Indirect Environmental Effects of Dikes on Estuarine Tidal Channels: Thinking Outside of the Dike for Habitat Restoration and Monitoring
TL;DR: In this article, the authors analyzed historical photos of the Skagit River delta marshes (Washington, U.S.) and compared changes in estuarine marsh and tidal channel surface area from 1956-2000 in the Wiley Slough area of the South Fork Skagits delta, and from 1937-2000 on the North Fork delta.
Abstract: While the most obvious effects of dike construction and marsh conversion are those affecting the con- verted land (direct or intended effects), less immediately apparent effects also occur seaward of dikes (indirect or unintended effects). I analyzed historical photos of the Skagit River delta marshes (Washington, U.S.) and compared changes in estuarine marsh and tidal channel surface area from 1956-2000 in the Wiley Slough area of the South Fork Skagit delta, and from 1937-2000 in the North Fork delta. Dike construction in the late 1950s caused the loss of 80 ha of estuarine marsh and 6.7 ha of tidal channel landward of the Wiley Slough dikes. A greater amount of tidal channel surface area, 9.6 ha, was lost seaward of the dikes. Similar losses were observed for two smaller North Fork tidal channel systems. Tidal channels far from dikes did not show comparable changes in channel surface area. These results are consistent with hydraulic geometry theory, which predicts that diking reduces tidal flushing in the undiked channel remnants and this results in sedimentation. Dikes may have significant seaward effects on plants and animals associated with tidal channel habitat. Another likely indirect dike effect is decreased sinuosity in a distributary channel of the South Fork Skagit River adjacent to and downstream of the Wiley Slough dikes, compared to distributary channels upstream or distant from the dikes. Loss of floodplain area to diking and marsh conversion prevents flood energy dissipation over the marsh surface. The distributary channel has responded to greater flood energy by increasing mean channel width and decreasing sinuosity. Restoration of diked areas should consider historic habitat loss seaward of dikes, as well as possible benefits to these areas from dike breaching or removal. Habitat restoration by breaching or removal of dikes should be monitored in areas directly affected by dikes, areas indirectly affected, and distinct reference areas.
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TL;DR: This article studied the effect of stepwise embankments of brackish and salt marshes and subsequent marsh progradation on organic carbon stocks in the Scheldt estuary (the Netherlands).
Abstract: Tidal marshes are coastal and estuarine ecosystems that store large amounts of sedimentary organic carbon (OC). Despite the valuable ecosystem services they deliver, tidal marshes have been converted to other land‐use types over the past centuries. Although previous studies have reported large decreases in soil organic carbon (SOC) stocks after tidal marsh embankment, knowledge on the magnitude and rate of OC losses is still limited. Here, we studied the effect of stepwise embankments of brackish and salt marshes and subsequent marsh progradation on SOC stocks in the Scheldt estuary (the Netherlands). We collected samples from soil profiles along tidal marsh–reclaimed tidal marsh chronosequences and determined total OC stocks and the stable carbon signature of the OC. Our results showed that large losses of previously sequestered SOC occur on a decadal timescale with the embankment of brackish (−8.7 ± 0.7 kg OC m⁻²) and salt marshes (−6.7 ± 0.8 kg OC m⁻²). The (incomplete) replacement of tidal marsh OC by agricultural OC is substantially faster in topsoils (ca. a century) compared with subsoils (multiple centuries). Simulations with a coupled land use–SOC model showed that large rates of marsh progradation following embankment construction resulted in a substantial increase in landscape‐scale SOC storage, whereas large SOC losses occurred in landscapes dominated by embanked tidal marshes. The findings of our study might help to assess how these management practices affect regional SOC stocks. HIGHLIGHTS: We studied how OC stocks in tidal marsh sediments are affected by embankment construction OC stocks of both brackish and salt marsh sediments were reduced by ca. 60% with embankment Gains in landscape‐scale SOC storage occurred with marsh progradation after embankment If no marsh progradation occurs, embankments always lead to SOC loss at the landscape scale
11 citations
Cites background from "Indirect Environmental Effects of D..."
...The destruction of natural coastal wetlands has important consequences for the health of coastal ecosystems (Hood, 2004; Ma et al., 2014) and can cause considerable economic losses in regions that are affected (Zhu et al....
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...This reduction leads to smaller water velocities and increasing rates of sediment deposition after embankment construction (Hood, 2004; Cuvilliez et al., 2009; Xie et al., 2018)....
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...The destruction of natural coastal wetlands has important consequences for the health of coastal ecosystems (Hood, 2004; Ma et al., 2014) and can cause considerable economic losses in regions that are affected (Zhu et al., 2017)....
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TL;DR: In this paper, the specific regeneration requirements of four dominant coastal wetland macrophytes along the Northern Gulf of Mexico (NGoM) are described and compared with current hydrologic alterations to provide insights into potential future changes in dominant ecosystem structure and function and to highlight knowledge gaps in the current literature.
Abstract: Tidal saline wetlands in the Northern Gulf of Mexico (NGoM) are dynamic and frequently disturbed systems that provide myriad ecosystem services. For these services to be sustained, dominant macrophytes must continuously recolonize and establish after disturbance. Macrophytes accomplish this regeneration through combinations of vegetative propagation and sexual reproduction, the relative importance of which varies by species. Concurrently, tidal saline wetland systems experience both anthropogenic and natural hydrologic alterations, such as levee construction, sea-level rise, storm impacts, and restoration activities. These hydrologic alterations can affect the success of plant regeneration, leading to large-scale, variable changes in ecosystem structure and function. This review describes the specific regeneration requirements of four dominant coastal wetland macrophytes along the NGoM ( Spartina alterniflora , Avicennia germinans , Juncus roemerianus , and Batis maritima ) and compares them with current hydrologic alterations to provide insights into potential future changes in dominant ecosystem structure and function and to highlight knowledge gaps in the current literature that need to be addressed.
11 citations
TL;DR: In this paper, a 60-year time series of high-resolution maps was developed, analysing the changes in feature surfaces, showing that beaches and dunes serve as a protective barrier for the tidal flats, acting as a sediment buffer for the entire system.
Abstract: Geomorphological changes in recent decades in three estuaries along the Iberian coast were analysed using aerial orthophotographs. A hierarchical classification scheme, based on a literature review representing 26 estuarine eco-geomorphological features relevant to estuarine dynamics and functioning, is described. The estuaries selected were San Vicente de la Barquera (N Spain), Guadiana River (SW border between Spain and Portugal) and the Ebro River Delta mouth (NE Spain). For these systems, a 60-year time series of high-resolution maps was developed, analysing the changes in feature surfaces. The main subsystems analysed were beach, dunes, saltmarshes and the drainage network. The results of the cartographies showed general behaviour common to all transitional systems, relationships among main subsystems and processes inherent to each one. This work illustrates how beaches and dunes serve as a protective barrier for the tidal flats, acting as a sediment buffer for the entire system. The subsystems are connected by the drainage network responsible for the exchange of matter and energy between them. Furthermore, an accuracy assessment was performed in one of the study zones to identify the limitations of mapping with aerial photographs. The results explain the changes with time but also the processes and relationships between the estuarine features at a long-term scale. This work adds an important perspective towards a general understanding of their dependence on intrinsic and boundary conditions.
10 citations
Cites background from "Indirect Environmental Effects of D..."
...This had led to the loss of a large part of the surface occupied by intertidal areas [7], directly affecting the general functioning of the system and, therefore, associated subsystems and the processes taking place on them....
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TL;DR: Examining whether small semipermanent tidal channels were preferentially used by foraging Western Sandpipers and Dunlins during a spring migratory stopover in Bandon Marsh concluded that shorebirds selected microhabitats near channels because of the greater food abundance and availability.
Abstract: Estuarine intertidal habitats are heterogeneous, therefore migratory shorebirds are expected to forage in microhabitats where they can maximize their energy intake. Identifying proximate factors that migratory shorebirds use to accept or reject a particular habitat patch will help land managers make conservation and restoration decisions that provide the greatest benefits to shorebird populations during migration, a period of intense energy usage. We examined whether small semipermanent tidal channels were preferentially used by foraging Western Sandpipers (Calidris mauri) and Dunlins (C. alpina) during a spring migratory stopover in Bandon Marsh, an Oregon, USA, estuary. Further, we tested alternative hypotheses about how channels might be beneficial to shorebirds by examining infauna abundance, composition, and depth alongside channels compared with that in open mudflats. The densities of Western Sandpipers and Dunlins were at least 4 times higher along channels than in open mudflat habitats. I...
10 citations
01 Jan 2008
TL;DR: In this paper, the response of bathymetric change to initial conditions and model parameters with a simplified zero-dimensional cohesive sediment transport model, a two-dimensional hydrodynamic/sediment transport model and a tidally averaged box model was investigated.
Abstract: Bathymetric change in tidal environments is modulated by watershed sediment yield, hydrodynamic processes, benthic composition, and anthropogenic activities. These multiple forcings combine to complicate simple prediction of bathymetric change; therefore, numerical models are necessary to simulate sediment transport. Errors arise from these simulations, due to inaccurate initial conditions and model parameters. We investigated the response of bathymetric change to initial conditions and model parameters with a simplified zero-dimensional cohesive sediment transport model, a two-dimensional hydrodynamic/sediment transport model, and a tidally averaged box model. The zero-dimensional model consists of a well-mixed control volume subjected to a semidiurnal tide, with a cohesive sediment bed. Typical cohesive sediment parameters were utilized for both the bed and suspended sediment. The model was run until equilibrium in terms of bathymetric change was reached, where equilibrium is defined as less than the rate of sea level rise in San Francisco Bay (2.17 mm/year). Using this state as the initial condition, model parameters were perturbed 10% to favor deposition, and the model was resumed. Perturbed parameters included, but were not limited to, maximum tidal current, erosion rate constant, and critical shear stress for erosion. Bathymetric change was most sensitive to maximum tidal current, with a 10% perturbation resulting in an additional 1.4 m of deposition over 10 years. Re-establishing equilibrium in this model required 14 years. The next most sensitive parameter was the critical shear stress for erosion; when increased 10%, an additional 0.56 m of sediment was deposited and 13 years were required to re-establish equilibrium. The two-dimensional hydrodynamic/sediment transport model was calibrated to suspended-sediment concentration, and despite robust solution of hydrodynamic conditions it was unable to accurately hindcast bathymetric change. The tidally averaged box model was calibrated to bathymetric change data and shows rapidly evolving bathymetry in the first 10–20 years, though sediment supply and hydrodynamic forcing did not vary greatly. This initial burst of bathymetric change is believed to be model adjustment to initial conditions, and suggests a spin-up time of greater than 10 years. These three diverse modeling approaches reinforce the sensitivity of cohesive sediment transport models to initial conditions and model parameters, and highlight the importance of appropriate calibration data. Adequate spin-up time of the order of years is required to initialize models, otherwise the solution will contain bathymetric change that is not due to environmental forcings, but rather improper specification of initial conditions and model parameters. Temporally intensive bathymetric change data can assist in determining initial conditions and parameters, provided they are available. Computational effort may be reduced by selectively updating hydrodynamics and bathymetry, thereby allowing time for spin-up periods.
9 citations
Cites background from "Indirect Environmental Effects of D..."
...Diking of wetlands reduced tidal prism and caused adjacent tidal channels to fill with sediment ( Hood 2004 )....
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TL;DR: A blend of erudition (fascinating and sometimes obscure historical minutiae abound), popularization (mathematical rigor is relegated to appendices) and exposition (the reader need have little knowledge of the fields involved) is presented in this article.
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...Tidal channel allometry follows from a more general fractal theory of landforms (RodriguezIturbe and Rinaldo 1997), and the scaling of perimeter with surface area is a common reflection of landform fractal geometry (Mandelbrot 1983; Sugihara and May 1990)....
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...Greater adjustment in width relative to depth with changing discharge is consistent with hydraulic geometry theory (Leopold et al. 1964)....
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...Because high sinuosity is associated with small channel width relative to depth (Leopold et al. 1964), the observed correlation between changes in sinuosity and in mean channel width suggests that distributary channel widths changed to a greater degree than channel depths....
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...As a final error check, meander bends in tidal channels were examined at scales ranging from 1:1,000 to 1:10,000 to determine whether erosion had occurred in the cut banks of the meanders and sediment deposition at the point bars, in accord with theoretical expectations (Leopold et al. 1964)....
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