Flow Wetland Research Articles

Characterization of wind effect on environmental dispersion for a shallow wetland flow

The present work focuses on the dispersion of pollutants under the influence of wind and ecological degradation in a fully developed steady flow for a shallow wetland. The dispersion coefficient is determined by Aris’ method of moments and Meis’ multi-scale analysis. Based on the comparison study, the concentration profiles obtained using multi-scale analysis converge with Aris’ method of moments, indicating that both analytical approaches provide reliable and consistent descriptions of pollutant dispersion in the system. In first-order degradation reaction rates, high degradation rates lead to lower mean concentrations and potentially more pronounced concentration gradients, while low degradation rates result in higher mean concentrations. The critical length of the region influenced by the contaminated cloud is computed analytically. It shows that for the common contaminant constituent lead (Pb), initially, it increases gradually to reach the maximum; after that as time increases, it decreases to zero under wind conditions.

Water budgets in an arid and alpine permafrost basin: Observations from the High Mountain Asia

Ground freeze‒thaw processes have significant impacts on infiltration, runoff and evapotranspiration. However, there are still critical knowledge gaps in understanding of hydrological processes in permafrost regions, especially of the interactions among permafrost, ecology, and hydrology. In this study, an alpine permafrost basin on the northeastern Qinghai‒Tibet Plateau was selected to conduct hydrological and meteorological observations. We analyzed the annual variations in runoff, precipitation, evapotranspiration, and changes in water storage, as well as the mechanisms for runoff generation in the basin from May 2014 to December 2015. The annual flow curve in the basin exhibited peaks both in spring and autumn floods. The high ratio of evapotranspiration to annual precipitation (>1.0) in the investigated wetland is mainly due to the considerably underestimated ‘observed’ precipitation caused by the wind-induced instrumental error and the neglect of snow sublimation. The stream flow from early May to late October probably came from the lateral discharge of subsurface flow in alpine wetlands. This study can provide data support and validation for hydrological model simulation and prediction, as well as water resource assessment, in the upper Yellow River Basin, especially for the headwater area. The results also provide case support for permafrost hydrology modeling in ungauged or poorly gauged watersheds in the High Mountain Asia.

Environmental dispersion in wetland flow with wind effects under boundary absorptions

Environmental dispersion in wetland flow with wind effects under boundary absorptions

Transport of reactive contaminant in a wetland flow with the effects of reversible and irreversible reactions on the bed surface

Wetlands are crucial for maintaining biodiversity in ecosystems. The reversible chemical reactions can significantly affect the pollutant reduction capacity in wetland flow. The spatial transport of contaminants in wetlands is further complicated by phase exchange kinetics due to reversible reactions in the wetland bed. This paper provides an analytical solution for studying the multi-dimensional concentration distribution of solutes in wetland flow, considering both reversible and irreversible boundary reactions. Unlike previous one-dimensional studies (Jiang et al. (2022), Zhan et al. (2024)), our approach offers a comprehensive view of wetland contaminant transport, accounting for complex interactions between different phases and environmental factors. The solute may undergo reversible sorptive phase exchange between the immobile (wetland bed phase) and the mobile phase (fluid phase). Multi-scale homogenization methods are used to determine the dispersion coefficient, mean concentration, longitudinal and vertical real concentration distributions, rate of variation of vertical concentration distribution under the influence of vegetation force, and reversible and irreversible reactions at a stationary wetland bed. The effects of retention parameter (θ), Damkohler number (Da), vegetation effect (α), dispersion time (τ), and first-order irreversible boundary reaction (β′) on solute mixing are thoroughly analyzed. The study's analytical results are validated by numerical results obtained using the finite difference method with a Shishkin mesh, and other comparisons are made with the limiting case of Taylor dispersivity. Results show that an increase in Damkohler number and vegetation force weakens contaminant transport in wetland flow, but an increase in Da enhances contaminant concentration in the mobile phase. The presence of reversible phase exchange kinetics causes non-uniform vertical concentration variation across the wetland cross-section. Critical values where the multi-scale homogenization technique may fail are suggested as θ≤0.5 and Da≥1. The study's findings have potential applications to pollution control in wetlands.

Analysis of contaminant dispersion in constructed wetland flows with absorptive boundaries

Pollution in wetland flows poses a significant challenge to ecosystem preservation, underscoring the importance of wetland restoration. Constructed wetlands have emerged as a widely embraced solution for contaminant mitigation. In this study, we focus on the contaminant removal process within the wetland flows to contribute to wetland restoration. A constructed wetland with ecological floating and bottom absorptive beds has been employed to enhance the capacity of contaminant removal within wetland flows. However, the environmental dispersion in constructed wetland flows is further complicated by the presence of irreversible first-order absorptive boundaries at the upper and bottom beds. Therefore, our work focuses on comprehending the expansion processes of contaminant clouds under absorptive boundaries through a multiscale analysis to demonstrate the removal effects of constructed wetlands. The findings highlight significant deviations in the spatial distribution of contaminant clouds, particularly in the vertical dimension, attributed to absorptive effects. To analyze the impact of removal mechanisms on the dispersion patterns of contaminant clouds, variations in the vertical concentration peak are examined. A predictive model is developed to estimate the position of the concentration crest in the vertical direction based on changes in absorptive ratios between the upper and bottom boundaries. Furthermore, in order to explore the key factor on removal capacity and efficiency within constructed wetland flows, we look into the process of contaminant depletion by examining variations in removed mass and local absorptive and removal efficiency along the streamwise direction in response to deviations in absorptive strengths at the upper and bottom beds. The ratios of the two boundary removal intensities play a significant role in the absorptive dynamics within wetland flows, particularly during the early stages of cloud expansion. By adjusting the absorption ratio between two absorptive beds to 1:1 with a certain total depletion strength in wetland flows, the enhancement ratio of depletion efficiency can increase by nearly 30%. It has been proven that employing identical absorption strengths at two absorptive beds is an economical and efficient means to amplify the absorption efforts within designed constructed wetland flows. This study provides guidelines for the design of constructed wetlands aimed at enhancing their capacity for sewage treatment.

A holistic model for microplastic dispersion in a free-surface wetland flow

The holistic model for microplastic dispersion is essential to conserving natural wetlands and enhancing the sewage treatment efficiency of constructed wetlands. A holistic mode is presented to analyze the microplastic transport caused by a continuous point-source discharge of substances into a wetland with an exposed water surface. The microplastic cloud's total quantity and centroid movement over each streamline are rigorously derived using the method of separation of variables and integral transform, and its longitudinal dispersion, skewness, and kurtosis are numerically analyzed using the finite difference method. Three dimensionless groups for the microplastic movement in wetland are presented. The relative importance of autonomous movement to the vertical diffusion coefficient can noticeably influence the mass center velocity and the longitudinal spread of the microplastic cloud, and its augments can enhance the amplitude of skewness and kurtosis in the initial transport stage. For the transient stage of transport during which microplastic cloud develops, the pulsating term of emission intensity shows little effect on skewness and kurtosis. The oscillation of skewness and kurtosis show less obvious for the long term evolution of microplastic cloud when the time scale across the water depth by diffusion is much larger than the oscillatory period.

Analysis of environmental transport of suspended sediment particles in a tidal wetland flow under the effect of floating vegetation absorption

Wetlands play an important role in maintaining many natural cycles and supporting a wide range of biodiversity. In the current world, the transport of solute in a wetland with vegetation is an essential issue in environmental, biological, geophysical, and concerned applications. Specially, floating vegetated wetland which is a buoyant platform enveloped by plants, playing a pivotal role in filtering and purifying water in aquatic ecosystems The main focus of the present research is to investigate the transport of sediment particles in a depth-dominated tidal floating vegetated wetland (FVW) flow. The characteristics of floating vegetation absorption and vegetation parameter in FVW are explained to explore the transport of sediment particles. This work’s model relies on an advection-diffusion equation, the solution of which discloses the concentration of settling particles in the water phase. Utilizing the method of moments, a set of moment equations is derived from the governing equation. The equations of moment are then solved using a finite difference implicit scheme. Further, the four moments and Hermite polynomial illustration is adopted to derive the vertical mean concentration distribution profile. The effective dispersivity and the concentration distributions of the sediment particles are illustrated for three different situations of fluid flow: steady, purely oscillatory, and periodic flow with non-zero-mean for all time. The effects of the vegetation factor, settling velocity, absorption due to floating vegetation, and other important factors on sediment transport in FVW are discussed for three different cases separately. Result shows as settling velocity (ω) increases, the influence of vegetation absorption (β) on dispersion coefficient diminishes in the steady state, and its effect on mean concentration becomes less pronounced due to the downward movement of particles. This is because vegetation absorption is stronger near the upper surface, but higher ω values lead to particle downward, reducing β′s impact. The results are described in the context of some real-world situations, as the free surface of a tidal wetland is naturally covered with plants; FVW serve as a natural water purification filter for polluted estuaries, contaminated crude oil wastewater, and so on. This study has potential to aid in water purification efforts as well as for the protection and conservation of coastal environments to limit sea level rise.

Characterizing suspended particle dispersion in wetland flows: Impact of settling velocity and vegetation factor

Predicting the dispersion process of suspended particles with settling velocity in wetland flows holds significant implications for various ecological and environmental applications. This study analytically investigates the dispersion process of fine settling particles in wetland flows due to an instantaneous release source through the asymptotic expansion method. The effect of high-order terms is incorporated. The impact of vegetation factor and settling velocity on characteristic coefficients (including mass retained in the flow, advection velocity, longitudinal dispersion coefficient, skewness, and kurtosis), vertical mean, and two-dimensional concentration distribution are analyzed. Analytical solution is validated by numerical result through random displacement method. Results demonstrate that the vegetation factor does not influence the vertical mass distribution, and a larger settling velocity results in a higher concentration of mass in the bed wall layer. The longitudinal dispersion coefficient does not exhibit a monotonic relationship with the settling velocity. The position of mass centroid of the vertical mean concentration is biased more to the upstream with the larger settling velocity. At larger times, the vertical mean concentration approximates a normal distribution, with skewness and kurtosis nearing zero. Under the influence of settling velocity, the bed wall layer exhibits a high concentration zone in the two-dimensional concentration distribution. These results can help the understanding of sediment dynamics, nutrient cycling, pollutant transport associated with the wetland flows.

‘Dual Purpose’ Surface Flow Constructed Treatment Wetlands Support Native Biodiversity in Intensified Agricultural Landscapes

In agricultural landscapes, free-water surface flow wetlands (FWS) are constructed mainly to improve water quality; however, their contribution to biodiversity conservation is increasingly recognised. To inform biodiversity management in FWS treating agricultural runoff, we surveyed the vegetation and fauna assemblages in five established FWS in a lowland, pastoral landscape in the central North Island, New Zealand. The FWS had been established for between 3 and 19 years, planted with a restricted range of native plant species, and fenced to exclude livestock access. Larger wetlands hosted significantly more plant and mammal species. However, other than wetland size, we found few other significant relationships between wetland habitat, landscape characteristics, and measures of biodiversity (total species, proportion of native species, number of wetland specialists, or threatened species). We recorded one-hundred and thirteen plant, twenty bird, five mammal, eighty-five terrestrial invertebrates, forty-seven aquatic invertebrates, six fish, and two amphibian species inhabiting the FWS. Native species comprised 96% of the total aquatic invertebrate fauna identified. For other taxa, native flora and fauna accounted for half or less than half of all species identified: 53% terrestrial invertebrates, 50% fish, 45% birds, 32% plants, and 0% amphibian and mammal species. Few wetland specialists (aquatic or wetland-adapted) or threatened native species were detected, probably reflecting the limited range of wetland plant species in initial plantings and the difficulties native taxa face when colonising new habitat where potential reservoirs of colonist species are also depauperate or too distant. FWS support native biodiversity, but further enhancements may require active management of exotic and pest species to minimise competition or predation on native species.

Decreasing Richness and Biomass During a Flood Pulse Observed in a Southeastern US Coastal Floodplain Following a Multi-Year, Supra-Seasonal Drought

Floodplains of the southeastern United States exhibit high biological abundance and diversity, maintained by periodic inundation from seasonal flooding. To examine the relationship between invertebrate community composition and seasonal flooding following periods of drought, we quantified aquatic macroinvertebrate communities monthly in an inundated floodplain during the annual flood pulse (December-April) in two years: one following a multi-year drought and one during a larger than average flood. We predicted that floodplain communities would differ in richness, biomass, and community composition between years and that differences would be driven by the annual flood pulse and organic matter availability. We collected macroinvertebrates from a floodplain of the Altamaha River, a free-flowing 6th order river in the Coastal Plain region of the southeastern US. With invertebrates identified to genus, we estimated richness, abundance, biomass, community composition, and proportions of functional feeding group abundance. Richness was generally higher in the drought year but decreased throughout the flood pulse, while during the flood year richness was lower and increased over time. Biomass decreased throughout the flood pulse following the drought year and increased during the flood year. There was high overlap in invertebrate community composition based on abundance data during both years of the study with collector gatherers being the most abundant functional feeding group. Our study provides insight to the response of aquatic communities to an extended drought and subsequent return to normal flow in a lower river wetland.

Dispersion in a vegetated flow of solute from a continuous source with bed absorption

Predicting the dispersion process of environmental transport in wetland flows is significant to some ecological engineering applications. By extending a previous study (Guo and Chen, 2022), an analytical solution of the steady-state concentration field for solute transport from a continuous release source in a submerged vegetated flow with the effect of bed absorption is presented in this work. Results illustrate that adopting different orthogonal basis functions does not affect the result but affects the convergence rate of the solution near the release source. Under the bed absorption, concentration approaches zero at the far field. Concentration is affected by different bed absorption rates when the absorption rates are small, while it is hardly affected by different absorption rates when the bed absorption rates are large. When the release position is above the bed wall, different bed absorption rates do not affect the near field concentration where the vertical dispersion of solute has not arrived at the bed wall. Under the same bed absorption rate, concentration decays more quickly along the downstream distance when the release position is near the bed wall, but the release positions almost do not affect the downstream distance where the concentration tends to zero.

Municipal Wastewater Treatment uses Vertical Flow Followed by Horizontal Flow in a Two-Stage Hybrid-Constructed Wetland Planted with Calibanus hookeri and Canna indica (Cannaceae).

The online version contains supplementary material available at 10.1007/s11270-022-05984-0.

Dispersion of fine settling particles in a tidal wetland flow

An investigation on transport of fine sediment particles in a tidal wetland flow is presented in the current research. The model of this work is based on an advection diffusion equation whose solution reveals the water phase based concentration of settling particles. Using the method of moments, a system of moment equations are derived from the governing equation. A finite difference implicit scheme is employed to solve the equations of moment. The behavior of Taylor effective dispersivity due to the variation of settling velocity of fine particles for oscillatory current with or without nonzero mean is predicted. The mean concentration distribution along the longitudinal direction is obtained using the Hermite polynomial and first four central moments. It is shown that for greater settling velocity, the dispersion procedure is inhibited. Some significant effects of vegetation factor, time period, oscillation parameter on environmental dispersivity, skewness and mean concentration profile are shown. The results of the present study are very important to understand the process of sedimentation and wastewater treatment in a tidal wetland flow.

Multi‐scale analysis for environmental dispersion in wetland flow under the effect of wind

AbstractThe present study emphasizes a multi‐scale analysis of an environmental dispersionin a fully developed shallow wetland flow under the wind effect, based on the momentum and mass transfer equations. From the classical momentum equation, the depth‐dominated velocity profile is derived for the wetland flow. The environmental dispersion is examined using Mei's multi‐scale analysis on moment equations of concentration in wetlands with wind‐induced effect. Further, the maximum velocity, thickness of separation layer with recirculation and its position are obtained. The increase of depth‐averaged velocity was observed for the larger contribution of conveyance capacity in wetland flows for the enhancement of wind direction. Also, the analytical result showed that the higher magnitude of environmental dispersion led to intensive dispersion process for the depth‐dominated wetland flow. Moreover, for the hierarchical composition of contaminant constituents, the duration and length of influenced region are associated with a certain standard water quality level in wetland.

Holocene climate changes explain the spatial pattern in genetic diversity in populations of Cyperus papyrus from Southeast Africa wetlands.

Wetlands are one of the most threatened ecosystems in the world because more than 70% of the area worldwide has been lost since 1900. Wetland plant species rely greatly on water for seeds and propagules, which may lead to a downstream unidirectional dispersal and accumulation of genetic diversity downstream. However, several species show no support for unidirectional genetic diversity, revealing the complexity of population dynamics and gene flow in wetlands. Here, we used microsatellite loci to address how the past demographic dynamics shaped the contemporary spatial pattern in genetic diversity and population structure of Cyperus papyrus in wetlands of Southeast Africa. Using spatially explicit analysis and coalescent modelling, we found no support for unidirectional dispersal. Instead, we found higher genetic diversity in populations upstream than downstream in the river basin. We also found high admixture among populations, most likely due to connections between adjacent river basins during sporadic floods, and ongoing gene flow due to bird-mediated seed dispersal. Our results suggest stepping-stone migration due to strong isolation-by-distance, but not necessarily unidirectional. Moreover, the past demographic dynamics in the Holocene shaped the current pattern of genetic diversity and structure, leading to higher genetic diversity in populations upstream the Zambezi river basin. Our results also point to the very low genetic diversity of C. papyrus populations in Southeast Africa and the need for management and conservation strategies to guarantee the long-term persistence of the species in the region.

Hydrologic and water quality performance of a subsurface gravel wetland treating stormwater runoff

Subsurface gravel wetlands are an emerging type of green infrastructure that can be used to manage stormwater through the capture and slow release of runoff. They are unique to other types of green infrastructure in that they have a distinct fully saturated gravel layer below an occasionally saturated soil layer that influences pollutant removal processes. While they have been widely applied to treat wastewater, our understanding of their efficiency in treating stormwater with variable pollutant inputs is limited. To fill this gap, this study monitored the flow and water quality (total suspended solids, total nitrogen, total phosphorus, and chloride) in a subsurface gravel wetland in Oshkosh, Wisconsin at the influent, effluent, and in an observation well. Results from nine storm events indicated that the wetland had a median volume reduction of 74% and a median peak flow reduction of 89%. The reduction in pollutant concentrations where highly dependent upon the influent concentration. Average reductions of total suspended solids, total nitrogen, and total phosphorus were 49%, −21% and −0.2%, respectively, indicating an increase in nutrients; however, where influent concentrations were above irreducible levels, total phosphorus was reduced by 45% (influent ≥0.25 mg/L) and total nitrogen was reduced by 38% (influent ≥2.5 mg/L). Overall, this study shows that the subsurface gravel wetland performed similar to other types of green infrastructure and could be a good management practice to mitigate the harmful effects of stormwater runoff.

Effects of wind on transient dispersion of active particles in a free-surface wetland flow

Mechanisms of active-particle transport in a wetland flow under wind are significant for understanding various biological and ecological processes associated with wetlands. A transport model has been formulated to characterize the transient dispersion of active particles in a typical free-surface wetland flow exposed to wind. The transient evolution of total quantity, centred moving velocity, longitudinal dispersivity, skewness, and kurtosis of the active-particle cloud are analysed, using concentration moment method. It is found that the migration of active-particle cloud can eventually reach a stable status under the combined action of wind, hydrodynamics, and cell motility. The strong reverse wind can result in the negative centred moving velocity and longitudinal dispersivity along each streamline. The strong wind can considerably change the skewness and kurtosis of cell concentration distribution. The analytical solution of depth-averaged and two-dimensional concentration of active particles are derived based on Chatwin’s long-time expansion method, showing a distinct deviation from Gaussian distribution during the initial stage, which is in good agreement with the concentration moment analysis.

Salt Transport Under Tide and Evaporation in a Subtropical Wetland: Field Monitoring and Numerical Simulation

AbstractTidal wetland ecosystems are sensitive to porewater salinity dynamics. However, it is unclear how salts move and distribute in these wetlands, particularly how the salts accumulated by evaporation get removed from the wetland soil, so that the salinity levels may stabilize to accommodate vegetation. We conducted a combined field and modeling study to identify the porewater flow and salinity patterns in a subtropical wetland subjected to tidal inundation and evaporation. Measured and simulated salinity contours indicated the formation of hypersaline porewater plumes in the upper intertidal zone and the fresher porewater zones with salinity close to that of seawater near the creek and in the supratidal zone. Simulations indicated the discharge of the hypersaline upper intertidal porewater to the creek with a discharge pathway developed under the fresher near‐creek porewater zone, and this was further confirmed by the field‐observed significant salinity gradient under the creek. Our model suggested that both water and salt discharge from the wetland soil occurred predominantly at the creek bank and creek bed. The porewater discharge is more intensive through the creek bank than the creek bed, while the salt discharge across both the creek bank and creek bed was comparable due to the much higher salinity level under the creek bed. Salt discharge driven by density gradients and tidal‐induced porewater circulation provides a mechanism for removing salts accumulated in the upper intertidal zone due to evaporation and could prevent salt flat formation and marsh plants dieback.

Analysis of environmental dispersion in wetland flows with floating vegetation islands

The fate of the contaminant transport process within wetland flows considering contaminant depletion via a floating vegetation island (FVI) is the focus of this work. To identify the feature of contaminant cloud expansion under an FVI, multiscale theory is extended to obtain a two-dimensional spatial concentration distribution analytical solution. The characteristics of two-dimensional concentration distributions under upper FVI absorption and damping factor within wetland flows are illustrated. The performance of the contaminant depletion process via an FVI is also examined in this work, with discussions on removal efficiency, the absorption ratio, and the nonuniformity of contaminant mass. As FVI removal intensity changes along the stream direction, the analytical solution of removal efficiency is obtained to illustrate the longitudinal variation in the FVI removal intensity. Furthermore, the effects of removal intensity and damping factor on FVI removal efficiency are expressed separately. In addition, the removal intensity variance in the vertical direction is discussed using the defined absorption ratio. Moreover, as residual mass is a fatal issue in the contaminant removal process, temporal residual mass is discussed, and the residual mass proportion within different layers is depicted. Finally, the difference of the mass proportion between layers is employed to explain the transformation of the contaminant cloud.

Semi-analytical study on environmental dispersion of settling particles in a width-independent wetland flow

Semi-analytical study on environmental dispersion of settling particles in a width-independent wetland flow