Xiaoguang Liu

Flotation and settling of aquatic plant seeds are key processes for dispersal, colonization and succession of riparian and lacustrine vegetation. Studying these processes is crucial for understanding plant community regeneration, guiding wetland restoration and maintaining aquatic ecosystem stability. Despite significant progress in nonspherical particle settling research, current drag coefficient models were largely developed for sediment or volcanic particles and lack validation for biological seeds across a wide range of flow conditions. Furthermore, the quantitative link between easily measurable shape descriptors—such as the Corey Shape Factor () and sphericity ()—and the drag coefficient () of aquatic plant seeds has not been systematically clarified. To address this gap, systematic flotation and settling experiments on the seeds from four typical aquatic plants ( Nelumbo nucifera , Nymphaea spp., Acorus calamus and Nymphoides hydrophylla ) in still water were carried out, revealing distinct settling patterns driven by seed morphology and density. The main novel findings of this study are as follows: (i) the introduction of a unified predictive model for that incorporates and as simple, measurable shape descriptors; (ii) the identification of a critical hydrodynamic transition at particle Reynolds number = 10, leading to a piecewise model structure that significantly improves prediction accuracy across different flow regimes; and (iii) rigorous model development using a large literature dataset of 395 settling measurements ( range 0.03–10,000) and validation on an independent dataset of 59 measurements. The proposed model demonstrates high predictive accuracy and broad applicability, providing a reliable tool for simulating seed dispersal and supporting wetland vegetation restoration and aquatic plant population management.

Quantifying flow resistance in open channels with mixed‐height vegetation is essential for predicting stage–discharge relationships and assessing conveyance and habitat conditions in vegetated floodplains. In staggered tall–short vegetation, strong lateral velocity contrasts and inter‐patch momentum transfer alter the flow structure and hinder the direct use of conventional roughness formulations. Based on flume experiments with rigid cylindrical surrogates arranged as laterally adjacent tall and short patches in a staggered layout, this study develops a physics‐based procedure to estimate the drag coefficient and the equivalent Manning coefficient across emergent to submerged conditions. A two‐patch momentum‐balance model is formulated by explicitly accounting for the measured water‐surface slope, vegetation drag within each patch and an apparent shear stress representing interfacial momentum exchange between the tall and short patches. Closed‐form expressions are then derived to invert patch‐averaged drag coefficients from readily measurable hydraulic variables and flow‐facing area metrics, providing a tractable alternative to purely empirical calibration. The analytically inverted drag coefficients are further consolidated with literature data recast under consistent definitions of Reynolds number and a density descriptor, yielding an empirical predictor C _d ( R e, λ ) for rigid vegetation in staggered canopies. Finally, a practical linkage between the mean vegetation drag coefficient and Manning coefficient is established by incorporating vegetation area density and hydraulic‐radius scaling, enabling computation of an equivalent Manning coefficient for mixed‐height, staggered vegetation within the tested parameter range. The proposed framework offers a parameter‐consistent basis for resistance estimation in laterally heterogeneous vegetated channels and supports hydraulic assessment and management of vegetated floodplains.

Natural floodplain vegetation exhibits heterogeneous patterns in height and density that substantially affect flow and bed stability. Most previous studies have examined flows through uniformly distributed vegetation, resulting in a limited understanding of mixed-height canopies. Consequently, existing methods for estimating bed shear stress remain inadequately validated under such heterogeneous conditions. To bridge this gap, we conducted flume experiments to investigate how the density and height configuration of rigid vegetation affect the spatial distribution of bed shear stress, comparing three commonly used approaches: the Law of the Wall, Reynolds stress, and turbulent kinetic energy (TKE). Results showed strong agreement between TKE and Reynolds stress methods; the Law of the Wall produced larger errors (15–25%) due to log-layer disruption in vegetated zones, limiting its use. Vegetation density dominated bed shear stress: high-density areas reduced mean stress by 17–36%, promoting deposition, whereas tall–short vegetation interfaces increased local stress by 15–26%, elevating scour risk. Flow velocity raised overall stress by 15–25%, while water depth had minimal effect. Sparse vegetation led to patchy stress distributions and higher scour potential, while dense vegetation favored uniform stress and sediment accumulation. These findings clarify bed shear stress mechanisms in heterogeneous vegetation and provide a basis for floodplain restoration and stability management.

Accurate prediction of drag coefficient ( C _D ) and terminal settling velocity for irregular, bio‐origin particles is essential for dispersal assessment and eco‐hydraulic simulation; however, substantial uncertainty persists for living Oncomelania hupensis because its conical–spiral shell, surface roughness and heterogeneous mass distribution are not adequately represented by classical spherical or generic non‐spherical correlations. We quantified the settling of living O. hupensis collected from representative middle‐Yangtze habitats, obtaining 70 valid individuals and stratifying them into three size classes by major‐axis length. Tests were conducted in a transparent cylindrical column with a mid‐column observation window. Terminal settling segments were objectively delineated from the near‐zero‐acceleration intervals of vertical displacement–time records, enabling the back‐calculation of C _D and particle Reynolds number ( R _e ) via force–balance inversion. Measured terminal velocities spanned 7.08–15.324 cm/s, with corresponding C _D ranging 0.52–2.97 over R _e = 0.5–15. Building on the two‐term Haider–Levenspiel structure, a morphology‐aware drag correlation was developed in which model coefficients were parameterized as functions of shape descriptors (e.g., sphericity and Corey shape factor), supplemented by a smoothness‐stabilized correction and a nonlinear morphology–drag coupling term, and it was calibrated using constrained nonlinear least squares with multi‐start initialization. Relative to baseline spherical and commonly used non‐spherical formulas applied to the same dataset, the proposed correlation increased the coefficient of determination from 0.45 to 0.76 and reduced mean square error from 0.23 to 0.11. Size‐resolved results indicated the tightest C _D – R _e distributions for medium individuals, whereas small and large classes exhibited higher dispersion, consistent with posture/orientation variability and morphological heterogeneity. The resulting correlation and reproducible parameter‐inference workflow provide practically accurate inputs for particle‐tracking modules, improving predictions of settling distance, residence time and deposition hot spots of O. hupensis to support habitat management and schistosomiasis control strategies in river–floodplain systems.

River–lake systems are essential for sustaining ecosystems and human livelihoods. However, the complexity and variability of large river–lake systems, coupled with characteristic differences in water bodies across regions, have made quantifying their extent and changes inherently challenging. This study implements a robust water extraction method based on the multidimensional X-means clustering algorithm. This method leverages the advantages of Sentinel-2 imagery for water detection. Utilizing the X-means algorithm, it generates a new seasonal surface water area (SWA) product for the mid-lower reaches of the Yangtze River (MLRYR). The implemented method achieved an overall accuracy of 97.98%, a producer’s accuracy of 98.02%, a user’s accuracy of 96.01%, a Matthews correlation coefficient of 0.954, and a Kappa coefficient of 0.954. Analysis of water body dynamics reveals that over the past six years, the overall trend of SWA in the MLRYR has remained stable. However, within a broad range including multiple sub-basins, a decline in SWA has been observed on an inter-annual scale. Among the large lakes and reservoirs in the MLRYR, the water areas of Poyang Lake, Dongting Lake and Shijiu Lake all showed a marked decline. Among all water bodies with a significant increase in area, the Danjiangkou Reservoir is the largest. Further correlation analysis indicates that SWA exhibited the strongest correlations with precipitation and drought index in most sub-basins. In sub-basins where large lakes and reservoirs exist, the presence of river networks played a buffering role by regulating and storing water, thereby reducing the direct influence of climatic factors on lake and reservoir water extent. These findings highlight the complex interplay of climatic and hydrological factors. By integrating satellite imagery and Earth observation, this study advances understanding of MLRYR surface water dynamics, providing a robust framework for monitoring in other regions. It offers critical insights into drought impacts and informs effective water resource management and conservation strategies.

Plant cultivation is utilized in coastal ecological restoration to cope with shrinking wetlands, and, benefiting from hydrochory, disseminating indigenous plant seeds represents a high‐efficiency strategy. Random displacement model (RDM) is an efficient alternative to simulate seed dispersal progress via wave. Consequently, we investigated the effect of seed properties and wave characteristics on seeds motion in waves by RDM. Errors between the theoretical comprehensive longitudinal diffusion coefficient of the solute and the simulated one by RDM within an acceptable range indicate that the model is applicable for further simulation of particle dispersal in waves. Simulation results demonstrated that seeds with smaller size and density can transport farther in waves; larger wave heights, smaller water depths and longer wavelengths in linear waves and larger relative wave heights and smaller relative water depths in Stokes waves all promote longitudinally seed diffusion. Finally fitting formulas were proposed for the longitudinal propagation position (including mean and variance) of seed dispersal in linear and Stokes waves. Although this work can provide certain scientific guidance for the restoration of coastal vegetation ecology through natural colonization, there is still much work that needs to be conducted to further the research.

The oxbow lake located in the middle reaches of the Yangtze River (YR) serves as a primary relocation and protection area for nationally protected species such as the Yangtze finless porpoise, and is also an important natural gene pool for biodiversity conservation in the middle reaches of the Yangtze River (MYR). The operation of the Three Gorges Dam (TGD) has altered the frequency and intensity of water exchange between the oxbow lake and the YR, affecting the stability of its morphology and the maintenance of its ecological functions. Statistical modeling reveals that the duration of continuous rise in water level in the MYR follows a Gaussian distribution function. Following the full impoundment operation of the TGD, there is a significant increase in the frequency of short-duration rises in water level, a decrease in the frequency of medium-duration rises, and a decline in the frequency of long-duration rises. Moreover, the rate of water level change in the MYR follows a power function, with a decreasing trend before and during the initial operation of the TGD, and an overall increasing trend after full impoundment, significantly lower than the pre-operation average. By employing threshold regression models and Langmuir equations, a formula for calculating water exchange intensity has been established. The average annual water exchange intensity shows a significant overall decrease from the period after the operation of the TGD to the full impoundment operation phase. However, following full impoundment, there is a significant upward trend in water exchange intensity, reaching levels comparable to the pre-operation period. During the emptying and pre-release period of the TGD, water exchange intensity increases by 5.5 times, while during the seedling flood of the four major Chinese carps in the MYR, water exchange intensity decreases by 70%. Conversely, during the reservoir storage and utilization phase, water exchange intensity remains relatively stable.

Convection and diffusion processes of buoyant organisms are of great significance to ecological restoration or the restoration of the riparian and wetland system. Advection–diffusion models have been widely applied to describe the transport of particles through vegetation, assuming that the particle transport is driven by the mean flow, but few studies have been conducted on the diffusion process while considering the retention time. The authors conducted flume experiments of four runs with different vegetative densities and extracted and analysed the longitudinal moving and lateral oscillation trajectories of buoyant particles. The trapping and releasing mechanisms of buoyant particles due to capillary force were explored, and a dimensionless parameter is defined to reflect the effect of the physical properties of stems and particles on the retention time. The retention time of trapping events due to the capillary force between particles and the stem has been proven to follow a three‐parameter double exponential distribution, the duration time of both short and long retention events increases with the bulk flow velocity, and the proportion of long trapping events decreases with the increasing bulk flow velocity. The diffusion coefficient of buoyant particles is validated independently from the vegetative densities, increases with the flow velocity, and is approximately 100 times that of the solute in the flow through emergent vegetation under similar condition.

Sound knowledge of the local distribution and diversity of freshwater snail intermediate hosts and the factors driving the occurrence and abundance of them is crucial to understanding snail-borne parasitic disease transmission and to setting up effective interventions in endemic areas. In this study, we investigated the freshwater snails, water quality parameters, physical characteristics of habitats, predators and competitors, and human activity variables at 102 sites during December 2018 and August 2019 in Shenzhen and adjacent areas in China. We used decision tree models and canonical correspondence analysis to identify the main environmental and biotic factors affecting the occurrence and abundance of snail species. A total of nine species of snail were collected throughout the study area, with Biomphalaria straminea, Sinotaia quadrata, and Physella acuta being the most predominant species. Our study showed that the most important variables affecting the abundance and occurrence of snail species were the presence of predators and competitors, macrophyte cover, chlorophyll-a, substrate type, river depth, and water velocity. In terms of human activities, snail species occurred more frequently and in larger numbers in water bodies affected by human disturbances, especially for sewage discharge, which may reduce the occurrence and abundance of snail predators and competitors. These findings suggest that proper management of water bodies to reduce water pollution may increase the abundance of snail predators and competitors, and should be considered in integrated snail control strategies in the study area.