Current Issue http://www.jto.ac.cn EN-US http://www.jto.ac.cn/EN/1009-5470/current.shtml http://www.jto.ac.cn 1009-5470 http://www.jto.ac.cn/EN/10.11978/YG2021002 Green sea dyke represents a new concept of coastal defense, which combines traditional engineering structure with coastal ecosystem, to cope with the future trend of sea level rise and storm intensification. Before its application, however, the feasibility of such a system must be tested for low-lying coastal areas, where the risk of storm surge, storm-induced waves and shoreline erosion is greatest. The major issue is associated with the process of wave attenuation by the ecosystem and the way of using the ecosystem within the sea dyke system. For many years, wave energy dissipation has been an important research field for tidal flats, a typical environment of low-lying coasts, as well as beaches and rocky coast environments. Theoretical analysis, field observation and physical-mathematical modelling show that the coastal ecosystem indeed plays a significant role in wave energy dissipation: (1) resuspension and fluid mud movement dominate over bed friction in the mud area, in terms of wave height reduction; (2) wave attenuation occurs due to bed friction and bedload transport on the silt-sand flat at the lower part of the tidal flat, while on the upper mudflat it is caused mainly by re-suspension and suspended, fine-grained sediment transport; (3) in the vegetated ecosystems such as salt marsh, mangrove and seagrass beds, the efficiency of plants in reducing flow velocity and dissipating wave energy is higher than that of bare flats, due to plant morphological resistance and stem movement; and (4) wave attenuation is high when passing through biological reefs (e.g., coral and oyster reefs), especially during storms, with bed surface friction and wave breaking being the major mechanisms. Although the wave attenuation theory has been established, the optimization of the way the ecosystem is used within the sea dyke system requires further investigations, especially the techniques of ecological niche reconstruction on eroding coasts and the design of the sea dyke to improve structure safety. The relevant scientific problems include: adaptive biology for salt marsh plants and oysters in conjunction with hard engineering; stability of ecosystem in response to future environmental change; spatial configuration of ecosystem in the green sea dyke and the match between the ecosystem life cycle and the temporal scales of storm events; and the optimization of the sea dyke configuration, on the basis of the equilibrium coastal profile theory.

]]> http://www.jto.ac.cn/EN/10.11978/2022006 Continuous measurement technology of suspended sediment concentration is the most fundamental requirement in the research fields of hydraulics, environmental science, estuarine and coastal science, as well as marine science. The current popular technical routes including optical backscattering and transmission, specular reflection, remote sensing, acoustic backscattering and transmission attenuation, tuning fork resonance, pressure difference and gamma-ray attenuation and other principles of technical methods were summarized in this paper. The main advantages and problems of each technical method are then discussed, and the future research focus and development direction are prospected as: (1) the principle of optical backscattering is the optimal technical route for low-cost, miniaturized, and high-time-frequency measurement of suspended sediment concentration, and is necessary to focus on range expansion and particle size sensitivity weakening study; (2) low uncertainty suspended sediment concentration profile measurement relies on the development of the acoustic backscattering technical route; (3) the tuning fork resonance technical route is particularly suitable for ultra-high range application scenarios under turbid current and fluid mud conditions; (4) integrate multi-technology sensors and use the artificial intelligence algorithms to replace traditional inverse theory model, etc.

]]> http://www.jto.ac.cn/EN/10.11978/2021079 Global coastal ecological system is being threatened by climate change and human activities. Based on a typical profile of sandbar-lagoon system and designed wave flume experiments with moving bed, we carried out a quantitative analysis on the effects of submerged vegetation on erosion and deposition under erosion wave conditions. The results show that the submerged vegetation obviously weakens the wave height that increaes in the margin of surf zone on the fore slope of sandbar, and wave attenuation occurs behind the sandbar. Wave reflection and transmission coefficients reduce and wave dissipation coefficient increases due to submerged vegetation. Under the action of erosion waves, the sandbar crest was eroded distinctly, the lagoon showed a deposition trend, and the coastal foredune was eroded in a scarp form. With the influence of vegetation, the maximum erosion thickness of sandbar and foredune zone decreases. In general, vegetation can reduce the net sandbar erosion, the deposition in the lagoon and the offshore sediment transport, which has a good protective effect on the coastal foredune.

]]> http://www.jto.ac.cn/EN/10.11978/2021167 Suspended sediment concentration(SSC)observation in vertical profile near the bed of mangrove tidal flat under the waves and tidal currents, is important to understand the mechanisms of energy dissipation and deposition promotion by vegetations, and the ecological restoration in coastal zone. In this study, we measured the hydrological data using HR, ADV, Twave and ASM and the typical plants’ parameters of Aegiceras corniculatum for 3 consecutive days of flood tides in the summer of 2019. Then the process of the near-bed vertical SSC of mangrove tidal flat was analyzed in response to waves, tidal currents and spatial structure of Aegiceras corniculatum. The results showed that: (1) the variations of suspended sediment flux and SSC near bed in Aegiceras corniculatum tidal flat had the characteristic of tidal asymmetry, the SSC of flood tide was significantly greater than that of ebb tide. The vertical high SSC area of the profile changed from 0.1~0.37 m to 0.5-0.67 m from the bottom in the early flood tide to flood maximum, and from the upper to the bottom in ebb maximum to end. (2) In the intra-tide, the suspension and resuspension stages occurred at the early flood and latest ebb that were dominated by waves. The advection and deposition stages occurred at the whole period from flood maximum to ebb maximum dominated by tidal currents. (3) Dense branches and leaves in the canopy of Aegiceras corniculatum intercepted more than 40% of the suspended sediment in the upper canopy during flood tide. The SSC decreased by more than 71% when the flow during ebb tide. This dynamical deposition mechanism of asymmetrical flood and ebb tide was conducive to sediment transportation landward which then led to flat expansion.

]]> http://www.jto.ac.cn/EN/10.11978/2021096 The dynamic process of beach profile changes under the actions of waves and tides is the key to understanding coastal evolution, coastal defence design and tourism resource planning. Taking an artificial beach in the Shajing Peninsula of the Qinzhou Bay in Guangxi province as the study area, the study aims to explore the dynamic process of beach profile changes by analyzing the erosion and single-width volume of beach profile, as well as using EOF (Empirical Orthogonal Function) to reveal its model, based on the monthly surveyed profile elevation data from January 2018 to December 2019 using by GPS-RTK, The main results were shown as followed: (1) during the observation period, the artificial beach profile showed a regular variation characterized by accretion in winter and spring and erosion in summer and autumn; (2) due to the transverse sediment transport over the artificial beach, the single-width volumes of beach profile displayed opposite variation trends in adjacent transversal zones, which was manifested by a alternation between erosion and accretion; (3) the variation modes of artificial beach profiles could be divided into three parts that include the main model that beach profile elevations decreased significantly due to heavy rainfall and typhoon, the secondary model that the beach profile recovered gradually after heavy rainfall and typhoon under the influences of tides and normal waves, and the third model that beach profile changes resulted from wave breaking-induced currents under the action of normal waves.

]]> http://www.jto.ac.cn/EN/10.11978/2021141 The Swan Lake in Rongcheng of Shandong province is a typical lagoon-barriers system. Since 1980s, under the influence of human activities, the environmental system of the Swan Lake has changed with strong erosion of the sand dam. Studying the erosion and deposition of underwater bank slopes is of great significance for understanding the evolution of lagoon-sand dam system and protecting the environment of Swan Lake. This paper focus on the underwater bank slope of the sand dam at the east side of the Swan Lake. Based on the combination of chart data from 1960 to 2014 and geographic information technology, we have obtained multi-year water depth of the coastal waters on the east side of the Swan Lake since 1960, and analyzed the contour changes, scouring and silting changes and topographic changes of the set profile in the sand dam area on the east side of Swan Lake. The results show that the overall depth contours moved towards the sea from 1960 to 1980, while the tendency of contours moving towards the sea from 1980 to 2014 slowed down, the 0 m depth contour at the entrance of the tidal channel retreated 126.70 m to the shore from 1960 to 2014. The underwater bank slope of the Swan Lake was at a state of siltation from 1960 to 1980, the annual siltation rate is 3.60 cm·a^-1. The erosion area increased significantly from 1980 to 2014, and the erosion and siltation phases were distributed, the annual siltation rate is 0.79 cm·a^-1. The underwater bank slope of the Swan Lake sand dam is steep and gentle, and the north side of the tidal channel entrance is more likely to be eroded than the south side. Human activities have changed the environmental state of the Swan Lake, leading to partial erosion and retreat of the underwater bank slope of the Swan Lake.

]]> http://www.jto.ac.cn/EN/10.11978/2021150 As a new form of coastal engineering, the artificial island has been receiving increasing attentions from community to the beach erosion and accretion due to its construction. Based on the multi-temporal remote sensing images and four field surveys, the influence of winter waves combined with artificial islands on the erosion and accretion of the Riyue Bay beach has been analyzed. Besides, the mechanism of beach erosion and accretion was explored using the wave data in the adjacent sea area. Our new results show that the average significant wave heights and wave periods in the winter were obviously stronger than those in the summer, and the wave force generally shows an increasing trend year by year, but its variation is not significant around the artificial island before and after the construction of islands. The construction of artificial island has a significant impact on the beach topographic profile, showing the obvious characteristics of accretion in the area sheltered by the artificial island and erosion on two sides of the beach. The beach accreted continuously in the island shadow area, and the shoreline in that area moved up to 200 m towards the sea, which may even be linked with the artificial islands to form a tombolo. The beach was eroded and the maximum erosion distance of shoreline to land is about 50 m on both sides behind the artificial island. The Riyue Bay beach is strongly affected by the winter waves and artificial islands. From north to south, the beach was at a state of stability-erosion-accretion, relative stability, slight erosion or accretion-erosion-accretion.

]]> http://www.jto.ac.cn/EN/10.11978/2021091 The embayed sandy and gravel beaches are important tourism resources in the coastal zone of islands, with high socio-economic and ecological values and having received study attention for years. This study focuses on five representative embayed beaches on the east coast of the Zhujiajian Island in Zhejiang Province. The beach topography and sediment data were obtained from three field campaigns in the early, middle and late stages of the 2019 typhoon season, and the nearshore hydrodynamic data were also collected and analyzed. Then, the dynamic changes of topography and sediment characteristics of five different embayed beaches were detected. The results show that the five beaches experienced different volume changes during the typhoon season, i.e., 11.93 m³·m^-1(Dashali), -54.41 m³·m^-1 (Dongsha), -19.75 m³·m^-1 (Qiansha), 2.19 m³·m^-1 (Wushitang) and -1.96 m³·m^-1 (Xiaowushitang), respectively. The gravel beaches were more stable than the sandy beaches, and the sandy beach without human activity is less eroded during the typhoon season. The mean grain size of surficial sediments on Dashali, Dongsha, Qiansha, Wushitang and Xiaowushitang during the typhoon season are 2.47 Փ, 2.24 Փ, 2.64 Փ, -5.96 Փ and -6.03 Փ, respectively, with coarsening and onshore transport being the main performances of their changes. The change of sediment grain size on sandy beaches is more significant than that on the gravel beaches. The sediment grain size, the energy level of typhoon, and the angle between the main wave direction during the typhoon and the beach orientation, and coastal engineering can have impacts on beach morphological variation during typhoon seasons. This research can provide reference for the beach management during typhoon seasons.

]]> http://www.jto.ac.cn/EN/10.11978/2021097 The beach morphodynamic process under the influence of extreme high-energy events is directly related to coastal stability and seawalls safety. Based on the profile elevation and surface sediments of the Yintan Beach collected before and after the 2020 16^th typhoon “Nangka”, this paper explores the mechanism of morphological changes of a meso-tidal beach in response to typhoon actions. The results show that: (1) In post-typhoon period, the beach morphological changes are manifested by the disappearance of a large sand bar and the flattening of the bar-trough system, leading to a more gentle beach slope; (2) Sediment in Yintan Beach is mainly medium sand, fine sand and very fine sand, which account for more than 95%; The sediment grains become finer in the high tide zone and coarser in the low tide zone, while both increase and decrease in sediment grain size can occur near the sand bar; The morphodynamic process of mid-to-high tide zone of the Yintan Beach in response to a typhoon is similar to that of a macro-tidal beach, which is characterized by dissipative condition. However, the morphodynamic process of low tide zone of the Yintan Beach behaves like a micro-tidal beach due to the existence of a large sand bar; (3) During the typhoon, wave is the main dynamic factor affecting the beach, and the topography affects the manifestation of nearshore hydrodynamics, thereby changing the grain size distribution of sediment.

]]> http://www.jto.ac.cn/EN/10.11978/2022036 The Haitan Strait in Fujian province is an important channel for the southward transportation of material from the Minjiang River and the Zhejiang-Fujian Coastal Current to the Xinghua Bay and the south-central coast of Fujian. The topographic data of the Haitan Strait in the past 50 years was analyzed using GIS tools. The results indicate that strong siltation occurred in the Haitan Strait due to the influence of several catastrophic floods in the Minjiang River Basin during 1964~1975. The Haitan Strait experienced strong erosion during 1975~1990 which is caused by water and soil conservation and reservoir constructions in the Minjiang River Basin. After that, the erosion rate declined gradually and the strait maintained slight scouring. Large-scale artificial sand mining started since 2007 that caused severe erosion in the northern part of the Strait. Before 2007, sediment discharge from the Minjiang River was the main factor restricting the geomorphological evolution of the Haitan Strait. Flood, sand mining and reservoir construction had a direct impact on the geomorphologic evolution of the strait. However, after 2007, large-scale artificial sand mining activities and reclamation projects in the strait have gradually become the main factors to affect its geomorphologic evolution.

]]> http://www.jto.ac.cn/EN/10.11978/2021116 Coastline dynamic change is a common reflection of global change and human activities. Based on seven Landsat remote sensing images and Google Earth high-resolution images of the Guangdong-Hong Kong-Macao Greater Bay Area, Tokyo Bay and San Francisco Bay from 1980 to 2020, this paper used threshold segmentation combined with water index method and Sobel operator method to extract the coastline of each analysis period. In addition, this study also analyzed the changes of coastline in terms of length, spatial morphology, structure and utilization degree, and analyzed qualitatively and quantitatively the influencing factors with the help of geographic detectors. The results show that: (1) from 1980 to 2020, the intensity of annual average length change in the Tokyo Bay is the largest, which is 0.37%, and the coastline tends to be straight; (2) in the past 40 years, the depth of coastlines in all analyzed bay areas has remained stable, and the structures tend to be complex and the morphology tends to be dispersed. Among them, the difference of fractal dimension of coastlines in the Guangdong-Hong Kong-Macao Greater Bay Area is the smallest and the morphology is the most dispersed; (3) during the past 40 years, the natural coastline of each bay area decreased, while the length of port wharf coastline and other artificial coastline increased significantly, and the biological coastline of the Guangdong-Hong Kong-Macao Greater Bay Area fluctuated, and the coastline utilization index increased the most. The results show that temperature, wave height, tide, area and port throughput are the main factors that affect the coastline change, the interaction of any two factors is greater than the single factor.

]]> http://www.jto.ac.cn/EN/10.11978/2021152 In this paper, an extra-tropical storm surge in the Yangshan Port (YSP) and its coastal area caused by a strong cold front on 29th December, 2020 was investigated. Meteorological observation data was analyzed to study the development of the weather system. FVCOM-SWAVE model characterized by a high-resolution unstructured-grid with 10 m was used to simulate the storm surge. The observed tide data, wave data and current data were introduced to verify the result of simulation, and the result was proved to be accurate and credible. Maximum storm surge, maximum negative storm surge, current, total water level and wave were studied to describe the character of the extra-tropical storm surge of YSP and its coastal area. Finally, sensitive experiments were carried out to compare the contributions of mean sea level pressure (SLP), wind and wave to the maximum storm surge. The main conclusions can be summarized as follows: 1) affected by the topography of the channel, the main component of the tidal current was southeast or northwest, which was approximately parallel to the shoreline, the current velocity in the deep water channel of YSP was the highest with a value between 2.6~2.8 m·s^-1; 2) due to the influence of long term northerly gale and high SLP, the storm surge behave as a characteristics of short-term positive storm surge and long-term negative storm surge; 3) during the peak period of storm surge, the contribution of wind field to storm surge was ~ 90%, and the contribution of sea-level pressure field was approximately 5%; while during the peak period of negative storm surge, the contribution of sea-level pressure field was about 55%, the contribution of wind field was ~ 40%, In addition, the contribution of wave to both was less than 10%.

]]> http://www.jto.ac.cn/EN/10.11978/2021172 This study investigates the characteristics of the east Guangdong shelf front and its dynamical regime using in-situ measurements, satellite data, and high resolution simulations by the regional ocean modeling system (ROMS). Observation results show active upwelling thermal fronts with horizontal scale of 50km on the northern shelf of the South China Sea in summer. The horizontal temperature gradient at the front is up to 0.06 ℃∙km^-1 and is stronger than satellite observed results in the same period. The front can reach 20m depth, and has the characteristics of the order-one Richardson number. Further diagnostic analysis using ROMS model output also show that the horizontal buoyancy gradient is enhanced at the front, with order-one Richardson number, which is favorable for frontal instabilities. High-resolution simulation results indicate that driven by the southwest wind in summer, the Ekman transport across the continental shelf caused by down-front wind, will accumulate cold water of upwellings to the warm water, enhancing the horizontal buoyancy gradient and front sharpness, and change the frontal baroclinicity, which leads to negative Ertel potential vorticity (EPV). As such, the Ekman buoyancy flux caused by summer monsoon may significantly contribute to the formation and instability of the continental front in the northern South China Sea, and it has an important impact on the local dynamic environment.

]]> http://www.jto.ac.cn/EN/10.11978/2021080 Based on the measured wave data of the foreshore profile at the Changle beach, the variation rules of wave parameters and energy dissipation process in the tidal process are discussed using statistical analysis and spectral analysis. The results show that the wave in the observation period is mainly mixed wave, and the spectrum type of each sensor is wide, and the multi-peak oscillation is observed. In the process of shoreward propagation, the form of wave energy dissipation is changed from narrow frequency domain to broad frequency domain, the energy distribution tends to be dispersed, the energy of high frequency wave decreases, but the energy of low frequency wave increases, and infra-gravity wave is generated after wave breaking. There is a good correlation between the energy attenuation and the wave propagation distance in the surf zone. The energy attenuation of the broken wave in the surf zone is about 98.3%. The tidal level has obvious modulating effect on waves. The incident wave energy increases with the increase of tidal water level, and the higher the water level is, the more dispersed the distribution of incident wave energy is. There is a significant positive correlation between the effective wave height and the tidal level in the surf zone. The spectral variation of each sensor in tidal process has obvious similarity with the wave spectral variation along the profile.

]]> http://www.jto.ac.cn/EN/10.11978/2022002 Surface sediments were collected on the Dongshan Bay of Fujian Province China in November 2016. Dinoflagellate cysts were analyzed in the sediments with a particular focus on the distribution of toxic and harmful dinoflagellate cysts. The contents of biogenic elements were examined to reveal the relationships between cysts and biogenic elements. A total of 22 cyst taxa were identified, including 14 autotrophic and 8 heterotrophic taxa. Cysts of Protoperidinium dominated in the sediments. Shannon-Wiener diversity index (H') ranged from 1.70 to 2.38, and Pielou’s evenness index (J) ranged between 0.64 and 0.84. Cyst concentrations ranged from 70.6 to 136.4 cysts·g^-1, with an average of 107.2 cysts·g^-1. Cyst concentrations were lower in the Zhangjiang estuary and Bachimen area. The high percentages of cysts of heterotrophic dinoflagellates (averagely 75.5%) suggested the high primary productivity and eutrophication level on the Dongshan Bay. Notably, cysts of seven toxic and/or harmful algal bloom (HAB) species were identified in this study, including cysts of the paralytic shellfish toxin (PSP) producers Alexandrium ostenfeldii and A. catenella/tamarense, the yessotoxin (YTX) producers Gonyaulax spinifera, the potential azaspiracid (AZP) producer Azadinium sp., the ichthyotoxic species Polykrikos hartmannii, and the bloom species Barrufeta bravensis and Scrippsiella acuminata. Cysts of the HAB species generally occurred in small numbers, however, high numbers of cysts of G. spinifera in some stations need to be concerned.

]]> http://www.jto.ac.cn/EN/10.11978/2021173 To investigate the influencing factors of transformable total nitrogen (TTN) and its release potential, this paper used a graded leaching method to classify nitrogen in the Bohai Sea surface sediments into ion exchange nitrogen (IEF-N), weak acid extractable nitrogen (WAEF-N), strong alkali extractable nitrogen (SAEF-N), strong oxidizer extractable nitrogen (SOEF-N) and non-transformable nitrogen (NTN) states, the effects of sediment particle size and organic matter on the amount of released nitrogen were also investigated, and the effects of TTN release in sediment on dissolved inorganic nitrogen (DIN) and Chl a in the overlying water were examined. The results showed that the order of the content of each TTN was SOEF-N > SAEF-N > IEF-N > WAEF-N, the release amount was IEF-N > SAEF-N > SOEF-N > WAEF-N, and the release ratio was IEF-N > WAEF-N > SAEF-N > SOEF-N, respectively, 69.83% of IEF-N, 64.93% of WAEF-N, 56.27% of SAEF-N, and 29.56% of SOEF-N will be released again. Pearson correlation results showed that the release of SOEF-N in the sediment was negatively correlated with silt content, but is positively correlated with sand content; SOEF-N was negatively correlated with both Chl a and dissolved inorganic nitrogen (DIN) in the overlying water, indicating that the release of SOEF-N has less effect on the Chl a and DIN in the overlying water, while waters of surface and bottom had extremely strong positive correlations (r=0.803, P<0.01; r=0.831, P<0.01), respectively, which may imply that there is no significant stratification of surface and bottom waters in this study area.

]]> http://www.jto.ac.cn/EN/10.11978/2021156 We analyzed the principal components of hydrology, water quality, and meteorological data in Pingtan, Fujian province from 2013 to 2019. We selected 5 meteorological factors and 4 water quality factors. Our study establishes four early-warning model, KNN (K-nearest neighbor), RF (random forest), GBRT (gradient-boosted regression trees), Bagging (bootstrap aggregating) with meteorological factors and water quality factors as input indicators, and algal cell density as output indicators. After normalizing the 802 sets of marine monitoring data from 2013 to 2019, 80% of the data were randomly selected as the model training samples, and the remaining 20% were used as data of model verification. When temperature, wind speed, sea level pressure, and chlorophyll a are used as input parameters, the calculation result of KNN regression model is more accurate (R²=0.624, RMSE=0.821 μg·L^-1, MAE=0.836 μg·L^-1). In the sea area without chlorophyll a monitoring index, a BP neural network early-warning model with chlorophyll a concentration as the output index and temperature, sunshine, wind speed and AOI as input parameters was established, which has better warning accuracy (R²=0.651, RMSE=0.062 μg·L^-1, MAE=0.033 μg·L^-1). Our results can provide a reference for the red tide early warning research in the Pingtan coastal area.

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