Tidal Flat Research Articles

Spatial-temporal impacts of invasive Spartina anglica on the rates and pathways of organic carbon mineralization and resulting C-Fe-S cycles in the intertidal wetland of the Han River Estuary, Yellow Sea

To elucidate the spatial-temporal impact of invasive saltmarsh plant Spartina anglica on the biogeochemical processes in coastal wetlands, we investigated the rates and partitioning of organic carbon (Corg) mineralization in three representative benthic habitats: (1) vegetated sediments inhabited by invasive S. anglica (SA); vegetated sediments by indigenous Suaeda japonica; and (3) unvegetated mud flats. Microbial metabolic rates were greatly stimulated at the SA site during the active growing seasons of Spartina, indicating that a substantial amount of organic substrates was supplied from the high below-ground biomass of Spartina. At the SA site, sulfate reduction dominated the Corg mineralization pathways during the plant growing season, whereas iron reduction dominated during the non-growing season. Overall, due to its greater biomass and longer growing season than native Suaeda, the expansion of invasive Spartina is likely to greatly alter the Corg-Fe-S cycles and carbon storage capacity in the coastal wetlands.

The Holocene to modern Fraser River Delta, Canada: geological history, processes, deposits, natural hazards, and coastal management

The Fraser River Delta (FRD) is a large sedimentary system and home to Metro Vancouver, situated within the unceded territories of several First Nations. This review provides an overview of the geological evolution of the FRD, connecting hydrodynamic processes with sedimentary deposits across its diverse environments, from the river to the delta slope. The study emphasizes the implications of sedimentation and delta evolution for natural hazards and coastal/delta management, pinpointing knowledge gaps. Comprising four main zones—river, delta plain, tidal flats, and delta slope—the FRD is subject to several natural hazards, including subsidence, flooding, earthquakes, liquefaction, and tsunamis. The delta plain, bordering the Fraser River's distributary channels, hosts tidal marshes and flats, including both active and abandoned areas. Active tidal flats like Roberts Bank and Sturgeon Bank receive sediment directly from the Fraser River, while abandoned tidal flats, like those at Boundary Bay and Mud Bay, no longer receive sediment. The tidal flats transition into the delta slope, characterized by sand in the south and mud in the north of the Main Channel. The FRD's susceptibility to hazards necessitates protective measures, with approximately 250 km of dykes shielding the delta plain from river floods and storm surges. Subsidence amplifies the impact of rising sea levels. Earthquakes in the region can induce tsunamis, submarine slope failures, and liquefaction of delta sediments, emphasizing the importance of incorporating sedimentation patterns and delta evolution into management strategies for sustainable urban development, habitat restoration, and coastal defence initiatives.

The discovery of the church of Rungholt, a landmark for the drowned medieval landscapes of the Wadden Sea World Heritage

The UNESCO World Heritage Wadden Sea holds remains of a medieval cultural landscape shaped by interactions between man and natural forces. From the Netherlands to Denmark, human efforts of cultivating low-lying areas created a unique coastal landscape. Since the Middle Ages, storm floods widely drowned embanked cultural land and especially affected North Frisia (Germany), where once fertile marshland was permanently turned into tidal flats. One key region, the Edomsharde, was widely destroyed in 1362 AD. Medieval settlement remains still occur in the tidal flats around the island Hallig Südfall and are commonly associated with Edomsharde’s trading centre Rungholt—ever since a symbol for the region’s drowned landscapes and focus of this study. We present a first-time comprehensive reconstruction of this medieval settlement by means of new geophysical, geoarchaeological and archaeological data. Our results reveal remains of up to 64 newly found and rectified dwelling mounds, abundant drainage ditches, a seadike, and especially the discovery of Edomshardes’s main church as important landmark in this former cultural landscape. These finds together with the documented imported goods confirm a thriving society, involved in transregional trade and thereby close a significant gap in medieval history not only for North Frisia, but the entire Wadden Sea region.

Field observations on the characteristics of sand ripples on tidal flats

Ripples on tidal flats significantly influence bedform roughness and near-bed turbulence, yet their dynamics in sandy and muddy environments remain incompletely understood. While laboratory studies have elucidated the effects of mud content and extracellular polymeric substances (EPSs) on ripple formation and stability, the interactions between ripple characteristics, EPS, and mud content in natural settings are more complex and not thoroughly explored. To address this gap, we conducted field studies on sand ripples at the central Jiangsu coast, China, using high-resolution drone photogrammetry to accurately measure ripple dimensions. We performed bedload sampling at both ripple crests and troughs to analyze median grain size, mud content, and EPS concentrations. Our results show that the investigated ripple wavelengths range from 34 to 46 mm, and heights vary between 2.7 and 5.3 mm. Ripples developed near tidal creeks show pronounced asymmetry. Significantly, EPS concentrations are markedly higher at the ripple crests than at the troughs, and it follows a power-law relationship with the median grain size. These results highlight the complex intricate relationship between the ripple morphology, environmental forcing conditions, and EPS content. Our findings enrich the understanding of ripple development and the factors influencing current-dominated ripples in natural environments. This research also adds to the better prediction of the bedform roughness and quantification of the near bed sediment transport.

Dynamic evolution of tidal networks under the combined effect of de-reclamation and decrease of sediment supply

De-reclamation is a common strategy used for the restoration of tidal flats. In this study, we investigate the morphodynamic response of tidal channel networks and tidal flats after de-reclamation initiatives using the Delft3D numerical model. We find that tidal channel networks that have undergone reclamation and retreat projects have a lower drainage density (8.95 km−1) than that of channel networks that formed naturally (11.33 km−1), and the drainage efficiency of natural formed channel networks is almost three times greater than restored channel networks. These findings indicate that de-reclamation alone cannot fully erase the imprinting of the previous reclamation. We also find that the ultimate effectiveness of de-reclamation is affected by the geographical layout and unchanneled path length of the inchoate main creek system. In addition, following the implementation of de-reclamation, the immediate opening of previously enclosed areas amplifies the tidal prism, thereby intensifying tidal scouring and resulting in significant erosion, with erosion rate reaching hundreds of millimeters per day. Such losses can be remediated under sufficient sediment supply and prevented through the construction of artificial channels. However, this severe erosion may escalate under an insufficient sediment supply or a heightened tidal prism, potentially leading to permanent loss. These findings constitute an important reference for future engineering practices that support the safety and sustainability of coastal resources.

Extracting waterline and inverting tidal flats topography based on Sentinel-2 remote sensing images: A case study of the northern part of the North Jiangsu radial sand ridges

Muddy tidal flats with landforms vary widely over space and time. The evolution of tidal flats topography has had a significant impact on the region. Therefore, there is a need to develop methods for rapidly and accurately characterizing tidal flats topography. This study applied thresholding segmentation (TS), machine learning, and two image classification methods to Sentinel-2 remote sensing images to extract the instantaneous waterline of the northern part of the North Jiangsu Radial sand Ridges (NJRSR). Tidal level data at specific time intervals were obtained using the Delft3D and TPXO9 models, after which tidal flats topography inversion was conducted. As a result, varied among the different classification methods, with the K-Nearest Neighbors (KNN) algorithm producing the optimal waterline extraction. Furthermore, the accuracy of tidal level simulation was improved by employing Delft3D software and constructing a scaled-down model of the study area. Comparisons with Delft3D model simulations of tidal levels with observations at three tide gauge stations yielded accuracies of 17.5 cm, 18.5 cm and 17.9 cm, this result showed that the establishment of the tidal level model can enhance the accuracy of tidal flats Digital Elevation Model (DEM) inversion. In fact, the combined application of the KNN algorithm and Delft3D model within retrieval of tidal level provided the most accurate topographic inversion, with an average error of 0.297 m, which was reduced to 0.292 m after median filtering, and the results indicated a trend of southward erosion in the tidal flats in the study area, with a turning point roughly located in the southern part of Doulong Port. The results of this study can help improve the future monitoring of dynamic changes in intertidal wetland topography and the conservation and development of tidal flats areas.

Effects of burrowing crabs on coastal sediments and their functions: A systematic meta‐analysis

AbstractBurrowing ecosystem engineers, such as termites, crabs, marmots, and foxes, can profoundly affect the biological structure and ecosystem functions of their environments. However, the relative importance of the effects of burrowing engineers on sediments are challenging to predict and are expected to be influenced by engineer density, engineer functional traits (e.g., burrow morphology), and environmental conditions (e.g., geomorphology, vegetation presence). To develop robust hypotheses predicting the impacts of burrowing ecosystem engineers, we conducted a systematic meta‐analysis evaluating the effects of burrowing crabs on sediment properties, nutrient stocks, and ecosystem functions in soft‐sediment coastal habitats (e.g., salt marshes, mangrove forests, tidal flats). Additionally, we tested the impacts of crab burrow density, burrowing crab superfamily (a proxy for crab burrow morphology and diet), and biotic conditions (i.e., vegetation) on the effects of burrowing crab engineers on coastal sediments. Burrowing crabs rework and oxygenate sediments and accelerate rates of nutrient cycling (i.e., nitrification and CO2 flux). However, the magnitude and direction of burrowing crab effects depend on burrowing crab superfamily, the presence of vegetation, and their interaction. Crab burrow density did not consistently predict burrowing engineer effects on sediments. Future efforts need to focus on implementing rigorous manipulative experiments to assess crab ecosystem engineering effects, since methodological variation has hindered efforts to generalize their effects. Our findings suggest that crab engineering effects are predictable across environmental contexts, and understanding the context dependency of crab engineering effects may promote the management and restoration of the critical ecosystem services that are mediated by crab engineers.

Geotechnical Investigation of Exposed Intertidal Flats at the Great Bay Estuary Using Sediment Sampling and Satellite-Based Synthetic Aperture Radar

Geotechnical Investigation of Exposed Intertidal Flats at the Great Bay Estuary Using Sediment Sampling and Satellite-Based Synthetic Aperture Radar

갯벌의 보존 가치에 대한 분석

Tidal flats serve as a buffer zone between land and sea, providing a habitat and breeding ground for various intertidal and marine organisms, and play a crucial role in maintaining a healthy ecosystem by purifying various pollutants that flow from land to sea. Despite the significant value of tidal flats, research on this subject remains limited. Therefore, this study aimed to assess the value of preserving tidal flats using contingent valuation method (CVM) analysis based on survey data. Among 1,000 respondents, only 331 expressed a willingness to pay (WTP) for the conservation of tidal flats. Given the high proportion of non-paying respondents, this study utilized the spike and Turnbull models to compare estimates. The results from the Turnbull method estimated the WTP at 1,855 KRW, which was approximately half that derived from the Spike model. As the Turnbull estimate represents the lower bound of WTP, utilizing the estimate from the Spike model is deemed more appropriate. Additionally, the study differentiated between respondents willing and unwilling to visit tidal flats to derive separate WTP values for use and non-use values of tidal flat conservation. The non-use value was estimated at 1,741.5 KRW, while the use value was determined to be 4,179.2 KRW.

Empirical Orthogonal Function Analysis on Long-Term Profile Evolution of Tidal Flats along a Curved Coast in the Qiantang River Estuary, China

Abstract: Tidal flats are dynamic coastal ecosystems continually reshaped by natural processes and human activities. This study investigates the application of Empirical Orthogonal Function (EOF) analysis to the long-term profile evolution of tidal flats along the Jiansan Bend of the Qiantang River Estuary, China. By applying EOF analysis to profiles observed from 1984 to 2023, this study identifies dominant modes of variability and their spatial and temporal characteristics, offering insights into the complex sediment transport and morphological evolution processes. EOF analysis helps unravel the complex interactions between natural and anthropogenic factors shaping tidal flats, with the first three eigenfunctions accounting for over 90% of the observed variance. The first spatial eigenfunction captures the primary trend, while the subsequent two eigenfunctions reveal secondary and tertiary modes of variability. A conceptual model developed in this study elucidates the interplay between hydrodynamic forces and morphological changes, highlighting the rotation and oscillation of tidal flat profiles in response to seasonal variations in hydrological conditions. The findings emphasize the effectiveness of EOF analysis in capturing significant geomorphological processes and underscore its potential in enhancing the understanding of tidal flat dynamics, thereby informing more effective management and conservation strategies for these critical coastal environments.

Grain-size Characteristics and Net Transport Patterns of Surficial Sediments in the Day River Estuary

The Day estuary area is accreting relatively quickly, expanding the land area for Nam Dinh and Ninh Binh provinces. To understand the sediment accreting mechanism in this region, 42 surficial sediment samples were taken and analyzed for grain size to determine the rules of surficial sediment distribution and analyze the net sediment transport pattern. Research result shows that in the Day estuary area: sand is mainly dominated in the east and south, silty sand is distributed in front of the estuary and south of Con Noi, and sandy silt is distributed in the west and center of the study area. The coarsest-grained sediments are distributed in the North and South, while finer-grained sediments occupy the main area in the East and finest-grained sediments are spread out in the West of the study area. Well-sorted sediments are dominated throughout the region, covering the center and the East of the study area, showing that the hydrodynamic regime is relatively stable. Medium-sorted sediments are distributed in the West, North, and South, reflecting a less stable hydrodynamic regime. Poorly-sorted sediments at the Day estuary mouth represent the most complex hydrodynamic conditions here. Sediment tends to be transported from the southeast and west to the central area, causing a strong accretion process to create Con Noi and shallow mild tidal flats in the Day estuary area.

Tracking the Dynamics of Spartina alterniflora with WorldView-2/3 and Sentinel-1/2 Imagery in Zhangjiang Estuary, China

The invasion of Spartina alterniflora (S. alterniflora) has posed serious threats to the sustainability, quality and biodiversity of coastal wetlands. To safeguard coastal ecosystems, China has enacted large-scale S. alterniflora removal projects, which set the goal of effectively controlling S. alterniflora throughout China by 2025. The accurate monitoring of S. alterniflora with remote sensing is urgent and requisite for the scientific eradication, control and management of this invasive plant. In this study, we combined multi-temporal WorldView-2/3 (WV-2/3) and Sentinel-1/2 imagery to monitor the S. alterniflora dynamics before and after the S. alterniflora removal projects in Zhangjiang Estuary. We put forward a new method for S. alterniflora detection with eight-band WV-2/3 imagery. The proposed method first used NDVI to discriminate S. alterniflora from water, mud flats and mangroves based on Ostu thresholding and then used the red-edge, NIR1 and NIR2 bands and support vector machine (SVM) classifier to distinguish S. alterniflora from algae. Due to the contamination of frequent cloud cover and tidal inundation, the long revisit time of high-resolution satellite sensors and the short-term S. alterniflora removal projects, we combined Sentinel-1 SAR time series and Sentinel-2 optical imagery to monitor the S. alterniflora removal project status in 2023. The overall accuracies of the S. alterniflora detection results here are above 90%. Compared with the traditional SVM method, the proposed method achieved significantly higher identification accuracy. The S. alterniflora area was 115.19 hm2 in 2015, 152.40 hm2 in 2017 and 15.29 hm2 in 2023, respectively. The generated S. alterniflora maps clearly show the clonal growth of S. alterniflora in Zhangjiang Estuary from 2015 to 2017, and the large-scale S. alterniflora eradication project has achieved remarkable results with a removal rate of about 90% in the study area. With the continuous implementation of the “Special Action Plan for the Prevention and Control of Spartina alterniflora (2022–2025)” which aims to eliminate more than 90% of S. alterniflora in all provinces in China by 2025, the continual high-spatial resolution monitoring of S. alterniflora is crucial to control secondary invasion and restore coastal wetlands.

Dynamic migration and risk of cephalosporin antibiotic resistance genes: Move from pharmaceutical plants through wastewater treatment plants to coastal tidal flats sediments

The migration and dissemination of antibiotics and their corresponding antibiotic resistance genes (ARGs) from pharmaceutical plants through wastewater treatment to the environment introduce exogenous ARGs, increasing the risk of antibiotic resistance. Cephalosporin antibiotics (Ceps) are among the most widely used antibiotics with the largest market scale today, and the issue of resistance is becoming increasingly severe. In this study, a cephalosporin pharmaceutical plant was selected and metagenomic analysis was employed to investigate the dissemination patterns of cephalosporin antibiotics (Ceps) and their ARGs (CepARGs) from the pharmaceutical plant through the wastewater treatment plant to tidal flats sediments. The findings revealed a significant reduction in the total concentration of Ceps by 90.32 % from the pharmaceutical plant's Pioneer Bio Reactor (PBR) to the effluent of the wastewater treatment plant, and a notable surge of 172.13 % in the relative abundance of CepARGs. It was observed that CepARGs originating from the PBR could migrate along the dissemination chain, contributing to 60 % of the CepARGs composition in tidal flats sediments. Microorganisms play a crucial role in the migration of CepARGs, with efflux-mediated CepARGs, as an intrinsic resistance mechanism, exhibiting a higher prospensity for migration due to their presence in multiple hosts. While Class I risk CepARGs are present at the pharmaceutical and wastewater plant stages, Class I ina-CepARGs are completely removed during wastewater treatment and do not migrate to the environment. This study reveals the dynamic migration characteristics and potential risk changes regarding Ceps and CepARGs in real dissemination chains, providing new theoretical evidence for the mitigation, control, and risk prevention of CepARGs.

Dynamic behaviors of suspended sediment and chlorophyll-a in intertidal flats under episodic meteorological events

Intertidal flats are important shallow-water habitats and buffers against coastal erosion. Strong, short-lasting meteorological events, such as storms and rainfall, are the main mechanisms of transporting (in)organic materials and sediments. Two in-situ mooring systems were installed simultaneously in the tidal channel and mudflat of Jeungdo, Korea, to understand the dynamic behaviors of suspended sediment and chlorophyll-a (chl-a) under the episodic events. During fair-weather periods with a distinct tidal cycle, the sediment in the mudflat was resuspended during the flood and then advected to the tidal channel during the ebb. The maximum suspended sediment concentration (SSC) and chl-a under storm event were approximately 9 and 2 times higher than those under fair-weather periods, respectively. Under rainfall event, the maxima were approximately 7 and 1.2 times higher than fair-weather, suggesting that sediment and microphytobenthos were highest resuspended by the meteorological events. In addition, a time lag (∼ 1.5 h) between SSC and chl-a occurred in the tidal channel during ebb tide with a rainfall event. During the post-rainfall periods, the SSC and chl-a increased, showing a positive relationship with the bed shear stress, suggesting that the rainfall event could reduce sediment stabilization.

Quantifying Seepage‐Face Evaporation and Its Effects on Groundwater Flow and Solute Transport in Small‐Slope Tidal Flat

AbstractLarge‐scale seepage faces occur on tidal flats with gentle slope, which are widely distributed worldwide. Evaporation on these seepage faces, leading to salt retention and accumulation, may significantly impact the density‐dependent groundwater flow beneath the tidal flats. However, due to nonlinear complexities of the groundwater flow and solute transport on seepage faces, explicit boundary conditions and numerical models to quantify these processes are lacking. In this study, we present both mathematical and numerical models to quantify these processes. Compared to the results of our previous study, this paper shows that seepage‐face evaporation can (a) significantly increase the groundwater salinity in the upper intertidal zone, and form multiple groundwater circulation cells in the intertidal zone, (b) cause the disappearance of multiple seepage‐faces and reduce the spatial extent of seepage faces notably, (c) and intensify the groundwater and salt exchange as well as the seawater‐groundwater circulation through the intertidal zone.

Composition and Diversity Indices of the Fish Assemblage in the Tidal Mudflats of the Shatt Al-Arab Estuary in the Northwest Arabian Gulf

Ten thousand four hundred and thirty-five fish were collected from January 2021 to February 2022, belonging to 71 species distributed across 39 families and 20 orders. The study included the tidal zone of the Shatt al-Arab estuary in the northwest of the Arabian Gulf. Two methods used to collection the fishes; fixed gill nets and trowel nets. Various diversity indices, relative abundance, and richness were assessed. Several biodiversity indices were used to assess the area biologically and ecologically which Species diversity for Shannon and Simpson, species richness for Margalef and Menhinick, dominance for Berger-Parker, species similarity for Jaccard, numerical similarity for Bray – Curtis, and evenness for Peilou index. Nematalosa nasus had the highest relative abundance, which was recorded at 24.53%. However, the lowest relative abundance was observed for 20 species, with a value of 0.01% with only one individual. The Carangiformes had the highest percentage of 18.31% and the lowest percentage of 1.41 % for many orders only, with one species recorded. The Margalef index had its highest value on June 5.24 and its lowest on December 1.24. The Menhinick index had its highest value of 1.53 in October and its lowest value of 0.71 in November. The Shannon Index reached a peak of 2.69 in January 2021, and fell to 0.98 in September. The Simpson index recorded the highest value of 0.92 in January 2021 and the lowest value of 0.37 in September. The Peilou index reached its highest value of 0.965 in December, while its lowest value was 0.294 in September. The Jaccard index had its highest value of 0.667 between January 2021 and March, while its lowest value was 0.079 between December, June, and July. The highest value for the Bray-Curtis index occurred between July and August, reaching 0.644. In contrast, the lowest value observed was 0.005 between July and December.

The bimodal regime of ocean waves and winds over the continental shelf of Maranhão

This study analyzed surface waves and winds from ERA5 reanalysis dataset in the Western Equatorial Atlantic (WEA) Ocean in order to properly understand the long-term regime of oceanic waves over the Continental Shelf of Maranhão (CSMA), pointing to the changes that occur at the western and eastern sectors as the waves propagate to the coastal zone. A data validation with observational data collected in situ by the PNBOIA and PIRATA projects has been conducted. The parameters analyzed were significant wave height (Hs), peak period (Tp), mean wave direction (Dm), and the zonal (u10) and meridional (v10) components of wind at 10 m. The analysis covered a period of 43 years (1979–2023). The monthly climatology of the Hs, Tp and Dm found has revealed a semi-annual cycle in the waves pattern in the region. The wave direction variability executes a clockwise motion from northeast-east-southeast throughout a year. The annual climatology analysis reveals that 59 % of sea states in the region are characterized by swell conditions in the region, while wind-sea dominates in 41 % of cases, with seasonal variability. During the austral summer (autumn), swells prevail over wind-seas along the WEA, accounting for 77 % (84 %) of the cases. This coincides with the boreal winter, characterized by high storm activity, whose storms generate swells that traverse the ocean, reaching Maranhão's waters and resulting in the highest waves in the region (3.54 m in summer). In contrast, during the spring season, sea states are dominated by wind-sea conditions (70 %) due to the increase in southeast trade winds. The highest Hs observed from wind-sea conditions is 2.94 m. The largest contribution for the maxima Hs in the region is given by swells in the summer/autumn and by wind-seas in the winter/spring seasons, with swells propagating more energy and power to cause erosional processes on the eastern sector of Maranhão coast. Oppositely, in the western sector of the littoral, whose geomorphology is dominated by tidal flats, cheniers plains and mangroves, the Hs is small, indicating a depositional environment. The algorithm indicated that swells generated by tropical (extratropical) storms typically take approximately 3.5–4.5 (6−7) days to travel the distance to the CSMA, while in the equatorial zone, the arrival of swells at the CSMA averages between 3.5 and 7 days. In this study we demonstrated the CSMA region is dominated by a bimodal wave regime with a strong semi-annual cycle, which is driven by the tropical/extratropical storms propagating from the North Atlantic Ocean toward the study area and by trade winds variability.

Morphodynamics of meandering channels in non-vegetated monsoon-driven tidal flats in South Korea

To understand complex channel meandering dynamics and shape evolution in tidal flats, we analyzed tidal stream migration characteristics in the non-vegetated Gochang tidal flat over 9 years using Google Earth imagery. Large channels with tens of meters stream width migrated furthest, followed by creeks and small gullies with less than a meter of width. While annual migration speeds were fastest in large channels, normalizing by channel width revealed an opposite trend: small gullies migrated the fastest relative to their size, while large channels migrated the slowest. This unique pattern, compared to vegetated tidal flats, is likely driven by the interaction of three factors: (1) the non-vegetated Gochang flat's weak sediment cohesion, especially in the fine-grained upper intertidal zone; (2) strong hydraulic forces from typhoons and storms; and (3) the significant particle size gradient between upper and lower zones. The efficient reworking and re-deposition even in large channels highlight the importance of considering dynamic tidal migration as an advection term alongside bioturbation. This is crucial for sedimentological and biogeochemical studies, including tidal flat sedimentation rate calculations and carbon cycle research.

Coastal conversion alters topsoil carbon, nitrogen and phosphorus stocks and stoichiometric balances in subtropical coastal wetlands

The extensive conversion of coastal wetlands into agricultural and aquaculture areas has significant repercussions on soil nutrient balance. However, how coastal conversion specifically influences the dynamics and stoichiometry of topsoil carbon (C), nitrogen (N), and phosphorus (P) remains limited due to the considerable spatial variability and a lack of comprehensive field data. Here, we investigated the concentration and distribution of total C (TC), N (TN) and P (TP), along with their stoichiometric balance in four distinct coastal landscapes, including natural marshes and tidal flats, as well as converted agricultural croplands and ponds. The results revealed that converted croplands and ponds exhibited significantly higher concentrations of soil C, N and P, particularly in comparison to tidal flats. Furthermore, croplands and ponds have higher topsoil C stocks than tidal flats, but little difference or even lose stored C compared to marshes. Cropland soils showed considerably higher levels of available N (NH4+-N and NO3−-N) and available P compared to those in natural marshes and tidal flats. The distribution of soil TC, TN, and TP demonstrated greater spatial heterogeneity in natural marshes and tidal flats, while the converted areas were more uniform and became hotspots for N and P accumulation. Coastal conversion altered soil C:N:P stoichiometry, with cropland soils exhibiting a lower N:P ratio (2.9 ± 1.1), indicating that long-term application of N and P fertilizers could decrease the N:P ratio, as P is more retained in the soil than N. Furthermore, it was observed that the dynamics of C, N and P, as well as their stoichiometry, are closely linked to soil physicochemical properties, especially soil organic matter and texture. These findings highlight that coastal conversion and associated management practices markedly affected soil C, N and P dynamics in a representative wetland area of the subtropical regions, leading to a reshaping of their stoichiometric balances, particularly in the topsoil layer.

Response of macrobenthic communities to a Spartina alterniflora management project on tidal flats in Hangzhou Bay, China

Spartina alterniflora is one of the most invasive plants on Chinese tidal flats. To explore the responses of macrobenthic communities to the removal of S. alterniflora and the restoration of tidal flats, a survey of macrobenthic and sediment environmental factors was carried out in June 2022 in the mudflat recovery area (MRA) of tidal flats on the south bank of Hangzhou Bay, China. A proximate natural mudflat area (NMA), S. alterniflora area (SAA) and Scirpus mariqueter area (SMA) were selected for comparison with the MRA. A total of 48 macrobenthic species were identified, with 13, 28, 22 and 21species in the MRA, NMA, SAA and SMA, respectively. Cluster, multidimensional scaling (MDS) and SIMPER analysis suggested that the similarity between macrobenthic communities in the MRA and the NMA was high, whereas the similarity between macrobenthic communities in the MRA and SAA and the MRA and SMA was very low. The similarity between macrobenthic communities in the SAA and the SMA was high. ANOSIM analysis suggested that the differences between regions were greater than those within regions (R = 0.881). The sediment factors in the MRA were substantially different from those in the other three habitats, while the sediment factors in the SMA and the SAA were the most similar. Macrobenthos were mainly affected by the mean diameter of the sediment particles. After 1 year of natural recovery in the MRA, the macrobenthos approached the pre-project levels, but to ensure the effectiveness of the treatment project and prevent the recurrence of S. alterniflora, continuous monitoring should be carried out.