Tidal Flat Reclamation Research Articles

Soil biological fertility evolution in a chronosequence under long‐term rice cultivation after land reclamation in China

AbstractLand use significantly affects soil biological fertility through impacts on carbon (C) and nitrogen (N) cycling. The present study investigated the effects of long‐term rice cultivation after tidal flat reclamation on soil C and N metabolism, microbial biomass and biological fertility. Eighteen composite topsoil (0–20 cm) samples were identified in a chronosequence of coastal reclamation areas (0–700 years old) in subtropical monsoon climate zone, namely tidal flat (T0), salt marsh soil (S10) and paddy soil (P50, P100, P300 and P700). Using ANOVA analysis, mono‐exponential regression model, and multiple linear regressions, soil organic matter (SOM), total nitrogen (TN), cumulative C mineralization content (Ct) and N mineralization content (Nt), basal soil respiration (BSR) and microbial biomass C and N (MBC and MBN) in the P50‐P700 samples were significantly higher than those in the T0 and S10 samples, whereas C metabolic quotients (qCO2) in the P50‐P700 were significantly lower than those in the T0 and S10 samples. The time to steady state for SOM and TN are 357 years and 80 years, respectively; 133 and 221 years for Ct and Nt, respectively; and 318 and 183 years for MBC and MBN, respectively. Also, a soil biological fertility index (SBFI) was calculated on the basis of SOM, BSR, Ct, MBC, qCO2 and qCM. P100‐P300 samples had the highest SBFI score (28.7) and ranked in the class V (very high) of biological fertility, achieving steady‐state conditions after 146 years. SBFI was significantly positively correlated with SOM, TN, MBC, MBN, BSR, Ct and Nt, whereas it was significantly negatively correlated with pH, qCO2 and C mineralization quotient (qCM). MBC and qCM were two independent variables with considerable positive effects on SBFI. Long‐term rice cultivation could facilitate C and N accumulation and enhance biological fertility in soils via microbial activity, especially within 300 years. Our findings demonstrate that rice cultivation has the potential to enhance soil C and N accumulation. Carbon‐related SBFI is suitable for assessing soils under long‐term rice cultivation, mainly because the rice paddy field is an intensive and conservative system.

Long-term reclamation of tidal flats of Chongming Island and ecological security of Yangtze estuary, China

Long-term reclamation of tidal flats of Chongming Island and ecological security of Yangtze estuary, China

Changes of microbial residues over century-long soil development after tidal flat reclamation in eastern China

Growing evidence indicates that microbial residue carbon (MRC) accounted for a substantial proportion of soil organic carbon (SOC) pool. SOC tends to increase rapidly with the improvement of soil physicochemical and biological properties during the early stage of soil development. However, the changes of MRC and its contribution to SOC accumulation along with soil development are still unclear. Here, using amino sugars as biomarkers, we explored the changes of MRC with reclamation age (0, 11, 37, 102, and 200 years) in the soil profile (0–10, 10–20, 20–40, and 40–60 cm) after tidal flat reclamation in eastern China. Soil SOC and MRC slightly decreased over the first 11 years and then gradually increased with reclamation age. The more rapid increase in MRC than SOC led to the contribution of MRC to SOC increasing with reclamation age. The proportion of MRC in SOC increased from 6.74 to 13.25 % in the tidal flat sediment to 13.17–39.22 % in the 102 years old reclaimed soil. The MRC accrual mainly depended on the increase in fungal residues. Soil MRC and its contribution to SOC decreased with soil depth, and the vertical difference increased with reclamation age. The temporal accumulation of soil MRC was driven primarily by soil nitrogen and salinity, while the vertical distribution of MRC in the soil profile was controlled mainly by SOC and soil pH. Our work highlighted the increasing role of microbial C sequestration in SOC accumulation during early soil development after tidal flat reclamation. Further studies are needed to investigate whether the temporal and vertical changes of MRC revealed in this study also widely occur under other soil-forming conditions.

Spatial distribution of antibiotics and antibiotic resistance genes in tidal flat reclamation areas in China.

Tidal flat areas are important resources for land development and are becoming antibiotic resistance receivers that trigger major health concerns. The spatial distributions of forty-nine antibiotics, nine antibiotic resistance genes (ARGs), one mobile gene element (MGE) gene, and nine available metals in the soils and sediments along the coastlines of the Yellow Sea in China were quantified. Hierarchical linear model analysis was used to explore relationships between the antibiotics and ARGs across multiple effects resulting from human activities and environmental factors. Fish farm sediments and farmland soils showed high levels of quinolones (QNs) (maximum 637ng·g-1), sulfonamides (SAs) (maximum 221ng·g-1), and corresponding ARGs. Significant positive correlations (P from 5.47 × 10-14 to 0.0487) were observed between the antibiotics (QNs, SAs, and chlortetracycline) and their corresponding ARGs (qnrA, qnrD, aac(6')-Ib-cr, dfrA, sul2, and tetA), indicating the selective pressure from antibiotics in soils and sediments. Nine available metals had positive correlations with at least one ARG, indicating heavy metal pollution could enhance the ARGs. Sheep and poultry husbandry and marine aquaculture contribute the most to the antibiotic resistance in the coastlines. In conclusion, antibiotic pollutions have promoting effects at sub-inhibitory concentrations and more attention should be given to inhibit the enrichment of ARGs during tidal flat reclamation processes. The study also suggests the induction effects from metal pollutions, MGE spread, and the antibiotic pollutions from the usage in livestock and aquaculture.

Effects of stepwise tidal flat reclamation on tidal evolution in the East China and Yellow Sea

Abstract Because many coastal developments have been continuously occurred in the Yellow and the East China Sea, it is necessary to analyze the effect of persistent topographic change. This study simulated the tidal change in response to stepwise tidal flat reclamation in East China and the Yellow Sea using the MOdelo HIDrodinâmico (MOHID) ocean model. Based on previous studies and historical coastal information maps, we conducted several numerical experiments with reliable coastal topography changes around two areas (Jiangsu Shoalwater and Gyeonggi Bay) from 1990 to 1994 when the most active development took place. The results show that, unlike other components (S2, O1, and K1), the simulated amplitude of the M2 constituent significantly increased with the disappearance of the tidal flat in the Yellow Sea. At the same time, it decreased in the East China Sea. These results are consistent with the quantile regression analysis using observational data. We also found an accumulating effect of tidal energy flux when the reclamation continued, which does not appear in the previous studies. These results indicate persistent man-made tidal flat reclamation in a specific area can cause more remarkable regional tidal changes through tidal energy redistribution and modification.

A quantitative analysis of the impact of reclamation on the stability of coastal wetlands

The ecological stability of coastal areas is seriously affected by tidal flat reclamation. Understanding the spatial characteristics of the impact of reclamation on stability, as well as the contribution of different use types of reclamation to stability change, is important for mitigating the negative effects of reclamation. In this study, multi-source and multi-temporal remote sensing images were combined to quantitatively analyze the relationship between reclamation and stability in different regions of the coastal area in Jiangsu Province, as well as the relative contribution of different use types of reclamation to the stability change. The results showed that: Different forms of statistical relationships between reclamation and stability existed in reclaimed area and non-reclaimed area, respectively, while a significant quadratic function relationship existed in the whole affected area, and the stability index decreased first and then increased with the increase of reclamation amount, with a threshold of 1243 km2; In different buffer zones within the non-reclaimed area, the impact intensity of reclamation showed spatial decay characteristics; The use type of reclamation that has the greatest impact on stability in the reclaimed area is aquaculture land, while in the non-reclaimed area it is arable land. In addition, aquaculture land, arable land and hydraulic engineering land have negative effects on stability, while salt industry land has positive effects.

The colonizers, the developmental state, and uneven geography of development: Reclamation of South Korea's tidal flats, 1900s-1980s

South Korea's tidal flats, called getbol, are muddy and grayish coastal wetlands under the tidal influence that constitute the predominant landform of South Korea's west and southwest coasts. Today, getbol is appreciated for its biological and geological diversity, for which it recently earned UNESCO's World Heritage status. Yet, throughout the 20th century, more than 50% of getbol areas were lost due to coastal reclamation, a civil engineering practice of enclosing and filling in getbol. This paper closely examines the history of getbol from the 1900s to the 1980s. While being messy and complex, the history shows a tendency for reclamation to have evolved from small to large in terms of scale and from private-led to state-led initiatives. In popular imaginations, the reclamation of getbol is thought to have been driven top-down by governing authorities, particularly by the “developmental state” that roughly governed from the 1960s through the 1980s. While this explanation aligns with the general trend, this paper highlights that the state did not act solely upon its own will but responded to the desires of those that the state had to satisfy to gain political legitimacy. Ultimately, within the context of South Korea's uneven geography of development, this paper argues that the reclamation of getbol transitioned from a project for the entire nation to a project for the rural populations and the agricultural sector, which lagged behind the country's tantalizing economic growth.

Reclamation of tidal flats to paddy soils reshuffles the soil microbiomes along a 53-year reclamation chronosequence: Evidence from assembly processes, co-occurrence patterns and multifunctionality

Coastal soil microbiomes play a key role in coastal ecosystem functioning and are intensely threatened by land reclamation. However, the impacts of coastal reclamation on soil microbial communities, particularly on their assembly processes, co-occurrence patterns, and the multiple soil functions they support, remain poorly understood. This impedes our capability to comprehensively evaluate the impacts of coastal reclamation on soil microbiomes and to restore coastal ecosystem functions degraded by reclamation. Here, we investigated the temporal dynamics of bacterial and fungal communities, community assembly processes, co-occurrence patterns, and ecosystem multifunctionality along a 53-year chronosequence of paddy soil following reclamation from tidal flats. Reclamation of tidal flats to paddy soils resulted in decreased β-diversity, increased homogeneous selection, and decreased network complexity and robustness of both bacterial and fungal communities, but caused contrasting α-diversity response patterns of them. Reclamation of tidal flats to paddy soils also decreased the multifunctionality of coastal ecosystems, which was largely associated with the fungal network complexity and α-diversity. Collectively, this work demonstrates that coastal reclamation strongly reshaped the soil microbiomes at the level of assembly mechanisms, interaction patterns, and functionality level, and highlights that soil fungal community complexity should be considered as a key factor in restoring coastal ecosystem functions deteriorated by land reclamation.

Evaluation of the Stability of Muddy Coastline Based on Satellite Imagery: A Case Study in the Central Coasts of Jiangsu, China

Monitoring the coastline dynamic can provide the basis for the balance of sediment erosion and deposition. The evaluation of coastal stability is beneficial to decision makers for the rational development and ecological conservation of coastal resources. The present study first collected 61 scenes of remote sensing images and extracted the multi-temporal coastlines from the years 1990–2020 in Jiangsu Province, China using an improved waterline method. Given the characteristics of gentle slopes of our study area, we modified the coastlines using actual tidal level data to avoid the influence from different tidal regimes. Finally, the coastal stability analysis was conducted on the central coast of Jiangsu, which experiences frequent changes in erosion and siltation. The results showed that the coastline has changed significantly; the natural coastline decreased by 116 km, while the artificial coastline increased by 108 km. the area of tidal flats decreased by 1152 km2, and the average width of the tidal flats decreased from 8.83 km to 3.55 km. In general, the coastline advanced seawards for many years, mainly due to sediment siltation and tidal flat reclamation, with annual average rates of siltation and reclamation of 9.67 km/a and 40.75 km/a, respectively. The node of siltation and erosion migrated 1.8 km southwards, moving from the Sheyang Estuary to the Doulong Port. The coastal stability gradually decreased from north to south, by values of 88.5 km (40%) for stable coast and 63.97 km (28.9%) for extremely unstable coast. The most unstable coast came from frequent reclamation areas. The method in this study is expected to provide a reference for evaluating the stability of typical muddy coasts, and our results can provide a basis for the sustainable development, utilization, and protection of coastal areas.

Positive Feedback Between the Tidal Flat Variations and Sediment Dynamics: An Example Study in the Macro‐Tidal Turbid Hangzhou Bay

AbstractTidal flat variations (curvature) in macro‐tidal turbid bays highly correlate with sediment dynamics. Interactions between tidal flats and sediment dynamics in macro‐tidal turbid estuaries, like Hangzhou Bay, China, have been studied through a fully validated 3D sediment model by considering high‐turbidity, flocculation, and water‐sediment density coupling. Numerical results show that the circulation and sediment flux in the curvature of Andong tidal flat have similar magnitudes in the along‐estuarine and lateral directions, demonstrating the important impact of the geometry on hydrodynamics and sediment transport processes. Sediment moves toward the southern/northern bank near the bottom/surface level in curvature. Tidally averaged net sediment flux is southward in the curvature. Tidal flat reclamation changes the curvature of the tidal channel, and modulates the circulation and sediment transport, and then feeds back to the tidal flat evolution subsequently. Bottom friction, nonlinear advection, and centrifugal force are dominant forces for inducing the lateral circulation, followed by the Coriolis force and sediment‐induced baroclinic process. Lateral circulation combined with the suspended sediment concentration (SSC) profile controls the distribution of instantaneous and tidally averaged net sediment fluxes in the curvature. The sediment flux positively correlates with the curvature of channel bends. The increased curvature of channel bends enhances the southward sediment fluxes mainly by increasing the effects of the centrifugal force, nonlinear advection, and Coriolis force on the lateral circulation and SSC. This study revealed a two‐way feedback system between tidal flat and sediment dynamics, which contributes to the impact of anthropogenic activities on geomorphological evolution of similar estuaries worldwide.

Relative contribution of the presence of an estuarine dam and land reclamation to sediment dynamics of the Nakdong Estuary

The Nakdong Estuary of Korea is a dramatic example of an urban estuary that has been heavily developed with the installation of two estuarine dams and approximately 17 km2 of tidal flat reclamation. This study aims to understand the relative contribution of the different physical alterations by implementing four model simulations of the COAWST modeling system: (1) present condition, (2) pre-estuarine dam construction, (3) pre-tidal flat reclamation, (4) both pre-estuarine dam construction and pre-reclamation. In Cases 2 and 4, the model grid was modified to extend the Nakdong estuary upriver about 60 km and remove the estuarine dam. In Cases 3 and 4, the model grid was modified to restore the reclaimed tidal flats. All simulations shared the same initial conditions, boundary conditions, and forcing. Then, the simulation results for current velocity, suspended sediment concentration (SSC), and deposition were used to estimate the relative contribution of each alteration. The results showed that the annual, depth-averaged currents for the pre-estuarine dam (Case 2) were 80% faster than the present condition but were 10% slower for Case 3 (no land reclamation case). Likewise, the depth-averaged SSC was higher by about 25 mg/L in the estuary for Case 2, but it was reduced by about 9 mg/L for Case 3. The increase of velocity and SSC for Case 2 resulted from the removal of the estuarine dam, which changed both the tidal properties (tidal amplitude was reduced by about 40 cm) and estuarine circulation (factor of 5 reductions in the vertical salinity gradient), while the decrease for Case 3 was induced by the reduction in sediment accommodation space (15% of water volume) without a change in the circulation. These results also revealed that the estuarine dam enhanced deposition more than the land reclamation that showed very little change. The changes in current velocity, SSC, and deposition for Case 4 (no dam/reclamation) were very similar to Case 2. Overall, this study suggests that the influence of the estuarine dam was larger than that of the land reclamation in the altered Nakdong Estuary. Moreover, the combination of estuarine alterations acted to enhance the effects. These findings can serve as analogs that can be applied to other estuaries where various human alterations have occurred.

Hydrodynamic interactions between tide and runoff in the Luanhe Estuary in Bohai Sea, China: From aquaculture reclamation to restoration

Tidal flat reclamation causes a series of negative consequences for the coast-estuary hydrodynamics and environment. This might lead to implementing the restoration of the reclaimed areas. However, the restoration induced hydrodynamics changes have not been comprehensively understood in estuaries. In this study, the hydrodynamic interactions between tide and runoff are investigated using a numerical modelling of the Luanhe River Estuary, China, a typical micro-tidal estuary just experienced the restoration from the densely covered reclamations. The focus of this study is on the changes of the tidal field, characteristics of tidal prism and asymmetry and evaluation of flood risk. The results indicate that the restoration has significantly decreased the flow velocity by as much as 60% in the estuarine river during flood season. In dry season, the interaction between runoff and tide will be enhanced with larger tidal velocity, longer tide intrusion and very tiny area with static water due to the restoration. The tidal prism has been significantly increased by more than twice in the dry season owing to the both enhancements in intrusion velocity and rising duration of the flooding tide. Also, the restoration has effectively dropped the flood water level and slow down current flow speed in the river channel. In conclusion, the restoration project is of great significance to reduce storm surge risk and to improve water quality. The restoration project provides an effective reference for the spatial arrangement of the aquaculture reclamation and primitive tidal flat, which is conducive to the efficient and coordinated utilization of coastal zones.

Impacts of tidal flat reclamation on suspended sediment dynamics in the tidal-dominated Wenzhou Coast, China

Reclamation of tidal flats is one of the engineering measures of expanding land area and developing the economy in coastal areas; however, this process disturbs the natural processes of the tidal flat system. Taking the flood-tidal dominant Oufei tidal flat at the Wenzhou coast as a study area, the influences of tidal flat reclamation on tidal and suspended sediment dynamics were comprehensively investigated via numerical modeling. Before the reclamation, the Eulerian residual current flows alongshore and the residual sediment transport on-shore in the tidal flat area. The reclamation reduces the tidal flat area, shifting the M4 co-phase line toward the coast and squeezing the flood-dominated area. Consequently, the tidal current is weakened and the suspended sediment concentration (SSC) is reduced, but the residual sediment transport change insignificantly. The residual sediment transport in the Feiyunjiang Estuary is controlled by the tidal pumping effect. The upper estuary shows a net sediment transport landward, while a seaward transport is observed in the lower estuary, which further splits into two circulation outside the estuary. The south Oufei dike construction interferes the northern sediment circulation, resulting in the alteration of local SSC and enhancing landward sediment transport inside the estuary. The methodology and understandings arising from this study could be a good reference for the analysis of suspended sediment transport under tidal flat reclamation effects at other sites.

Tracking annual changes in the distribution and composition of saltmarsh vegetation on the Jiangsu coast of China using Landsat time series–based phenological parameters

Saltmarshes provide among the most valuable ecosystem services but have undergone continuous modification under the combined pressures of climate change and anthropogenic disturbance. Dynamic monitoring of the distribution and composition of saltmarsh vegetation is an urgent need for understanding the balance of saltmarshes. Previous studies have examined the possibility of identifying the plant species of saltmarshes using Land Surface Phenology (LSP). However, balancing species identification with the timespan of the monitoring remains challenging, given that the available observations are limited by the frequent occurrence of cloudy weather and periodic tidal fluctuations in coastal areas. To overcome the difficulty, we first filtered out observations contaminated by cloud cover and tidal flooding, then proposed an intra-annual time-series model by incorporating inter-annual observations using the inter-calibrated Landsat observations, finally classified the plant species of saltmarshes using phenological parameters derived from the intra-annual time-series model. The annual changes of the three dominant plant species—Spartina alterniflora (S. alterniflora), Suaeda salsa (S. salsa), and Phragmites australis (P. australis) during 2000–2020 in Jiangsu Province, the most abundant salt marsh area of China, were tracked. The results demonstrate the following: (i) The intrinsic phenological differences among the plant species (∼32 days between S. alterniflora and P. australis) are greater than the latitudinal and temporal phenological variations (9–24 days). Large-scale and long-term classification mapping using LSP was thus feasible. (ii) The annual classification maps achieved a favorable performance with an average overall accuracy of 84.8% with minor fluctuations of 5.5%. Sufficient available observations for the spring and autumn seasons (R2 = 0.78, p < 0.05) and for locations far from the sea (>240 m) were the reasons for this good performance. (iii) The saltmarsh vegetation was resilient to tidal flat reclamation on the Jiangsu coast, as indicated by a slight increase in the area from 300.30 to 336.38 km2. However, this was concentrated within the Nature Reserve (38.3%), with the increasing dominance of two species: S. alterniflora (49.6%) and P. australis (42.7%). Special conservation measures are needed for S. salsa to prevent its continuing decrease and possible future disappearance.

Effects of tidal flat reclamation on the stability of coastal wetland ecosystem services: A case study in Jiangsu Coast, China

Tidal flats have great potential to expand human living space and provide abundant resources. However, large-scale reclamation and development activities have had profound impacts on regional ecosystems, and it is important to grasp the comprehensive characteristics of the effects from a macro perspective. We selected the coastal area Jiangsu, China, as a typical area, and investigated the impact of reclamation on the coastal wetland system from the perspective of ecosystem services stability. The optimal equilibrium state was used as a benchmark and a stability deviation index (SDI) of ecosystem services was constructed by clarifying the connotation of stability. The stable state and evolution characteristics of ecosystems in different areas (coastal administrative areas, tidal flat areas, and Yancheng National Nature Reserve (YNNR)) were screened and evaluated. Based on the SDI, an overall ecological impact assessment system was developed, and the impact of tidal flat reclamation on ecological stability and its cumulative effects were quantified. The results showed that in the past 40 years, the overall ecological stability of Jiangsu coastal area was “Basically Stable (II)”, while that of the YNNR was “Weakly Stable (III)”. The impact of reclamation on the ecosystem stability of the coastal tidal flat area was significant, with a contribution rate of 73.5 %, and the threshold of stability transition in this area was reached when the reclamation amount was 1251.33 km2. The extent to which reclamation explained the stability variation in the core zone, buffer zone, and experimental zone of YNNR gradually decreased, indicating that the impact of reclamation was greater when strong protection measures were in place. The southern region will reach the maximum threshold of the cumulative effect of instability in 2072. This study provides ideas for the analysis of the comprehensive impact of reclamation on coastal wetland ecosystems, and can provide guidance for the efficient utilization and protection of tidal flats.

Biochar Effects Coastal Saline Soil and Improves Crop Yields in a Maize-Barley Rotation System in the Tidal Flat Reclamation Zone, China

The summer maize-winter barley (or wheat) rotation system is a conventional farming method in coastal areas of east China. However, researchers have paid little attention to the increasing soil degradation after successive crop rotation in coastal saline agriculture. In the current study, a two-year field experiment was conducted to investigate the changes in soil physio-chemical properties and crop grain yields under the maize-barley rotation system. Wheat straw derived biochar (BC) was applied to topsoil (0~20 cm) at four different rates (0, 7.5, 15 and 30 Mg ha−1) before summer maize cultivation, and no biochar was added in the cultivation of the winter barley. Bulk density (BD), water holding capacity (WHC), water stable aggregate (WSA), soil electrical conductivity (EC), pH (1:5 water w/v) and soil organic carbon (SOC), at the harvesting time of maize and barley, were analyzed. The application of biochar increased WHC and macro-aggregate (&gt;2 mm) content after barley harvest. Soil EC was mainly affected by the rain during maize cultivation and increased only slightly under BC treatments. However, no difference in EC was found among all treatments after barley harvest. The application of BC at 30 Mg ha−1 increased the maize yield by 66% but produced no difference in the barley yield. We concluded that biochar could be an effective option to mitigate soil degradation and improve crop productivity in coastal saline agriculture.

The Hwaseong Wetlands Reclamation Area and Tidal Flats, Republic of Korea: A Case of Waterbird Conservation in the Yellow Sea

The reclamation of tidal flats is implicated in the declines of a large number of migratory waterbird species along the East Asia-Australasian Flyway, and has resulted in the assessment of Yellow Sea tidal flats as an Endangered habitat by the IUCN. Created in their present form by large-scale reclamation, the Hwaseong Wetlands on the Yellow Sea coast of the Republic of Korea are comprised of tidal flats, a large reclamation lake, and extensive areas of rice-fields and fallow land. As part of preparation for increased protections for these wetlands, we conducted bird surveys between late June 2020 and mid-June 2021. During this period, we recorded more than 150,000 waterbirds in the wetland and concentrations of 1% or more of 25 populations of waterbird. We also recorded a total of 16 globally threatened wetland species. As at many other coastal wetlands in the Yellow Sea, tidal flat obligate waterbird species used the tidal flats for foraging; and roosted in artificial wetlands which had been created through the reclamation process. The extensive areas of rice-field and other freshwater habitats in the Hwaseong Wetlands were also internationally important in their own right, supporting globally threatened amphibians and internationally important concentrations of foraging geese and floodplain-associated waterbird species. The movements of waterbirds between foraging and roosting areas we recorded make clear that conservation of the site’s biodiversity either as a Ramsar site or within a serial World Heritage Property would require protection of all the contiguous tidal flats and also of the most biodiverse rice-field and freshwater wetland areas. As elsewhere in the coastal zone of the Republic of Korea, this would first require the support of local stakeholders and also a reduction in jurisdictional issues between various local and national decision-making bodies.

Monitoring the Invasive Plant Spartina alterniflora in Jiangsu Coastal Wetland Using MRCNN and Long-Time Series Landsat Data

Jiangsu coastal wetland has the largest area of the invasive plant, Spartina alterniflora (S. alterniflora), in China. S. alterniflora has been present in the wetland for nearly 40 years and poses a substantial threat to the safety of coastal wetland ecosystems. There is an urgent need to control the distribution of S. alterniflora. The biological characteristics of the invasion process of S. alterniflora contribute to its multi-scale distribution. However, the current classification methods do not deal successfully with multi-scale problems, and it is also difficult to perform high-precision land cover classification on multi-temporal remote sensing images. In this study, based on Landsat data from 1990 to 2020, a new deep learning multi-scale residual convolutional neural network (MRCNN) model was developed to identify S. alterniflora. In this method, features at different scales are extracted and concatenated to obtain multi-scale information, and residual connections are introduced to ensure gradient propagation. A multi-year data unified training method was adopted to improve the temporal scalability of the MRCNN. The MRCNN model was able to identify the annual S. alterniflora distribution more accurately, overcame the disadvantage that traditional CNNs can only extract feature information at a single scale, and offered significant advantages in spatial characterization. A thematic map of S. alterniflora distribution was obtained. Since it was introduced in 1982, the distribution of S. alterniflora has expanded to approximately 17,400 ha. In Jiangsu, the expansion process of S. alterniflora over time was divided into three stages: the growth period (1982–1994), the outbreak period (1995–2004), and the plateau period (2005–2020). The spatial expansion direction was mainly parallel and perpendicular to the coastline. The hydrodynamic conditions and tidal flat environment on the coast of Jiangsu Province are suitable for the growth of S. alterniflora. Reclamation of tidal flats is the main factor affecting the expansion of S. alterniflora.

The Effects of Tidal Flat Reclamation on the Stability of the Coastal Area in the Jiangsu Province, China, from the Perspective of Landscape Structure

As one of the most important wetland systems, coastal wetlands play an important role in conserving water, regulating the climate and protecting biodiversity. However, due to large-scale and long-term tidal flat reclamations, the landscape structure and function of the coastal wetlands have been greatly affected. Therefore, it is necessary to understand the spatio-temporal characteristics of the impact of tidal flat reclamation on regional ecology and to quantitatively assess the relationships between them. In this study based on long-term, multiperiod remote sensing data, the main spatio-temporal variation characteristics of stability, and the relationship between stability and tidal flat reclamation were analyzed with regard to the influence scope of tidal flat reclamation. The results showed that a substantial decrease in natural wetlands in 1980, mainly caused by tidal flat reclamation, was discovered in the Jiangsu coastal area, and the influence scope of tidal flat reclamation on regional landscape ecology was roughly 30 km. In the affected area, the overall stability had a tendency to improve, but the stability change characteristics between reclamation area and non-reclamation area varied greatly. Especially in the reclamation area, the stability of construction wetlands and non-wetlands deteriorated. Spatially, the stability outside the reclamation area had the characteristics of first deteriorating and then improving as the distance from the reclamation area increased. Under the influence of tidal flat reclamation, the influence of different use types of TFR on stability was not completely consistent, and the influence of the same uses type of tidal flat reclamation on different landscapes was also different.

Quantitative analysis of microplastics in coastal tidal-flat reclamation in Dongtai, China

Quantitative analysis of microplastics in coastal tidal-flat reclamation in Dongtai, China