Development Of Tidal Flats Research Articles

Paleogeographic reconstruction and sedimentary evolution of tidal-dominated estuarine depositional systems: Insights from the campanian M1 sandstone formation, Oriente Basin, Ecuador

The Oriente Basin is a back-arc basin located east of the Ecuadorian Andes in South America. Evidence suggests that during the Cretaceous period, the basin's margins received a terrigenous shallow marine sedimentation. Due to regional variations in accommodation and depositional controlling factors near a shoreline, the sedimentary environments in the fluvial-marine transitional zones exhibit considerable variability. In this study, we analyzed the sedimentological characteristics of the M1 Sandstone Formation unit (∼83 Ma-72 Ma), which comprises a set of ancient estuarine deposits preserved in the northern part of the basin. We quantified the impact of mixed hydrodynamic processes on the distribution of tidal-dominated estuarine facies and discussed the development conditions and evolutionary processes of an estuarine formation under the background of persistent transgression. Core, well log, and seismic data provide evidence for reconstructing the tidal-dominated estuarine environment. In the core section, we identified 14 lithofacies and 7 major facies association types. The frequent occurrence of sedimentary structures associated with tidal currents indicates that tidal processes extensively reworked the deposits. The spatial distribution trends of facies associations reveal the evolution of mixed hydrodynamic conditions dominated by tidal processes in the estuary and allow us to divide the M1 Sandstone Formation into four depositional periods: the initial development, rapid development, decline, and the post-infilling open coast tidal flat development periods. Furthermore, through a systematic analysis of hydrodynamic conditions and sediment distributions, we identified multiple depositional centers in the tidal-dominated estuary influenced by different hydrodynamic processes. These correspond to the upstream fluvial-dominated tidal point bar depositional region, the middle mixed-energy depositional interaction zone, and the downstream tidal-dominated tidal sand bar depositional region. In these regions, the substantial accumulation of sandy deposits, represented by tidal sand bars, reflects the high accommodation space characteristic of tidal-dominated estuaries. Our findings indicate that the slow subsidence of a broad and gently sloping coastal topography, stable material transport, and sea level change dominated by marine transgression ensured the necessary accommodation for the development of the estuary in the M1 Sandstone Formation. The sedimentological study of the M1 Sandstone Formation provides a case for understanding the sedimentary evolution in fluvial-marine transitional zones.

Cellular automata to understand the prograding limit of deltaic tidal flat

Deltaic tidal flat is an important ecosystem that supports the livelihoods of millions of people globally. Due to the complexity and stochastic nature of tidal flat development, it is a challenging task to predict the tidal flat prograding limit accurately. In this study, we fill out this gap from the perspective of numerical simulation by focusing on the tidal flat extension limit of Nanhui Shoal (NHS), the largest marginal shoal of the Changjiang Estuary. Our results suggest that the tidal flat of NHS extended 29.16 m/y seaward in 1989–2002, had a rapid progradation of 158.08 m/y in 2002–2012 and a retreat rate of 26.88 m/y in 2012–2019, while the fluvial sediment supply decreased 56.78% from 1989–2002 to 2003–2012 and another 20.68% from 2003–2012 to 2013–2019. During the 1989–2002 period, the advancing rate of the −5 m isobaths followed a Gaussian frequency distribution, in agreement with simulation results of cellular automata. We suggest that in the absence of human perturbations, as the sediment input to NHS declines to the threshold of 0.01 × 108 t/y, the seaward advance of tidal flats may significantly slow down. However, human interferences generated large uncertainties on the development tendency of the NHS.

Morphodynamic signatures derived from daily surface elevation dynamics can explain the morphodynamic development of tidal flats

Understanding the sensitivity of tidal flats to environmental changes is challenging. Currently, most studies rely on process-based models to systematically explain the morphodynamic evolution of tidal flats. In this study, we proposed an alternative empirical approach to explore tidal flat dynamics using statistical indices based on long-term time series of daily surface elevation development. Surface elevation dynamic (SED) indices focus on the magnitude and period of surface elevation changes, while morphodynamic signature (MDS) indices relate sediment dynamics to environmental drivers. The statistical analyses were applied to an intervention site in the Netherlands to determine the effect of recently constructed groynes on the tidal flat. Using these analyses, we were able to (1) detect a reduction in the daily SED and (2) determine that the changes in the daily SED were predominantly caused by the reduction in wave impact between the groynes rather than the reduction in tidal currents. Overall, the presented results showed that the combination of novel statistical indices provides new insights into the trajectories of tidal flats, ecosystem functioning, and sensitivity to physical drivers (wind and tides). Finally, we suggested how the SED and MDS indices may help to explore the future trajectories and climate resilience of intertidal habitats.

Late Holocene mangrove dynamics of the Doce River delta, southeastern Brazil: Implications for the understanding of mangrove resilience to sea-level changes and channel dynamics

This work aims to understand mangrove resilience to changes in a wave-influenced delta in southeastern Brazil during the late Holocene using an integrated analysis of palynology, sedimentology, and geochemistry (δ13C, δ15N, C:N and C:S ratio), and radiocarbon dating on two sediment cores. The data indicated three mangrove succession phases: 1) an estuarine point bar/tidal flat occupied by a mixture of mangrove species (~2660 - ~ 2050 cal yr BP); 2) a tidal flat dominated by Laguncularia mangroves (~2050 - ~ 900 cal yr BP); and 3) tidal flats with Laguncularia mangroves upstream and establishment of Rhizophora/Avicennia mangrove at the river mouth (~900 cal yr BP until present). The geochemical results suggest a dominance of C3 terrestrial plants with a mixture of C4 plants and organic matter of marine/estuarine origin throughout the late Holocene. Laguncularia and Rhizophora trees were established since ~ 2660 cal yr BP as pioneers, followed thereafter by Avicennia. Currently, tidal flats upstream are occupied by mangroves mainly represented by Laguncularia. Rhizophora/Avicennia mangroves occur at the mouth of the river. The relative sea-level fall during the late Holocene, as well as the channel dynamics, caused the development of tidal flats and mangrove succession inland. The succession of Rhizophora, Laguncularia, and Avicennia, followed by the permanence of only Laguncularia, is likely related to the resilience of each mangrove genus to habitat disturbance (e.g., salinity and sediment grain size fractions) caused by sea-level changes and channel dynamics. Our results show that mangroves may be resilient to the effects of Atlantic sea-level fluctuations, but the floristic structure in the past is different from that of today.

Fluvial sand, Amazon mud, and sediment accommodation in the tropical Maroni River estuary: Controls on the transition from estuary to delta and chenier plain

The Maroni River, South America, is a tropical estuary encased in a narrow lower valley with a limited area of estuarine tidal flat development, and displays a channel with large downstream-migrating sandy bedforms linked to a large sand-filled shallow mouth. The sand-rich nature of the lower Maroni River reflects significant fluvial bedload supply, and the Maroni is among rivers with the lowest suspension-sized sediment load in the world. During the dry season, the estuary shows high suspended sediment concentrations near the bottom (several g/l) that are due to the ingress of mud streaming alongshore from the Amazon River delta. However, Amazon mud is expelled from the estuary during the high-discharge rainy-season, and seems to be essentially restricted to this seasonal intrusion along the main channel with little net estuarine sedimentation because of limited channel overbank sediment accommodation space. Sand actively supplied by the Maroni River to the coast has been diverted by wave-generated longshore transport westwards, towards the Suriname coast. This has resulted in the construction of numerous sandy cheniers within a muddy coastal plain built from Amazon mud. This sediment-source dichotomy is an important original feature of the Guiana Shield estuaries. The asymmetric progradation at the mouth of the Maroni fingerprints the westward growth, in the vicinity of river mouths, of the muddy, chenier-studded, coastal plain of the Guianas. The propensity for these rivers to supply sand to the coast, eventually evolving into deltas, depends on the ability of their estuaries to limit westward (downdrift) deflection by long-term updrift coastal sedimentation. The Maroni estuary has tended to evolve towards a delta built from both Maroni river sand and Amazon mud, a stage, among the Guiana Shield Rivers, that only the large Essequibo River estuary in Guyana has achieved. Further studies will be needed in order to constrain the infill pattern of the Maroni River estuary and its mouth.

Evolution of the topography of tidal flats and sandbanks along the Jiangsu coast from 1973 to 2016 observed from satellites

Understanding the evolutionary trends of tidal flat development is crucial for local ecological protection, tidal flat development and utilization. However, obtaining such knowledge is often challenging due to the lack of frequently updated topography. This is particularly true for the middle section of Jiangsu Coast, which has complex sedimentary features and is the largest and the most rapidly changing tidal flat area in China. In this study, long-term remote sensing images (1973–2016) and a recently developed method for generating a Digital Elevation Model (DEM) were combined to construct a historical topological dataset with 24 phases of DEM, which was used to track changes of the Jiangsu Coast during the past four decades. The results demonstrate that: (1) the slope of the Jiangsu Coast from north to south exhibits a prominent increasing trend during the past 40 years, with the high tidal flat moving seawards and the low tidal flat moving landwards. (2) Large offshore sandbanks (Dongsha Sandbank, especially) are generally undergoing erosion in both the high tidal flat and low tidal flat, with the exception of Gaoni Sandbank where the high tidal flat is still in accretion. (3) Although there are discernible differences in rate, almost all the small offshore sandbanks have moved in the principal direction of the tidal channels, in good agreement with an independent sediment transport model study. Our findings provide useful baseline information for both future researchers and local authorities, in support of future environmental management, coastal protection, and storm forecasting.

Coastal development history and tidal flat ecosystem conservation along the coast of Jiangsu Province, China

Jiangsu coast, with the unique feature of expanding tidal flat along the west border of the South Yellow Sea, has the famous coastal ecosystem of tidal flat, which is also the habitat for the long-distance migration birds. Using the comprehensive analysis of the historical documents and historical maps as well as the remote sensing images, the authors reviewed the development and conservation of the tidal flat in Jiangsu coast. The development of the tidal flat has a long history of more than two thousand years. Salt production was the earliest economic purpose of the tidal flat development, obvious transition of the tidal flat use changed from salt production to farming in the late nineteenth century. The large-scale reclamation began in the early time of 1910s and the fast reclamation periods in the past century corresponded with the policy-oriented supporting from the government. The conservation of the tidal flat and the salt marsh in the central part of the Jiangsu coast oriented the setup of the Yancheng Wetland Conserves in the year of 1983. The conflicts between the tidal flat conservation and the development in the past decades was discussed in the aspect of the key periods. Large amount loss of tidal flat resulted in the food-rich, continuous wetland became more fragmental and food shortage along the tidal flat of Jiangsu coast. The author believed the policy and the decision- making play important role in the conflicts about the coastal wetland conservation and development in Jiangsu Province. There are more potentials for the improvement of the coastal development policy and decision-making in the future.

Optimal Allocation Model of Water Resources in Tidal Flat Development of Coastal Areas

Huang, X.; Chen, Y., and Fang, G., 2018. Optimal allocation model of water resources in tidal flat development of coastal areas. In: Wang, D. and Guido-Aldana, P.A. (eds.), Select Proceedings from the 3rd International Conference on Water Resource and Environment (WRE2017). Journal of Coastal Research, Special Issue No. 84, pp. 89–93. Coconut Creek (Florida), ISSN 0749-0208.As a result of economic and population development in coastal areas, the conflict of water utilization is becoming increasingly serious. To ensure rational utilization, the optimal allocation model of water resources was constructed for the development of coastal tidal flats based on the analysis of the coastal area development model. The goal of optimal allocation was to achieve optimal economic, social, and ecological benefits under the conditions of coordinated use of water and soil resources. Due to the complexity of the water resources system, the model used various land areas, in addition to economic, social, and ecological data, to establish target measures, and a multi-objective genetic algorithm was used to solve the problem. Following each iteration, individuals' fitness was ranked and constantly updated according to population evolution, since individuals learn from the fittest and genes are improved accordingly. The coastal area of Dongtai in Jiangsu province, China, was considered a case study, in which the scheme of the city's water resources was optimized. The optimal allocation results show that by 2020, the agricultural and construction land will have increased, and the unused land will decrease, with the construction land area being 36185 hm2; thus, conforming to the future trend of Dongtai land utilization. The results verify the rationality and feasibility of the model and the algorithm, which provides ideas and experience for the optimal allocation of water resources during beach development in coastal areas.

A Study on the Dynamic Mechanism of Optimizing Tidal Flats Development

The tidal flats has a long history of development in human history, but the traditional development model of tidal flats has not been able to adapt to the actual needs. The economic development, the transformation of the mode of production, the natural environment are the endogenous power to optimize development model while technological innovation, financial support and policy system are the exogenous dynamic. Developing the beach in both inside and outside power source can gradually ease the contradiction between people and land, and to realize the economic benefit and enriching effect. The dynamic mechanism of optimizing development of tidal flats shows that development and environment interact with each other, and developing targets may even be contrary to ecological goals. Government and society should follow the idea of green development, adhere to the principle of ecological priority, strengthen government guidance, develop high-tech industries and clean energy in order to promote sustainable development of economy and society.

South Flank of the Yangtze Delta: Past, present, and future

Chenier plain and mudflat development in the South Flank of the Yangtze Delta are examined by multi-disciplinary methods over different spatiotemporal scales and changing human-earth interactions. The study site contains a narrow belt of elongated ridge complexes that formed along the sediment-deficient open coast from 6500 to 4000yr BP. Since then and until the past two decades, shoreline progradation has accelerated due to increasing sediment supply, fueling rapid deltaic expansion. Superimposed on this trend are a series of discrete sand-dominated ridges deposited during several stormy intervals. Tidal flat development is regulated by complex estuarine processes. Short-term morphodynamic variations at the site are caused by the alternations of tides and waves, while intermediate morphodynamic variations are controlled by the multi-decadal shifting of river stem channel and stormy climates. The ongoing rapid accretion on the tidal flats is predicted to continue into the near future because the estuarine buffer effect is expected to balance the adverse impacts of decreasing riverine sediment discharge and rising sea level. Technological developments during the last ~2000years are exemplified by seawall construction against sea flooding, marking a transition from passive to active. Dike construction has been used more frequently and intensively to reclaim land since the 1970s, in support of the booming socioeconomic development in the region. Lessons from complex morphodynamic change and human-earth interactions in the Southern Yangtze Delta admonish us to not reclaim coastal wetland by lower-flat enclosures (constructing new dikes near the low waterline), while an optimal alternative would be to implement upper-flat enclosures (constructing new dikes around the high waterline) on the continuously accretionary tidal flats, with auxiliary biological restoration engineering, to satisfy both socioeconomic development and sustainable wetland conservancy.

Morphodynamic modeling of a large inside sandbar and its dextral morphology in a convergent estuary: Qiantang Estuary, China

AbstractWe investigate the evolution of a large‐scale sand body, a unique type of sandbars in a convergent estuary. Specifically, we analyze and simulate the sand deposition system (defined as an inside bar) in the Qiantang Estuary (QE) in China. The deposit is 130 km long and up to 10 m thick and is characterized by a dextral morphology in the lower QE. Numerical simulation is carried out using an idealized horizontal 2‐D morphodynamic model mimicking the present QE settings. Our results indicate that the morphological evolution is controlled by the combination of river discharge and tides. The seasonal and interannual cycles of river discharges play a major role on the inside bar evolution. The bar is eroding during high river discharge periods, but accretion prevails during low river discharge periods. Meanwhile, the highest part of the sand body can move downstream or upstream by several kilometers, modifying the seasonal sediment exchange patterns. We also show that the Coriolis force plays an important role on the dextral morphology patterns in wide, convergent estuaries. It induces a significant lateral water level difference and a large‐scale gyre of residual sediment transport. Subsequently, the seaward tail of the inside bar shifts southward to help create a condition for the development of tidal flats in the lower reach of the estuary. The lateral bed level differences induced by Coriolis force are up to several meters. Coriolis effects also modify the behavior of flood and ebb tidal channels.

Innovative Artificial Agro‐Ecosystems Enhance Soil Carbon Sequestration in Coastal Zones of Southeast China

AbstractTidal flats, which are important reserved land resources, have a vital role in climate change. To evaluate the contribution of coastal saline soils to carbon sequestration, field tests were performed over a 3 year period at the Dafeng Wanggang Experimental Station in Jiangsu Province, China. Six artificial agro‐ecosystems, including wasteland (WL), freshwater fish culture (FC), Sesbania culture (SC), barley culture (BC), mixed culture of fish and Sesbania (MCFS) and mixed culture of fish and barley (MCFB), were established according to developmental processes of coastal saline soils. At the initial stage of tidal flat reclamation, the soil organic carbon (SOC) increased by 59.4 t ha−1 in the FC system during 3 years, which was much higher than that of the WL system (40.7 t ha−1). When the tidal flats evolved into high saline soils, the MCFS system sequestered SOC more effectively than the FC or SC systems with increases of 53.1, 16.9 and 8.3 t ha−1, respectively. Subsequently, in the low saline soils, the maximum soil carbon sequestration was obtained in the MCFB system (35.8 t ha−1) followed by the BC (17.5 t ha−1) and FC (13.5 t ha−1) systems. Therefore, proper development of tidal flats to farmland and the subsequent establishment of optimised artificial agro‐ecosystems make an important contribution to carbon sequestration and climate changes in coastal areas.

Modelling the equilibrium hypsometry of back-barrier tidal flats in the German Wadden Sea (southern North Sea)

Hypsometry is the distribution of volume or horizontal surface area with respect to elevation. Some observations show contradictory scale-dependent characteristics of tidal flat hypsometries in back-barrier tidal basin environments, and traditional theory explains the flattening hypsometry by relating concave-up hypsometries in low tidal range basins to the dominating influence of wind waves rather than tidal currents. In order to investigate these two problems, two series of numerical modelling exercises were carried out using schematized rectangular back-barrier tidal basins roughly corresponding to the tidal basins found in the German Wadden Sea. The results show that, in the equilibrium states of tidal basins, hypsometries of back-barrier tidal flats are dependent on the basin scale and tidal range. Thus, large basin areas and low tidal ranges favour strong concave-up hypsometries, whereas small basin areas and high tidal ranges favour less concave-up hypsometries. Because wind waves were excluded in the model, these relationships are purely associated with tidal-current action. In addition to the traditional theory, which emphasises the relative importance of wind waves, the flattening of hypsometric profile shapes can, therefore, also be interpreted as a response to the relative area of intertidal areas or channels in the tidal basins. Thus, if tidal channels have relatively large areas, the development of tidal flats between channels is markedly restrained, the tidal flats being prevented from growing upward to higher elevations. As a result, strong concave-up hypsometries are formed that are associated with relatively large areas of low tidal flats and small areas of high tidal flats. As basins with large areas and low tidal ranges have large relative channel areas, this results in pronounced concave-up hypsometries, and vice versa.

Democratizing Urban Politics and Civic Environmentalism in Taiwan

What makes urban policies more responsive to environment problems? Local politics in Taiwan is considered to have combined features of both the pro-growth urban regimes of Western democracies and the clientele network of an authoritarian regime. Such features have made the sector resistant to democratic reforms: long after the introduction of competitive elections, urban policies were still overwhelmingly controlled by a handful of power elites and thus the interest of disadvantaged groups was seriously under-represented. Nevertheless, cases of anti-growth politics in different localities indicate the possibility of democracy trickling down to the local level, thereby moving local politics beyond a mere preoccupation in rent-seeking activities towards a civic activism based on a shared agenda of social and environmental issues. How such a transformation can occur can be illustrated by the Hsiangshan Tidal Flat Development Project in Hsinchu city. That incident demonstrated that such procedural requirements as environmental impact assessment in public policy-making provided civic groups with a very powerful tool to prevent an unpopular developmental project from destroying the local ecosystem. The Hsinchu case illustrates the dynamics among institutional reforms, informal political arrangements and strategic responses of civil groups that have resulted in a transformation of traditional urban politics in Taiwan.

Glacioeustatic Transgressive Reflux: Stratiform Dolomite in Pennsylvanian Bioherms of the Western Orogrande Basin, New Mexico

ABSTRACT Upper Paleozoic (Pennsylvanian) algal bioherms of the western Orogrande basin consist of multiple high-frequency sequences with stratiform dolomitization that preferentially affects peritidal facies and strata proximal to sequence boundaries. Field, petrographic, and geochemical analyses reveal two replacive dolomite phases, and several dolomite cements. The facies-selective (FS) replacive phase affects peritidal facies, and consists of micritic to finely crystalline, fabric-preserving dolomite with high Sr and Na concentrations and low to moderate Fe and Mn. The non-facies-selective (NFS) phase affects facies proximal to sequence boundaries, and consists of finely to medium crystalline dolomite that is both fabric-selective and commonly fabric-destructive. This phase has moderate to locally elevated Sr and Na concentrations, and moderate to high Fe and Mn. Dolomite cements line and occlude pores and molds, and consist of medium to coarsely crystalline rhombs with moderate Sr and Mn, low Na, and high Fe. Stable oxygen isotope values for bulk dolostones exhibit a wide range and include relatively low values, suggesting precipitation and recrystallization over a wide range of conditions. FS dolomitization occurred penecontemporaneously with peritidal deposition at glacioeustatic fall to lowstand. NFS dolomitization occurred early postdepositionally, by reflux of mesosaline to hypersaline brines during early-middle stages of each glacioeustatic transgression. Virgilian lowstand gypsum deposits of the southwestern Orogrande provided the Mg source for the transgressive brines. Dolomite cements precipitated largely under reducing conditions of the burial environment. Early dolomite in the western Orogrande basin and its absence in the eastern Orogrande basin reflects local and regional physiographic asymmetry. The western shelf was of low relief, with an archipelago of high-relief mounds, which favored fall-stage peritidal conditions with local restriction in the mounded region. In contrast, the eastern shelf was of high relief and relatively elevated, which precluded tidal-flat development and allowed marine inundation only at late transgressive to highstand stages, by nearly normal-marine waters. Development of both peritidal (penecontemporaneous) and transgressive reflux (early postdepositional) dolomitization was therefore restricted largely to the western Orogrande basin.

Discussion

This work aims to understand mangrove resilience to changes in a wave-influenced delta in southeastern Brazil during the late Holocene using an integrated analysis of palynology, sedimentology, and geochemistry (δ13C, δ15N, C:N and C:S ratio), and radiocarbon dating on two sediment cores. The data indicated three mangrove succession phases: 1) an estuarine point bar/tidal flat occupied by a mixture of mangrove species (~2660 - ~ 2050 cal yr BP); 2) a tidal flat dominated by Laguncularia mangroves (~2050 - ~ 900 cal yr BP); and 3) tidal flats with Laguncularia mangroves upstream and establishment of Rhizophora/Avicennia mangrove at the river mouth (~900 cal yr BP until present). The geochemical results suggest a dominance of C3 terrestrial plants with a mixture of C4 plants and organic matter of marine/estuarine origin throughout the late Holocene. Laguncularia and Rhizophora trees were established since ~ 2660 cal yr BP as pioneers, followed thereafter by Avicennia. Currently, tidal flats upstream are occupied by mangroves mainly represented by Laguncularia. Rhizophora/Avicennia mangroves occur at the mouth of the river. The relative sea-level fall during the late Holocene, as well as the channel dynamics, caused the development of tidal flats and mangrove succession inland. The succession of Rhizophora, Laguncularia, and Avicennia, followed by the permanence of only Laguncularia, is likely related to the resilience of each mangrove genus to habitat disturbance (e.g., salinity and sediment grain size fractions) caused by sea-level changes and channel dynamics. Our results show that mangroves may be resilient to the effects of Atlantic sea-level fluctuations, but the floristic structure in the past is different from that of today.

Depositional facies and environments in the Umm Ishrin Sandstone Formation, Dead Sea area, Jordan

The Umm Ishrin Sandstone Formation between Wadi Manshala and Wadi Abu Khusheiba, along the northeastern margin of the Dead Sea, consists of a quartz arenite facies and a subordinate heterolithic facies of siltstone and mudstone with sandy lenses. The former are trough cross-bedded with unidirectional northwesterly mode. The Umm Ishrin sediments were deposited on a braidplain and tidal flat in response to periodic shifting of the active part of the braidplain system. Reworking of the abandoned parts of the braidplain by tidal currents and subsidence led to marine incursions and the development of tidal flats.