding intensity and body injuries of representative taxa were conducted at different inshore mesohabitats along semi‐natural and stabilized shores in a free‐flowing section in the middle Yangtze River. Species were unambiguously identified by a combination of DNA barcoding and morphological analyses. Overall, 37 taxa from seven families were detected from a total of 9,915 fish larvae caught. Earlier developmental stages greatly outnumbered the later stages in diversity and abundance in each investigated mesohabitat. Abundance and assemblage structure as well as the body injury rate differed significantly between mesohabitats. Generally, overall species richness and abundance tended to be lower, and divergence of the assemblage and body injury rates tended to be higher at heavily hardened shores, which could be contributed to the poor riparian vegetation and restricted suitable hydraulic conditions there. Our results may reflect the underestimated impact of inshore habitat degradation on larval fishes and highlight the demand for creating adequate areas of shallow and slow‐flow habitats with good riparian vegetation conditions along the shores. These measures will foster an appropriate connectivity between spawning areas and high‐quality nurseries for larval fishes.

Investigating the origins of metals used in the Early Shang capital of Zhengzhou

Lead isotope analysis of crucibles and a metal droplet has revealed new information about the provenance of the lead and copper resources used at Zhengzhou Shang City during the Upper Erligang period. The crucibles were found to be divided into three types and associated with copper smelting/refining, leaded tin bronze alloying, and bronze pouring. The copper smelting/refining crucible contains common lead (206Pb/204Pb = 18.12) and low Pb content in its slag layer. In contrast, the bronze processing crucibles mostly contained highly radiogenic lead (206Pb/204Pb ≥ 19). One bronze pouring crucible was found to have an exceptionally low 206Pb/204Pb ratio (≤17.2), indicating that it was made with recycled bronze from an earlier period. This research is the first to reveal the lead isotope characteristics of the copper material used during the Upper Erligang period, which is strikingly different from the dominant highly radiogenic lead reported in previous research. The Middle Yangtze River Valley is tentatively proposed as the geological source. This result also shows that the Upper Erligang Shang people had a complex metal supply network, including at least southern copper, highly radiogenic lead, and recycled early bronze.

Remote sensing inversion and prediction of land use land cover in the middle reaches of the Yangtze River basin, China.

Land use and land cover (LULC) changes are dynamic and have been extensively studied; the change in LULC has become a crucial factor in decision making for planners and conservationists owing to its impact on natural ecosystems. Deriving accurate LULC data and analyzing their changes are important for assessing the energy balance, carbon balance, and hydrological cycle in a region. Therefore, we investigated the best classification method from the four methods and analyzed the change in LULC in the middle Yangtze River basin (MYRB) from 2001 to 2020 using the Google Earth Engine (GEE). The results suggest that (1) GEE platform enables to rapidly acquire and process remote sensing images for deriving LULC, and the random forest (RF) algorithm was able to calculate the highest overall accuracy and kappa coefficient (KC) of 87.7% and 0.84, respectively; (2) forestland occupied the largest area from 2001 to 2020, followed by water bodies and buildings. During the study period, there was a significant change in area occupied by both water bodies (overall increase of 46.2%) and buildings (decrease of 14.3% from 2001 to 2005); and (3) the simulation of LULC in the MYRB area was based on the primary drivers in the area, of which elevation changes had the largest effect on LULC changes. The patch generated land use simulation model (PLUS) was used to produce the simulation, with an overall accuracy and KC of 89.6% and 0.82, respectively. This study not only was useful for understanding the spatial and temporal characteristics of LULC in the MYRB, but also offered the basis for the simulation of ecological quality in this region.

Heavy metal content and health risk assessment of atmospheric particles in China: A meta-analysis

In recent decades, China has devoted significant attention to the heavy metals pollution in particulate matter. However, the majority of studies have only focused on the field monitoring in relatively remote areas, which may not be representative of air quality across the country. This study reevaluated the characteristics, temporal and spatial changes, and health concerns associated with heavy metal pollution in atmospheric particulates on a national scale by coupling Meta-analysis and Monte Carlo simulation analysis. In terms of spatial distribution, the heavy metals pollution levels in the northern coast and northeastern regions are relatively high, whereas it is low along the middle Yellow River, middle Yangtze River, as well as Southwest. With the exception of Cu, the distribution of all elements in PM2.5 steadily decreased over time Moreover, PM10 and PM2.5 performed similar where Cd and Ni both first increased followed by a decline while, Cr displayed a decrease before it showed an increment. And since the implementation of prevention and control policies about the atmospheric release, the focus of industrial emission has gradually shifted from energy production and processing to living products manufacturing. Moreover, the carcinogenic risk was shown to be Cr > As, Pb > Ni, Cd, while the non-carcinogenic risk was as follows: As, Ni > Cr, Cd. Among all contaminants, Cd, As, and Cr in PM2.5 and PM10 exceeded the WHO standard in the cities with worst air quality. It was observed that As posed the largest non-carcinogenic risk to adults while, Cr caused the most carcinogenic risk to adults and children, where the carcinogenic risk of children remains higher than that of adults. Therefore, the findings of this study may offer data support to the China's heavy metal pollution standards in airborne particles and offer theoretical data support for pollution management.

Spatiotemporal Distribution and Driving Factors of Polycyclic Aromatic Hydrocarbons (PAHs) in Inland Sediments of China

This study reviewed the spatial and temporal distributions of polycyclic aromatic hydrocarbons (PAHs) during 2000-2010 in inland sediments of China and quantified the underlying socioeconomic determinants based on the structural equation model and gravity model. We found that PAHs concentrations in the sediments of eight different regions followed the order of Northern coast>Northeast>Eastern coast>Southern coast>Middle Yellow River>Middle Yangtze River>Southwest>Northwest. The Southern coast, Middle Yangtze River, and Southern coast regions showed large contributions to the high-molecular weight PAHs, whereas the Northeast, Northwest, and Middle Yellow River regions showed high contributions to the low-molecular weight PAHs. PAHs concentrations continuously increased from the year 2000 followed by a gradual decline after 2006, with significant differences in the year when PAHs levels reached their peak. PAHs concentrations of sediment in developed regions declined in recent years following a continuous increase in the 2000s; however, they still increased rapidly in developing regions owing to fast economic development. In addition, the increment rate of PAHs concentrations in sediment at the remote or less-developed regions was slower than that at the developed regions. Urbanization and industrialization had an important effect on PAHs in the sediments, and the largest influencing factor was the economic development.

R-statistic based predictor variables selection and vine structure determination approach for stochastic streamflow generation considering temporal and spatial dependence

Stochastic streamflow generation is crucial for water resources planning and management as well as water conservancy project design and operation. This study proposes an accurate, reliable and parsimonious approach for stochastic streamflow generation considering temporal and spatial dependence on the basis of regular vine copula model. The emphasis is on advancing an R-statistic based strategy of vine structure determination that divide the vine copula model construction into two independent parts and avoid continuous accumulation of uncertainty in the traditional Kendall's tau based method. Two study regions (the Upper Colorado River basin and Middle Yangtze River basin) with diverse hydrology regime and available data length are selected as case studies to showcase the performance of the proposed approach in practice. The results indicate better performance than two existing models in terms of streamflow estimation, and demonstrate that stochastic simulation series can preserve distribution and statistical characteristics of observed records. R-vine copula model constructed by the proposed approach is confirmed to possess low sensitivity to the number of predictor variables as well as good adaptability and robustness to streamflow series with diverse characteristics and abundances. The enhanced capability and performance stem from the accurate identification of predictor variables and characterization of complex and diverse dependence structures among different streamflow series, on the basis of a comprehensive and precise dependence measure, R-statistic.

The role of landscape evolution in the genetic diversification of a stream fish Sarcocheilichthys parvus from Southern China.

Sarcocheilichthys parvus (Cypriniformes: Gobionidae) is a stream fish which is endemic to sub-tropical coastal drainages in southern China, thus offering a valuable model for understanding how genetic divergence arises in stream-adapting freshwater fishes in this region. Using the mitochondrial Cyt b gene, integrative analyses of phylogeny, population demography, and ancestral area and paleo-drainage reconstructions are carried out to explicitly explore the role of landscape evolution in genetic diversification of S. parvus. The time-calibrated phylogeny of S. parvus indicates the splitting of two major lineages (A and B) at ∼3.66Ma. Lineage A inhabits the Poyang Lake sub-drainage of the middle Yangtze River, Han River and Pearl River, and can be split into two sub-lineages (A-I and A-II), where sub-lineage A-II can be further sub-divided into three infra-sub-lineages (A-IIa, A-IIb and A-IIc). Except for the infra-sub-lineage A-IIc, which is restricted to the Han River and Pearl River, the other sub-lineages and infra-sub-lineages live exclusively in the Poyang Lake sub-drainage. Lineage B lives in the lower Yangtze River, Qiantang River, Jiaojiang River and Ou River, displaying close genetic relationships among the drainages. Rapid population expansion has occurred since the Late Pleistocene. Our findings indicate that the splitting of lineages A and B could be attributed to geographic isolation due to the Zhe-Min Uplift, acting as a biogeographic barrier before the late Early Pleistocene. Furthermore, the strong genetic divergence within Lineage A could be explained by the isolation role of the Nanling Mountains and Poyang Lake acting as an ecological barrier; while the lack of phylogenetic structure within Lineage B may have been the result of paleo-drainage connections or episodic freshwater connections during the eustatic low stand of sea level in the late Middle-Late Pleistocene.

Longitudinal variation of channel evolution along the middle Yangtze River after the operation of the Three Gorges Project

三峡工程运行后,坝下游河道发生持续冲刷。本文研究了长江中游(955 km)不同河段沿程演变差异及其原因。总体而言,河床形态调整幅度自上而下减弱,这是因为在河床持续冲刷过程中,水流含沙量沿程恢复,故越往下游冲刷相对缓慢。平面形态方面,长江中游岸线崩退及洲滩变形的强度均呈沿程减弱趋势,且在荆江河段最为显著。断面形态方面,河床冲深幅度在宜枝下段＞荆江河段＞宜枝上段＞城汉河段＞汉湖河段。理论上距离三峡工程最近的河段冲刷应最为剧烈,但由于宜枝上段床沙粗化显著,限制了冲刷的进一步发展。过流能力方面,宜枝河段由于距洞庭湖较远,并未受到入汇顶托作用,故其平滩流量的调整基本由进口水沙条件控制,并随着河床冲深下切而增大;对于荆江、城汉和汉湖河段,河床冲刷虽显著,但支流或湖泊的入汇顶托对平滩流量产生的影响大于前者,故平滩流量总体随上下游水位差同步波动。;Significant degradation have occurred in the middle Yangtze River since the operation of the Three Gorges Project. In the current study, longitudinal evolution differences of different reaches along the middle Yangtze River were quantitatively compared, and the main reasons were investigated. In terms of planform geometry, the intensity of bank retreat and central-bar deformation showed a decreasing trend along the reach, and it was most significant in the Jingjiang Reach. With respect to cross-sectional geometry, channel degradation developed gradually from the Yizhi Reach to downstream reaches. It is uncommon that the adjustments of bankfull channel geometry in the upper Yizhi Reach were smaller than those in the downstream reaches. The reason is that the significant coarsening of bed-material composition in the upper Yizhi Reach hindered the development of channel degradation. In terms of discharge capacity, the variations of reach-scale bankfull discharge in the Yizhi Reach were mainly controlled by the incoming flow and sediment conditions, and it increased with the process of channel degradation. In the other subreaches, the variations of bankfull discharge were mainly influenced by the backwater effects owing to the confluences of tributaries and lakes.

A new formula of recovery factor for non-equilibrium transport of graded suspended sediment in the Middle Yangtze River

A new formula of recovery factor for non-equilibrium transport of graded suspended sediment in the Middle Yangtze River