Topographical Mapping of a Bare Tidal Flat Outside a Mangrove Area based on the Waterline Method and an Iterative Hydrodynamic Model: A Case Study of Yingluo Bay,South China

A change in the elevation of bare tidal flats outside a mangrove area is an indispensable factor for the sustainable development of mangroves. Waterline extraction, as an effective and economical tool used in reconstructing the terrain of an intertidal zone, has been widely applied to open-coast tidal flats by constructing a digital elevation model (DEM). However, mangrove wetlands are usually located in wave-sheltered sites, such as estuaries and bays that have narrow tidal channels flanked by tidal flats. Changes in water level are affected by the dry-wet processes of complex landforms caused by tides. This article takes as a study case the area of Yingluo Bay, which covers the core region of the Zhanjiang and Shankou National Mangrove National Nature Reserve in southwestern China. Waterline extraction based on seventeen multisource and multispectral satellite images obtained from December 2014 to April 2015, combining the finite-volume coastal ocean model (FVCOM) hydrodynamic model in an iterative process, was used to generate a topographical map of the bare tidal flat outside the mangrove area in Yingluo Bay. The quality of the iterative DEMs was evaluated via six transects of a ground-based survey using Real - time kinematic (RKT) GPS in May 2015. The mean absolute error (MAE) and root mean square error (RMSE) of the DEM decreased with an increase in the number of iterations. In this study, the DEM in the third iteration was used as the final output because the difference from the previous iterative DEM satisfied an inversion-stopping criterion. The MAE and RMSE of the final DEM with the measured data were 0.072 and 0.09?m, respectively, without considering small tidal creeks. The method used in this study can be an effective and highly precise approach for detecting and reconstructing the historical terrain of a bare tidal flat outside a mangrove area. This work also has great importance regarding intertidal resource management and the sustainable development of mangroves facing the vulnerable coastal ecological environment.     

The exchange of organic carbon in basin mangrove forests in a southwest Florida estuary

The magnitude and seasonality of organic carbon exchange was estimated for two basin mangrove forests in Rookery Bay, Florida. Runoff and tidal inundation in the forests were seasonal with half the annual total of each occurring from August to October. In each forest there were 152 tides yr^?1 with a cumulative depth of about 12 m. Total organic carbon increased in bay waters exporting from the mangroves following a flood tide and peak concentrations were associated with export due to rainfall. The amount of net export from each basin forest was similar, although the concentration of organic carbon in each were different. Monthly net organic carbon export was proportional to the cumulative tidal amplitude within the forest. Total organic carbon export was 64 gC m^?2 yr^?1 and DOC was 75% of the total. A comparison of organic carbon export among riverine, fringe and basin mangroves suggests that tidal hydrology influences the proportion of litter fall that is exported from mangroves; and the magnitude of this organic carbon export from mangroves is related to the cumulative tidal amplitude within the forests.     

红树林遥感智能分类方法研究

利用ＧＩＳ信息中的红树林地域分布规律作向导，充分利用械树林区的光谱信息进行红树林植被信息提取。在对比研究常规的红树林图象自理方法的基础上，提出了适用于红树林植被信息遥感监测的智能分类方法。     

Topographic Mapping of Offshore Sandbank Tidal Flats Using the Waterline Detection Method: A Case Study on the Dongsha Sandbank of Jiangsu Radial Tidal Sand Ridges,China

The waterline detection method (WDM) based on satellite images is one of the most effective methods for constructing digital elevation models (DEMs) for tidal flats. The general practicability of the WDM has been demonstrated in previous studies for small areas. This article attempts to generate a DEM over a large offshore sandbank with a tidal flat area of more than 620 km² by integrating the conventional WDM with a hydraulic model and multitemporal satellite images. For illustration purposes, a case study was conducted at the Dongsha sandbank, one of the largest sandbanks among the radial tidal sand ridges of Jiangsu Province, China. In this study, 34 multitemporal satellite images acquired at different tidal phases in 2006 were analyzed to detect the waterlines. The water level at each satellite overpass moment was simulated by a south Yellow Sea hydraulic model, and discrete waterline points were combined with the corresponding water levels to produce a topographic map. Compared with the DEM produced during the same period by the airborne light detection and ranging (LiDAR) data, the DEM derived from WDM effectively contains the average height error within 47 cm, which is satisfactory. All of these findings may be useful for researchers and local authorities, as the findings could be used as a reference for sandbank evolution research or to support environmental management, coast protection, and storm forecasting.     

Temperature variability caused by internal tides in the coastal waters of east coast of Peninsular Malaysia

The effects of tidal currents (i.e., barotropic and internal tides) are important in the biogeochemistry of a coastal shelf sea. The high-frequency of currents and near-bottom temperatures collected in three consecutive southwest monsoon seasons (May, June, July and August of 2013 until 2015) is presented to reveal the role of the tidal currents to the temperature variability in the coastal shelf sea of the east coast of Peninsular Malaysia (ECPM), south of the South China Sea (SCS). The results of a spectral density and harmonic analysis demonstrate that the near-bottom temperature variability and the tidal currents are influenced by diurnal (O₁ and K₁) and semidiurnal (M₂) tidal currents. The spectral density of residual currents (detided data) at 5, 10 and 16 m depth also shows significant peaks at the diurnal tidal frequency (K₁) and small peaks at the semidiurnal tidal frequency (M₂) indicating the existence of internal tides. The result of the horizontal kinetic energy (HKE) shows a strong intermittent energy of internal tides in the ECPM with the strongest energy is found at 16 m depth during a sporadic cooling event in June and July. A high horizontal cross-shore heat flux (16 m) also indicates strong intrusions of cooler water into the ECPM in June and July. During the short duration of cold pulse water observed in June and July, a cross-wavelet analysis also reveals the strong relationship between the near-bottom temperatures and the internal tidal currents at the diurnal tidal frequency. The intrusion of this cooler water is probably related to the monsoon-induced upwelling in June. It is loosely interpreted that the interaction between the strong barotropic tides and the steep slope in the central basin of the SCS under the stratified condition in southwest monsoon has generated these internal tides. The dissipation of internal tides from the slope area probably has driven the cold-upwelled water into the ECPM coastal shelf sea when the upwelling intensity is the highest in June and July.     

岸外沙洲潮间带地形的增强型遥感构建方法

水边线法是潮间带地形遥感反演的重要方法。针对常规水边线方法在应用于地形多变的岸外沙洲潮间带数字高程模型（DEM）构建中出现的水边线交叉和缺乏表现潮沟微地形特征的问题,本文提出了一种增强型地形遥感构建方法:首先通过潮位排序,筛选出具有正确高程变化趋势、空间分离的水边线;然后对筛选过程中水边线位置相近的影像组按像元计算改进的归一化差值水体指数并进行均值序列合成,提取出合成海陆边界线,二者共同构建出初始的潮间带DEM;进一步利用低潮期的潮沟边界线和中线生成潮沟DEM,通过潮沟镶嵌处理,最终获得可表达滩面微地形起伏的潮滩DEM。该方法在江苏岸外辐射沙洲中部核心区域的模拟应用表明,对比4条验证剖面的平均结果,高程平均绝对误差为0.43 m,均方根误差为0.54 m,相关系数（r）为0.75,模拟高程与验证高程在剖面起伏形态变化方面具有良好的一致性,同时模拟DEM的空间破碎度小,能够反映更多的细节地形特征。该方法可为利用多源遥感数据构建考虑微地形变化的高精度潮间带地形DEM提供新的思路。     

Patterns of tidal flooding within a mangrove forest: Coombabah Lake,Southeast Queensland,Australia

Tidal flooding and surface drainage patterns have often been used to describe mangrove species zonation. However, in mangrove forests exhibiting little topography, ambiguous species distributions and/or few species, such approaches are ineffective. We identified four physiognomic mangrove forest types (Riverine, Fringing, Overwash and Basin) at Coombabah Lake, a tidal lake in southeast Queensland, Australia and investigated tidal flooding patterns using synoptic surveys of tidal observations at the local Standard Port combined with local water depth observation. Subsequently three sub-types of the basin forest type were identified: (1) Deep Basin Forest with mature trees, ∼50 cm standing water and ∼3 tides per year; (2) Medium Depth Basin Forest with intermediate tree development, ∼15–30 cm standing water and 20–40 tides per year; and (3) Shallow Basin Forest with relatively recent mangrove establishment, 5–15 cm standing water and ∼80 tides per year. These three basin sub-types were found to flood at different tide heights with the Shallow Basin flooding for tides above mean high water springs and the Deep Basin flooding only for tide heights approaching the highest astronomical tide. We propose that these basin types represent a succession in mangrove forest development that corresponds with increasing water depth and tree maturation over time. The succession not only represents increasing age but also change in basin substrate composition. This is manifest as increasing pneumatophore density and an increasing area of basin surface occupied by contiguous pneumatophore cover. As a result, it seems that mangrove development is able to modify tidal flooding into the basin by increasingly impeding water movement.     

椒江河口层化动力特性研究

基于椒江河口大、小潮期间水位、流速、盐度和悬沙浓度观测数据,研究了椒江河口主潮汐通道的水动力、盐度和悬沙浓度的时空变化特征,解释了高浊度强潮作用下的层化物理机制。椒江河口大潮期悬沙浓度和盐度均大于小潮期,主潮汐通道区域落潮期悬沙浓度大于涨潮期;盐度随潮变化,盐水锋面出现在S2测站,锋面附近出现最大浑浊带;自陆向海,悬沙浓度递减,盐度递增;随水深增加,悬沙浓度与盐度递增。Richardson数与混合参数显示,盐度和悬沙引起的层化现象,是随着潮汐的变化而变化,涨潮时的层化均强于落潮,小潮时的层化持续时间最长,区域更广。混合参数随潮周期变化,大潮期高于临界值1.0,小潮期低于临界值1.0。小潮期水体层化强于大潮期;潮汐应变项是影响势能差异变化率的重要因素;落潮期间层化向混合状态转化,涨潮相反。     

Internal tide in the Kara Gates Strait

We observed strong internal tidal waves in the Kara Gates Strait. Internal tides are superimposed over a system of mean currents from the Barents to the Kara Sea. Field studies of internal tides in the Kara Gates were performed in 1997, 2007, and 2015. In 2015, we analyzed data from towed CTD measurements, numerical model calculations, and satellite images in the region. An internal tidal wave with a period of 12.4 h is generated due to the interaction between the currents of the barotropic tide and the bottom relief on the slopes of a ridge that crosses the strait from Novaya Zemlya to the continent. The depths of the ridge crest are 30–40 m. A constant current of relatively warm water flows from the Barents to the Kara Sea. An internal wave propagates in both directions from the ridge. In the Barents Sea, internal waves are intensified by the current from the Barents to the Kara Sea. Internal bores followed by a packet of short-period internal waves are found in both directions from the strait. Satellite images show that short-period internal waves are generated after the internal bore. A hydraulic jump was found on the eastern side of the strait. Numerical modeling agrees with the experimental results.     

南麂岛附近海域潮汐和潮流的特征

以2008年冬季在浙江近海南麂岛附近投放的4个底锚系观测的水位和流速资料为依据,分析了潮汐和潮流特征。水位谱分析结果显示半日分潮最显著,全日分潮其次;近岸的浅水分潮比离岸大。水位调和分析结果表明:潮汐类型均为正规半日潮,近岸处的平均潮差大于3m,最大可能潮差大于6m,潮汐呈现出显著的低潮日不等和回归潮特征。流速谱分析结果显示半日分潮流最强,全日分潮流其次,且比半日分潮流小得多;近岸浅水分潮流比远离岸显著。流速调和分析结果表明:潮流类型均为正规半日潮流,靠近岸的两个站浅水分潮流较显著;最显著的半日分潮流是M2分潮流,其最大流速介于0.32～0.48m/s之间,全日分潮流均很弱,最大流速小于0.06m/s。M2分潮流均为逆时针旋转,椭圆率越靠近海底越大;最大分潮流流速分布为中上层最大、表层略小、底层最小;最大分潮流流速方向的垂向变化很小,底层比表层略为偏左;最大分潮流流速到达时间随深度的加深而提前,底层比中上层约提前30min。潮流椭圆的垂向分布显示这里的半日分潮流以正压潮流为主;日分潮流则表现出很强的斜压性。     

基于机载LiDAR与潮汐推算的海岸带自然岸线遥感提取方法研究

海岸线对于海岸带保护与管理具有重要意义。海岸线现场测绘施测周期长且在地形复杂的区域施测难度大,基于遥感影像的海岸线判绘对解译人员的要求高,难以获取严格意义的海岸线。针对上述问题,本文提出一种基于机载LiDAR与潮汐推算的自然岸线遥感提取方法:基于机载LiDAR系统获取的航空正射影像解译瞬时水边线,应用LiDAR系统提取的DEM和建立的高程系统转换模型,通过潮汐数据推算研究区域的海岸线。通过与“908专项”航空遥感调查岸线结果比对,按本文方法所提取的3种自然岸线(砂质岸线、基岩岸线和淤泥质岸线)的均方根误差分别为1.66,5.23和32.48 m。结果表明,该方法可用于砂质岸线和基岩岸线的提取,且具有无需开展现场测量工作的优势,可提高海岸线提取的效率。     

黄海在有无潮作用下对“布拉万”不同响应的数值模拟研究

黄海是典型的强潮驱动的陆架浅海。为了研究黄海对台风的响应特点,本文利用区域海洋模式(Regional Ocean Modeling Systems,ROMS)分别模拟了在有潮和无潮作用下黄海对台风"布拉万"的响应过程。结果表明,不管潮存在与否,"布拉万"经过黄海后都引起了海表面降温和流速的近惯性振荡响应,这种响应主要分布于黄海中部较深区域,带通滤波提取的近惯性流速具有垂向第一模态特征。同时,研究发现强背景潮流能显著地影响黄海对"布拉万"的响应过程。主要结论如下:一方面,由于潮的存在,近岸垂向混合均匀的较暖水体与远岸较冷水体之间会形成潮混合温度锋面,"布拉万"过后,暖水发生了明显的离岸扩张,尽管路径右侧的混合层降温更显著,但是左侧即黄海西岸的暖水扩张更明显;另一方面,潮的存在减弱了布拉万产生的近惯性振荡响应,半日潮流在黄海仍然占据主导地位。在混合层中潮流的作用减弱了"布拉万"产生的近惯性能量,但也使其更易穿过跃层传入黄海内部。     

Tidal effect on nutrient exchange in Xiangshan Bay, China

Xiangshan Bay is an estuary in China which borders on the East China Sea. The circulation in the estuary is driven by tidal movement, residual current, the internal density distribution, and synoptic wind forcing; however, the last three are not the main dynamic factors affecting nutrient transport. Because the estuary tends to be eutrophic, a synoptic study was carried out to assess the influence of tidal movement on the nutrient distribution patterns within the estuary and to estimate the fluxes of nutrient transport between the estuary and the sea. Nitrate and ammonium are found to be exported from the estuarine water to the coastal water under usual tidal conditions, except for storm tides which result in large amounts being imported because of the extremely high concentrations in the coastal bottom water. Exports of phosphate and silicate are shown to be consistent during spring tides and neap tides in all seasons. However, the usual tidal regimes resulted in only minor nutrient exchange except during abnormal events.     

Numerical study of baroclinic tides in Luzon Strait

The spatial and temporal variations of baroclinic tides in the Luzon Strait (LS) are investigated using a three-dimensional tide model driven by four principal constituents, O₁, K₁, M₂ and S₂, individually or together with seasonal mean summer or winter stratifications as the initial field. Barotropic tides propagate predominantly westward from the Pacific Ocean, impinge on two prominent north-south running submarine ridges in LS, and generate strong baroclinic tides propagating into both the South China Sea (SCS) and the Pacific Ocean. Strong baroclinic tides, ∼19 GW for diurnal tides and ∼11 GW for semidiurnal tides, are excited on both the east ridge (70%) and the west ridge (30%). The barotropic to baroclinic energy conversion rate reaches 30% for diurnal tides and ∼20% for semidiurnal tides. Diurnal (O₁ and K₁) and semidiurnal (M₂) baroclinic tides have a comparable depth-integrated energy flux 10–20 kW m⁻¹ emanating from the LS into the SCS and the Pacific basin. The spring-neap averaged, meridionally integrated baroclinic tidal energy flux is ∼7 GW into the SCS and ∼6 GW into the Pacific Ocean, representing one of the strongest baroclinic tidal energy flux regimes in the World Ocean. About 18 GW of baroclinic tidal energy, ∼50% of that generated in the LS, is lost locally, which is more than five times that estimated in the vicinity of the Hawaiian ridge. The strong westward-propagating semidiurnal baroclinic tidal energy flux is likely the energy source for the large-amplitude nonlinear internal waves found in the SCS. The baroclinic tidal energy generation, energy fluxes, and energy dissipation rates in the spring tide are about five times those in the neap tide; while there is no significant seasonal variation of energetics, but the propagation speed of baroclinic tide is about 10% faster in summer than in winter. Within the LS, the average turbulence kinetic energy dissipation rate is O(10⁻⁷) W kg^{− 1} and the turbulence diffusivity is O(10⁻³) m²s⁻¹, a factor of 100 greater than those in the typical open ocean. This strong turbulence mixing induced by the baroclinic tidal energy dissipation exists in the main path of the Kuroshio and is important in mixing the Pacific Ocean, Kuroshio, and the SCS waters.     

A method of accounting for tidal changes in regional climates of a water basin under conditions of an ice-free Barents Sea

To account for tidal variations in the regional climate of a water basin, we propose adding up the vertical eddy diffusivity, determined by wind and thermohaline forcings, and the diapycnal diffusivity, determined from the solution to the problem of the internal tidal wave (ITW) dynamics. This approach agrees with the approximation of “weak interaction” between turbulence of various origins. Then, the hydrothermodynamics equations are integrated with and without regard for ITW-induced diapycnal diffusion until a quasistationary solution is reached. Next we compare these solutions, found by using the 3D finite-element hydrostatic model QUODDY-4. This comparison shows that the contribution of tides to the formation of the Barents Sea climate in summer is not negligible with respect to certain hydrological characteristics. We present the fields of the dynamic topography of a free surface, surface current velocities, and seawater temperature and salinity at the depth of the pycnocline in the sea to illustrate the occurrence of tidal effects.     

Tides—a modern perspective

Progress in tidal science has been rapid in recent years. The advent of precision altimetry has enabled, for the very first time in tidal history, an accurate measurement of tides in most of the global oceans. This has revolutionized our knowledge of tides and tidal processes. Combined with high‐resolution numerical models of tides (and other recent advances in astronomy and geodesy), this increased knowledge is providing valuable assistance in effecting closure on many outstanding problems in this three‐centuries‐old science. For example, we now know the dissipation rate of lunar tides to be 3.17 TW to within 2%. However, there do remain some outstanding issues. While we know the rate at which tidal energy is being dissipated in the global oceans, there is still considerable uncertainty as to the mechanisms, locations, and magnitudes of various tidal energy sinks. Imminent advances in shallow‐water barotropic and deep‐water baroclinic tides hold the prospect of a better understanding of these also. Improved knowledge of oceanic tides and high‐precision satellite measurements of tides are enabling better assessment of some matters of geophysical interest, such as the anelasticity and the length‐of‐day fluctuations of the Earth's mantle. It has been possible to map long‐period lunar tides more accurately and derive their contribution to the Earth's rotation rate fluctuations and its anelasticity at these frequencies. We discuss various aspects related to tides, including tidal dissipation and its consequences, as well as several other topics such as tidal energetics, internal tides, and long‐period tides, where considerable progress has been made in the last decade. Both oceanographic and geophysical implications are mentioned.     

Studies of a mangrove basin,Tuff Crater,New Zealand: III. The flux of organic and inorganic particulate matter

Water samples were collected at 15 min intervals over 11 tidal cycles from a tidal creek draining the mangrove-covered basin of Tuff Crater, Auckland, New Zealand. The samples were filtered and total suspended sediment (TSS), inorganic suspended sediment (ISS) and organic suspended sediment (OSS) were determined. Variation in TSS was high, the concentration varied over a tidal cycle and during over-bank flows concentrations were lowest at or near slack high water. Covariance between TSS concentrations and velocity and discharge meant that the calculation of particulate matter flux over tidal hemicycles was particularly dependent on the method of estimating tidal flux. The hypsometrically-based volumetric method was found to be inappropriate, predicting a positive budget (import) more often than observed. Instead particulate matter budgets were calculated by means of the velocity-area method and indicate a net export of TSS, ISS and OSS. Floating macrodetritus was observed on both the flood and ebb tides, but a net export was found on the two tides monitored. It is considered that on an annual basis floating macrodetritus export accounts for less than 2% of the detrital production in the basin, and organic suspended sediment export from the basin is less than 3 kg C ha^?1 day^?1 and is below the rate of detrital production. It is implied that a proportion of the organic detritus produced in this basin is degraded and recycled in situ.     

Effect of hydrodynamic properties of the sea bottom on the tidal dynamics in a rectangular basin

Expressions derived for the friction coefficient in an oscillatory rotating turbulent bottom boundary layer (BBL) over rough, incompletely rough (smoothly rough), and smooth underlying surfaces are incorporated as an individual module into a two-dimensional nonlinear tidal model, and the standard version of the model and its modified analogue are used to discuss the titular subject. It is established that the dynamics of tides in the Taylor basin can change noticeably under the effect of hydrodynamic properties of the sea bottom. Such changes occur mainly in the influence domains of amphidromies. In the remaining parts of the basin, relative changes in the amplitudes and phases of tidal sea-surface level elevations do not exceed ±10% and ±10°, respectively. The largest discrepancies of tidal characteristics take place in the cases of the incompletely rough and smooth sea bottoms; the smallest discrepancies, in the case of the rough sea bottom. Estimates for the changes in tidal characteristics that are caused by the usually neglected effects of rotation and phase difference between the bottom friction and the tidal velocity at the upper BBL boundary are presented as well.     

Wave attenuation in mangroves: A quantitative approach to field observations

Coastal mangroves, dwelling at the interface between land and sea, provide an important contribution to reducing risk from coastal hazards by attenuating incident waves and by trapping and stabilizing sediments. This paper focusses on relations between vegetation densities, wave attenuation rates, sediment characteristics and sedimentation rates in mangroves. These processes were studied along two cross-shore transects through mangroves fringing estuaries in the southern Andaman region of Thailand. Volumetric vegetation densities in these mangroves were ranging up to 32‰, depending on the water depth. Generalized total wave attenuation rates increased from 0.002 m^− 1 in the sparsely vegetated forest fringes with Avicennia and Sonneratia species, up to 0.012 m^− 1 in the dense Rhizophora vegetation in the back of the forests. The total wave attenuation rates integrate effects of shoaling and energy losses due to various bio-physical interactions within the mangrove ecosystem. Wave attenuation in the mangroves is presumably dominated by energy losses due to vegetation drag, since wave attenuation due to bottom friction and viscous dissipation on the bare mudflats is significantly lower than those inside the mangrove vegetation.Additionally, wave attenuation in the mangroves was found to facilitate enhanced net sediment deposition and a gradual fining of the bed material. These findings corroborate the coastal defence function of mangroves by quantifying their contribution to wave attenuation and sediment trapping. The explicit linking of these properties to vegetation composition and structure facilitates modelling studies investigating the mechanisms determining the coastal defence capacities of mangroves.     

Patterns of K1 and M2 internal tides and their seasonal variations in the northern South China Sea

Seasonal variations of baroclinic tides for K₁ and M₂ constituents were separately studied using two-dimensional numerical simulations along the 21°N section of the northern South China Sea (SCS). Results show that the continental slope of the northern SCS and the west ridge of the Luzon Strait are supercritical to K₁ internal tides, which may be trapped in the deep basin of the SCS and form standing or partial standing waves. Meanwhile, these areas are sub-critical to M₂ internal tides, which can transmit onto the shelf and are seldom reflected back into the basin. The trapped K₁ internal tides are dominated by mode-2 and mode-3 in summer and by mode-1 and mode-3 in winter. Moreover, high mode K₁ internal tides account for nearly 20–40 % of the total energy density in winter and 15–20 % in summer. The pattern of K₁ internal tides in the basin is mainly determined by the percentage of reflected energy from the continental slope. The phase difference between the incoming mode-1 and mode-2 K₁ internal tides near the continental slope are nearly out of phase in winter, which means that the percentage of reflection of the K₁ internal tide is larger than that in summer. Both the convergence and high mode K₁ internal tides can enhance the vertical shear. The above results indicate that, in the deep basin of the SCS, water mixing potentially induced by internal tides in winter is stronger than in summer.