Modeling mobility and effects of contaminants in wetlands

Dixon, Kenneth R.; Florian, James D.

doi:10.1002/etc.5620121210

Cited by 7 publications

(4 citation statements)

References 37 publications

(8 reference statements)

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“…Second, submerged macrophytes, common seen in shallow eutrophic lakes, can affect the lake's ecology and water quality [10,11]. Littoral macrophytes can form a transition zone between terrestrial and aquatic systems [12,13]. The concentration gradient in nutrients, sediment and other contaminants between littoral macrophytes and open pelagic zones can be large, causing an active exchange of constituents [14].…”

Section: Introductionmentioning

confidence: 99%

Temperature and Circulation Dynamics in a Small and Shallow Lake: Effects of Weak Stratification and Littoral Submerged Macrophytes

Torma

2019

Water

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In this paper, the effects of littoral submerged macrophytes on weak stratification conditions in a small and shallow lake are investigated. Diverse submerged macrophytes occupying a large portion of the littoral zone act as resistance to water motions and affect lake hydrodynamics. Strong solar radiation and mild wind forcing typically occurring during the summer season result in weak stratification characterized by a diurnal cycle with a temperature differential of 1-3 • C. Temperature and circulation dynamics of a small and shallow lake are depicted by extensive field measurements and a three-dimensional non-hydrostatic model with a generic length scale (GLS) approach for the turbulence closure and drag forces induced by macrophytes. Results show that the effects of macrophytes on velocity profiles are apparent. In the pelagic area, the circulation patterns with and without macrophytes are similar. The velocity profile is generally characterized by a two-layer structure with the maximum velocity at both the water surface and the mid-depth. In contrast, inside the littoral zone, the mean flow is retarded by macrophytes and the velocity profile is changed to only one maximum velocity at the surface with a steeper decrease until 2.0 m depth and another slight decrease to the lake bottom. From the whole lake perspective, littoral macrophytes dampen the horizontal water temperature difference between the upwind side and download side of the lake. Macrophytes promote a stronger temperature stratification by retarding mean flows and reducing vertical mixing. Overall, this study shows that the temperature structures and circulation patterns under weak stratification conditions in a small and shallow lake are strongly affected by littoral vegetation.

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Section: Introductionmentioning

confidence: 99%

Temperature and Circulation Dynamics in a Small and Shallow Lake: Effects of Weak Stratification and Littoral Submerged Macrophytes

Torma

2019

Water

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“…Freshwater and saltwater wetlands provide important transitional zones between terrestrial and aquatic systems, mediating exchanges between nutrients (Nixon, 1980; Barko et al, 1991) and other contaminants (Dixon and Florian, 1993). Wetland plants control these exchanges both directly through the process of uptake and biological transformation and indirectly by altering the hydrodynamic conditions (Kadlec, 1995).…”

Section: Introductionmentioning

confidence: 99%

“…Plants' influences on the pollutant diffusion include three aspects:(1) Vegetative resistance from stems and branches changes flow paths; (2) The role of convection diffusion results in uneven distribution of flow velocity; (3) The wake from vegetation involves entrainment. The present research on pollutant diffusion in flow through vegetation is still on experimental research stage.…”

Section: Introductionmentioning

confidence: 99%

Longitudinal Dispersion of Pollutants in Flow through Natural Vegetation

Er-qing

Cao

Jiang

et al. 2010

2010 4th International Conference on Bioinformatics and Biomedical Engineering

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The drag due to the vegetation affects of pollutant dispersion as it flows through vegetation. The previous research has aimed mostly at a cylinder-based model in which the vertical vegetative characteristics are homogenous. It rarely mentions natural vegetation in which the vertical vegetative characteristics undergo steep changes. Based on the laboratory measurements and observations, an empirical model is built to calculate the longitudinal dispersion coefficient for flow through natural shrubs using the multiple regression analysis method. The calculation model is developed by relating the longitudinal dispersion coefficient to plant diameter, the stem Reynolds number and the drag coefficient. The natural shrubs are chosen to examine in which the vertical characteristics make substantial changes and natural reeds in which the vertical characteristics change little.Shrubs and reeds, reeds and herbs in different cooperating ways are fixed on a flume. Then ammonia nitrogen is used as a tracer, an Acoustic Doppler as a velocity meter, and a water level sensor and multi-parameter water quality instruments to measure respectively the velocity, water level, and the pollutant concentration process curve.

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“…As Simmons et al [2001] stated, the free convection fingering could lead to much faster and more extensive solute transport. It should be noted that the marsh interior is close to the inland boundary, although the inland freshwater input was not considered in this study, the terrestrially-derived contaminant, nutrients and chemicals tend to enter the marsh system from such inland boundary [Dixon and Florian, 1993]. Therefore, the solute transport process complicated by the unstable fingers might largely modify the path and residence time of these materials when they are moving towards the seaward boundary.…”

Section: Numerical Simulationsmentioning

confidence: 99%

Effects of salinity variations on subsurface flow in salt marshes

Shen¹

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Salt marshes are important intertidal wetlands at the land-ocean interface with a wide range of ecological functions, such as providing essential habitats for intertidal fauna, affecting the productivity of coastal waters via nutrient exchange, maintaining coastal biodiversity and moderating greenhouse gas emission. However, over the past few decades the area of salt marshes worldwide has declined sharply due to human activities. To reverse such a trend, it is urgent for us to understand the various processes that underpin the ecological functions of marsh systems. Among these processes, the pore-water flow plays an important role. Many studies, including field investigations and numerical simulations, have been conducted to examine the pore-water flow in salt marshes under the influences of tidal oscillation, evapotranspiration, precipitation, soil properties, topography and inland freshwater input.However, the impacts of salinity variations have been neglected.The study in this thesis aimed to explore the effects of salinity variations, especially due to salinity differences between the surface and subsurface water, on pore-water flow in salt marshes. Laboratory experiments and numerical simulations were carried out to examine the influences of upward and downward salinity gradients on pore-water flow and associated solute transport in the marsh soil. The study also provided insights into unstable pore-water flow in the soil under variably-saturated conditions.In the investigation on the impacts of upward salinity gradient on pore-water flow in salt marshes, both laboratory experiment and numerical simulations revealed that, combined with tidal fluctuations, the upward salinity gradient modified the stability of the system, and induced unstable flow and salt fingers in the marsh soil. The size and number of salt fingers both varied from the near-creek zone to marsh interior. Near the creek the finger size was larger but there were less fingers, while in the interior area there were more fingers but of smaller sizes. This was because that a relatively strong circulation and advection near the creek overwhelmed the density effect, which became dominant as the circulation and advection weakened in marsh interior. The unstable fingers altered largely the pore-water ii flow locally and the associated solute transport, especially in the marsh interior. The results of particle tracking showed that the downward penetration of fingers led to wider and faster exchange in the marsh interior. However, the overall water exchange between marsh sediments and coastal water was only slightly enhanced as it was still largely controlled by the tidal oscillation.In the investigation on the effects of downward salinity gradient on pore-water flow in salt marshes, both laboratory experiments and numerical simulations found that, unlike the case of upward salinity gradient, the downward salinity gradient maintained the stability of the system with the plume moving steadily downward in a manner similar to that of the case wit...

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Modeling mobility and effects of contaminants in wetlands

Cited by 7 publications

References 37 publications

Temperature and Circulation Dynamics in a Small and Shallow Lake: Effects of Weak Stratification and Littoral Submerged Macrophytes

Temperature and Circulation Dynamics in a Small and Shallow Lake: Effects of Weak Stratification and Littoral Submerged Macrophytes

Longitudinal Dispersion of Pollutants in Flow through Natural Vegetation

Effects of salinity variations on subsurface flow in salt marshes

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