Tidal Beach Research Articles

Metagenomic survey reveals hydrocarbon biodegradation potential of Canadian high Arctic beaches

BackgroundDecreasing sea ice coverage across the Arctic Ocean due to climate change is expected to increase shipping activity through previously inaccessible shipping routes, including the Northwest Passage (NWP). Changing weather conditions typically encountered in the Arctic will still pose a risk for ships which could lead to an accident and the uncontrolled release of hydrocarbons onto NWP shorelines. We performed a metagenomic survey to characterize the microbial communities of various NWP shorelines and to determine whether there is a metabolic potential for hydrocarbon degradation in these microbiomes.ResultsWe observed taxonomic and functional gene evidence supporting the potential of NWP beach microbes to degrade various types of hydrocarbons. The metagenomic and metagenome-assembled genome (MAG) taxonomy showed that known hydrocarbon-degrading taxa are present in these beaches. Additionally, we detected the presence of biomarker genes of aerobic and anaerobic degradation pathways of alkane and aromatic hydrocarbons along with complete degradation pathways for aerobic alkane degradation. Alkane degradation genes were present in all samples and were also more abundant (33.8 ± 34.5 hits per million genes, HPM) than their aromatic hydrocarbon counterparts (11.7 ± 12.3 HPM). Due to the ubiquity of MAGs from the genus Rhodococcus (23.8% of the MAGs), we compared our MAGs with Rhodococcus genomes from NWP isolates obtained using hydrocarbons as the carbon source to corroborate our results and to develop a pangenome of Arctic Rhodococcus. Our analysis revealed that the biodegradation of alkanes is part of the core pangenome of this genus. We also detected nitrogen and sulfur pathways as additional energy sources and electron donors as well as carbon pathways providing alternative carbon sources. These pathways occur in the absence of hydrocarbons allowing microbes to survive in these nutrient-poor beaches.ConclusionsOur metagenomic analyses detected the genetic potential for hydrocarbon biodegradation in these NWP shoreline microbiomes. Alkane metabolism was the most prevalent type of hydrocarbon degradation observed in these tidal beach ecosystems. Our results indicate that bioremediation could be used as a cleanup strategy, but the addition of adequate amounts of N and P fertilizers, should be considered to help bacteria overcome the oligotrophic nature of NWP shorelines.

Wave, flow, and suspended sediment dynamics under strong winds on a tidal beach

Tidal beaches are shaped by intense wave-current interactions, leading to dynamic sediment erosion and accretion, which can be further complicated by strong winds. In this study, field observations were conducted on a tidal beach at the junction of Yangtze Estuary and Hangzhou Bay (China), to investigate the dynamics of wave, flow, and suspended sediment under strong winds. Observations were carried out synchronously at two sites on the middle and lower intertidal beach covering 4 semidiurnal tides (52 h) including a ∼20 h-long strong wind period. During the strong wind period, wave motions and flood currents were significantly enhanced, leading to a high combined wave-current bed shear stress (τcw). The wave-induced bed shear stress (τw) greatly exceeded current-induced bed shear stress (τc). Breaking waves generated turbulence at the surface and amplified the near-bed turbulent Reynolds stress (−u′w′‾ and −v′w′‾) at the shallow, middle intertidal beach. The intense hydrodynamics and turbulence kept sediments in suspension and hindered any settling, resulting in net erosion of the intertidal beach. These findings provide valuable insights into the complex interplay among waves, currents, and sediment dynamics under short-duration strong winds on tidal beaches. A key emphasis is placed on the significant role of breaking waves, underscoring the critical importance of their contribution to near-bed turbulence.

Optimizing groundwater radium end-members in submarine groundwater discharge estimation by incorporating groundwater flow information

Submarine groundwater discharge (SGD) can be as important as river discharge for marine ecosystems. Radium (Ra) isotopes are excellent tracers of SGD estimation, and the selection of groundwater radium end-members is the most critical step in using the radium mass balance model to evaluate SGD. However, where and when to collect groundwater Ra end-members and their relationship with groundwater flow were not fully considered in previous studies. Based on field investigations and numerical simulations, this study systematically analyzed the influence of groundwater flow on the spatial distribution of 224Ra activity, and a new method was proposed to determine groundwater Ra end-members by incorporating groundwater flow information in a sandy beach at Xiaojing Bay, China. The results show that the groundwater radium activity collected near the low tide mark at low tides may be the most suitable groundwater Ra end-member. Compared with the newly-proposed method, we found that the traditional methods for determining groundwater Ra end-members such as the mean value and quartile methods may overestimate the SGD rates. Our study provides new insights into the determination of groundwater Ra end-members in a tidal beach and highlights that the groundwater Ra end-members should be determined based on groundwater flow information in SGD estimations by radium mass balance model.

Dissolved carbon dynamics and exchange in a high permeability beach aquifer

The biogeochemical transformation of dissolved carbon in tidal beaches affects the coastal carbon cycle and budget. Yet, the influence of groundwater flow on the behavior of dissolved carbon and CO2 flux across the different interfaces in these dynamic beach systems remains poorly understood, especially in deep beach aquifers. In this study, we investigated the biogeochemical reactions and origins of dissolved carbon and quantitatively evaluated CO2 outgassing driven by submarine groundwater discharge (SGD) in a high permeability beach aquifer (9–13 m depth) located in the South China Sea shelf. Results revealed that both dissolved inorganic carbon (DIC) and total alkalinity (TA) exhibited non-conservative additions across the salinity gradient. The excess DIC and TA most likely resulted from organic carbon decomposition in the brackish and saline zones. Aerobic respiration (upper saline plume zone), anaerobic reactions, and tidal mixing were identified as the dominant processes controlling DIC and TA dynamics. The mean CO2 outgassing flux across the beach sediment-air interface was estimated to be 1.05 g m−2 d−1, significantly higher than the CO2 flux across the sea-air interface. The outgassing pattern of groundwater CO2 from beach aquifer appeared to be driven by tidal pumping. Considering the combined effects of SGD-derived dissolved carbon and nutrients, we suggest that SGD yielded a net CO2 flux, contributing to 45 % of the CO2 flux across the sea-air interface. SGD directly and indirectly delivered substantial CO2 from the beach aquifer to the atmosphere, approximately (4.89–9.21) × 103 tons of CO2 per year along the 76.2 km long sandy coast. These findings demonstrate that intertidal beach aquifers, as active biogeochemical reactors have the strong potential to intensify CO2 emissions to the atmosphere through both beach sediment-air and sea-air interfaces. This study provides a better understanding of the links between carbon biogeochemical cycles and hydrologic processes in the coastal zones.

Species composition of Ostracoda in the Okinawa islands, and geographical distribution of the two genera \(\textit{Loxoconcha}\) and \(\textit{Xestoleberis}\) (Arthropoda: Crustacea) around Japan

This study was conducted in the period of 2012 to 2015 in some locations of Japan. At each location, samplings were carried out on reef slopes using SCUBA diving, on reef flats, tidal beaches and river mouths during low tide. The specimens then were treated using a differential interference contrast microscope with a camera lucida (BX-50, OLYMPUS), a quick auto-coater (JFC-1500, Ion Sputtering Device), a scanning electron microscope (SEM) in the laboratory of Shizuoka University,… The result shows that total 139 species of recent ostracoda belonging to 28 families, 70 genera recorded in the Okinawa Islands, southern Japan are found. Most diversified families include Loxoconchidae (26 species - 18.7%), Xestoleberididae (17 species - 12.2%), Bairdiidae (13 species - 9.4%), Hemicytheridae (13 species - 9.4%), Leptocytheridae (8 species - 5.8%). Based on the distributional pattern of pore systems located below the eye tubercle of Loxoconcha and the types of pores on carapaces of Xestoleberis, the species groups of the two genera were divided into three groups, i.e., Groups A, B and C. Geographical distribution of three species groups was shown for each location in the present report. The geographical distribution of three species phylogenetic groups (i.e. Groups A, B and C) of the two genera Loxoconcha and Xestoleberis suggests that the fauna of two genera in the Okinawa islands are more similar to southern faunas (e.g., Vietnam, Philippines, Australia,…) than Japanese Island Arc fauna. Hence, the origin of two genera Loxoconcha and Xestoleberis in the Okinawa islands, southern Japan may be from the South.

Exploring distinct types of intertidal bars on either side of a small estuary using a multifaceted approach

Multiple intertidal bars are common sedimentary landforms found on low-gradient sandy coasts exposed to low to moderate wave energy with a significant tidal range. However, studying the factors that influence their morphology can be challenging due to limited high-resolution field data and tools for bedform analysis. To address this, a multifaceted approach was used to investigate the morphology of intertidal bars at two adjacent tidal beaches on the north and south coasts of a small estuary on the Lianyungang coast of China. This approach included repeated real-time kinematic-global positioning system (RTK-GPS) leveling, unmanned aerial vehicle (UAV) surveys, surface sediment sampling, satellite remote sensing analysis, and automated bedform analysis. The study revealed two distinct types of intertidal bars on either side of the estuary with similar hydrodynamic settings. The north coast presented low-amplitude ridges (also called ridges and runnels), while the south coast had sand waves. The north coast displayed 2–5 oblique, asymmetrical, and dynamic bars that appeared at the seaward end of the intertidal zone and migrated landward to eventually attach to the steep beach on the landward end of the intertidal zone, representing a life cycle. The south coast had 6–9 parallel, continuous, symmetrical, and stable sand bars occupying the lower part of the intertidal zone. Due to the nearly identical hydrodynamic background, the alongshore variability in sediment supply is suggested as a key factor driving the formation of distinct types of bars.

Video-Monitoring Tools for Assessing Beach Morphodynamics in Tidal Beaches

Beach behaviour and evolution are controlled by a large number of factors, being susceptible to human-derived pressures and the impacts of climate change. In order to understand beach behaviour at different scales, systematic monitoring programs that assess shoreline and volumetric changes are required. Video-monitoring systems are widely used in this regard, as they are cost-effective and acquire data automatically and continuously, even in bad weather conditions. This work presents a methodology to use the basic products of low-cost IP video cameras to identify both the cross-shore and long-shore variability of tidal beaches. Shorelines were automatically obtained, digital elevation models (DEMs) were generated and validated with real data, and the outputs were combined to analyse beach behaviour from a morphodynamic perspective. The proposed methodology was applied to La Victoria Beach (SW Spain) for the analysis of beach variations over a 5-year period. The combination of shoreline position analysis and data from DEMs facilitates understanding and provides a complete overview of beach behaviour, revealing alongshore differences in an apparently homogeneous beach. Furthermore, the methods used allowed us to inter-relate the different processes occurring on the beach, which is difficult to achieve with other types of techniques.

Effects of porous media thickness and its hydraulic gradient history on the formation of sand boils: Experimental investigation

Sand boils occur where groundwater discharges to the land surface under sufficient hydraulic gradient to cause internal erosion and the upward transport of particles. A proper understanding of sand boil processes is essential in evaluating a wide range of geomechanical and sediment transport situations under which groundwater seepage occurs, such as the effects of groundwater discharge on beach stability. Although various empirical methods have been developed to estimate the critical hydraulic gradient (icr) leading to sand liquefaction, a prerequisite for sand boil occurrence, the effect of sand layer thickness and the implications of driving head fluctuations on the formation and reformation of sand boils have not been explored previously. This paper uses laboratory experiments to study sand boil formation and reformation for various sand thicknesses and hydraulic gradients to fill this knowledge gap. Sand layer thicknesses of 90 mm, 180 mm and 360 mm were adopted in evaluating sand boil reactivation, which was created by imposing hydraulic head fluctuations. While the first experiment (i.e., 90 mm sand layer) yielded a value for icr smaller (by 5%) than Terzaghi's (1922) value, the same theory underestimated icr by 12% and 4% for 180 mm and 360 mm sand layers, respectively. Moreover, icr needed for the reformation of sand boils decreased by 22%, 22% and 26% (relative to icr applicable to the initial sand boil) for the 90 mm, 180 mm and 360 mm sand layer thicknesses, respectively. We conclude that the formation of sand boils requires consideration of sand depth and the history of sand boil formation, particularly in relation to sand boils that form (and potentially reform) under oscillating pressures (e.g., tidal beaches).

Coastal switching of dominant depositional processes driven by decreasing rates of Holocene sea-level rise along the macrotidal coast of Gochang, SW Korea

ABSTRACTDecreasing rates of eustatic sea-level rise during the Holocene accompanied the deposition of transgressive coastal deposits worldwide. However, unraveling how transgressive deposition varies in response to different rates of relative sea-level (RSL) rise is limited by the scarcity of long (10+ m) well-dated cores spanning the entire middle to late Holocene record along macrotidal coasts. To investigate the sedimentary response of this macrotidal coast to decreasing rates of RSL rise, we acquired four cores up to 32 m in length and Chirp seismic profiles along the west coast of Korea. Core sediments were analyzed in terms of sedimentary texture, structure, and facies. Nineteen optically stimulated luminescence (OSL) and fourteen 14C accelerated mass spectrometry (AMS) ages constrain the timing of deposition of the sandy sediments. This relatively dense distribution of ages is used to determine how deposition rates changed through time. We also use a compilation of previously published RSL indices for the southwestern Korean coast in order to better constrain RSL changes through time. Results show that the evolution of the Gochang coastline switched from a tide-dominated environment to a wave-dominated environment during the latter stage of transgression as the rate of the sea-level rise decreased. Rugged antecedent topography likely led to the development of tidal currents and the formation of a tide-dominated tidal flat during rapid RSL rise from 10 to 6 ka. As the tidal channels filled with fine-grained sediments from 6 to 1 ka, tidal amplification likely waned leading to a greater role of wave energy in shaping the formation of the sandy open-coast tidal flat. Since 1 ka, wave-dominated environments formed sand-rich tidal beaches and flats. Decreasing changes in rates of the RSL rise resulted in changes in depositional environments from a tide-dominated intertidal flat to an open-coast tidal flat and finally a wave-dominated tidal beach. This study highlights the important role that rates of RSL rise play on not only sedimentation rates in a shelf setting but also playing a role in the switch from a tide-dominated to a wave-dominated setting.

The biomass characteristics of \(\textit{Hydropuntia eucheumatoides}\) (Harvey) in the tidal beach of Hon Rua Island, Nha Trang Bay: potential source for exploitation, culture, and food processing

The study of biomass characteristics of Hydropuntia eucheumatoides (Harvey) (local name in Vietnam, Rong Cau chan vit) in Hon Rua - Nha Trang bay is a comprehensive study of its resources. The results of the study have described in detail the morphological characteristics, reproductive organs, weight and coverage of its in quadrat and habitats. As a result, other has successfully stored seaweed algae under laboratory condition for 30 days. The results can be shown that determined the appropriate harvesting time and direction to exploit and conserve resources and propagate this seaweed. In addition, the main chemical and carbohydrate components of this seaweed have also been identified which has shown great potential for their application in the processing of high value food and medicine products in Vietnam in the future.

Soil Physical Characteristics and Saturated Hydraulic Conductivity in the Landform of Barito Delta, Kalimantan, Indonesia

We explore the soil physical characteristics in wetland of Barito Delta from primary data of soil sample and electrical resistivity measurement with the support from some secondary data. We also estimate saturated hydraulic conductivity (Ks) in Barito Delta from soil physical characteristics applying Saxton and Rawls (1986) and Weynants et al. (2009). Soil texture profile is determined from interpolation of soil fraction in each layer applying Bayesian statistics to analyze soil physical characteristics in the landforms of Delta. Clay is the dominant soil fraction in the soil of Barito Delta. Clay fraction percentage decrease along the depth of soil profile as it reaches fine sand particles deriving from ancient sedimentation from the past. It is an opposite with soil organic matter content that has contrast value from 1st to 2nd soil depth, but a few discrepancy from 3rd depth to downward direction. The content of clay in the soil depends on the sedimentation activity in the landform. Clay is dominant soil particle in the Delta; in case, it is in flat area and there is no intensive of sea water sedimentation such as in Basin of Peat Anticline and Natural Levee. In more than 2 m depth of soil, loamy sand and silty clay textures are mostly in the landform that is influenced by sea water activity, while by river water is clay loam. Ks values from Saxton and Rawls (1986) are close to Ks values from the measurement of previous studies. Ks values are generally small in Barito Delta that is mostly ranging from 1.10−7 to 2 m s−1. Ks values are larger following the depth of soil profile. The values of Ks are smaller in Basin of Peat Anticline and Natural Levee than in Tidal Flat and Beach Ridge. It is because both landforms have clay as dominant soil particles.

Cyclostratigraphy of the Middle to Upper Ordovician successions of the Armorican Massif (western France) using portable X-ray fluorescence

Abstract. To expand traditional cyclostratigraphic numerical methods beyond their common technical limitations and apply them to truly deep-time archives, we need to reflect on the development of new approaches to sedimentary archives that are not traditionally targeted for cyclostratigraphic analysis but that frequently occur in the impoverished deep-time record. Siliciclastic storm-dominated shelf environments are a good example of such records. Our case study focuses on the Middle to Upper Ordovician siliciclastic successions of the Armorican Massif (western France) that are well-studied examples in terms of sedimentology and sequence stratigraphy. In addition, these sections are protected geological heritage due to the extraordinary quality of the outcrops. We therefore tested the performance of non-destructive high-resolution (centimeter-scale) portable X-ray fluorescence and natural gamma-ray analyses on an outcrop to obtain major and trace element compositions. Despite the challenging outcrop conditions in the tidal beach zone, our geochemical analyses provide useful information regarding general lithology and several specific sedimentary features such as the detection of paleo-placers or the discrimination between different types of diagenetic concretions such as nodules. Secondly, these new high-resolution data are used to experiment with the application of commonly used numerical cyclostratigraphic techniques on this siliciclastic storm-dominated shelf environment, a non-traditional sedimentological setting for cyclostratigraphic analysis. In the parts of the section with a relatively homogeneous lithology, spectral power analyses and bandpass filtering hint towards a potential astronomical imprint of some sedimentary cycles, but this needs further confirmation in the absence of more robust independent age constraints.

The Strength of Traditional Villages in Managing Coastal Areas in Bali

The existence of Traditional Villages in Bali is still alive and active, supported by Hindu religious culture which is very thick in the daily life of the people who support the Traditional Village. The island of Bali is an island that has a very charming coastline that surrounds it. From the beach in the west of the island of Bali, namely in Jembrana Regency, there are Gilimanuk Beach, Melaya Beach, Candikusuma Beach, Pefruit Beach, Baluk Rening Beach, Pengambengan Beach, Perancak Beach, Tumbles Beach, Yeh Embang Beach, Rambut Siwi Beach, Pulukan Beach, Pekutatan Beach, Selabih Beach. In Tabanan Regency there are Soka Beach, Antap Beach, Bebali Beach, Kelecung Beach, Tidal Beach, Batu Tampih Beach, Belong Beach, Kutikan Beach, Tanah Lot Beach. In Badung Regency there are Nyanyi Beach, Cemagi Beach, Munggu Beach, Seseh Beach, Canggu Beach, Batu Bolong Beach, Berawa Beach, Kayu Putih Beach, Batu Belig Beach, Petitenget Beach, Seminyak Beach, Legian Beach, Kuta Beach, Segara Beach, Beach Germany, Tuban Beach, Kelan Beach, Kedonganan Beach, Jimbaran Beach, Uluwatu Beach, Nyang Nyang Beach, Pandawa Beach, Tanjung Benoa Beach. In Denpasar City there are Benoa Beach, Serangan Beach, and Sanur Beach. In Gianyar there is Purnama Beach, Saba Beach, More Beach. In Klungkung Regency there is Watu Klotok Beach. In Karangasem Regency there are Padangbai Beach, Candidasa Beach, Tulamben Beach. In Buleleng Regency there is Lovina Beach, and other beaches.

Carbon dynamics driven by seawater recirculation and groundwater discharge along a forest-dune-beach continuum of a high-energy meso-macro-tidal sandy coast

High-energy tidal beaches are exposed to strong physical forcings. The submarine groundwater discharge (SGD) that occurs in intertidal sandy sediments includes both terrestrial, fresh groundwater flow and seawater recirculation, and plays a significant role in regulating biogeochemical cycles in some coastal zones. In this transition zone between land and sea, complex biogeochemical reactions alter the chemical composition of pore waters that discharge to the coastal ocean. Recent studies highlight that SGD can be a significant source of carbon to the coastal ocean but very few have investigated SGD in high-energy environments. We have characterized the dissolved carbon dynamics in such a high-energy environment (Truc Vert Beach, SW France) through pore-water sampling in key compartments of the SGD system. Dissolved organic carbon (DOC), pH, total alkalinity (TA), and the isotopic composition of dissolved inorganic carbon (δ13C-DIC) were measured in pore waters sampled at regular intervals between 2011 and 2014 in the intertidal zone of the beach, the mixing zone of the subterranean estuary (STE), and the freshwater aquifer upstream from the beach. Results reveal that SGD exports dissolved carbon mostly as DIC to the Aquitaine coast, some of which originates from the aerobic respiration of marine organic matter within the beach aquifer. This is highlighted by the reverse spatial trend of DOC, which is consumed, and DIC, which is produced. Saline pore waters expelled from the beach through tidally-driven recirculation of seawater provide about 4400 tons of carbon per year to the coastal zone of the 240-km long Aquitaine sandy coast. Terrestrial groundwater, characterized by high pCO2 values, is also a significant contributor to the DIC flux to the coastal ocean (16,200 tons per year). This flux is abated by CO2 evasion in the upper beach, at the onset of the salinity gradient in the STE, and within the surficial freshwater aquifer along the forest-beach transect below the coastal foredune. Accordingly, the DIC:TA ratio evolves to below 1, suggesting that this SGD increases the buffer capacity of coastal seawater against acidification. This study demonstrates that high-energy beaches are active vectors of DIC from the land to the coastal ocean as well as significant sources of CO2 to the atmosphere, and must therefore be taken into consideration in SGD carbon budgets.

ADV-Based Investigation on Bed Level Changes Over a Meso-Macro Tidal Beach

Beach intra-tidal bed level changes are of significance to coastal protection amid global climate changes. However, due to the limitation of instruments and the disturbance induced by wave motions superimposed on water levels, it was difficult to detect the high-frequency oscillation of the submerged beach bed level. In this study, an observation, lasting for 12 days and covering the middle tide to the following spring tide, was conducted on a meso-macro tidal beach, Yintan Beach, to simultaneously detect the characteristics and influence mechanism of bed level changes at intra-tidal and tidal cycle scales. The collected data included water depth, suspended sediment concentration (SSC), waves, high-frequency three-dimensional (3-D) velocity, and the distance of the seabed to the acoustic Doppler velocimeter (ADV) probe, which were measured by an optical backscatter sensor, two Tide & Wave Recorder-2050s, and an ADV, respectively. The results showed that the tidal cycle-averaged bed level decreased by 58.8 mm, increased by 12.6 mm, and increased by 28.9 mm during neap, middle, and spring tides in succession, respectively, compared with the preceding tidal regimes. The net erosion mainly resulted from large incident wave heights and the consequent strong offshore-directed sediment transport induced by undertows. Moreover, the variations in the bed level were more prominent during a neap to middle tides than during middle to spring tides, which were jointly caused by the wave-breaking probability regulated by water depth and the relative residence times of shoaling wave, breaker, and surf zones that were determined by relative tidal range. In terms of the intra-tidal bed level, it displayed an intra-tidal tendency of increase during floods and decrease during ebb tides, i.e., the intra-tidal bed level changes were controlled by water depth, which modulated the effects of waves on sediment resuspension and vertical sediment exchange. To be specific, waves and SSC were responsible for the intra-tidal bed level changes under low-energy wave conditions, while mean current and bedform exerted important influences on the variations of the intra-tidal bed level under moderate wave conditions, which broke the foregoing interrelation between bed level, waves, and SSC. This study, therefore, emphasizes the usage of ADV measurement to investigate bed level changes in sandy coasts.

Influence of Tide‐Induced Unstable Flow on Seawater Intrusion and Submarine Groundwater Discharge

AbstractRecent studies have confirmed the instability of tide‐induced upper saline plume (USP) in tidal beach aquifers. A systematic understanding of how the unstable USP contributes to groundwater flow and salinity distribution is still lacking. Here we used laboratory experiments and numerical simulations to examine the responses of the salinity distribution and submarine groundwater discharge (SGD) to tide‐induced unstable flow. The results revealed that changes in physical forcing conditions (tides and inland freshwater input) drove the transition of the USP from stable to unstable states. Meanwhile, the phase‐averaged SGD and its components fluctuated over time, and their oscillation amplitudes depended on the physical forcing conditions. There was a correlation between USP instability and the fluctuation of water exchange across the aquifer‐sea interface. The fluxes across the aquifer‐sea interface under unstable conditions usually varied considerably over time with a lower frequency in comparison to stable conditions. The extent of seawater intrusion (SWI) measured by the total salt mass stored in the aquifer also varied over time, especially under unstable conditions. The vibration tendency of the total salt mass was opposite to that of the sum of inland freshwater discharge and tide‐induced circulation efflux. For coastal aquifers affected by tides, SWI was dominated by the sum of inland freshwater discharge and tide‐induced circulation efflux, followed by the sum of inland freshwater input and tide‐induced circulation influx. These findings lay the foundation for gaining a better understanding of tide‐induced unstable flow and its potential implications.

Satellite-derived shoreline detection at a high-energy meso-macrotidal beach

Publicly available satellite imagery can now provide multi-decadal time series of shoreline data from local to global scale, enabling analysis of sandy beach shoreline variability across a spectrum of temporal scales. Such data can, however, be associated with large uncertainties, particularly for beaches experiencing a large tidal range (>2 m) and energetic incident waves. We use a decade of bi-monthly topographic surveys at the high-energy meso-macrotidal beach of Truc Vert, southwest France, and concurrent wave and water-level hindcast to investigate the uncertainties associated with satellite-derived time series of the shoreline position. We show that consideration of the water level and wave runup elevation is critical for accurately estimating waterline position and, in turn, shoreline position. At Truc Vert, including non-tidal water level residuals (e.g. wind-driven surge) and accounting for time- and elevation-varying beach slope for horizontal correction did not improve satellite-derived shoreline position. A new total water level threshold is proposed to maximize the number of usable images while minimizing errors. Accounting for wave runup and the new water level threshold at Truc Vert, the number of usable satellite images is doubled and shoreline position errors are at least halved compared to previous work at this site. Using the 1984–2019 reconstructed shoreline, we also show that the satellite-derived shoreline trends and interannual variability are in better agreement with field measurements. Although the approach proposed here needs to be tested on other sites in different tidal/wave forcing environments with different morphological and sediment characteristics, we anticipate that it will improve the temporal and spatial description of shoreline change on most surf tidal beaches where accurate continuous water level and wave hindcasts and/or observations are available.

A DSAS-based study of central shoreline change in Jiangsu over 45 years

A large-scale sand ridge group is distributed in the central Jiangsu coastal area, and a deposition muddy sea bank was developed in the nearshore area. Quantitative monitoring of coastline changes is of great significance for tidal beach development and protection. The shorelines of the central coast of Jiangsu within six periods (1973–2018) were extracted in this study, and their length changes over the years were analyzed. The Digital Shoreline Analysis System (DSAS) was employed to generate a cross section perpendicular to the baseline and calculate the linear regression rate (LRR) of the shoreline, changes in end point rate (EPR), and net shoreline movement (NSM), based on which the shoreline change features were analyzed. The DSAS results indicated that the shorelines in the study area maintained fluctuating growth and presented a continuous advancing trend towards the sea. From the changes in shoreline evolution distance during 1973–2018, the advancing shorelines in the study area accounted for over 50% of the total shorelines and presented first rising and then declining trends with the period of 2003–2013 taken as the time boundary. The average shoreline change rate was 207 m/year, and the periods with the highest change degrees were 1983–1993 and 1993–2013. The shoreline change tended to be stable during 2013–2018, and only a few estuaries and ports underwent obvious erosion and sedimentation.

Evaluating on flooding area and tidal beach change in Quang Ninh coastal zone due to sea level rise

Viet Nam is considered one of countries most affected by climate change and sea-level rise. It results in many negative effects, such as flooding, saline intrusion and beach erosion occurred in the coastal zones. Quang Ninh with more than 250 km coastline, located in the northeastern part of Vietnam, is one of the vulnerable coastal provinces under the heavily affected due to the sea level rise. In order to evaluate the changes of flooded areas and tidal beaches due to the sea level rise in Quang Ninh coastal zone a 2D numerical model is set up, using the 3-grids nesting technique. The numerical model is calibrated by using the harmonic constants of 8 tidal constituents at Hon Dau tide station and validated with the observed data. On the basis of the climate change scenarios (RCP4.5, RCP8.5) in the period from 2020 to 2100, the corresponding sea level values are used in the numerical modeling to calculate the changes of flooded areas and tidal beaches due to the sea level rise. The obtained results on changing of the flooded area and tidal beach in Quang Ninh coastal zone are not only statically by changing water sea levels but also due to changing of the tidal range in this area. The calculated results point out that districts under the most affected of the sea level rise are Quang Yen, Tien Yen, Hai Ha, Mong Cai.

Rapid Change in Sedimentary Facies from Wave- to Tide-dominated Macrotidal Flat in the Sinduri Bay, West Coast of Korea

Yoon, H.H.; Chun, S.S., and Hong, S.H., 2020. Rapid change in sedimentary facies from wave- to tide-dominated macrotidal flat in the Sinduri Bay, west coast of Korea. In: Malvarez, G. and Navas, F. (eds.), Global Coastal Issues of 2020. Journal of Coastal Research, Special Issue No. 95, pp. 728-732. Coconut Creek (Florida), ISSN 0749-0208.Macrotidal wave-dominated coastal environments are widely distributed on the western open coasts of Korea, although various muddy intertidal flats occur also in the inner part of embayed areas influenced strongly by geomorphological factor. The surface sediment of wave-dominated sandflat and tidal beach, which are developed on the northern Sinduri Bay coast, consists mostly of very well sorted medium to fine sand. Swash bars, which are parallel to the coastline and continuously migrating landward, play the important role in the formation of this macrotidal sandflat. The surface sedimentary facies in this southern embayed area consists mostly of mud. The mud flat is very gentle in slope with slight concave-up profile, and dominantly shows a highly bioturbated mud facies. The distribution of surface sedimentary facies, slope profile, hydrodynamic analysis and the transport pattern of coarse-grained sediment show a rapid change in sedimentary facies with very narrow transition zone from wave-dominated sandflat facies to tide-dominated mudflat facies. Both wave- and tide-dominated coasts have been formed together within a small single geomorphological unit. The co-occurrence of different types of coasts and the rapid shift of sedimentary facies can be indicative of one of characteristics in the macrotidal open-coast depositional environment in which geomorphology, sediment supply and hydrodynamic factors have been closely associated within a relatively small bay area. Sedimentary processes in the two coastal sytems are separated and independent each other. The development of separated depositional systems are also evident even in cored sediments, indicating that the recent depositional setting has been continued much longer time.