Jiangsu Coast Research Articles

The southern Jiangsu coast is a critical moulting site for Spoon-billed Sandpiper Calidris pygmaea and Nordmann’s Greenshank Tringa guttifer

SummaryThe extent of intertidal flats in the Yellow Sea region has declined significantly in the past few decades, resulting in severe population declines in several waterbird species. The Yellow Sea region holds the primary stopover sites for many shorebirds during their migration to and from northern breeding grounds. However, the functional roles of these sites in shorebirds’ stopover ecology remain poorly understood. Through field surveys between July and November 2015, we investigated the stopover and moult schedules of migratory shorebirds along the southern Jiangsu coast, eastern China during their southbound migration, with a focus on the ‘Critically Endangered’ Spoon-billed Sandpiper Calidris pygmaea and ‘Endangered’ Nordmann’s Greenshank Tringa guttifer. Long-term count data indicate that both species regularly occur in globally important number in southern Jiangsu coast, constituting 16.67–49.34% and 64.0–80.67% of their global population estimates respectively, and it is highly likely that most adults undergo their primary moult during this southbound migration stopover. Our results show that Spoon-billed Sandpiper and Nordmann’s Greenshank staged for an extended period of time (66 and 84 days, respectively) to complete their primary moult. On average, Spoon-billed Sandpipers and Nordmann’s Greenshanks started moulting primary feathers on 8 August ± 4.52 and 27 July ± 1.56 days respectively, and their moult durations were 72.58 ± 9.08 and 65.09 ± 2.40 days. In addition, some individuals of several other shorebird species including the ‘Endangered’ Great Knot Calidris tenuirostris, ‘Near Threatened’ Bar-tailed Godwit Limosa lapponica, ‘Near Threatened’ Eurasian Curlew Numenius arquata and Greater Sand Plover Charadrius leschenaultii also underwent primary moult. Our work highlights the importance of the southern Jiangsu region as the primary moulting ground for these species, reinforcing that conservation of shorebird habitat including both intertidal flats and supratidal roosting sites in this region is critical to safeguard the future of some highly threatened shorebird species.

Sensitivities of Bottom Stress Estimation to Sediment Stratification in a Tidal Coastal Bottom Boundary Layer

The bottom friction velocity (U*), which controls seabed erosion and deposition, plays a critical role in sediment transport in tidal coastal bottom boundary layers. Approaches have been proposed to calculate U*, including the log profile (LP) estimation, the direct covariance (COV) measurement, and the turbulent kinetic energy (TKE) method. However, the LP method assumes homogeneous flow and the effects of stratification need to be taken into account. Here, field investigations of hydrodynamics and sediment dynamics were carried out on the Jiangsu Coast, China. Two acoustic Doppler velocimeters (ADV) velocity measurements at 0.2 and 1 m above the seabed have been used to estimate U*, based on the aforementioned three methods. The COV and TKE methods provided reasonable estimations of U*, while a pronounced overestimation was identified when using the LP method. This overestimation can be attributed to the stratification effects associated with the vertical suspended sediment concentration (SSC) gradient near the bottom. Then, three models were utilized to correct the overestimation, in which the gradient/flux Richardson number was modified with empirical constants α, β, and A to parameterize the stratification effects in the logarithmic velocity distribution. The values of α, β, and A derived from the observation are smaller than the results from previous investigations. These modified logarithmic velocity distribution models can be applied in numerical simulations when sediment stratification is important.

Hydro-biogeochemical modeling of the early-stage outbreak of green tide (Ulva prolifera) driven by land-based nutrient loads in the Jiangsu coast

The outbreak of a large-scale green tide (Ulva prolifera) will have a serious impact on marine environment, ecological functions, landscape, and coastal social economy. Eutrophication is generally considered to be the most important driving factor of this phenomenon. It is difficult to obtain the pressure-impact relationship between land-based loading and green tides by only surveying or monitoring, whereas modeling can perform this task easily. In this study, therefore, a hydro-biogeochemical model was established and verified by the measured hydrodynamic and water quality variables. In the initial outbreak area of Jiangsu coast, China, we studied the relationship between U. prolifera bloom and the driving factors of nutrient loads and structures by modeling different scenarios of land source inputs. It was found that the ratio of nitrogen to phosphorus could be affected significantly, which triggered the bloom of U. prolifera. When the land-based input doubled or halved, the dissolved inorganic nitrogen concentration increased 20.6% or decreased 9.5%, respectively, which might result in 14.5% increase or 46.3% decrease in the green tide, respectively. It was also found that the nutrient distribution and structure was affected by the land-based load, which caused the outbreak of U. prolifera. Moreover, the total nutrient load must be controlled to prevent the outbreak of green tide in the Jiangsu coast.

Exploring records of typhoon variability in eastern China over the past 2000 years

AbstractHow climate controls tropical cyclone variability has critical implications for modern human society but is not well understood due to the short length of observational records. To probe this knowledge gap, we present a synthesis of intense typhoon activity from the northwestern Pacific over the past 2000 years, which is supported by a new, well-resolved tidal flat sedimentary record from the Jiangsu coast, eastern China. The record reveals nine intervals of typhoon frequency, indicating that the frequency of intense typhoons has varied on multi-centennial scales over the past 2000 years. Our synthesis shows strong evidence for a seesaw pattern of intense typhoon frequency between southeastern China and Japan and Korea. This pattern can be explained by the El Niño and Southern Oscillation–East Asian Monsoon–sea surface temperature hypothesis, which potentially explains the basin-wide typhoon climate in the northwestern Pacific region. A shift in typhoon activity was identified from 550–280 to 280–50 yr B.P. during the Little Ice Age, when typhoon activity changed from active to quiescent or vice versa. Centennial-scale shifts in Intertropical Convergence Zone and Western Pacific Warm Pool sea surface temperature are likely to be the primary forcing mechanisms driving this shift. Results obtained here provide links between typhoon activity and the El Niño and Southern Oscillation, the East Asian Monsoon, and the Western Pacific Warm Pool sea surface temperature, and therefore improve our ability to fully assess intense typhoon activity in future climate warming.

Ecological impact of land reclamation on Jiangsu coast (China): A novel ecotope assessment for Tongzhou Bay

China's continuous and rapid economic growth has led to the reclamation of large sections of the intertidal mud coast in combination with port construction, such as that of the proposed Tongzhou Bay port on the Jiangsu coast. These reclamations threaten the local ecosystem services. An ecotope distribution map was created and a hydrodynamic numerical model of Tongzhou Bay was set up to quantify the impacts of reclamation on the ecosystem. Based on the field data and model results, several abiotic features were classified into 11 ecotopes and visualized in an ecotope map of the Tongzhou Bay ecosystem. Validation with spatial distributions of two threatened shorebird species (bar-tailed godwit and great knot) showed confirmation with the mid-range and low-range littoral zones (inundated from 40% to 100% of a tidal cycle), indicating the importance of the areas with these conditions to these populations. Overlaying the ecotope map with recent and proposed land reclamation schemes revealed a loss of ecotopes, composed of the high-range (42%), mid-range (48%), and low-range (38%) littoral habitats, corresponding to a 44%–45% loss of the most important ecotopes for bar-tailed godwit and great knot (mid-range and low-range littoral zones). These results confirm the applicability of the novel ecotope assessment approach in practice.

Rapid Loss of Tidal Flats in the Yangtze River Delta since 1974.

As the home to national nature reserves and a Ramsar wetland, the tidal flats of the Yangtze River Delta are of great significance for ecological security, at both the local and global scales. However, a comprehensive understanding of the spatiotemporal conditions of the tidal flats in the Yangtze River Delta remains lacking. Here, we propose using remote sensing to obtain a detailed spatiotemporal profile of the tidal flats, using all available Landsat images from 1974 to 2018 with the help of the Google Earth Engine cloud platform. In addition, reclamation data were manually extracted from time series Landsat images for the same period. We found that approximately 40.0% (34.9–43.1%) of the tidal flats in the study area have been lost since 1980, the year in which the tidal flat area was maximal. The change in the tidal flat areas was consistent with the change in the riverine sediment supply. We also found that the cumulative reclamation areas totaled 816.6 km2 and 431.9 km2 in the Yangtze estuary zone and along the Jiangsu coast, respectively, between 1974 and 2018. Because of reclamation, some areas (e.g., the Hengsha eastern shoal and Pudong bank), which used to be quite rich, have lost most of their tidal flats. Currently, almost 70% of the remaining tidal flats are located in the shrinking branch (North Branch) and the two National Nature Reserves (Chongming Dongtan and Jiuduansha) in the Yangtze estuary zone. Consequently, the large-scale loss of tidal flats observed was primarily associated with reduced sediment supply and land reclamation at the time scale of the study. Because increasing demand for land and rising sea levels are expected in the future, immediate steps should be taken to prevent the further deterioration of this valuable ecosystem.

Importance of Diurnal Forcing on the Summer Salinity Variability in the East China Sea

AbstractThe impacts of diurnal atmospheric forcing on the summer salinity change in the East China Sea are investigated using the Regional Ocean Modeling System, forced by the hourly and daily reanalysis of wind and insolation. The differences between the forcing of these two frequencies reveal a dipole pattern of salinity change with a positive salinity deviation (1–2 psu) offshore of the Yangtze River estuary, and a negative deviation (from −1 to −0.5 psu) along the Jiangsu Coast. Further dye tracking experiments confirm that diurnal forcing strengthened the northwestward longshore freshwater transport (NLFT) of the Yangtze River by 5.2 × 109m3and reduced the mean water age of 7 days. Sensitivity experiments using different forcing combinations suggest that the diurnal wind, that is, the land–sea breeze, is the key to developing the dipole pattern of salinity change and the NLFT. Through the experiment, the land–sea breeze induced a mean clockwise circulation offshore of the Yangtze River estuary. The above changes resulted from both the nonlinearity of wind stress averaging (i.e., the square nature of wind stress) and the baroclinic adjustment related to the diurnal salinity variation, which is directly connected to the diurnal swing of the Yangtze River front. The baroclinic adjustment generated a dipole pattern of vorticity changes offshore of the Yangtze River estuary and a coherent northwestward jet current strengthening the NLFT. These processes developed the summer dipole pattern of the salinity change.

Indication of size distribution of suspended particulate matter for sediment transport in the South Yellow Sea

The Yellow Sea is a key area for studying source-to-sink sediment transport systems in East China shelf seas. However, the sediment transport and dispersal patterns in the Yellow Sea are not fully understood because of the significant seasonal variation in ocean circulation. In this study, we identify the ocean circulation patterns in the South Yellow Sea based on temperature, salinity and depth data collected from 52 hydrographic stations during the winter of 2016. The mass concentrations and particle size distributions of suspended particulate matter are also determined to decipher the sediment transport pattern in the South Yellow Sea. The results show that particles from the Yellow Sea Coastal Current and Shandong Peninsula Coastal Current display a bimodal size distribution, with peaks at approximately 2.5 μm and 32–64 μm, while particles from the Yellow Sea Warm Current and residual Yellow Sea Cold Water Mass display a trimodal size distribution, with peaks at 2.5 μm, 32–64 μm and 391 μm. The fine and medium particles (<256 μm) are mainly inorganic particles, while the coarse particles (>256 μm) include organic materials. The peak at 391 μm is dominated by organic particles and reflects the influence of the Yellow Sea Warm Current in the surface layer. The Yellow Sea Warm Current enhances the nutrient and temperature conditions in the South Yellow Sea, which facilitates phytoplankton growth under appropriate light conditions. The content of inorganic particles with sizes of 64–159 μm decreases sharply in the central South Yellow Sea, which reflects the transport of suspended particulate matter from the southern study area to the central Yellow Sea mud area. The synthesized evidence suggests that the Yellow Sea Warm Current, as the main driving force, transports particles from the Jiangsu coast or the Changjiang River into the central Yellow Sea mud area in winter.

Determining the carrying capacity and environmental risks of livestock and poultry breeding in coastal areas of eastern China: an empirical model.

The scale of regional livestock and poultry breeding (LPB) is generally not determined by the supporting capacity (fodder supply), but by the environmental carrying capacity of wastes from the LPB. The soil's own nutrient-supplying capacity used to be overlooked, which consequently produced an inaccurate result of carrying capacity estimation of the LPB. An empirical method was, therefore, employed to evaluate the soil's own nutrient-supplying capacity and further determine the carrying capacity and environmental risks of the LPB accurately. Thirteen counties along the coast of Jiangsu were selected to conduct this study, according to the framework of planting-breeding balance. Our results indicate that, including the soil's own nutrient-supplying capacity in the estimation of the carrying capacity of the LPB, it can reduce the original carrying capacity by 50%. This suggests that our empirical method can significantly increase the accuracy of estimating the carrying capacity of the LPB. The carrying capacity of the LPB in the study area varies from 1.5 to 48.08pigs/hm2, with a mean of 14pigs/hm2 based on phosphorus (P) balance. Furthermore, four sub-regions (Ganyu, Dongtai, Dafeng, and Guannan) that have a high P pollution risk should focus on controlling the scale of the LPB. The nitrogen (N) pollution risk in the study area is generally low. Results suggest that the soil's own nutrient-supplying capacity plays an important role in estimating the carrying capacity of the LPB accurately. This study can provide insights on reducing environmental risks of the LPB, which may be beneficial for decision makers.

Observed cross-shelf suspended sediment flux in the southern Yellow Sea in winter

The cross-shelf circulation and its transport in the Yellow and East China Seas (YECSs) are very important to global ocean material exchanges and regional environment. A field survey including a long-term mooring, 89 sample stations, 25 drifters, etc., was conducted in the YECSs in the winter of 2015 to investigate the cross-shelf transport of the sediment plume over the Changjiang Bank. The observation shows that the northern East China Sea (ECS) current carries low temperature, low salinity, and high turbidity coastal waters southeastward from the radial tidal sand ridge off the Jiangsu coast to the outer shelf south of Cheju Island. The northern ECS current with an average speed of 4.7 cm/s and in the average direction of 100° from due north is not only measured directly by the 21-day mooring, but also recorded in trajectories of 6 satellite-tracked surface drifters. The mean current of the northern ECS current flows roughly along the 30–50 m isobaths with a small cross-isobath component. The mooring data indicate that the sediment flux is dominated by the mean advection of mean sediment concentration, resulting in an average suspended sediment flux of 52.23 g s−1 m−1 in the direction of 105°. According to the suspended sediment flux decomposition, the flux due to tidal currents is calculated to be one order of magnitude smaller than the advection by subtidal currents, implying that the sediment plume is unlikely generated by the tidal pumping, but is likely maintained by the advection. The amount of the suspended sediments carried by the northern ECS current is estimated to reach 40.62 million tons assuming an average width of 100 km of the turbid plume during December through February. The transport by the northern ECS current is suggested to provide sufficient amount of sediments for the Southwestern Cheju Island Mud to grow in time.

A Study on the Response of the Hydrodynamic Environment to the Morphology of Radial Sand Ridges in the Coastal Waters of Jiangsu

A two-dimensional hydrodynamic model for the waters off the coast of Jiangsu, where there are radial sand ridges (RSRs) (hereinafter, the RSR area), was established based on measured topographic, tide level and tidal current data. Considering the complex topographic and geomorphic characteristics of the RSR group in this area, an unstructured grid was used for the calculation. A four-layer refinement was applied to the grid from outside to inside to better fit the complex topography. The simulations were performed to examine the response of the hydrodynamic environment to the morphology of the RSRs in three scenarios, namely, when there are natural RSRs, no RSRs, and partially reclaimed RSRs. When there are no or partially reclaimed RSRs, the tidal current field still exists in a radial pattern in the RSR area. The radial tidal current field is relatively stable and is not controlled by the morphologies of the RSRs. The topographic changes do not alter the distribution pattern of the radial tidal current field but do affect the local current fields. When there are no RSRs, the flood currents can directly reach Jianggang. Under practical conditions, the RSRs block the tidal currents during a flood tide to some extent. This phenomenon is particularly pronounced when the RSRs are partially reclaimed. For example, during an ebb tide, when the tidal currents encounter sand ridges or reclamation areas, their streamlines bend, and they flow around the obstacles. This change will affect the material transport, sediment deposition and seabed erosion.

Morphological Characteristics of Tidal Creeks in the Central Coastal Region of Jiangsu, China, Using LiDAR

Tidal creeks are an important component of the intertidal zone and are essential for maintaining the balance between sedimentary processes and the hydrodynamic environment. A quantitative analysis of the morphological characteristics of tidal creeks is essential for understanding their processes of evolution and to evaluate the stability of tidal flats. This study describes the morphological characteristics of tidal creeks using a high-resolution airborne LiDAR DEM. The parameters include the number, order, length, width, depth, and width/depth ratio. The results show that the number and degree of development tidal creeks along the central coast of Jiangsu are higher than those in the radial sandbanks, and the mean width and length increase with the increasing tidal creek order. The number, length, and depth of tidal creeks in the salt marsh zone with well-developed vegetation are higher than those areas with little vegetation cover. The number of tidal creeks in the mid-upper intertidal zone is the largest, while the length and width of tidal creeks in the lower intertidal zone are the greatest. The differences in these characteristics are mainly related to the vegetation distribution, tidal flat width, and hydrodynamic conditions. Our findings potentially provide guidelines for coastal management and the evaluation of tidal flat stability.

Centralization and decentralization: Coastal management pattern changes since the late 19th century, Jiangsu Province, China

With rapid industrialization over the Asian-Pacific coastal region, sustainable management has received increased levels of attention. The way to construct the sustainable management mode suitable for local characteristics becomes an important issue; it requires an in-depth understanding of local management practices changes and historical culture. In this respect, there is a lack of comprehensive discussions on centralized/decentralized management pattern change for this region. Based on historical document analysis for the Jiangsu coast, we reconstruct the evolution of coastal management modes. Here we show that coastal management in Jiangsu has witnessed repeated transitions between centralized and decentralized mode, encompassing four periods: traditional management before the late 19th century, the decentralized practice in the early 20th century, the centralized management associated with the planned economic system from the 1950s–1980s, and the decentralized management in response to the adoption of a market economic system after the 1980s. The driving forces for the changes identified include geomorphological changes, population growth and social-economic regime shifts. We propose that, to optimize coastal management, a hybrid model should be established to take into account both centralized and decentralized components. Although coastal management is decentralization-oriented in most western countries, in the Asia-Pacific coastal regions, local conditions and historical features should be taken into account to adjust the balance between centralized and decentralized variables in the management. With the increasing attention to ecosystem health in China, together with future climate changes and population dynamics, the centralized component should be re-considered within the hybrid model.

Effects of tidal variations on storm waves: A case study of the radial sand ridges along China's Jiangsu coast during Typhoon Muifa

The radial sand ridges in China's southern Yellow Sea are famous for their fan-shaped pattern with complex channel-shoals. The area's large tidal range results in waves propagating onshore when most ridges are submerged at high tide, while that process is limited by the exposure of sand ridges at low tide. We investigated these processes using the WRF-ARW and MIKE21 models to assess the different spatiotemporal distributions of storm waves during normal spring tide (TSWR) and the tidal conditions present during the passage of Typhoon Muifa (TMWR) in August 2011. Spatial analysis showed that wave directions had few changes at high tide but changed significantly at low tide owing to the sheltering effects of sand ridges in the central and southern parts of the area. Differences in water level (WLD) and significant wave height (HsD) between TSWR and TMWR were high in the central and southern parts, where maximum values were twice those further north. Temporal analysis showed that WLD and HsD at twelve observation points within the sand ridges were significantly correlated. Our results show how employing WLD and HsD data can be used to improve the science-based prediction and prevention of storm disasters under similar conditions.

Effects of increased CO2 and temperature on the physiological characteristics of the golden tide blooming macroalgae Sargassum horneri in the Yellow Sea, China

The golden tide, caused by the brown algae Sargassum horneri, exerts severe influences on the Pyropia aquaculture of Jiangsu coast, China. To study the outbreak of the golden tide in response to increasing greenhouse gas emissions, S. horneri was cultured under four conditions: ambient condition (10 °C, 400 μatm), elevated temperature condition (14 °C, 400 μatm), elevated CO2 level (10 °C, 1000 μatm), and potential greenhouse condition (14 °C, 1000 μatm). The growth, photosynthetic performances, and inorganic carbon affinity of S. horneri were studied. The results showed that elevated temperature exerted a more pronounced positive influence on S. horneri growth, photosynthesis, and carbon assimilation than CO2 enrichment. The growth of S. horneri was significantly improved by moderately elevated temperatures, especially under concurrently elevated CO2 levels. This suggests that the greenhouse effect will benefit growth and carbon sequestration of S. horneri, which may enhance the frequency and scale of golden tides.

Sand‐Mud Tidal Flat Morphodynamics Influenced by Alongshore Tidal Currents

AbstractTidal flats, where significant land‐ocean interactions take place, are often abstracted as a cross‐shore bed profile with sediment zonation from the lower sand flat to the upper mud flat. However, in addition to cross‐shore tidal currents, the impact of the alongshore components on cross‐shore sediment transport, morphological evolution, and sediment grain‐size change remains unclear. Here we investigated sand‐mud tidal flat morphodynamics in the absence of waves by combining approaches of field observations, numerical modeling, and analytical interpretations, based on the example of the tidal flat on the central Jiangsu coast, China. The results show that the morphodynamic processes are complicated by the interactions of cross‐shore and alongshore tidal currents, cross‐shore flat morphology, and sediment zonation. With amplified phase lags of the alongshore tidal level at the boundaries, alongshore currents become dominant over cross‐shore tidal currents on the lower flat, while the upper flat is always dominated by the cross‐shore currents. Therefore, bed profiles and mud content on the upper flat were independent of the alongshore tidal current magnitude, being convex‐up and consisting of mud. In contrast, the strong alongshore currents can erode mud on the lower flat and promote landward sand transport from the subtidal area to the lower flat, forming a sand flat. The maximum tidal bed shear stress is almost spatially uniform across the muddy area but pronouncedly elevated where the bed sediment coarsens on the lower flat. The contributions of the alongshore tidal currents and sand‐mud sorting processes should be appropriately addressed in similar coastal environments.

The observed variations of the north intrusion of the bottom Taiwan Warm Current Inshore Branch and its response to wind

Current measurements from three moored Acoustic Doppler Current Profilers (ADCPs) and hydrographic measurements from cruises in the Yellow and East China Seas were used to investigate the North Intrusion of the bottom Taiwan Warm Current Inshore Branch (NI-TWCIB) and its response to wind. The vertical structure of the mean current suggests that NI-TWCIB intrudes into the Jiangsu coasts from the bottom. The observed bottom residual currents run continuously northward at 32∘N from June 12 to August 22, 2014. Synoptic-scale variations of the residual currents indicate that the bottom NI-TWCIB is highly influenced by synoptic process such as wind. Significant variations of the paths of NI-TWCIB are observed from salinity data. The intrusion paths are extracted using a horizontal salinity gradient method, and we characterize the paths by defining the eastern boundary, northern boundary and turning point. The monsoon over the Yellow and East China Seas plays an important role in the variations of the paths of the bottom NI-TWCIB. The pressure gradient set up through Ekman transport and surface transport by easterly and northerly winds promotes the offshore movement of the bottom NI-TWCIB, the northward intrusion, and the northward movement of the turning point. The westerly and southerly winds have opposite effects. We propose a regression method to estimate the intrusion path as a function of east–west winds and north–south winds. The regression results prove that the northern boundary of the bottom NI-TWCIB can arrive at approximately 32 ∘N, which is consistent with ADCP measurements.

Shift in soil organic carbon and nitrogen pools in different reclaimed lands following intensive coastal reclamation on the coasts of eastern China

The impacts of coastal reclamation on carbon (C) and nitrogen (N) sinks of coastal wetlands remain unclearly understood. This study was conducted to investigate the alterations of soil organic C and N (SOC and SON) pools following conversion of Phragmites australis salt marsh into fishpond, wheat and rapeseed fields and town construction land through reclamation along Jiangsu coast in eastern China. Coastal reclamation significantly increased stocks of soil total, labile and recalcitrant organic C and N (SLOC, SLON, SROC, and SRON), and concentrations of water-soluble organic C (WSOC), microbial biomass C and N (SMBC and SMBN), cumulative CO2-C mineralization (MINC) following conversion of P. australis salt marsh into fishpond, wheat and rapeseed fields. However, coastal reclamation reduced SOC, SLOC, SROC, SRON, WSOC, SMBC, SMBN, and MINC following conversion of P. australis salt marsh into town construction land. Our results suggest that coastal reclamation affects C and N sinks of coastal wetlands by changing SOC and SON pools size, stability and dynamics changes following conversion of P. australis salt marsh into other land use types. This finding were primarily attributed to alterations in quantity and quality of exogenous materials returning the soil, and soil physiochemical properties as affected by coastal reclamation.

Salt and Wetland: Traditional Development Landscape, Land Use Changes and Environmental Adaptation on the Central Jiangsu Coast, China, 1450–1900

China’s coastal wetlands are subjected to increasing pressure in terms of the sustainability of the economic and social development, due to the rapid industrialization and urbanization over the last 30 years; the protection and sustainable use of wetland resource requires local knowledge of traditional development model, management policy and historical landscape change. However, there is a lack of the relevant research of traditional wetland utilization and environmental adaptation practice for China’s coast. Using the various data sets of the central Jiangsu coast, we reconstruct traditional development patterns of wetland and environmental adaptation process, based on a historical approach. The results show that, in this dynamic tidal flat wetland, with continued shoreline advancement, traditional salt-making activity in this region formed a low-density distribution and labor-intensive pattern, which had a remarkable adaptive change of production pattern from centralization to dispersion; this unique cultural ecological landscape was the result of the combined action between wetland evolution and monopolistic land use policies. This study reveals a representative cultural ecological landscape of coastal wetland development in China; an improved understanding of human-coast interaction and local knowledge is beneficial to the management of wetland resource uses, enhancing the value of ecosystem services provided by coastal wetlands.

Hydrodynamics, erosion and accretion of intertidal mudflats in extremely shallow waters

Intertidal flats are shallow-water environments that undergo cyclical variations in water depth, leading to a frequent occurrence of extremely shallow water stages (ESWS; water depths <0.2 m). However, relatively little is known about the hydrodynamic conditions and erosion–accretion processes during ESWS, because the water depth is too shallow to measure in situ sediment dynamic processes using traditional methods. To address this gap, based on in situ measurements with four advanced instruments, we quantified the hydrodynamic conditions, erosion and accretion during ESWS in calm weather conditions on a highly turbid intertidal flat in Jiangsu coast, China. Our results revealed that marked erosion and accretion occurred during ESWS at the flood and ebb tidal stages, respectively. The resulting bed-level changes were three times greater during ESWS than relatively deep water stages (RDWS; water depths >0.2 m), and the rate of change was an order of magnitude faster than during RDWS. This larger and faster bed-level change occurred even though the ESWS duration only accounted for 10% of the entire tidal cycle. This result occurred because the bed shear stress due to combined current–wave action during ESWS, was, on average, two times higher than during RDWS at the flood stage causing more extensive erosion. Whereas during the ebb stage, this shear stress during ESWS was only half of that during RDWS resulting in greater accretion. The main implications of these results are that, because ESWS occur frequently (twice every tide) and are associated with large bed shear stress and bed-level changes, these conditions are likely to play an important role in morphological changes of intertidal flats. Our study shows that ESWS have a key influence on intertidal flat hydrodynamics and sediment dynamics. Thus our results are the basis for an improved understanding of the coastal morphodynamic processes on intertidal flats.