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W. Gregory Hood - One of the best experts on this subject based on the ideXlab platform.
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Geographic variation in Puget Sound Tidal Channel planform geometry
Geomorphology, 2015Co-Authors: W. Gregory HoodAbstract:Tidal Channels are central elements of salt marsh hydrodynamics, sediment dynamics, and habitat. To develop allometric models predicting the number and size of Tidal Channels that could develop following salt marsh restoration, Channels were digitized from aerial photographs of Puget Sound river delta marshes. Salt marsh area was the independent variable for all dependent Channel planform metrics. Tidal Channel allometry showed similar scaling exponents for Channel planform metrics throughout Puget Sound, simplifying comparisons between locations. Y-intercepts of allometric relationships showed geographic variation, which multiple-regression indicated was associated with Tidal range and storm significant wave height. Channel size and complexity were positively related to Tidal range and negatively related to wave height. Four case studies, each with paired regions of similar Tidal range and contrasting wave environments, further indicated wave environment affected Channel geometry. Wave-mediated sediment delivery may be the mechanism involved, with wave-sheltered areas experiencing relative sediment deficits, such that some salt marshes in Puget Sound are already suffering sea-level rise impacts that are reflected in their Channel network geometry.
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Differences in Tidal Channel network geometry between reference marshes and marshes restored by historical dike breaching
Ecological Engineering, 2014Co-Authors: W. Gregory HoodAbstract:Tidal marsh restoration generally involves dike breaching rather than complete dike removal to restore Tidal inundation. Dike removal more completely restores hydrodynamic processes, but dike breaching is more economical. Thus, without a clear demonstration of the ecological benefits of complete or extensive dike removal, economic considerations are likely to cause restoration planners and engineers to prefer dike breaching. To provide some insight into the relative benefit of dike breaching versus dike removal, Tidal Channel planform geometry was compared between historical dike breach sites (>15 years old) and reference Tidal marsh. Tidal Channel networks were examined because they mediate many hydrodynamic, sedimentary, and ecological processes. Dike breach sites were found to have fewer Tidal Channel outlets than reference sites, but greater total Channel surface area and length. These differences were likely the result of remnant dikes constraining Tidal prism entirely to Channel networks rather than allowing a portion of the prism to transit site boundaries as sheet flow. Allometric analysis of GIS-calculated Tidal Channel drainage basin area relative to total marsh area indicated the proportion of Tidal prism comprised of sheet flow was inversely related to total marsh area, with the smallest marsh islands having no Tidal Channels and all of their Tidal prism consisting of sheet flow. This suggests dike removal to restore sheet flow is most important for small restoration projects. However, dike removal may still be important for large restoration sites depending on issues not examined in this paper, e.g., remnant dike effects on river flood hydrodynamics.
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Tidal Channel meander formation by depositional rather than erosional processes: examples from the prograding Skagit River Delta (Washington, USA)
Earth Surface Processes and Landforms, 2010Co-Authors: W. Gregory HoodAbstract:Channel meander dynamics in fluvial systems and many Tidal systems result from erosion of concave banks coupled with sediment deposition on convex bars. However, geographic information system (GIS) analysis of historical aerial photographs of the Skagit Delta marshes provides examples of an alternative meander forming process in a rapidly prograding river delta: deposition-dominated Tidal Channel meander formation through a developmental sequence beginning with sandbar formation at the confluence of a blind Tidal Channel and delta distributary, proceeding to sandbar colonization and stabilization by marsh vegetation to form a marsh island opposite the blind Tidal Channel outlet, followed by narrowing of the gap between the island and mainland marsh, closure of one half of the gap to join the marsh island to the mainland, and formation of an approximately right-angle blind Tidal Channel meander bend in the remaining half of the gap. Topographic signatures analogous to fluvial meander scroll bars accompany these planform changes. Parallel sequences of marsh ridges and swales indicate locations of historical distributary shoreline levees adjacent to filled former island/mainland gaps. Additionally, the location of marsh islands within delta distributaries is not random; islands are disproportionately associated with blind Tidal Channel/distributary confluences. Furthermore, blind Tidal Channel outlet width is positively correlated with the size of the marsh island that forms at the outlet, and the time until island fusion with mainland marsh. These observations suggest confluence hydrodynamics favor sandbar/marsh island development. The transition from confluence sandbar to Tidal Channel meander can take as little as 10 years, but more typically occurs over several decades. This depositional blind Tidal Channel meander formation process is part of a larger scale systemic depositional process of delta progradation that includes distributary elongation, gradient reduction, flow-switching, shoaling, and narrowing. Copyright © 2010 John Wiley & Sons, Ltd.
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A conceptual model of depositional, rather than erosional, Tidal Channel development in the rapidly prograding Skagit River Delta (Washington, USA)
Earth Surface Processes and Landforms, 2006Co-Authors: W. Gregory HoodAbstract:The origin and growth of blind Tidal Channels is generally considered to be an erosional process. This paper describes a contrasting depositional model for blind Tidal Channel origin and development in the Skagit River delta, Washington, USA. Chronological sequences of historical maps and photos spanning the last century show that as sediments accumulated at the river mouth, vegetation colonization created marsh islands that splintered the river into distributaries. The marsh islands coalesced when intervening distributary Channels gradually narrowed and finally closed at the upstream end to form a blind Tidal Channel, or at mid-length to form two blind Tidal Channels. Channel closure was probably often mediated through gradient reduction associated with marsh progradation and Channel lengthening, coupled with large woody debris blockages. Blind Tidal Channel evolution from distributaries was common in the Skagit marshes from 1889 to the present, and it can account for the origin of very small modern blind Tidal Channels. The smallest observed distributary-derived modern blind Tidal Channels have mean widths of 0·3 m, at the resolution limit of the modern orthophotographs. While Channel initiation and persistence are similar processes in erosional systems, they are different processes in this depositional model. Once a Channel is obstructed and isolated from distributary flow, only Tidal flow remains and Channel persistence becomes a function of Tidal prism and Tidal or wind/wave erosion. In rapidly prograding systems like the Skagit, blind Tidal Channel networks are probably inherited from the antecedent distributary network. Examination of large-scale Channel network geometry of such systems should therefore consider distributaries and blind Tidal Channels part of a common Channel network and not entirely distinct elements of the system. Finally, managers of Tidal habitat restoration projects generally assume an erosional model of Tidal Channel development. However, under circumstances conducive to progradation, depositional Channel development may prevail instead. Copyright © 2006 John Wiley & Sons, Ltd.
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Indirect Environmental Effects of Dikes on Estuarine Tidal Channels: Thinking Outside of the Dike for Habitat Restoration and Monitoring
Estuaries, 2004Co-Authors: W. Gregory HoodAbstract: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.
Sergio Fagherazzi - One of the best experts on this subject based on the ideXlab platform.
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efficient Tidal Channel networks alleviate the drought induced die off of salt marshes implications for coastal restoration and management
Science of The Total Environment, 2020Co-Authors: Zezheng Liu, Sergio Fagherazzi, Chengjie Xie, Xiaojun She, Baoshan CuiAbstract:Massive die-off in salt marshes is one of the most common examples of widespread degradation in marine and coastal ecosystems. In salt marshes, Tidal Channel networks facilitate the exchange of water, nutrients, sediments and biota with the open marine environments. However, quantitative analyses of the role of Channel networks in alleviating vegetation die-off in salt marshes are scarce. Here we quantified the spatial-temporal development of marsh vegetation die-off in the northern Liaodong Bay by analyzing aerial images before, during, and after a drought (from 2014 to 2018). We found that Suaeda salsa marshes have recently experienced large-scale die-off. The extent of vegetation die-off increases with increasing distance from the Channel network. Moreover, our results suggested that efficient Tidal Channel networks (high drainage density, low mean unChanneled path length) can mitigate die-off at the watershed scale. We presented possible abiotic & biotic processes in Channel networks that explain this spatial dynamic. Our study highlights the importance of efficient Tidal Channel networks in mitigating die-off and enhancing the resistance of marshes to droughts, and call for incorporating theses dynamics in coastal restoration and management.
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Salt marsh vegetation promotes efficient Tidal Channel networks.
Nature communications, 2016Co-Authors: William S. Kearney, Sergio FagherazziAbstract:Tidal Channel networks mediate the exchange of water, nutrients and sediment between an estuary and marshes. Biology feeds back into Channel morphodynamics through the influence of vegetation on both flow and the cohesive strength of Channel banks. Determining how vegetation affects Channel networks is essential in understanding the biological functioning of interTidal ecosystems and their ecosystem services. However, the processes that control the formation of an efficient Tidal Channel network remain unclear. Here we compare the Channel networks of vegetated salt marshes in Massachusetts and the Venice Lagoon to unvegetated systems in the arid environments of the Gulf of California and Yemen. We find that the unvegetated systems are dissected by less efficient Channel networks than the vegetated salt marshes. These differences in network geometry reflect differences in the branching and meandering of the Channels in the network, characteristics that are related to the density of vegetation on the marsh. Tidal Channel networks mediate the exchange of water, nutrients, sediment and biota between an estuary and marshes. Here, the authors show that the presence of vegetation on the marsh platform contributes to the formation of an efficient Channel network.
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Sediments and water fluxes in a muddy coastline: interplay between waves and Tidal Channel hydrodynamics
Earth Surface Processes and Landforms, 2010Co-Authors: Sergio Fagherazzi, Anthony M. PriestasAbstract:Tidal Channels are ubiquitous in muddy coastlines and play a critical role in the redistribution of sediments, thus dictating the general evolution of interTidal landforms. In muddy coastlines, the morphology of Tidal Channels and adjacent marshes strongly depends on the supply of fine sediments from the shelf and on the resuspension of sediments by wind waves. To investigate the processes that regulate sediment fluxes in muddy coastlines, we measured Tidal velocity and sediment concentration in Little Constance Bayou, a Tidal Channel in the Rockefeller State Wildlife Refuge, Louisiana, USA. The Tidal measurements were integrated with measurements of wave activity in the bay at the mouth of the Channel, thus allowing the quantification of feedbacks between waves and sediment fluxes. Results indicate that the sediment concentration in the Channel is directly related to the wave height in the adjacent bay during flood and high slack water, whereas the concentration during ebb depends on local Channel velocity. Moreover, the sediment flux during ebb is of the same order of magnitude as the sediment flux during the previous flood, indicating that only a small fraction of transported sediments are stored in the marsh during a Tidal cycle. Finally, very low tides, characterized by high ebb velocities, export large volumes of sediment to the ocean. Copyright © 2010 John Wiley & Sons, Ltd.
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THE EFFECT OF BIDIRECTIONAL FLOW ON Tidal Channel PLANFORMS
Earth Surface Processes and Landforms, 2004Co-Authors: Sergio Fagherazzi, Emmanuel J. Gabet, David Jon FurbishAbstract:Salt marsh Tidal Channels are highly sinuous. For this project, field surveys and aerial photographs were used to characterize the planform of Tidal Channels at China Camp Marsh in the San Francisco Bay, California. To model the planform evolution, we assume that the topographic curvature of the Channel centreline is a key element driving meander migration. Extraction of curvature data from a planimetric survey, however, presents certain problems because simple calculations based on equally distanced points on the Channel axis produce numerical noise that pollutes the final curvature data. We found that a spline interpolation and a polynomial fit to the survey data provided us with a robust means of calculating Channel curvature. The curvature calculations, combined with data from numerous cross-sections along the Tidal Channel, were used to parameterize a computer model. With this model, based on recent theoretical work, the relationship between planform shape and meander migration as well as the consequences of bidirectional flow on planform evolution have been investigated. Bank failure in vegetated salt marsh Channels is characterized by slump blocks that persist in the Channel for several years. It is therefore possible to identify reaches of active bank erosion and test model predictions. Our results suggest that the geometry and evolution of meanders at China Camp Marsh, California, reflect the ebb-dominated regime. Copyright © 2004 John Wiley & Sons, Ltd.
Ross Vennell - One of the best experts on this subject based on the ideXlab platform.
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Distribution of vertical velocity inferred from secondary flow in a curved Tidal Channel
Journal of Geophysical Research, 2014Co-Authors: Peter Russell, Ross VennellAbstract:High-resolution observations from the curved Tidal Channel of the Otago Harbour shows secondary flows up to 20% of the primary flow and vertical velocity inferred from secondary flow up to 1% of the primary flow. This vertical velocity is inferred on a much finer scale than previous works. The spatial pattern of this vertical velocity is upward on the inside and downward on the outside of the bend, consistent with previous laboratory flume measurements. Linear regression, rp = 0.95, shows the cross-Channel distribution of the observed secondary flow can be resolved from the horizontal ADCP measurements well enough to be consistent with the cross-Channel distribution of secondary flow derived from the observed primary flow using the model of Kalkwijk and Booij (1986). Linear regression, rp = 0.80, shows the vertical velocity inferred from observed secondary flow is consistent with vertical velocity derived from the observed primary flow using the model of Kalkwijk and Booij (1986). This also shows the cross-Channel distribution of the observed secondary flow is resolved well enough from the horizontal ADCP measurements to be able to infer the vertical velocity from mass continuity. The required horizontal resolution is made possible by Radial Basis Function (RBF) smoothing and spatial interpolation that allows for continuity of the spatial derivatives. Modeling trajectories using Channel dimensions and velocity field values equivalent to the observations show that 3-dimensional secondary circulation forms a loose helical flow pattern.
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tuning turbines in a Tidal Channel
Journal of Fluid Mechanics, 2010Co-Authors: Ross VennellAbstract:As Tidal turbine farms grow they interact with the larger scale flow along a Channel by increasing the Channel's drag coefficient. This interaction limits a Channel's potential to produce power. A 1D model for a Tidal Channel is combined with a theory for turbines in a Channel to show that the tuning of the flow through the turbines and the density of turbines in a Channel's cross-section also interact with the larger scale flow, via the drag coefficient, to determine the power available for production. To maximise turbine efficiency, i.e. the power available per turbine, farms must occupy the largest fraction of a Channel's cross-section permitted by navigational and environmental constraints. Maximising of power available with these necessarily densely packed farms requires turbines to be tuned for a particular Channel and turbine density. The optimal through-flow tuning fraction varies from near 1/3 for small farms occupying a small fraction of the cross-section, to near 1 for large farms occupying most of the cross-section. Consequently, tunings are higher than the optimal through-flow tuning of 1/3 for an isolated turbine from the classic turbine theory. Large optimally tuned farms can realise most of a Channel's potential. Optimal tunings are dependent on the number of turbines per row, the number of rows, as well as the Channel geometry, the background bottom friction coefficient and the Tidal forcing.
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high resolution observations of the intensity of secondary circulation along a curved Tidal Channel
Journal of Geophysical Research, 2007Co-Authors: Ross Vennell, Chris OldAbstract:[1] High horizontal resolution moving vessel acoustic Doppler current profiler (ADCP) observations of the spatial pattern of cross-stream velocities in a curved Tidal Channel show radially outward surface velocities up to 10 cm s−1 which are maximum midChannel, consistent with helical secondary flow in a vertical plane normal to the depth-averaged velocity. The 30-m-cross- and 150-m-along-Channel resolution observations are from a 2700-m-long section of a 350-m-wide horizontally and vertically well mixed Tidal Channel with a radius of curvature 1–5 km. The along-Channel resolution allows the intensity of the curvature induced secondary flow to be estimated from the linear correlation between the observed cross-Channel component of vertical shear and the shear estimated from the streamwise velocity and its varying curvature using an existing analytic model. The two shears are highly correlated and the regression line slope demonstrates that the observed curvature induced secondary flow is 30% more intense than that predicted by the model for a typical bottom drag coefficient. The secondary flow is 50% more intense than that predicted using the drag coefficient which best fits the streamwise velocity profile. Numerical solutions demonstrate that the intensity of the secondary flow is sensitive to small changes in the shape of the eddy viscosity profile; hence intensity may be sensitive to the way turbulence is modeled. Lagged correlation of the observations showed that the secondary flow adapts to changes in curvature and primary flow over a 300-m length scale, or 20 water depths, consistent with the existing model and laboratory studies.
Morten Pejrup - One of the best experts on this subject based on the ideXlab platform.
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On luminescence bleaching of Tidal Channel sediments
Geografisk Tidsskrift-Danish Journal of Geography, 2015Co-Authors: Mikkel Fruergaard, Morten Pejrup, Andrew S. Murray, Thorbjørn Joest AndersenAbstract:We investigate the processes responsible for bleaching of the quartz OSL signal from Tidal Channel sediment. Tidal dynamics are expected to play an important role for complete bleaching of Tidal sediments. However, no studies have examined the amount of reworking occurring in Tidal Channels and on Tidal flats due to the mixing caused by currents and waves. We apply bed level data to evaluate the amount of vertical sediment reworking in modern Tidal Channels and at a Tidal flat. Cycles of deposition and erosion are measured with a bed level sensor, and the results show that gross sedimentation was several times higher than net sedimentation. We propose that Tidal Channel sediment is bleached either on the Tidal flat before it is transported to the Tidal Channels and incorporated in Channel-fill successions or, alternatively, on the shallow interTidal part of the Channel banks. Based on the quantitative measures of sediment reworking, we suggest that repeated depositional and erosional cycles allow for comp...
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punctuated sediment record resulting from Channel migration in a shallow sand dominated micro Tidal lagoon northern wadden sea denmark
Marine Geology, 2011Co-Authors: Mikkel Fruergaard, Thorbjørn Joest Andersen, Lars Henrik Nielsen, A T Madsen, Peter N Johannessen, A S Murray, L Kirkegaard, Morten PejrupAbstract:Abstract Facies analysis of five sediment cores and a detailed absolute chronology, consisting of 35 optically stimulated luminescence (OSL) ages, form the basis for reconstruction of the paleoenvironmental evolution of the coastal lagoon behind the barrier island of Fano, in the Northern Wadden Sea, SW Denmark. The lagoonal sedimentary succession was deposited within the last 5500 yr, and 5 principal depositional environments are identified in the lagoonal fill. These are: 1) Tidal Channel, 2) sand flat, 3) mouth bar, 4) reed swamp, and 5) mudflat/salt marsh. Sand flats are the dominant present day depositional environment, but Tidal Channel sediments dominate in the five sediment cores, making up 56% of the 15 m of sediment core. Sedimentation in the lagoon alternated between slow vertical aggradation of sand flats (1.5–2 mm yr − 1 ) and very fast lateral progradation of point bars in Tidal Channels, which caused the formation of a punctuated lagoonal fill. Frequent and comprehensive reworking of the sand flat sediments by Tidal Channel migration entails loss of sedimentary structures and bioturbation related to sand flat deposits, and old sand flat sediments are only very sparsely preserved. We further conclude that long-term (millennial timescale) sediment accumulation in the lagoon was controlled by rising sea-level, whereas short-term (centurial timescale) sediment accumulation was controlled by local erosion and depositional events caused by lateral migration of Channels. Records of short-term sea-level fluctuations are not preserved, due to continuous reworking of the lagoonal sediment within the study area. The paper provides significant inputs to a conceptual model describing the Holocene sedimentation in the sand-dominated Tidal lagoon. Furthermore, the study successfully demonstrates the role of OSL dating in deciphering complicated sedimentology and stratigraphy of Tidal lagoonal environments.
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Tidal Variation in Field Settling Velocities of Suspended Sediment in a Tidal Channel
Geografisk Tidsskrift-Danish Journal of Geography, 1992Co-Authors: Karen Edelvang, Michael Larsen, Morten PejrupAbstract:Edelvang, Karen; Larsen, Michael; Pejrup, Morten: Tidal Variation in Field Settling Velocities of Suspended Sediment in a Tidal Channel. Geografisk Tidsskrift 92:116–121. Copenhagen 1992. Particles of silt and clay may form large, low density floes when suspended in salt water. The sediment floes have settling velocities much higher than the single small particles constituting them and therefore, the flocculation process may strongly influence the transport of cohesive sediment in estuarine environments. will be described in this paper, the field settling velocities of suspended sediment were investigated in a large Tidal Channel with Tidal current velocities up to 1.3 m/s and depths of about 10 m. The analyses of suspended sediment were made on both bottom and surface samples. For the bottom samples, equivalent median fall diameters in the range 26–98 μm were measured. For surface samples, the range was 15–40 μm. During most of the Tidal period, the occurrence of much larger settling diameters near the b...
Zhonghua Ning - One of the best experts on this subject based on the ideXlab platform.
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How Does Spartina alterniflora Invade in Salt Marsh in Relation to Tidal Channel Networks? Patterns and Processes
Remote Sensing, 2020Co-Authors: Limin Sun, Tian Xie, Zhonghua Ning, Dongdong Shao, Weilun Gao, Baoshan CuiAbstract:Rapid invasion of Spartina alterniflora in coastal wetlands throughout the world has attracted much attention. Some field and imagery evidence has shown that the landward invasion of S. alterniflora follows the Tidal Channel networks as the main pathway. However, the specific patterns and processes of its invasion in salt marshes in relation to Tidal Channel networks are still unclear. Based on yearly satellite images from 2010 to 2018, we studied the patterning relationship between Tidal Channel networks and the invasion of S. alterniflora at the south bank of the Yellow River Estuary (SBYRE). At the landscape (watershed and cross-watershed) scale, we analyzed the correlation between proxies of Tidal Channel network drainage efficiency (unChanneled flow lengths (UFL), overmarsh path length (OPL), and Tidal Channels density (TCD)) and spatial distribution of S. alterniflora. At the local (Channel) scale, we examined the area and number of patches of S. alterniflora in different distance buffer zones outward from the Tidal Channels. Our results showed that, overall, the invasion of S. alterniflora had a strong association with Tidal Channel networks. Watershed with higher drainage efficiency (smaller OPL) attained larger S. alterniflora area, and higher-order (third-order and above) Channels tended to be the main pathway of S. alterniflora invasion. At the local scale, the total area of S. alterniflora in each distance buffer zones increased with distance within 15 m from the Tidal Channels, whereas the number of patches decreased with distance as expansion stabilized. Overall, the S. alterniflora area within 30 m from the Tidal Channels remained approximately 14% of its entire distribution throughout the invasion. The results implicated that early control of S. alterniflora invasion should pay close attention to higher-order Tidal Channels as the main pathway
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Reclamation shifts the evolutionary paradigms of Tidal Channel networks in the Yellow River Delta, China
The Science of the total environment, 2020Co-Authors: Chengjie Xie, Baoshan Cui, Tian Xie, Zezheng Liu, Qing Wang, Zhonghua NingAbstract:Tidal Channel networks are ubiquitous features of coastal landforms that control the input and output of interTidal water, sediment and nutrients. Nevertheless, those interTidal platforms have undergone extensive losses due to human activities such as land reclamation. Identifying how Tidal Channel networks respond to land reclamation is critical to our prediction of the fate of residual Tidal landforms. However, the morphological changes in the Channel networks in the Yellow River Delta (YRD) impacted by severe reclamation remain unclear. Here, we analyzed the spatiotemporal dynamics of Channel networks on two scales (the delta scale and the zone scale) under the double stress of land reclamation and natural pressure by comparing a comprehensive suite of morphological Channel characteristics, including Channel segment count, Channel order, length, fractal dimension, drainage density and drainage efficiency. The results show that the interannual dynamics of Tidal Channel networks in the delta over the last three decades have experienced two periods: a favorable period during 1984-2000 and an adverse period during 2001-2018. The spatiotemporal patterns of Channel networks varied with zones. Land reclamation exerted a dominant influence on shifting the evolutionary trend of Channel networks on both the delta scale and the zone scale when reclamation proportion exceeded a certain threshold. Sediment siltation could to a certain degree mitigate the impact of reclamation on Tidal Channel networks development. Our study highlighted the effect of reclamation on the geomorphological evolution of Tidal Channel networks and identified its impact threshold which could further be used to guide coastal zone restoration and management.
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Windows of opportunity for smooth cordgrass landward invasion to Tidal Channel margins: The importance of hydrodynamic disturbance to seedling establishment.
Journal of environmental management, 2020Co-Authors: Zhonghua Ning, Tian Xie, Qing Wang, Dongdong Shao, Cong Chen, Junhong Bai, Ying Man, Baoshan CuiAbstract:Despite increasing concerns about the global threat of cordgrass (S. alterniflora) expansion and the interest in its invasion mechanisms, there is not yet a general understanding of the mechanistic processes underlying the interaction between cordgrass invasion and geomorphic structures such as Tidal Channels. This study elucidated the effects of the hydrodynamic disturbance of Tidal Channels on initial seedling establishment of cordgrass in the margins of two different types of Tidal Channels (i.e., main Tidal Channels and secondary tributaries). We performed field experiments that transplanted cordgrass seedlings to above-mentioned Tidal Channel margins with on-site controlled hydrodynamic conditions. The results showed that high hydrodynamic disturbance intensity (i.e., HDI) on the margin of main Tidal Channels (i.e., MMC) was not beneficial to cordgrass invasion, whereas low HDI created windows of opportunity for cordgrass invasion to the margin of secondary tributaries (i.e., MST) by facilitating the survival, growth, and stability of cordgrass seedlings. The presence of high HDI predominantly reduced the seedling survival and total biomass of cordgrass, whereas root biomass allocation of cordgrass increased significantly to resist dislodgment and toppling. Moreover, field investigations showed that soil salinity and moisture in the margin of Tidal Channels were not the limiting factors affecting the establishment of cordgrass seedlings. However, higher propagule pressure combined with suitable soil salinity-moisture conditions (i.e., low salinity and high moisture) laid a firm foundation favoring seedling establishment. Our results highlight the importance of hydrodynamic disturbance as a dominating driver regulating seedling establishment of cordgrass in Tidal Channel margins and the potential implications for controlling cordgrass landward invasions.
