Flow Wetland Research Articles

Succession of fish and crustacean assemblages following reinstatement of tidal flow in a temperate coastal wetland

Fish and decapod crustacean assemblages were sampled from two manipulated creeks in which tidal flow had been increased through culvert removal. Assemblages were compared to those of two control creeks where culverts remained and two reference creeks without culverts. The presence of culverts reduced the richness and abundance of estuarine–marine dwelling species. Successional changes over a 16 year period (2 years prior to culvert removal and 14 years after) showed an immediate response at one manipulated creek but many years to attain reference condition. The other manipulated creek showed a completely different trajectory: oscillation between control and reference status with no clear intermediary condition. We concur with other investigators that short-term studies may give only a partial indication of response to rehabilitation efforts in coastal wetlands and longer-term studies (5–10 years) are recommended. There is some evidence that over longer-time frames, the presence of distinct groups of fish and/or decapods may indicate stages in the maturation of a rehabilitated wetland.

Temporal variation of rhizodeposit-C assimilating microbial communities in a natural wetland

The objective of this study was to apply phospholipid fatty acid (PLFA)-based stable isotope probing to assess the temporal variation of active microorganisms associated with rhizosphere-C flow in a natural wetland. We applied 13CO2 pulse labeling at three different times throughout the vegetation period: spring (April), early summer (June), and early autumn (October). Soil redox potentials (Eh) at 10 cm depth ranged from moderately reduced (October) to oxidized conditions (June). Based on combined PLFA relative abundance and 13C enrichment results, we suggest that gram-negative bacteria play a main role in rhizodeposit-C uptake in these wetland ecosystems, especially when reduced soil conditions prevail in October. Arbuscular and saprotrophic fungi also take up a significant proportion of the belowground allocated C, though mostly in the summer period. Gram-positive bacteria showed only a minor reliance on rhizodeposit-C throughout the year. It is concluded that rhizodeposit-C-assimilating microbial communities are heterogeneous and temporal variable entities with groups that are capable of adapting differently to seasonally varying environmental conditions.

Environmental dispersion in a tidal flow through a depth-dominated wetland

Presented in this paper is a theoretical analysis for longitudinal evolution of mean concentration of an environmental emission into a tidal wetland flow. The velocity distribution of the periodic flow through the wetland is derived, with that for a fully developed steady wetland flow included as a special case. The zero-th, first and the growth of the second order moments of the concentration are rigorously obtained by applying Aris’s method of concentration moments to derive the environmental dispersivity. The necessary time needed for the environmental dispersivity to attain a steady oscillating status is analyzed. The effects of some characteristic parameters, especially one representing the impact of vegetation in the wetland on both velocity profile and environmental dispersivity, and another identifying the effect of flow oscillation on the environmental dispersivity, are illustrated in detail. To reflect the dispersion enhancement by the flow oscillation, a typical example is given to characterize the critical length and duration of the contaminant cloud.

Effect of wind on contaminant dispersion in a wetland flow dominated by free-surface effect

Flow and environmental dispersion are essential to ecological risk assessment and ecological restoration associated with wetlands. Presented in this paper is an analytical study for effect of wind on contaminant dispersion in a wetland flow dominated by free-surface effect. Based on the momentum transport equation generally adopted for wetland flow, the solution for velocity distribution in a free-surface wetland flow under wind is rigorously derived, with a limiting case covering the known solution of flow in the absence of wind. The thickness of inverse flow layer, maximum velocity, and its location are obtained. By use of Aris's method of concentration moments, the expression for environmental dispersivity in the free-surface wetland flow under wind is derived, and that in the absence of wind can be included as a special case. The direction and intensity of wind can influence greatly the environmental dispersivity at a stable stage. The time scale for environmental dispersivity to approach the stable stage is independent of wind. Analytical solution of mean concentration is derived and illustrated for a pulsed contaminant emission into a wetland flow dominated by free-surface effect under wind. For typical pollutant Pb, the length and duration of influence region with contaminant concentration beyond given standard level of water quality are illustrated.

Flow distribution and environmental dispersivity in a tidal wetland channel of rectangular cross-section

Presented in this paper is a theoretical analysis on flow distribution and environmental dispersivity for a tidal wetland channel of rectangular cross-section. The analytical solution of velocity distribution for the tidal wetland flow is obtained and illustrated with a limiting case covering the known solution for a steady wetland flow. By use of Aris’s method of concentration moments, the environmental dispersivity for a pulsed contaminant emission into the tidal wetland flow is rigorously derived and characterized in terms of dimensionless parameters. The solution is shown to be a generalization of the environmental dispersivity for the corresponding steady wetland flow, taking into account the combined action of periodic oscillation and cross-sectional variation of superficial flow as well as the difference between superficial mass dispersivities in the vertical and lateral directions. For a long time evolution of the contaminant cloud, the environmental dispersivity may approach a stable stage of oscillation with a period equal to the period of the superficial flow. The evolution of environmental dispersivity at the initial stage for the tidal wetland flow is shown not monotonous as it does in the case of the steady wetland flow. It is also found that the period of superficial flow has no impact on the necessary time for the environmental dispersivity to attain the stable stage.

Uniform laminar wetland flow through submerged and floating plants

Wetland flow is currently actively studied because of its applications in stormwater management, wastewater treatment and habitat restoration. This research applies the well-established poroelastic media flow theory to uniform laminar wetland flow through submerged and floating vegetation, where the linear interaction between the pore water and the vegetation skeleton is considered in the equations of motion. The effects of vegetation porosity on the velocity, the shear stress and the energy distributions in different layers are first derived analytically and interpreted graphically and physically. As special cases, the homogeneous water flow, as also floating, submerged and emergent vegetation flows are then discussed. This research provides qualitative understanding of wetland flow on velocity, shear stress and energy distributions, indicating that a plant applies a significant resistance to the flow system and dissipates most of the flow energy. The results serve a benchmark framework for the future study on turbulent vegetation flow.

Environmental dispersion in a two-layer wetland: Analytical solution by method of concentration moments

For the most typical two-layer wetland with free-water-surface-effect, analytically explored in this paper is the environmental dispersion in terms of the longitudinal evolution of the depth-averaged concentration. Taylor’s classical analysis for soluble matter dispersion in a single phase fluid flow is rigorously generalized for the two-layer case of a wetland flow to develop the dispersion model. The velocity profile of the fully developed flow through the wetland is derived, with that for the single-layer wetland flow included as a special case. Aris’s method of concentration moments is applied to determine the dispersivity with an asymptotic time variation. For typical contaminant constituents of chemical oxygen demand, biochemical oxygen demand, total phosphorus, total nitrogen and heavy metal, the process of dispersion is shown characteristic of a hierarchical structure in the critical length and duration of the contaminant cloud.

Nitrogen Removal Capacity in Horizon Subsurface Flow and Vertical Flow Constructed Wetland in Relation to Operational Mode

Two laboratory scale constructed wetlands were designed as horizon subsurface flow constructed wetland (HFCW) and vertical flow constructed wetland (VFCW) and were utilized to study the treatment capacity to reduce nitrogen. According to different inflow concentration and height of water surface, HFCW was analyzed in two operational modes and VFCW in four operational modes. The semi-submerged VFCW had the best capacity to remove nitrogen and the total nitrogen removal rate reached to 92% and the removal rate of HFCW was 90%. Moreover, the un-submerged VFCW could reduce 93% ammonia but nitrate removal rate just was 9%. And the removal rates of NH4+-N, NO3--N and TN respectively were 85%, 80% and 81% in submerged VFCW.

Performance of Eleocharis macrostachya and its importance for arsenic retention in constructed wetlands

Arsenic (As) can be removed from water via rhizofiltration using phytostabilizing plants. The aim of this study was to investigate the performance of Eleocharis macrostachya in constructed wetland prototypes, as well as the plant's arsenic mass retention and the distribution of As along the wetland flow gradient and the soil in the wetland mesocosmos. Experiments were carried out in laboratory-scale wetland prototypes, two planted with E. macrostachya and one without plants. Samples of water were taken at the inlet and outlet of the wetlands during the 33-week test period. At the end of the experiment, plants and soil (silty-sand) from each prototype were divided in three equal segments (entrance, middle and exit) and analyzed for their arsenic content. Results revealed that the planted wetlands have a higher As-mass retention capacity (87-90% of the total As inflow) than prototypes without plants (27%). As mass balance in the planted wetlands revealed that 78% of the total inflowing As was retained in the soil bed. Nearly 2% was absorbed in the plant roots, 11% was flushed as outflow, and the fate of the remaining 9% is unknown. In the prototype without plants, the soil retained 16% of As mass, 72% of the arsenic was accounted for in the outflow, and 12% was considered unknown. Although E. macrostachya retained only 2% of the total arsenic mass in their roots, its presence was a determining factor for arsenic retention in the wetland soil medium. Hence, planted wetlands might be a suitable option for treating As-contaminated water.

Modeling flow in wetlands and underlying aquifers using a discharge potential formulation

Summary An accurate assessment of water and nutrient balances in large scale wetland systems such as the Florida Everglades requires conjunctive modeling of surface water flow in wetlands and groundwater flow in underlying aquifers. Earlier work was based on the finite difference code MODFLOW with a special “wetlands package.” This model treats the wetland flow as laminar with a very high transmissivity that is proportional to the wetland water depth cubed. However, these MODFLOW solutions appear sensitive to this highly non-linear wetland transmissivity, particularly under conditions of low vegetation density when the model may fail to converge. We propose to formulate the governing differential equation in terms of a discharge potential instead of potentiometric heads as done in MODFLOW, but otherwise using the same assumptions as in its wetlands package. We tested our approach on a few cases of one- and two-dimensional flow, both with a constant and a varying wetland bottom elevation. For the latter the discharge potential represents an irrotational part of the flow field which is combined with a component of the flow field that contains the curl. We found that both the robustness and the accuracy of the solution in terms of potentials was superior to the solution in terms of heads. In some cases the latter solution failed altogether, even for simple one-dimensional flow. We applied our method to model the effects of wetland hydrology on the nutrient redistribution in and near tree islands. We found that the subtle velocity distributions near these tree islands, as resulted from our conjunctive wetlands and groundwater flow solution, could help explain the increased nutrient depositions at these islands, particularly at the head of the islands, where, consequently, most of the vegetation occurs.

Comparison of Rhodamine-WT and bromide as a tracer for elucidating internal wetland flow dynamics

Artificially constructed wetlands offer a low-cost treatment alternative to remove a number of pollutants found in effluent water from industry, mining, agriculture, and urban areas. The determination of treatment efficiency cannot be determined without understanding the flow dynamics of individual parcels of water through the wetland. A method for tracking parcels of water is proposed, using Rhodamine-WT as a tracer. A series of tracer tests were conducted on a 1.2 ha treatment wetland. Bromide and Rhodamine-WT were simultaneously dosed into the inlet and monitored at 60 sampling locations for 5 weeks. Rhodamine-WT concentrations were found to be coincident with bromide. For all three events the relationship between Rhodamine-WT concentration and bromide concentration was linear at each sampling point with a slope of 0.82. The peak concentration of Rhodamine-WT and bromide was also found to coincide throughout the wetland. Rhodamine-WT can be used to determine the movement of individual parcels of water through a treatment wetland and used to determine treatment efficiencies at individual locations within a wetland.

Environmental dispersivity in free-water-surface-effect dominated wetland: multi-scale analysis

Distinct from the case with width-dominated shallow wetland flows, the longitudinal evolution of contaminant concentration in the most-typical pattern of wetland as dominated by free-water-surface-effect is characterized by a multi-scale analysis in the present study. An environmental dispersion model for the evolution of the mean concentration is deduced as an extension of Taylor’s classical formulation by Mei’s multi-scale analysis. Corresponding environmental dispersivity is found identical to that determined by the method of concentration moments.

Evaluating Complex Hydrogeological Settings in a Constructed Wetland: An Isotopic/Chemical Mass Balance Approach

The objective of this study was to investigate the hydrogeological conditions of an artificial wetland, with four possible sources of water: (1) ground water, (2) industrial waste water, (3) seepage from a water body to the north, and (4) seepage from a water body to the south. The wetland was designed to improve the quality of municipal effluent and industrial wastewater. To evaluate and separate the impact of wetland processes from those due to dilution with water from "clean" sources (i.e., rain water or ground water), a combined isotope/chemical mass- balance approach was employed. The δD, δ 18 O, and Na were monitored for 18 months. Based on the data, the variation of individual proportions of each water type in the wetland and monitor wells was calculated. The isotopic composition of water in the wetland varied throughout the study period changing along the wetland flow path. The wetland contained mainly wastewater (88%-100%) during normal operations; however, hurricanes and inconsistent pumping added low conductivity water directly and triggered enhanced groundwater inflow into the wetland of up to 78%. Finally, the composition of water in monitor wells was mostly groundwater dominated; however seepage from a water body to the north was detected.

Sulfur biogeochemical cycling and novel Fe–S mineralization pathways in a tidally re-flooded wetland

Sulfur biogeochemical cycling and associated Fe–S mineralization processes exert a major influence over acidity dynamics, electron flow and contaminant mobility in wetlands, benthic sediments and groundwater systems. While S biogeochemical cycling has been studied intensively in many environmental settings, relatively little direct information exists on S cycling in formerly drained wetlands that have been remediated via tidal re-flooding. This study focuses on a tidal wetland that was drained in the 1970s (causing severe soil and water acidification), and subsequently remediated by controlled re-flooding in 2002. We examine SO 4 2 - reduction rates and Fe–S mineralization at the tidal fringe, 7 years after the commencement of re-flooding. The initial drainage of the wetland examined here caused in-situ pyrite (FeS 2) oxidation, resulting in the drained soil layers being highly acidic and rich in SO 4 2 - -bearing Fe(III) minerals, including jarosite (KFe 3(SO 4) 2(OH) 6). Tidal re-flooding has neutralized much of the previous acidity, with the pore-water pH now mostly spanning pH 5–7. The fastest rates of in-situ SO 4 2 - reduction (up to ∼300 nmol cm −3 day −1) occur within the inter-tidal zone in the near-surface soil layers (to ∼60 cm below ground surface). The SO 4 2 - reduction rates correlate with pore-water dissolved organic C concentrations, thereby suggesting that electron donor supply was the predominant rate determining factor. Elemental S was a major short-term product of SO 4 2 - reduction, comprising up to 69% of reduced inorganic S in the near-surface soil layers. This enrichment in elemental S can be partly attributed to interactions between biogenic H 2S and jarosite – a process that also contributed to enrichment in pore-water Fe 2+ (up to 55 mM) and SO 4 2 - (up to 50 mM). The iron sulfide thiospinel, greigite (Fe 3S 4), was abundant in near-surface soil layers within the inter- to sub-tidal zone where tidal water level fluctuations created oscillatory redox conditions. There was evidence for relatively rapid pyrite re-formation within the re-flooded soil layers. However, the results indicate that pyrite re-formation has occurred mainly in the lower formerly drained soil layers, whereas the accumulation of elemental S and greigite has been confined towards the soil surface. The discovery that pyrite formation was spatially decoupled from that of elemental S and greigite challenges the concept that greigite is an essential precursor required for sedimentary pyrite formation. In fact, the results suggest that greigite and pyrite may represent distinct end-points of divergent Fe–S mineralization pathways. Overall, this study highlights novel aspects of Fe–S mineralization within tidal wetlands that have been drained and re-flooded, in contrast to normal, undisturbed tidal wetlands. As such, the long-term biogeochemical trajectory of drained and acidified wetlands that are remediated by tidal re-flooding cannot be predicted from the well-studied behaviour of normal tidal wetlands.

Mechanistic Biogeochemical Model Applications for Everglades Restoration: A Review of Case Studies and Suggestions for Future Modeling Needs

Mechanistic biogeochemical model applications for freshwater wetland ecosystems are reviewed with an emphasis on applications in the Florida Everglades. Two significant human impacts on the Everglades have been hydrologic alteration and phosphorus (P) enrichment. Thus, it is important for research conducted in support of Everglades restoration to integrate understanding of the coupled effects of hydrologic and biogeochemical processes. Models are tools that can facilitate such integration, but an important challenge in model development is determining the appropriate level of model complexity. Previous wetland biogeochemical and flow modeling efforts are categorized across the spectrum of complexity from empirical and spatially aggregated to mechanistic and spatially distributed. The focus of this review is on mercury and P, as these two elements represent major environmental concerns in this ecosystem. Two case studies of coupled hydrologic and biogeochemical modeling for P transport are described in further detail to illustrate the implications of different levels of model complexity. The case study simulation results on time series TP data revealed that the mechanistic biogeochemical model with more complexity did not guarantee significantly better simulation accuracy compared to the simpler one. It is concluded that the level of model complexity should be represented appropriately based on the modeling objectives, hypotheses to be tested, and data availability. Finally, better integration between data collection and model development is encouraged as cross-fertilization between these processes may stimulate improved system understanding.

Turbulent Flow in Wetlands with Submerged and Floating Vegetation

Turbulent Flow in wetlands with submerged and floating aquatic plants was studied by applying Boit’s poroelastic theory to turbulent flow. The velocity distribution formulas were described by solving the modified Bessel equations. The effects of plant porosity and turbulent coefficient on the velocity distribution, shear stress distribution and energy relations were analytically derived. Several illustrative cases were given to show the details of the applications. The results of the study can help water resources, environmental and ecological engineers design and manage surface water flows in natural and constructed wetlands. 

Multi-scale analysis for environmental dispersion in wetland flow

Presented in this work is a multi-scale analysis for longitudinal evolution of contaminant concentration in a fully developed flow through a shallow wetland channel. An environmental dispersion model for the mean concentration is devised as an extension of Taylor’s classical formulation by a multi-scale analysis. Corresponding environmental dispersivity is found identical to that determined by the method of concentration moments. For typical contaminant constituents of chemical oxygen demand, biochemical oxygen demand, total phosphorus, total nitrogen and heavy metal, the evolution of contaminant cloud is illustrated with the critical length and duration of the contaminant cloud with constituent concentration beyond some given environmental standard level.

Environmental dispersion in a two-zone wetland

Abstract As an extension of the modelling on environmental dispersion in a single zone wetland [Zeng, L., Chen, G.Q., 2009. Ecological degradation and hydraulic dispersion of contaminant in wetland. Ecol. Model., 222, 293–300], the typical case of a pulsed contaminant emission into a steady flow through a distinctively vegetated two-zone shallow wetland channel is analytically explored in this paper in terms of the longitudinal evolution of the lateral mean concentration under environmental dispersion. The velocity profile of a fully developed flow through the wetland is derived, with that for a single zone wetland flow included as a special case. Taylor’s classical analysis and Aris’s method of concentration moments for solute dispersion in a single phase fluid flow are rigorously generalized for the two-zone case of a wetland flow to develop the dispersion model and to determine the dispersivity, which is illustrated with an asymptotic time variation characterized by stem dominated, transitional, and width-stem dominated stages. For typical contaminant constituents of chemical oxygen demand, biochemical oxygen demand, total phosphorus, total nitrogen and heavy metal, the evolution of contaminant cloud is illustrated with the critical length and duration of the contaminant cloud with constituent concentration beyond some given environmental standard level.

An ecological risk assessment model for a pulsed contaminant emission into a wetland channel flow

As a continuation of the modelling on ecological degradation and hydraulic dispersion of pollutant emission into an idealized two-dimensional free-surface wetland flow (Zeng, L., Chen, G.Q., 2009b. Ecological degradation and hydraulic dispersion of contaminant in wetland. Ecol. Model., doi:10.1016/j.ecolmodel.2009.10.024), an ecological risk assessment model for the typical case of a pulsed contaminant emission into a realistic three-dimensional wetland channel flow is presented in this paper for the fate of cross-sectional mean concentration under environmental dispersion. An environmental dispersion model for the mean concentration is devised as an extension of Taylor’s classical analysis on dispersion in fluid flows. The velocity distribution and the environmental dispersivity in the fully developed steady flow through the wetland is found and illustrated with limiting cases covering various known solutions for the porous media flow between parallel plates, flow in a shallow wetland, sweeping flow in a densely vegetated wetland, and single phase flow in a channel. Obtained by Aris’s method of moments, the environmental dispersivity is shown characterized with multi-scale asymptotic time variations with stem dominated stage, transitional stage, and width–depth-stem dominated stage. Based on the solution for the evolution of contaminant cloud in the wetland channel flow, critical length and duration of the contaminant cloud with concentration beyond given environmental standard level are concretely illustrated for typical pollutant constituents in wastewater emission. Under the same emission intensity and environmental standard, the duration of contaminant cloud in the wetland channel is revealed shorter than that in a free surface wetland, due to the lateral effect.

Depth‐averaged, spatially distributed flow dynamic and solute transport modelling of a large‐scaled, subtropical constructed wetland

AbstractConstructed wetlands are being utilized worldwide to effectively reduce excess nutrients in agricultural runoff and wastewater. Despite their frequency, a multi‐dimensional, physically based, spatially distributed modelling approach has rarely been applied for flow and solute transport in treatment wetlands. This article presents a two‐dimensional hydrodynamic and solute transport modelling of a large‐scaled, subtropical, free water surface constructed wetland of about 8 km2 in the Everglades of Florida, USA. In this study, MIKE 21 was adopted as the basic model framework. Field monitoring of the time series hydrological and chloride data, as well as spatially distributed data such as bathymetry and vegetation distribution, provided the necessary model input and testing data. Simulated water level profiles were in good agreement with the spatio‐temporal variations of measured ones. On average, the root‐mean‐square error of model calibration on annual water level fluctuations was 0·09 m. Manning's roughness coefficients for the dense emergent and submerged aquatic vegetation areas, which were estimated as a function of vegetation type, ranged from 0·67 to 1·0 and 0·12 to 0·15 s/m1/3, respectively. The solute transport model calibration for four monitoring sites agreed well with the measured annual variations in chloride concentration with an average percent model error of about 15%. The longitudinal dispersivity was estimated to be about 2 m and was more than an order of magnitude higher than the transverse one. This study is expected to play the role of a stepping stone for future modelling efforts on the development and application of more advanced flow and transport models applicable to a variety of constructed wetland systems, as well as to the Everglades stormwater treatment areas in operation or in preparation. Copyright © 2010 John Wiley & Sons, Ltd.