Jiangsu Coastal Plain Research Articles

Tracking annual changes of coastal aquaculture ponds in China during 1986–2021

The rapid expansion of coastal aquaculture ponds has made outstanding contributions to global food security and economic development in coastal areas, but this expansion inevitably has a significant impact on coastal ecosystems. Strengthening the spatiotemporal monitoring of aquaculture ponds is crucial for optimizing coastal land use and efficiently managing aquaculture ponds. However, aquaculture pond data on national scale and interannual variability are lacking. Here, we utilized Landsat times series images from 1986 to 2021 to generate annual maps of aquaculture ponds in China's coastal areas and investigated its spatiotemporal characteristics. We find that the overall accuracy of our aquaculture ponds classification was over 90% each year. Aquaculture ponds were concentrated in Bohai Bay, the Jiangsu Coastal Plain, and the Pearl River Delta in China's coastal areas. The time series of aquaculture ponds change could be divided into three stages: rapid growth (1986–2000), stable growth (2001–2016), and a slow decline (2017–2021). The spatial evolution of aquaculture ponds was characterized by (1) continuous seaward expansion, (2) continuous inland and seaward expansion, (3) continuous inland expansion, (4) continuous expansion and then shrinkage, and (5) rapid shrinkage. Moreover, the main aquaculture ponds classification errors were salt pans, reservoirs, abandoned ponds, port facilities, lakes, and pit ponds. Our study demonstrated a new method for applying satellite remote sensing for coastal ecosystem management, and our maps and findings can be used to optimize the development and sustainability of coastal aquaculture ponds.

Sedimentology and evolution of the Holocene radial tidal sand ridge in the south Yellow Sea, China

The radial tidal sand ridge (RTSR) off the Jiangsu Coast in the south Yellow Sea is one of the most fantastic and unique natural landscapes in the world. A large number of investigations on geomorphology and marine geology have been implemented during the last several decades. The formation and evolution of the RTSR, however, are still under debate. To resolve this issue, 10 ∼30–60 m-long cores were retrieved from the Jiangsu coastal plain and offshore sand ridge field in 2018–2019. Stratigraphic transects chronologically constrained by abundant radiocarbon dates were built based on sedimentological and paleoecological (i.e., foraminifer) data from selected cores. Combined with well-documented core stratigraphy from earlier studies, an age–depth plot with a local sea-level change curve revealed that the RTSR initiated approximately 9,000 cal a BP in a sandy bedform shape under transgressive conditions, continued throughout the Holocene, but developed mostly after 1128 AD, when the Yellow River flowed southward into the Yellow Sea. Abundant sediment supply, thus, appears to have played a major role in the formation and evolution of the RTSR in the south Yellow Sea.

Salinity evolution of aquitard porewater associated with transgression and regression in the coastal plain of Eastern China

Aquitards can preserve paleo-saltwater and have a long and profound influence on the aquifer groundwater, yet they have received less attention. Here, five one-dimensional vertical profiles of the natural tracers, Cl−, Br−, δ2H, and δ18O of aquitard porewater were measured and combined with eight existing profiles collected from previous studies in three Eastern China coastal plains, Bohai bay, Laizhou bay, and Jiangsu coastal plain, to show the salinity origin and the timescale of the transport of porewater across aquitards since the mid-Holocene. Evidence of paleo-seawater impacted by Holocene transgression is noticed as peak Cl− concentration, enriched water isotopes, and lower Cl/Br ratios are observed in the porewater at about the bottom depth of Holocene of 25 m. The shape of Cl− profiles and associated 1-D transport models confirms Holocene seawater's presence in the sediment and the alternating transgression and regression control the salinity evolution of coastal aquitard porewater. Diffusion is the dominant transport across aquitard with an upward velocity between 0.03 and 0.6 mm/yr. Reverse advective flow has affected the solute transport in areas of extensive pumping. Anthropogenic activities enhance the leaching of salty porewater into aquifers in coastal areas, necessitating the need for research focused on marine aquitard salty water.

Early–Middle Holocene marine–terrestrial changes in the southeastern Lixiahe Plain, East China: Land-forming mechanisms, regional significance, and implications for Neolithic cultural origins

The southeastern Lixiahe Plain (SELP) is the site of the only identified Neolithic human settlements in the eastern Northern Jiangsu Plain, East China, and it also represents the junction of the Lixiahe Plain (LP), the Northern Jiangsu coastal Plain, and the Yangtze River Delta northern flank Plain. Based on previous studies and lithology, marine micropaleontological analysis, and the results of AMS 14C dating of three sets of strata from the Neolithic “ruins area”, we discussed the timings and mechanisms and the regional significance of the Early–Middle Holocene marine–terrestrial transitions in the SELP as well as the origins of its Neolithic culture. A rare phenomenon is identified in the study: Under the background of the rapid sea-level rise in the Early Holocene, the eastern part of the area accreted from the marine environment to a coastal tidal flat at approximately 8000 a BP (8900 cal a BP). This accretion was due to the obstruction of the palaeogeomorphic uplift belts to the east and south of the LP and the convergence and accumulation of sediments caused by the radiating tidal current field in the South Yellow Sea. The western part transformed into a swamp environment at approximately 5500 a BP (6300 cal a BP) due to the formation of the Yangtze River north coastal sand bank during the Early to Middle Holocene. As the first new land formed in the study area during the Holocene, the marine–terrestrial changes of the SELP formed the boundaries of the spatial evolution of the three plains, thus limiting their respective evolution range. As the archaeological evidence necessary to build a complete evidence chain is lacking, palaeogeography and traffic problems limit our current understanding on the Neolithic cultural origins in the SELP, which may be the future direction of research efforts.

A ~130 ka terrestrial-marine interaction sedimentary history of the northern Jiangsu coastal plain in China

Coastal deposits are ideal archives to decipher the history of terrestrial-marine interactions in response to sea-level changes. Over the last decades, numerous investigations have been implemented to uncover the stratigraphic framework and the paleoenvironment evolution of the Jiangsu coastal plain (JCP), China. However, there have been limited studies on the sedimentary history over the glacial-interglacial timescales because of the lack of reliable chronostratigraphy. Here, we selected a 30-m-long sediment core in the northern JCP for luminescence dating, and carried out comprehensive sedimentological and paleontological analyses to ascertain the sedimentary history. Multiple luminescence dating techniques, including quartz optically-stimulated luminescence (OSL) and feldspar (polymineral) post-infrared (IR) IR stimulated luminescence (pIRIR) dating, were applied to determine the chronology of the sediment core. The obtained chronostratigraphy of core JCP01 spanning ~130 ka reveals that terrestrial deposition occurred in Marine Isotope Stage (MIS) 6, MIS 4–2 and the late stage of MIS 1. In contrast, marine influenced deposition is identified in MIS 5e and early MIS 1. The terrestrial interval of core JCP01 mainly consists of stiff clay and floodplain facies occurring at depths of 30–24 m, 12–5 m and 2–1 m, formed in relation to sea-level lowstands; whereas marine-influenced sediments at depths of 24–12 m and 5–2 m correspond to sea-level highstands, respectively. Our results highlight two sets of marine influenced sedimentary stratigraphy (T1, T2) dated to ~7 ka and around 130–120 ka, but no obvious MIS 3 transgression recorded in this core. In general, the conclusion is consistent with previous studies in East Asia and beyond, but not with previous work in this region that relied on radiocarbon dating. This suggests that re-dating with luminescence techniques is required for deposits correlated with the MIS 3 transgression in the northern JCP. Our reconstructed terrestrial-marine alternation sedimentary history of the northern JCP also shows a strong linkage with changes in the relative sea-level over the glacial-interglacial cycles.

Evolution of groundwater chemistry in coastal aquifers of the Jiangsu, east China: Insights from a multi-isotope (δ2H, δ18O, 87Sr/86Sr, and δ11B) approach

Groundwater salinization is currently a very serious and challenging issue in many parts of the world. With an increasing demographic pressure and remarkable changes of water and land uses over the last decades, the multilayer coastal aquifer system of Jiangsu province, east China, was affected by increasing salinization. In this study, we investigate the groundwater salinization process and the salinity sources of the aquifer system in Nantong area (southern part of the Jiangsu coastal plain) using a multi-isotope (δ2H, δ18O, 87Sr/86Sr, and δ11B) approach. The results show that the TDS (total dissolved solids) values in most deep groundwater samples are generally lower than those of the shallow groundwater samples. The TDS of both shallow and deep groundwater increase from western Nantong (inland) to the eastern coastal region of the Yellow Sea. The chemical types transform from Ca-Mg-HCO3 or Mg-Ca-HCO3 to NaCl. The stable hydrogen and oxygen isotopes signatures of the groundwater samples indicate that local precipitation likely acts as the main recharge source of both the shallow and deep confined groundwater systems. The deep groundwater shows more depleted isotopes, suggesting recharging by the precipitation under a cold climate before the Holocene period. The shallow groundwater features heavier water isotopes, indicating recharging source from recent precipitation under a warm climate. The variations in δ11B and 87Sr/86Sr of groundwater samples can be explained by the changes of solute sources. In the inland region (western Nantong), shallow groundwater with higher TDS is mainly caused by evaporation-induced concentration, whereas in coastal areas, seawater intrusion exerts a major influence on the chemical composition of the shallow groundwater.Our results show that that seawater intrusion mainly occurs in eastern and southeastern Nantong area. We also find that hydraulic connection between shallow and deep groundwater is strengthened by continuous overexploitation, and deep groundwater is mixed with shallow groundwater at some points. The mixing between upper saline water and deep freshwater, together with water-rock interactions, likely explain the observed low salinity in deep groundwater in coastal areas. Overall, with growing observations of salty seawater intrusion in the estuary region of the Yangtze River, future efforts are needed to prevent further seawater intrusion as sea level rises and groundwater table declines. In this context, our findings provide key information for groundwater management in other coastal aquifers, east China.

Sedimentary history of the coastal plain of the south Yellow Sea since 5.1 Ma constrained by high-resolution magnetostratigraphy of onshore borehole core GZK01

The thick sedimentary sequences of the East Asian continental shelves are archives of information on tectonics, sea-level fluctuations, flood plain evolution, and changes in the East Asian monsoon climate. However, long sedimentary sequences with a reliable chronological framework from this setting are scarce. Here, we present an integration of lithostratigraphic, rock magnetic, and magnetostratigraphic results for the sedimentary sequence of a 285.0 m core (GZK01) recovered from the northern Jiangsu coastal plain of the onshore South Yellow Sea, eastern China. Alluvial, fluvial, lacustrine, and marine deposits were identified according to lithofacies analysis, and detrital magnetite and hematite are the main magnetic carriers. The magnetostratigraphic results show that core GZK01 records the Brunhes, Matuyama, Gauss, and Gilbert chrons, and has an extrapolated basal age of ∼5.1 Ma. This record is the oldest sedimentary sequence yet reported from the continental shelf of the South Yellow Sea. Integrating the geochronological framework with changes in lithofacies, a conceptual model of the environmental evolution of the northern Jiangsu coastal plain is proposed. For a long interval during the Pliocene, the drilling area was a lacustrine environment. From the Late Pliocene to the Early Pleistocene, the disappearance of the paleolake and a transition to a fluvial and marine environment suggests the peneplanation of the northern Jiangsu coastal plain. Cumulative land-sea interactions since 0.8 Ma subsequently shaped the modern geomorphology. The observed process of sedimentary evolution was possibly controlled by regional tectonics and long-term climate changes.

Mapping national-scale aquaculture ponds based on the Google Earth Engine in the Chinese coastal zone

Aquaculture plays a key role in addressing global food security and nutrition issues. However, the rapid expansion of the aquaculture industry has imposed tremendous pressure on coastal environments in some developing countries. The aquaculture industry in China is the largest worldwide. However, to date, we know little about the spatial distribution of aquaculture ponds. This study proposed an efficient method for mapping aquaculture ponds on a national scale using Landsat 8 images based on the Google Earth Engine (GEE) platform. We integrated spectral, spatial characteristics and morphological operations to construct a decision tree classifier that was successfully used to extract the aquaculture pond regions in the Chinese coastal zone in 2017, with an overall accuracy of 0.96 (0.94–0.97, 95% confidence interval) and kappa coefficient of 0.82. When compared with the results of visual interpretation and other relevant studies, our method exhibited good consistency. The results provided a detailed spatial distribution of the aquaculture ponds in the Chinese coastal zone and revealed that the total area of aquaculture ponds is approximately 15632.64 km2 (14386.98 km2–17924.95 km2, 95% confidence interval), which is mainly concentrated in the Bohai Rim, Jiangsu Coastal Plain, and Guangdong coastal region. This work demonstrated that this method can generate high-quality datasets of the spatial distribution of aquaculture ponds and could map the global aquaculture ponds distribution.

Identifying the Origins and Spatial Distributions of Heavy Metals in the Soils of the Jiangsu Coast

A total of 239 samples of surface soils were collected along the Xiangshui to Rudong coast, in Jiangsu Province, and analyzed for Cd, Cr, Cu, Hg, Ni, Pb, and Zn. A multivariate analysis was applied to identify the sources of heavy metals, and ordinary kriging was used to map the spatial distributions of the heavy metal concentration. The mean contents of Cd, Cu, Hg, Pb, and Zn in the surface soils of the Jiangsu Coastal Zone were higher than the background values of the Jiangsu Coastal Plain, which indicated that there were obvious accumulations of these heavy metals in surface soils; while the mean contents of Cr and Ni were lower than the background values. The contents of Cd, Cr, Cu, Pb, Ni, and Zn in soils that originated from marine deposition were significantly lower than those from alluvium and lagoon facies deposition, including the Yangtze River Delta deposition. Urban areas exhibited higher Cd, Cu, Hg, Pb, and Zn contents than other land covers. Cr and Ni were controlled by the parent material and seemed to originate from a natural source. Cd, Cu, Pb, and Zn were associated with the combination of parent material and anthropogenic inputs. Hg was dominated by atmospheric deposition related to various human activities. The high values of Cd, Cu, Pb, and Zn were distributed in the northern, western, and southern parts of the study area, and Hg exhibited high values around the urban areas in the western and southern parts.

Using environmental isotopes along with major hydro-geochemical compositions to assess deep groundwater formation and evolution in eastern coastal China

Hydrochemical analysis and environmental isotopic tracing are successfully applied to study groundwater evolution processes. Located in eastern China, the Jiangsu Coastal Plain is characterized by an extensively exploited deep groundwater system, and groundwater salinization has become the primary water environmental problem. This paper provides a case study on the use of a hydrochemical and environmental isotopic approach to assess possible mixing and evolution processes at Yoco Port, Jiangsu Province, China. Hydrochemical and isotopic patterns of deep groundwater allow one to distinguish different origins in deep water systems. HCO3– is the dominant anion in the freshwater samples, whereas Na+ and Cl− are the dominant major ions in the saline samples. According to δ18O, δ2H and 14C dating, the fresh water is derived from precipitation under a colder climate during the Glacial Maximum (Dali Glacial), while the saline groundwater is influenced by glacial-interglacial cycles during the Holocene Hypsithermal. The δ18O, δ2H and 3H data confirm that deep groundwater in some boreholes is mixed with overlying saline water. The deep groundwater reservoir can be divided into a saline water sector and a fresh water sector, and each show distinct hydrochemical and isotopic compositions. The saline groundwater found in the deep aquifer cannot be associated with present seawater intrusion. Since the Last Glacial Maximum in the Late Pleistocene, the deep groundwater flow system has evolved to its current status with the decrease in ice cover and the rising of sea level. However, the hydraulic connection is strengthened by continuous overexploitation, and deep groundwater is mixed with shallow groundwater at some points.

Salinization of porewater in a multiple aquitard-aquifer system in Jiangsu coastal plain, China

Chemical and isotopic compositions were analyzed in porewater squeezed from a clayey aquitard in Jiangsu coastal plain, eastern China, to interpret the salinity origin, chemical evolution and water-mass mixing process. A strong geochemical fingerprint was obtained with an aligned Cl/Br ratio of 154 in the salinized aquitard porewater over a wide Cl− concentration range (396–9,720 mg/L), indicating that porewater salinity is likely derived from a mixing with old brine with a proportion of less than 20%. Very small contributions of brine exerted limited effects on water stable isotopes. The relationships between porewater δ18O and δD indicate that shallow and intermediate porewaters could be original seawater and were subsequently diluted with modern meteoric water, whereas deep porewaters with depleted stable isotopic values were probably recharged during a cooler period and modified by evaporation and seawater infiltration. The cation–Cl relationship and mineralogy of associated strata indicate that porewater has been chemically modified by silicate weathering and ion-exchange reactions. 87Sr/86Sr ratios of 0.7094–0.7112 further confirm the input source of silicate minerals. Numerical simulations were used to evaluate the long-term salinity evolution of the deep porewater. The alternations of boundary conditions (i.e., the third aquifer mixed with brine at approximately 70 ka BP, followed by recharge of glacial meltwater at 20–25 ka BP, and then mixing with Holocene seawater at 7–10 ka BP) are responsible for the shift in porewater salinity. These timeframes correspond with the results of previous studies on ancient marine transgression-regression in Jiangsu coastal plain.

Cl− as a Chemical Fingerprint of Solute Transport in the Aquitard-Aquifer System of the North Jiangsu Coastal Plain, China

Detailed vertical profiles of Cl− in porewaters through the aquitard-aquifer system were used to yield solute transport mechanism and build a conceptual model regarding evolution processes and transport time of natural tracer migration in North Jiangsu coastal plain, China. One-dimensional vertical simulated models of Cl− profiles illustrate that diffusion appeared to be the dominant solute transport mechanism in the aquitard-aquifer system. A downward groundwater flow did not improve the fitness between simulated and measured values. Several simulated models were constructed and suggested that the evolution of the Cl− profiles is mainly ascribed to the introduction of seawater and freshwater of transgression-regression to the first confined aquifer and the upper boundary. Groundwater in the first confined aquifer recharged by the Late Pleistocene glacial meltwater (25–15 ka BP) was supported in response to the low Cl− concentrations. The shallow groundwater in the first confined aquifer and porewater with high salt were attributable to the Holocene seawater intrusion. These timeframes were also consistent favorably with the results of previous studies into the palaeohydrology of the study area.

Origin and Geochemical Processes of Porewater in Clay-Rich Deposits in the North Jiangsu Coastal Plain, China

The hydrogeochemical and stable isotope compositions of aquitard porewater samples from three boreholes were investigated to determine the origin, salinization, and hydrochemical evolution of water in the North Jiangsu coastal plain, China. Three porewater groups were identified based on the water-bearing subsystems. The total dissolved solids (TDS) of porewater samples highly varied from 0.03 to 26.1 g/L. Molar Cl/Br ratios and δ18O and δ2H data indicate that the source of Group 1 salinized porewater was the Holocene seawater, whereas Group 3 salinized samples were probably related to the remnant palaeoseawater of the Late Pleistocene. Group 2 samples had low salinity (TDS < 1 g/L) and undetectable Br− concentrations, which were probably recharged during a colder period and without evidence of seawater involvement. The salinized porewater was likely diluted by freshwater, as evidenced by its depleted isotopes and low salinity relative to standard seawater. The ionic ratios and ionic deltas indicate that considerable water-rock interactions (e.g., cation exchange and mineral weathering) also accounted for the hydrochemical constituents of porewaters, and cation exchange seems to be more noticeable at low salinity.

The Yangtze River deposition in southern Yellow Sea during Marine Oxygen Isotope Stage 3 and its implications for sea-level changes

The depositional history of the lower Yangtze River and sea-level changes during Marine Oxygen Isotope Stage (MIS) 3 was established using three long drill cores from the northern Yangtze deltaic plain and southern Yellow Sea by using sedimentary analysis and AMS 14C dates. Voluminous channel deposits of the lower Yangtze River in MIS 3 were found from the northern deltaic plain and offshore area, with a thickness of over 30m. The thick channel deposits are characterized by massive medium-to-fine sand deposits with sporadic tidal influence. During MIS 3, the Yangtze River appears to have mainly migrated between the modern river mouth and middle Jiangsu coastal plain, and likely built a delta complex in the field of Yangtze Sand Shoal in northern East China Sea. A large sediment supply and rapid sea-level variations promoted rapid progradation of the delta onto the flat shelf. The highest sea levels during MIS 3 are estimated to have reached 25±5m below the present sea level.

Seal Level and Coastal Environment during MIS3 recorded by BY1 Core in North Jiangsu Plain, Eastern China

The depositional history of the lower Yangtze River and sea-level changes during Marine Oxygen Isotope Stage (MIS) 3 was established using three long drill cores from the northern Yangtze deltaic plain and southern Yellow Sea by using sedimentary analysis and AMS 14C dates. Voluminous channel deposits of the lower Yangtze River in MIS 3 were found from the northern deltaic plain and offshore area, with a thickness of over 30 m. The thick channel deposits are characterized by massive medium-to-fine sand deposits with sporadic tidal influence. During MIS 3, the Yangtze River appears to have mainly migrated between the modern river mouth and middle Jiangsu coastal plain, and likely built a delta complex in the field of Yangtze Sand Shoal in northern East China Sea. A large sediment supply and rapid sea-level variations promoted rapid progradation of the delta onto the flat shelf. The highest sea levels during MIS 3 are estimated to have reached 25 ± 5 m below the present sea level.

Discrimination of geochemical compositions between the Changjiang and the Huanghe sediments and its application for the identification of sediment source in the Jiangsu coastal plain, China

Concentrations of 25 elements in the fine-grained fraction (<63 μm) of bottom sediments of the Changjiang and the Huanghe were determined to characterize the geochemical compositions of each riverine origin. Most of the elements, except for alkali and alkaline earth elements (Na, Ca, Sr and Ba), are highly enriched in the Changjiang sediments compared to those in the Huanghe sediments. Differences in source rocks and weathering mechanisms between the two drainage basins are the major factors controlling those compositional characteristics. The provenance index of core sediments from the northern Jiangsu coastal plain, calculated with nine elements with distinct compositional differences between both river sediments, indicates that the Changjiang had prevailed in the coastal plain sedimentation during the early stage of Holocene, while the Huanghe dominated over the area during the late Holocene. However, neither of the signatures of the modern Changjiang- and Huanghe-derived sediments is remarkable in the present-day coastal plain.

Manufacture of silicon carbide reinforced steels by spray forming

Hydrochemical analysis and environmental isotopic tracing are successfully applied to study groundwater evolution processes. Located in eastern China, the Jiangsu Coastal Plain is characterized by an extensively exploited deep groundwater system, and groundwater salinization has become the primary water environmental problem. This paper provides a case study on the use of a hydrochemical and environmental isotopic approach to assess possible mixing and evolution processes at Yoco Port, Jiangsu Province, China. Hydrochemical and isotopic patterns of deep groundwater allow one to distinguish different origins in deep water systems. HCO3– is the dominant anion in the freshwater samples, whereas Na+ and Cl− are the dominant major ions in the saline samples. According to δ18O, δ2H and 14C dating, the fresh water is derived from precipitation under a colder climate during the Glacial Maximum (Dali Glacial), while the saline groundwater is influenced by glacial-interglacial cycles during the Holocene Hypsithermal. The δ18O, δ2H and 3H data confirm that deep groundwater in some boreholes is mixed with overlying saline water. The deep groundwater reservoir can be divided into a saline water sector and a fresh water sector, and each show distinct hydrochemical and isotopic compositions. The saline groundwater found in the deep aquifer cannot be associated with present seawater intrusion. Since the Last Glacial Maximum in the Late Pleistocene, the deep groundwater flow system has evolved to its current status with the decrease in ice cover and the rising of sea level. However, the hydraulic connection is strengthened by continuous overexploitation, and deep groundwater is mixed with shallow groundwater at some points.

Holocene regression and the tidal radial sand ridge system formation in the Jiangsu coastal zone, east China

Abstract A radial tidal sand ridge system (RTSRS) spans more than 20 000 km 2 in the southwest Yellow Sea, is fan-shaped and stretches from Qianggang toward the sea. The marine RTSRS is located in a convergent–divergent tidal current field (CDTCF). Numerous drilling holes reveal an area of 3000 km 2 containing tidal sand strata in the Jiangsu coastal plain on land, adjacent to the marine RTSRS, which stretches eastward from Chengdong and is also a fan-shaped with a central angle of 130°. The tidal sand unit lies on a transgressive coastal barrier-lagoon unit with an erosional surface between them, and the latter unit is in turn lying on late Pleistocene stiff mud. The tidal sand unit is overlain by the littoral–tidal-flat unit and together they constitute the Holocene regressive succession. Paleo-current study reveals that a paleo-current pattern similar to the modern marine CDTCF was present in the Holocene sub-aerial tidal sand strata. Therefore, the sub-aerial tidal sand bodies are deduced to be an ancient RTSRS that was formed during the Holocene regression, and gradually exposed and changed into land as the Changjiang and Huanghe deltas prograded. Both sub-aerial and marine RTSRS should be formed in the same tidal depositional environment but in different development stages. Thus, the radial tidal sand ridges in southwestern Yellow Sea should have formed not during the Holocene transgression, as most previous studies have inferred, but in the process of Holocene regression. Mineralogical analyses demonstrate that the sediment source of the sub-aerial RTSRS initially came from the Changjiang and later predominantly from the Huanghe. Sea-floor erosion by tidal currents may also provide sandy material to form the RTSRS. Drilling cores and ground-penetrating profiles show that the paleo-valleys in the study area are much smaller than the present distributaries of the Changjiang River. Thus, the presumption of direct sand supply by a large river to form the RTSRS through its apical area is cannot be supported. After the sea level reached the present high stand, the Jiangsu coastline has been prograding seaward as the Changjiang Delta expanded and this progradation was accelerated when the Huanghe debouched in the study area. The nearshore part of RTSRS has been gradually changing into land while the entire RTSRS extends seawards. In the process of the development, the RTSRS apex changed from Chengdong to Qianggang. At present, the coastline is still moving seaward while the outer part of the RTSRS suffers from some erosion owing to reduction of sediment supply from both the Changjiang Delta and the abandoned Huanghe Delta.

Assessment of coastal vulnerability to environmental change in Jiangsu coastal plain

Assessment of coastal vulnerability to future environmental change has been emphasized in coastal nations or regions. The Jiangsu coastal plain, located to the north of the Yangtze River Delta in China, is most vulnerable to sea level rise and exacerbating coastal hazards. This paper develops the method of delimiting vulnerable scope and assessing coastal vulnerability through field observations and sampling and by applying remote sensing and GIS, which are suitable for great river delta and coastal plains with large area, relative complex micro-geomorphology and the protection of seawall. Applying this method, the coastal vulnerability of the Jiangsu coastal plain to relative sea level rise (approximately 50 cm up to the year 2050) and exacerbating storm surges have been assessed. The results show that, up to the year 2050, the Jiangsu coastal plain will probably lose 12.8 % of tidal flats (about 5.8x104 hm2) and 7.9 % of cultivated land (about 7.2x104 hm2). Meanwhile, 2.0 % of population, 3.8 % of original value of fixed assets, 3.2% of GDP (Gross Domestic Product), 40.3 % of salt industry and 5.8 % of aquiculture respectively will be affected due to coastal environmental change.

Prediction and prevention of the impacts of sea level rise on the Yangtze River Delta and its adjacent areas

The Yangtze River Delta region is characterized by high density of population and rapidly developing economy. There are low lying coastal plain and deltaic plain in this region. Thus, the study area could be highly vulnerable to accelerated sea level rise caused by global warming. This paper deals with the scenarios of the relative sea level rise in the early half period of the 21st century in the study area. The authors suggested that relative sea level would rise 25-50 cm by the year 2050 in the study area, of which the magnitude of relative sea level rise in the Yangtze River Delta would double the perspective worldwide average. The impacts of sea level rise include: (i) exacerbation of coastline recession in several sections and vertical erosion of tidal flat, and increase in length of eroding coastline; (ii) decrease in area of tidal flat and coastal wetland due to erosion and inundation; (iii) increase in frequency and intensity of storm surge, which would threaten the coastal protection works; (iv) reduction of drainage capacity due to backwater effect in the Lixiahe lowland and the eastern lowland of Taihu Lake region, and exacerbation of flood and waterlogging disasters; and (v) increase in salt water intrusion into the Yangtze Estuary. Comprehensive evaluation of sea level rise impacts shows that the Yangtze River Delta and eastern lowland of Taihu Lake region, especially Shanghai Municipality, belong in the district in the extreme risk category and the next is the northern bank of Hangzhou Bay, the third is the abandoned Yellow River delta, and the district at low risk includes the central part of north Jiangsu coastal plain and Lixiahe lowland.