Seasonal response of nitrogen exchange fluxes to crab disturbance at sediment-water interface in coastal tidal wetlands

Coastal wetlands are hotspots for nitrogen(N)cycling,and crab burrowing is known to transform N in intertidal marsh soils.However,the underlying mechanisms remain unclear.This study conducted field experiments and used indoor control test devices to investigate the seasonal response of nitrogen to crab disturbance at the sediment-water interface in coastal tidal flat wetlands.The results showed that crab disturbance exhibited significant seasonality with large seasonal differences in cave density and depth.Due to crab disturbance,nitrogen fuxes at the sediment-water interface were much greater in the box with crabs than in the box without crabs.In summer,NH-N showed a positive flux from the sediment to the overlying water,but NO2-N and NOg-N showed positive fluxes from the sediment to the overlying water only in early stages.In winter,NH-N showed a positive flux from the sediment to the overlying water,but NO-N and NO,-N both exhibited positive and negative fluxes.These results indicated that the presence of crab burrows can cause the aerobic layer to move downward by approximately 8-15 cm in summer and directly promote nitrification at the sediment surface.

Changes of coastline and tidal flat and its implication for ecological protection under human activities: Take China’s Bohai Bay as an example

The change processes and trends of shoreline and tidal flat forced by human activities are essential issues for the sustainability of coastal area,which is also of great significance for understanding coastal ecological environment changes and even global changes.Based on field measurements,combined with Linear Regression(LR)model and Inverse Distance Weighing(IDW)method,this paper presents detailed analysis on the change history and trend of the shoreline and tidal flat in Bohai Bay.The shoreline faces a high erosion chance under the action of natural factors,while the tidal flat faces a different erosion and deposition patterns in Bohai Bay due to the impact of human activities.The implication of change rule for ecological protection and recovery is also discussed.Measures should be taken to protect the coastal ecological environment.The models used in this paper show a high correlation coefficient between observed and modeling data,which means that this method can be used to predict the changing trend of shoreline and tidal flat.The research results of present study can provide scientific supports for future coastal protection and management.

Dramatical hydro-sedimentary changes induced by bamboo fences over mangrove tidal flat of the largest delta in Beibu Gulf, southwestern China

Mangrove forest is one of the most important ecological and environmental resources by effectively promoting tidal flat deposition and preventing the coastal region from typhoon.However,there have been mass loss of mangrove forests due to anthropogenic activities.It is an urgent need to explore an effective way for mangrove restoration.Here,three rows of bamboo fences with hydro-sedimentary observation set over Aegiceras corniculatum mangrove tidal flat of the Nanliu Delta,the largest delta of Beibu Gulf,China,were conducted to analyze the hydro-sedimentary variations induced by bamboo fences.Results identified that the mean horizontal velocity Um per burst(20 min)decreased by as much as 71%and 40%in comparison with those without bamboo fences in March and November,respectively,when the tidal current entering the bamboo area during flood.The maximum of mean horizontal flow velocity Um-max at bamboo area was 50%–75%of that without bamboo fences during ebb tide.The suspended sediment concentration of bamboo area suggested a maximum reduction of 57%relative to bare flat during flood,and was 80%lower than bare flat at ebb peak.Moreover,the turbulent kinetic dissipationεat flood tide was significantly higher than that at ebb tide,while the bamboo fences greatly increased the turbulent kinetic dissipationεby 2 to 5 times relative to bare flat,resulting in an increase of the bed elevation by inhibiting the sediment incipient motion and intercepting suspended sediment.The siltation rate at the bamboo area was 140%and 29.3%higher than that at the bare flat and the region covered with A.corniculatum,respectively.These results highlight that bamboo fences can effectively attenuate tidal current and thus promote siltation over mangrove flat,which contribute great benefit to mangrove survival.

基于CB-RRT^(*)算法的滩涂履带车路径规划

针对滩涂履带车在受潮汐影响的滩涂环境中进行长时间勘测作业的需求,提出柯西贝塞尔快速搜索随机树星(Cauchy Bessel Rapidly-exploring Random Tree Star,CB-RRT^(*))算法进行路径规划。为规划出安全路径,基于全局地图和潮汐数据,并通过滩涂履带车到分界区的距离构建出滩涂预测模型;为提高滩涂履带车移动到目标点需进行多次路径规划的速度,对初始路径的关键树节点使用柯西概率密度函数进行采样缩小采样范围来提高节点的利用率,进而提高算法的收敛性;在重选父节点过程中考虑最大转角约束设定相应系数,并使用连续二次贝塞尔曲线进行拼接的方式来生成路径,达到提高路径平滑度的目的和解决平滑后路径与原路径偏差过大造成的安全性问题。仿真实验结果表明,CB-RRT^(*)算法在静态滩涂环境和动态滩涂环境中,能大大提高算法的收敛性和路径的平滑性,且保证路径长度最优,研究内容可以保证滩涂履带车在各种滩涂环境中进行长时间安全作业。

Distribution of benthic macrofaunal communities in intertidal flat under hydrodynamic influence:a case study of Jiangsu coast,East China

To identify the distribution pattern of macrofaunal assemblages of the Dafeng intertidal flats in response to hydrodynamic and sediment dynamic processes in the northern Jiangsu coast,East China,macrofauna sampling and hydrodynamic observations were carried out simultaneously across the mud flat,mixed mud-sand flat,and silt-sand flat of the intertidal zone in June 2018.Results show that there was a clear zonal distribution pattern of the macrofaunal communities,as is controlled by local hydrological and sedimentary environments.Principal component analysis(PCA)revealed three types of intertidal area in terms of hydrological and surficial sediment parameters.Similarly,three distinct groups of the macrofaunal communities,i.e.,mud flat,mix mud-sand,and silt-sand groups,were recognized at similarity level of 24%based on the CLUSTER analysis in similarity profile(SIMPROF)test.Correlation analysis upon best variables stepwise search(BVSTEP)indicated the importance of the hydrodynamics(e.g.,water temperature and salinity,tidal duration,flow speed,suspended sediment concentration,and wave height)in the differentiation of macrofaunal communities with different taxonomic classes over the intertidal zone.Therefore,macrofaunal assemblages,similar to hydrology and surficial sediment,have a unique zonation pattern.Small-sized deposit feeders adapt better to low energy environments,thus dominated the upper part of the intertidal flat,whilst the heavy and large-sized filter feeders and deposit feeders were dominant over the middle and lower parts.The hydrodynamic and sediment processes cause biota-niche separation,which affected the biological processes across the intertidal flat.

滨海盐沼湿地地貌形态和植被格局的生态-地貌耦合模拟研究

滨海盐沼湿地是重要的海岸带生态系统,其地貌形态和植被格局受潮汐动力、泥沙供给等条件影响显著。近年来,盐沼生态-地貌动力学研究成为前沿研究热点。以我国典型潮滩盐沼的动力环境为原型,建立考虑水动力-泥沙-地貌-植被互馈过程的动态耦合模型,研究了不同潮差、海平面上升速率、泥沙供给与泥沙性质等关键变量影响下的盐沼湿地植被-地貌耦合演变过程。研究结果表明,外部泥沙供给是控制潮滩-盐沼高程和植被范围的关键要素,外海悬沙浓度越大,滩面坡度越缓、滩面高程越高、植被的海向延伸越宽;泥沙沉降速度越小,易形成上凸型剖面,且湿地植被分布范围更宽;潮差同时影响盐沼在潮间带的下部边界和上部边界,更大的潮差、更强的潮汐水动力有助于形成更高的潮沟密度和泥沙向盐沼内部的输送效率。研究结果可为滨海湿地保护和修复工程提供理论参考。

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.

The Effects of Farmyard Manure and Mulch on Soil Physical Properties in a Reclaimed Coastal Tidal Flat Salt-Affected Soil

Careful soil management is important for the soil quality and productivity improvement of the reclaimed coastal tidal flat saline land in northern Jiangsu Province, China. Farmyard manure（ FYM） and mulch applications, which affect soil characteristics and plant significantly, are regard as an effective pattern of saline land improvement. As a conventional management in the study region, FYM and mulch are used for the amendment of the new reclaimed tidal flat regularly, but little is known about their effects on soil physical properties functioning. A study was conducted on a typical coastal tidal flat saline land, which was reclaimed in 2005, to evaluate the effects of FYM, polyethylene film mulch（PM）, straw mulch（SM）, FYM combined with PM（FYM＋PM）, FYM combined with SM（FYM＋SM）, on soil hydraulic properties and soil mechanical impedance. CK represented conventional cultivation in study area without FYM and mulch application and served as a control. The experiment, laid out in a randomized complete block design with three replications, was studied in Huanghaiyuan Farm, which specialized in the agricultural utilization for coastal tidal flat. Result showed that capillary water holding capacity（CHC）, saturated water content（SWC）, saturated hydraulic conductivity（ Ks） and bulk density（BD）, cone index（CI） were affected significantly by the FYM and mulch application, especially in the 0-10 cm soil layer. FYM and mulch management increased CHC, SWC and Ks over all soil depth in the order of FYM＋SM〉FYM＋PM〉FYM〉SM〉PM〉CK. With the contrary sequence, BD and CI decreased significantly; however, FYM and mulch application affected BD and CI only in the upper soil layers. CHC, SWC and Ks decreased significantly with the increasing of soil depth, BD and CI, and a significant liner equation was found between CHC, SWC, Ks and BD, CI. With the highest CHC（38.15%）, SWC（39.55%）, Ks（6.00 mm h-1） and the lowest BD（1.26 g cm-3） and CI（2.71 MPa）, the combined management of FYM and SM was recommend to be an effective method for the melioration of reclaimed coastal tidal flat saline soil.

Spatial-temporal changes of tidal flats in the Huanghe River Delta using Landsat TM/ETM+ images

Integrating remote sensing, geographic information system (GIS) and fractal theory, change characteristics of tidal flats and tidal creeks in the Huanghe (Yellow) River Delta over the period of 1986-2001 were discussed. The results show that evolutions of tidal flats throughout the Huanghe River Delta are influenced by various factors, and that progressive succession and regression of tidal flats concur in different coastal segments of the delta. Human activities have played an increasingly important role in the succession process of tidal flats. Due to land reclamation in coastal zones of the delta in the last 15 years, lots of tidal flats were occupied, the artificial coastline migrated seaward (the maximum change rate was 0.8 kmyr-1) and tidal creeks became sparser (the highest decreasing rate of length of tidal creeks was 14.9 kmyr-1). Except for two coastal segments from the Tiaohe Estuary to the 106 Station and from the south of the Huanghe River mouth to the north of the Xiaodao River Estuary, fractal dimension values of tidal creeks in the remaining coastal segments of the delta decreased. In addition, the time dimension, sediment fluxes into the sea, waves and tidal-currents have profound influences on the evolution process of tidal flats. Four types of tidal flats-river-dominated tidal flats, tide-dominated tidal flats, wave-dominated tidal flats and man-dominated tidal flats can be identified. Owing to the intensification of human activities in coastal zones of the delta, man-dominated tidal flats have become the main kind of tidal flats.

Processes,feedbacks,and morphodynamic evolution of tidal flat-marsh systems:Progress and challenges

Tidal flats and saltmarshes have been a long-standing research focus because of their high socio-economic and ecological values.The evolution of tidal flat-marsh systems is highly complex due to the intertwined processes operating over a variety of spatial and temporal scales.As a traditional research highlight,the role of regular hydrodynamic processes such as tides,waves,and river flows have been explored comprehensively with fruitful outcomes.Over past decades,the changing environment(e.g.,sea level rise,increasing anthropogenic activities,and extreme weather conditions)has attracted more attention with many reported insightful results.More recent advances indicate that biological activities play a critical role in tidal flat-marsh morphodynamics but are still poorly understood.The field of research that connects the bio-logical and physical processes is commonly described as"biogeomorphology"and requires the joint efforts by scientists from multiple dis-ciplines ranging from hydraulics,ecology,and geography to sociology.This review aims to provide a synthesis of the current research status of tidal flat-marsh morphodynamics,with a particular emphasis on the understanding of various processes and feedbacks underlying the devel-opment of morphodynamic models.Some future research needs and challenges are identified to facilitate a more sustainable management strategy for tidal flats and saltmarshes under climate change.

Numerical Tidal Current Modeling Using Fine Boundary-Fitted Grids for Tidal Flats

Fine grids with small spacing in boundary-fitted coordinates are normally used to treat the computation of fluid dynamics for estuarine areas and tidal flats. However, the adoption of Cartesian components of velocity vectors in this kind of non-orthogonal coordinates will definitely result in a difficulty in solving implicitly the transformed momentum equations, and also complicate the wet-dry point judgement used for flood areas. To solve this problem, equations in terms of generalized contravariant velocity vectors in curvilinear coordinates are derived in the present study, by virtue of which, an Alternative-Direction-Implicit numerical scheme in non-orthogonal grids would then be easily obtained, and wet-dry point judgement would as well be largely simplified. A comparison is made between the explicit scheme and implicit scheme, showing that the present model is accurate and numerically stable for computations of fluid dynamics for estuarine areas and tidal flats.

Relative importance of tidal flats and artificial habitats for two spoonbill species and related interspecific differences

Artificial/seminatural environments,such as aquacultural ponds,saltpans,and croplands,have recently been acknowledged as important habitats for coastal waterbirds.Although coastal waterbirds tend to use artificial habitats around tidal flats as roosting sites during high-tide,it remains unclear whether the importance of surrounding habitats relative to tidal flats varies among landscape types,seasons,species,or tidal conditions.The Black-faced Spoonbill(Platalea minor)and Eurasian Spoonbill(P.leucorodia)are two closely related sympatric species in East Asia with narrow and wide distribution ranges and habitat requirements,respectively.We therefore expect that both species will use surrounding artificial habitats across seasons at high tides,but Blackfaced Spoonbills will use them less frequently than Eurasian Spoonbills.Here,we address these hypotheses in the Imazu tidal flat and its surrounding environments in southern Japan.We investigated the habitat use and behavioral patterns of both species through route and behavioral surveys during the fall migration and wintering seasons in 2021.We found that both species used surrounding habitats including artificial ones more frequently than the tidal flat regardless of the tidal condition or season,but spoonbills used these habitats more frequently in winter than in autumn.We also found that Eurasian Spoonbills foraged in surrounding artificial habitats more frequently than Black-faced Spoonbills.These results not only demonstrate how coastal waterbirds exploit surrounding habitats relative to tidal flats but also suggest that the importance of surrounding habitats varies among species and seasons.Our study thus emphasizes that valuing and managing surrounding habitats in addition to tidal flats are key to conserving globally declining waterbirds.

Processes of small-scale tidal flat accretion and salt marsh changes on the plain coast of Jiangsu Province,China

Large-scaled reclamation modifies the coastal environment dramatically while accelerating the disappearance of salt marshes,which causes the degradation of the coastal ecosystem and the biodiversity function.In this study,we explored the changes of tidal flat and salt marsh coverage in a small-scale tidal flat with an area of ~160 000 m^2 in the plain coast of Jiangsu Province,China.Human activities（e.g.,the construction of dikes） are a crucial contributor that benefits for the tidal flat accretions and the following changes of salt marsh coverage.Located in the front of the man-made ＂concave coastline＂,the study area is suitable for sediment accretion after the dike construction in the end of 2006.On the basis of the annual tidal surface elevation survey from 2007 to 2012,the sedimentation rates in the human influenced tidal flat varied from a few centimeters per year to 23 cm/a.The study area experienced a rapid accretion in the tidal flat and the expansion of the salt marsh,with the formation of a longshore bar,and a subsequent decline of the salt marsh.Breaking waves during the flooding tide brought much sediment from the adjacent tidal flat to the study area,which caused burial and degeneration of the salt marsh.The vertical grain size changes within a 66 cm long core in the study area also demonstrated the above changes in the tidal environment.This study indicates that the responses of small-scale tidal flat changes to reclamation are significant,and the rational reclamation would benefit for the new salt marsh formation in front of the dikes.Further research about the evolution of small scale tidal flat as well as the spatial planning of the polder dike should be strengthened for the purpose to maintain a healthier coastal environment.

1988-2021年珠江口内伶仃洋滩涂结构遥感监测研究

【目的】为揭示沿海城市周期性潮位影响下滩涂范围与地貌结构,【方法】基于GEE平台搜集Landsat影像数据,通过潮位影像融合算法构建珠江口内伶仃洋1988—2021年逐3 a海岸带滩涂结构数据集,辨析滩涂结构时空演变过程及其与海岸带工程的关系。【结果】结果显示,截至2021年,内伶仃洋(含深圳湾北部)共有滩涂33.7 km^(2),主要分布于深圳湾北部、龙穴岛、蕉门至横门海岸带,深圳段占比42%,中山段占比25%,广州段和东莞段面积狭小。内伶仃洋滩涂整体呈现出波动下降趋势,且出现频率逐渐降低,12期滩涂总面积累计减少65.39 km^(2),潮上带从15.67 km^(2)减少至4.25 km^(2),潮间带37.32 km^(2)减少至5.44 km^(2),潮下带则46.14 km^(2)减少至24.04 km^(2),整体上滩涂潮间带和潮上带缩减面积最大。【结论】长序列影像序列可有效识别潮上带和潮间带的动态转化,填海造陆工程扩张导致整体滩涂的永久性占用,而生态修复工程则有效维持了部分滩涂的面积和分布范围。

FACTORIAL ANALYSIS OF ANNUAL EROSION-ACCRETION CYCLES OF TIDAL FLATS IN THE FRONT AREA OF THE SOUTHERN CHANGJIANG RIVER DELTA

Based on surveyed data from seven coastal sections and the collected data of wind, sea level, tide, nearshore suspended sediment concentration and river flux from adjacent stations, this paper deals with regressive correlation between monthly average flat elevation and monthly average figures of the influential factors. All sections except one which is located within the river mouth showed negative correlation between flat elevation and sea level and between flat elevation and tidal range, with correlation coefficients being 0.53- 0.91(-0.77 on the average) in the former condition and 0.56- 0.97 (-0.80 on the average) under the latter. Each of the sections with available suspended sediment concentration (SSC) data shows a positive correlation between flat elevation and SSC, with correlative coefficients being 0.35-0.97 (0.66 on the average). Only two sections (one in the Changjiang River Estuary and the other in the Hangzhou Bay) which are similar to beaches in sediment grain size and slope gradient showed a negative correlation between flat elevation and onshore wind frequency and between flat elevation and average wind velocity, with correlative coefficients being respectively -0.57 and -0.69 (-0.63 on the average) in the former situation and -0.61 and -0.75 (-0.68 on the average) in the latter. Other sections did not show uniform relationship between flat elevation and wind conditions. Due to local marine factors the nearshore SSC in the studied area is negatively correlated with the Changjiang River sediment flux (r=-0.78), which results in false negative correlation between flat elevation and river sediment flux. The paper also gives sediment dynamic and morphodynamic explanation for the above correlations. Sea level rise results in the spread of breaker zone from subtidal area to intertidal area and then increases the intertidal water energy. The larger the tidal range, the stronger the tide currents and the easier for the flat to be eroded. The higher the SSC of flood water, the easier for the sediment to deposit down. Because of correlations among the influential factors, it is difficult to give the prime one which dominates the erosion and accretion processes in tidal flats.

Study on Peat-Forming Mechanism of Tropic and Sub-TropicTidal Flats

Tropic and sub-tropic tidal flats (generalised) are a kind of speific peat-forming environments. Taking the Mangrove tidal flats and mangrove pets in Hainan island as a example, the authors deeply study and discuss the peat-forming mechanism of tropic and sub-tropic tidal flats. The conclusions are as follows: intrusion accretiou of plant organic matter is more important ; the organic matter has accumulated witk high productivity, high return rate and high decompeition rate ;anaerobic bacterin play a more important role during early peatification ; sea level change is the fundameutal factor controlling the formation and evolution of tidal flat peat-forming environments; lagoon peat-flat and delta peat-flat are main types of tidal flat peat-forming euvironments ;tidal flat peat-forming environments are remarkably characterized by low-level and rabe properties.

Influence of Seawall Line Choice on Tide Lock Drainage in Tidal Flat Inning——Cangdongpian Inning Area on the west part of Tiaozini Sand as a case study

Most of the flood from the wide inner lowland plain discharges through tide locks on coast, and the influence of tidal flat inning projects on the tide lock drainage must be solved by seawall line choice. Taking the Cangdongpian inning area on the west side of Tiaozini Sand as a case study, the paper analyzed the compages and validity of ebb tide water to maintain the flood discharge creek below the tide lock for different projects of seawall line. Result indicates that a rational seawall line program has little influence on the flood discharge of lock during the mean tide or general spring tides, but has certain influences during a storm surge or an extreme spring tide in autumn. However it could be resolved by several times of artificial scour on the creek.

Impact of the cord-grass Spartina alterniflora on sedimentary and morphological evolution of tidal salt marshes on the Jiangsu coast,China

The tidal flats of the Wanggang area, on the Jiangsu coast, represent the largest continuously distributed coastal wetland in terms of area coverage in China, and the dynamics of tidal flat accretion and erosion is highly complicated. The cord-grass Spartina alterniflora, which was introduced artificially into the Jiangsu coast, has significant influences on the regional tidal flat evolution in terms of deposition rate, spacial sediment distribution patterns and tidal creek morphology. On the basis of the data set of bed elevation and accumulation rate for different periods of time, the applicability of the Pethick - Allen model to the Jiangsu tidal salt marshes is discussed. In addition, caesium-137 dating was carried out for sediment samples collected from the salt marsh of the Wangang area. In combination with the caesium-137 analysis and the data collected from literature, the Pethick - Allen model was used to derive the accumulation rate in the Wanggang tidal flat for the various periods. The results show that the pattern of tidal flat accretion has been modified, due to more rapid accretion following the iatroduction of S. alterniflora to the region. Surficial sediment samples were collected from representative profiles and analyzed for grain size with a laser particle analyzer. The result shows that fine-grained sediment has been trapped by the plant, with most of the sediment deposited on the Suaeda salsa and Spartina angelica flats being derived from drainage creeks rather than the from gently sloping tidal flats. Remote sensing analysis and in situ observations indicate that the creeks formed in the S. alterniflora flat have a relatively small ratio of width to depth, a relatively high density, and are more stable than the other tidal flat creek systems in the study area.

Distribution of ^137Cs and ^210Ppb in sediments of tidal flats in north Jiangsu Province

Seven cores were collected from different sediment zones of tidal flats at Xin- yanggang in north Jiangsu province in August 2007. Sediment grain-size distribution and radioisotopes of ^137Cs and ^210Ppb analysis were carried out for these cores. Sediment rates of the cores and radioisotopes distribution in surface sediment in different zones of the tidal flat were calculated from the ^137Cs and ^210Ppb activities in sediments cores. The results indicated that each tidal zone had experienced different evolution phases, hydrological dynamics in the tidal flats made the grain-size of the surface sediment change gradually. ^137Cs and ^210Ppb activities on the superficial layer of the cores varied spatially and the reason was discussed. On tidal flats, the fluctuation of ^137Cs and ^210Ppb activities in the cores reflected the special sedimentary characteristics. Vegetation affects the grain-size distribution and the vertical profiles of ^137Cs and ^210Ppb in the upper depths. ^137Cs and ^210Ppb chronology got the comparable average sediment rates on the tidal flat. The characteristics of ^137Cs and ^210Ppb in the cores reflected various depositional dynamical environments in different tidal zones and gave information on the different evolvement phases of the tidal zones. Based on the information of grain-size distribution, texture of the cores, sediment rates and topography, the evolution lines of the tidal flat were reconstructed.

The variation of sediments organic carbon content in Chongming east tidal flat during Scirpus mariqueter growing stage

The investigations on the organic carbon （OC） of core sediments were carried out in Chongming east tidal fiat （CM） during Scirpus mariqueter growing stage （from April to December 2004） in Yangtze Estuary. The Yangtze River annually transports a runoff discharge of 30,000 m^3/s, carrying about 480 million tons of sediments to the estuarine and coastal area, which formed a great OC pool. In the sampling spots, seven quadrats of 50 cm × 50 cm and five sediments cores of 20 cm deep （40 cm deep in December） were randomly established in order to collect vegetations and core sediments samples during the low tide each month except November. After pretreatment, the core sediments were sieved and their OC contents were measured according to the potassium dichromate method. The results show that the higher surface sediment OC content in summer comes from allochthonous terrigenous particle settlements on the Chongming east middle tidal fiat S. mariqueter zone. In autumn and winter, the decomposing of the defoliated S. mariqueter increases the surface sediments OC content. Settling velocity, sediment temperature and S. mariqueter growth are the main factors that can control the sediment carbon content. Summer is the “carbon losing” period of the tidal fiat sediments, while from September, it changes into the “carbon accumulating” period of sediment OC pool because of the decomposing of dead S. mariqueter community in the sediments. From this alternation of “carbon losing” period and “carbon accumulating” period, we conclude that carbon in the OC pool of the middle tidal fiat S. mariqueter zone sediments mainly comes from the atmospheric carbon rooted by S. mariqueter photosynthesis.