Coastal Wetland Ecosystems Research Articles

Responses of Soil Microbiota to Different Control Methods of the Spartina alterniflora in the Yellow River Delta.

Spartina alterniflora invasion has negative effects on the structure and functioning of coastal wetland ecosystems. Therefore, many methods for controlling S. alterniflora invasion have been developed. S. alterniflora control methods can affect plant community, which results in changes in microbial communities and subsequent changes in soil ecological processes. However, the effects of controlling S. alterniflora on soil microbial communities remain poorly understood. We aimed to examine the responses of bacterial and fungal communities to invasion control methods (cutting plus tilling treatment: CT; mechanical rolling treatment: MR). Soil bacterial and fungal community diversity and composition structure were assessed using high-throughput sequencing technology. The findings of the study showed that bacterial diversity and richness in the CT treatment reduced substantially, but fungal diversity and richness did not show any remarkable change. Bacterial and fungal diversity and richness in the MR treatment were not affected considerably. In addition, the two control methods significantly changed the soil microbial community structure. The relative abundance of bacteria negatively associated with nutrient cycling increased considerably in the CT treatment. The considerable increases in the relative abundance of certain bacterial taxa in the MR treatment may promote soil nutrient cycling. Compared with mechanical rolling, soil bacterial community diversity and structure were more sensitive to cutting plus tilling.

Spatiotemporal Change Detection of Coastal Wetlands Using Multi-Band SAR Coherence and Synergetic Classification

Synthetic aperture radar (SAR) signal can penetrate clouds and some vegetation canopies in all weather, and therefore, provides an important measurement tool for change detection and sustainable development of coastal wetland environments and ecosystems. However, there are a few quantitative estimations about the spatiotemporal coherence change with multi-band SAR images in complex coastal wetland ecosystems of the Yellow River Delta (YRD). In this study, C-band Sentinel-1 and L-band ALOS-2 PALSAR data were used to detect the spatiotemporal distribution and change pattern of interferometric coherence in the coastal wetlands of the YRD. The results show that the temporal baseline has a greater impact on the interferometric coherence than the perpendicular baseline, especially for short wavelength C-band SAR. Furthermore, the OTSU algorithm was proven to be able to distinguish the changing regions. The coherence mean and standard deviation values of different land cover types varied significantly in different seasons, while the minimum and maximum coherence changes occurred in February and August, respectively. In addition, considering three classical machine learning algorithms, namely naive Bayes (NB), random forest (RF), and multilayer perceptron (MLP), we proposed a method of synergetic classification with SAR coherence, backscatter intensity, and optical images for coastal wetland classification. The multilayer perceptron algorithm performs the best in synergetic classification with an overall accuracy of 98.3%, which is superior to a single data source or the other two algorithms. In this article, we provide an alternative cost-effective method for coastal wetland change detection, which contributes to more accurate dynamic land cover classification and to an understanding of the response mechanism of land features to climate change and human activities.

Assessment of the acidification risk of the acid sulfate soil materials in a tropical coastal peat bog:Muthurajawela Marsh, Sri Lanka

Coastal regions in tropical countries encompass a diverse set of highly productive ecosystems with underlying acid sulfate (AS) soil materials. Muthurajawela Marsh is a tropical, saline, peat bog on the western coast of Sri Lanka and is known to contain AS soil materials. It is a critically important coastal wetland ecosystem and provides a multitude of benefits and services to the surrounding environment and the people in the area. At present, the AS soil materials in the marsh are at risk of exposure due to development activities in the surrounding areas. In this study, net acidity (NA) was quantified using an acid base accounting approach which includes retained acidity (RA) in addition to actual and potential sulfidic acidity (AA and PSA). The NA and the other soil characteristics were investigated in three soil profiles down to 1.5 m, along a north–south transect. All sites contained hypersulfidic soil materials as confirmed by field pH (pHF) > 4, field oxidation pH (pHFOX) < 4 and sulfide content > 0.01%. Net acidity values ranged from 23 to 4000 mol H+ t-1which was above the recommended management requirement value for peat and medium clay soils (i.e. 18 and 36 mol H+ t−1). At the northern site (S1), PSA was the main contributor to the NA, indicating future risk if the site were to become exposed to air. Both AA and RA were major contributing fractions at the middle (S2) and southern (S3) sites, with a possible imminent acidity discharge. All sites lack inherent buffering capacity, consequently, acidity can be released from the oxidation of the AS soil materials leading to the potential impact on the marsh ecosystem. The findings of this study indicate that human activities should be carefully managed to minimize the hazards that can occur due to exposing AS soils in the marsh.

Distribution and disturbance dynamics of habitats suitable for Suaeda salsa

Suaeda salsa, as the last biological barrier of coastal wetlands from land to sea, is one of the best nature-based restoration solution for shoreline stabilization and soil improvement in coastal wetlands. The quality of habitat determines the potential scope of wetland ecological restoration. To enlarge the Suaeda salsa area and to prevent the erosion and degradation of coastal wetland shorelines, we assessed the suitability of habitats for Suaeda salsa growth and identified the causes of encroachment into areas suitable for Suaeda salsa growth. Assessing the habitat suitability of the community and its disturbance status can not only effectively determine the suitable areas for Suaeda salsa ecological restoration, but also can propose targeted solutions according to the interference factors. Moreover, this way can greatly improve the survival rate and coverage area of Suaeda salsa restoration, reduce unnecessary input and loss, enhance the ability to resist coastal wetland shoreline erosion and degradation, and maintain the stability and integrity of the coastal wetland ecosystem. In this study, based on the data of 180 sampling points in the Liaohe estuary wetland, habitat suitability was identified, and the MaxEnt model (habitat suitability model) was used to analyze the suitable distribution area. The interannual changes in Suaeda salsa and reclamation activities in the Liaohe estuary wetland during the past 30 years were extracted from Landsat remote sensing images, and the temporal and spatial dynamic relationship between the distribution of Suaeda salsa and reclamation was analyzed. The dominant factors affecting the distribution of Suaeda salsa were water salinity as well as soil Cd and Zn levels, with influence weights of 49.1%, 28.9%, and 18.0%, respectively, and a total weight of 96%. Compared with the existing 596 hm2 of Suaeda salsa vegetation in the Liaohe estuary wetland, the area highly suitable for growth was 12,306 hm2, whereas the area with medium suitability was 12,100 hm2. Reclamation and aquaculture areas accounted for 33.31% of the highly suitable area and were the main reasons for habitat fragmentation. The study explained the reasons for the difficulty of ecological restoration of Suaeda salsa due to unsuitable habitat quality, and revealed a strong conflict between coastal reclamation and environmental protection, suggesting that the protection of coastal wetlands should consider changes in industrial model strategy. The restoration, reconstruction, and sustainable management of Suaeda salsa communities can be achieved by reducing the proportion of reclamation areas. This study improves the ecological restoration theory of degraded wetlands and provides a theoretical basis for coastal wetland protection and nature-based restoration programs.

Assessing Coastal Reclamation Success in the East China Coast by Using Plant Species Composition

Quantitative analysis of the species composition and succession law of a plant community in a coastal reclamation area is of great significance for revealing the community construction and species coexistence mechanisms, and provides a basis for the rational use and conservation in coastal reclamation areas. Through the investigation of natural plant communities in Dongtai reclamation area and the adjacent national nature reserves in Jiangsu Province, eastern China, the composition and succession of plant communities were studied. A quantitative method was explored to analyze the process of plant succession and its representative species. The results showed that (1) A total of 65 species were found in the vegetation survey. These belonged to 26 families and 61 genera, and Poaceae is the most common plant species. The plant communities in the unreclaimed areas were mainly composed of Poaceae and Cyperaceae. The plant species increased after reclamation, which were mainly composed of Poaceae and Asteraceae; (2) The plant coverage greatly reduced after three years of reclamation, from 80% of the tidal flat to 37.34%, then gradually increased, and remained generally between 50% and 70%; (3) The above-ground biomass of the plant community was sharply reduced after reclamation, from 1.823 kg/m2 in the tidal flat to 0.321 kg/m2 in three years of reclamation, and then maintained at 0.11~0.27 kg/m2; (4)The species succession process of the plant community in the coastal wetland ecosystem that was affected by the reclamation activities transformed from a halophyte community that was dominated by a salt marsh plant community (Suaeda salsa, Spartina alterniflora, Scirpus mariqueter, and Phragmites australis) to a mesophyte plant community that was constructed with pioneer species such as Setaria viridis, Eleusine indica, etc., and eventually succeeded to a xerophyte plant community that was dominated by Humulus scandens and Cyperus difformis, etc. Reclamation activities have a profound impact on the characteristics and succession rules of natural vegetation communities along coastal wetland ecosystems. The period of seven years is presumed to be the tipping point in the succession of the plant community in coastal reclamation areas. The results of this study can provide a basis and reference for ecological protection and restoration in coastal reclamation areas.

Effects of Salinity and Oil Contamination on the Soil Seed Banks of Three Dominant Vegetation Communities in the Coastal Wetland of the Yellow River Delta

In view of the important role of vegetation in the integrity of structures and functions of coastal wetland ecosystems, the restoration of degraded coastal wetland vegetation has attracted increased attention. In this paper, the newborn coastal wetland in the Yellow River Delta (YRD) of China was selected to research the effect of salinity and oil exploitation on the germination of soil seed banks of three dominant vegetation communities. The germination experiment with three concentration gradients of NaCl and three concentration gradients of diesel treatments showed that there were 14 species present in the soil seed bank of the multi-species community: three species in the Phragmites australis community, and five species in the P. australis—Suaeda glauca community. The species in the seed bank of the three communities were much richer than the above-ground vegetation in this study. Soil salinity had a significant inhibitory effect on the seedling numbers of germinated species, the seedling density, and the species diversity of the soil seed banks, while the inhibitory effect of diesel was indistinctive under the designed concentrations. There existed significant interactions between the vegetation community type and soil salinity on the number of germinated species, the seedling density, and the Margalef index. Soil salinity is considered an important factor for wetland vegetation restoration in the YRD, but its effect had species-specific differences. Soil seed banks of the present three communities could be used to promote the restoration of degraded wetlands within certain soil salinity and oil concentration ranges.

Ecosystem Stability Assessment of Yancheng Coastal Wetlands, a World Natural Heritage Site

By evaluating the stability of coastal wetland ecosystems, health conditions of regional ecosystems can be revealed and the sustainable development of coastal wetlands can be promoted. Coastal wetlands have been scarcely involved in present ecosystem stability evaluation studies, these being performed with relatively simple evaluation data sources. Therefore, in this research, a comprehensive and representative ecosystem stability evaluation index system was constructed by using the pressure-state-response model and multi-source datasets from perspectives of internal and external environmental changes of the Yancheng coastal wetlands, Jiangsu, China. The analysis results indicated that: (1) The ecosystem stability of the Yancheng coastal wetlands was at an early warning stage, and all segments except the Binhai segment (relatively stable) were in an early warning state. (2) In the criterion layer, the Dafeng District and the whole Yancheng District were faced with the highest pressure, followed by the Dongtai, Xiangshui and Binhai segments, successively. The Sheyang segment reached the highest state level, followed by the Binhai, Xiangshui and Dafeng segments in succession. (3) In the factor layer, the whole Yancheng District was faced with high resource and socioeconomic double pressures, with a poor water quality state and relatively low environmental pressure; favorable soil, biological and landscape states; and positive response to wetland protection. Various factors varied from county to county. (4) In the index layer, the ecosystem stability of the Yancheng coastal wetlands was significantly influenced by the invasion of alien species, change rate of natural wetland area (D32), change rate of artificial wetland area, increment of aquafarm area, intensity of fertilizer application and coverage of dominant vegetations. The novel significance of this research lies in enriching global coastal wetlands ecosystem stability evaluation investigations by providing a typical case study.

Assessing Wetland ecosystem health in Sundarban Biosphere Reserve using pressure-state-response model and geospatial techniques

Coastal wetlands as the potential ecosystems, provide a wide range of benefits counting from ecosystem services to livelihood opportunities. Wetlands are continuously being degraded throughout the world especially in coastal ecosystems due to intensifying pressure on these resources and changing global climatic patterns. The wetlands in Sundarban Biosphere Reserve (SBR) are unique in character as these are surrounded by numerous rivers, creaks and mangrove forest. The present work is a concerted attempt to assess the health conditions of coastal wetland ecosystem in the SBR, India. Coastal wetlands of SBR were delineated during 1989–2017. Geospatial layers of site-specific indicators were prepared and were applied to the PSR model to examine the health of the wetland ecosystem. The model was also utilized to examine the impact of anthropogenic activities on wetland ecosystem and to ascertain the relationship among ecological pressure-state-response of ecosystem. The findings revealed that area under agriculture has been transformed into aquaculture. The shortage of fresh water supply for agriculture and increased salinity transformed many croplands to seasonal wetlands throughout the SBR. The overall ecosystem health of Sundarban has been decreased during the last two decades due to anthropogenic pressure and climate change issues. The result also indicated that the ecosystem fragmentation and human interference rate are two main dominating factors for declining wetland health in SBR. The findings of the study may help in formulating policy for the management of coastal wetland ecosystem.

The behavior of birds digging pits and foraging in the degraded coastal wetland promotes the restoration of vegetation

Birds are a very important part of the coastal wetland ecosystem, and they are also ecosystem engineers who can affect the abiotic environment and biological processes through their own behavior. Understanding the ecosystem engineering effect of birds in the coastal wetland ecosystem plays an important role in the ecological restoration of coastal wetlands. Through field investigation, the effects of pit digging and foraging behavior of coastal birds led by Grus grus and Anas poecilorhyncha on the topography and soil environmental physical and chemical indicators in the vegetation degradation area were studied, so as to promote the restoration of Suaeda salsa vegetation. The results showed that birds’ digging and foraging behavior in the degraded vegetation area changed the micro topography and soil environment in the degraded area, resulting in a significant decrease in soil hardness and soil salinity, while soil moisture content and soil carbon and nitrogen nutrition index were significantly higher than those in the degraded flat area without the influence of birds; in addition, the pit micro terrain environment improved by bird activities can significantly improve the seed retention, seedling colonization and adult survival of Suaeda salsa, and effectively promote the restoration of Suaeda salsa in the vegetation degradation area. Inspired by the change of microtopography by birds to promote vegetation restoration, it is proposed that we can try to artificially simulate and transform the microtopography environment in the degraded area, and promote the vegetation restoration in the degraded area of coastal wetlands through human intervention, which has important guiding significance for the ecological restoration of coastal wetlands.

Mangrove Growth Monitoring Based on Camera Visible Images—A Case Study on Typical Mangroves in Guangxi

Mangroves are an important coastal wetland ecosystem, and the high-throughput visible light (RGB) images of the canopy obtained by the ecological meteorological station can provide basic data for quantitative and continuous growth monitoring of mangroves. However, as for the mangroves that are subject to periodic seawater submersion, some key technical issues such as image selection, vegetation segmentation, and index applicability remain unsolved. With the typical mangroves in Beihai, Guangxi, as the object in this study, we used canopy RGB images and tidal data to find out the screening methods for high-quality nontidal submerged images, as well as the vegetation segmentation algorithms and RGB vegetation index applicability, so as to provide technical reference for the use of RGB images to monitor mangrove growth. The results showed that: 1) The critical tide levels can be determined according to the periodic changes of submersion in the mangroves, and critical tidal levels and image brightness can be used to quickly screen high-quality images of mangroves that are not submerged by seawater. 2) Machine learning and NLM filtering are effective strategies to obtain high-precision mangrove segmentation results. The machine learning algorithm has superiority in the segmentation of mangrove vegetation with a segmentation accuracy of higher than 80%, and the nonlocal mean filtering can effectively optimize the segmentation results of various algorithms. 3) The seasonal index VEG and antiseasonal index CIVE can be used as the optimal indices for mangrove growth monitoring, and the compound sine function can better simulate the change trend of various RGB vegetation indices, which is convenient for quickly judging mangrove growth changes. 4) Mangrove RGB vegetation indices are sensitive to meteorological factors and can be used to analyze the influence of meteorological conditions on mangrove growth.

Methane Contributions of Different Components of Kandelia candel–Soil System under Nitrogen Supplementation

Kandelia candel is the most widely distributed tree species on the southeast coast of China and is also the main afforestation tree species along the coastal wetland. In recent years, inorganic nitrogen pollution has become increasingly severe, and investigating the effects of nitrogen input on methane emissions in Kandelia candel–soil systems has become significant from a global change perspective. However, the effect of nitrogen input on methane emissions in coastal wetland systems is still uncertain. The field tidal environment is complex and varied, and thus it is difficult to accurately control the amount of nitrogen in the system. Therefore, in order to accurately assess the effects of different concentrations of foreign nitrogen input on methane emission fluxes in a Kandelia candel–soil system, we use indoor tidal simulation experimental devices and design two simulation systems with and without plant planting to explore the difference of methane emission flux in this system under five nitrogen input concentrations: N0 (0 g N·m−2·a−1), N1 (5 g N·m−2·a−1), N2 (10 g N·m−2·a−1), N3 (20 g N·m−2·a−1), and N4 (30 g N·m−2·a−1). The results showed that: (1) The introduction of Kandelia candel promoted methane emissions in coastal wetland ecosystem. Under each nitrogen application concentration, the mean CH4 emission flux in the planting group was 42.98%, 65.59%, 40.87%, 58.93% and 39.23% higher than that in the non-planting group, respectively. (2) Nitrogen input significantly promoted methane emissions in both planted and non-planted environments, and the promoting effect showed as follows: N4 &gt; N3 &gt; N2 &gt; N1 &gt; N0. (3) After the introduction of Kandelia candel, the contribution of Kandelia candel and soil microorganisms to methane emissions was different under different concentrations of nitrogen addition. The contribution rate of Kandelia candel to CH4 emission flux of Kandelia candel–soil system ranged from 10.74% to 60.25%, with an average contribution rate of 37.30%. The changed soil microbes contributed 39.75% to 89.26% to the CH4 emission flux in the Kandelia candel–soil system, with an average contribution rate of 62.60%. Under N3 nitrogen application concentration, the emission flux of plant was the largest, which was significantly higher than that of the soil microbial pathway; at other concentrations, the methane emissions from the soil microbial pathway were greater than that of the plant pathway, and the contribution rate to the plant–soil system reached 60.25%. The results of this study provide an important basis for improving the estimation accuracy of carbon emissions in coastal waters and formulating policies for the restoration and protection of coastal wetlands.

Environmental Filtering by pH and Salinity Jointly Drives Prokaryotic Community Assembly in Coastal Wetland Sediments

Understanding the microbial community assembly is an essential topic in microbial ecology. Coastal wetlands are an important blue carbon sink, where microbes play a key role in biogeochemical cycling of nutrients and energy transformation. However, the drivers controlling the distribution patterns and assembly of bacterial and archaeal communities in coastal wetland are unclear. Here we examined the diversity, co-occurrence network, assembly processes and environmental drivers of bacterial and archaeal communities from inshore to offshore sediments by the sequencing of 16S rRNA gene amplicons. The value of α- and β-diversity of bacterial and archaeal communities generally did not change significantly (P&amp;gt; 0.05) between offshore sites, but changed significantly (P&amp;lt; 0.05) among inshore sites. Sediment pH and salinity showed significant effects on the diversity and keystone taxa of bacterial and archaeal communities. The bacterial and archaeal co-occurrence networks were inextricably linked with pH and salinity to formed the large network nodes, suggesting that they were the key factors to drive the prokaryotic community. We also identified that heterogeneous and homogeneous selection drove the bacterial and archaeal community assembly, while the two selections became weaker from offshore sites to inshore sites, suggesting that deterministic processes were more important in offshore sites. Overall, these results suggested that the environmental filtering of pH and salinity jointly governed the assembly of prokaryotic community in offshore sediments. This study advances our understanding of microbial community assembly in coastal wetland ecosystems.

Research progress and development trend of coastal wetland restoration in greater bay areas

• We explored the progress and development trend of coastal restoration in greater bay. • Restoration methods are mainly based on biotic, hydrologic, and chemical processes. • Functional processes are critical to the maintenance of coastal ecosystem functions. We explored the potential for functional processes maintenance principles to be applied in coastal restoration. Greater bay areas are located in the transition zone between land and sea. Coastal wetlands play a key role in the ecological environment construction of greater bay areas. Due to the dual effects of high-intensity human activities and climate change, coastal wetlands in greater bay areas have suffered varying degrees of damage, including reduced area, habitat degradation, and impaired ecological functions. However, the research progress and development trend of restoration of damaged coastal wetland ecosystems has not yet been revealed, and the application theory of functional processes in coastal restoration is still unclear. Based on extensive literature research, our study reviewed the mechanisms and types of coastal wetland ecosystem restoration in greater bay areas. Coastal wetland ecosystem restoration technologies and methods are mainly based on the biological, hydrological, and chemical processes in greater bay areas. The current research progress and existing deficiencies of coastal wetland ecosystem restoration in greater bay areas are clarified. Combining years of research background in the coastal wetland field, focusing on the importance and criticality of coastal wetland functional processes to maintaining ecosystem functions, the main future research trends are proposed, which will solve the principal theory facing the restoration of coastal wetland ecosystems in greater bay areas. Our study will promote the application of new concepts and new techniques of coastal wetland restoration nationwide, and improve the overall level of ecological restoration in coastal wetland.

Floral Diversity Status in Urban Coastal Wetland &amp;amp; Associated Coastal Ecosystems of Crow Island Mattakkuliya, Sri Lanka

Colombo is the capital of Sri Lanka and the only wetland city in South Asia under the Ramsar Convention. Crow Island Beach Park and associated coastal area belong to the Colombo urban coastal wetland ecosystems. Crow Island wetland contributes diverse habitats for numerous flora and fauna species. The present study was conducted to assess the status of floral diversity in the Crow Island Beach Park and associated coastal ecosystem during the months of August to October 2021. Study area is divided in to three sites (A, B, C). Line transects method and field observations were used in the study. This coastal wetland consists of mosaic of five major vegetation types: Herbaceous, tree, shrub, creeper, grass and other than that marine algae namely Chaetomorpha antennina, Rhizoclonium africanum, Ulva compressa belonging to chlorophyta (green algae) and Grateloupia lithophila belonging to rhodophyta (red algae) were found in the study area. A total number of 102 flora species belonging to 50 families were recorded from the study area. There were two true mangrove species and 16 mangrove associated species in the study sites. Out of the 102 plant species 46 were recognized and documented as plants with medicinal values. Shannon-Wiener diversity indexes for mangrove and mangrove associated species were recorded as 2.378, 2.304 and 1.676 in site A, B and C respectively. Simpson’s diversity index for mangrove and mangrove associated species was recorded as 0.889, 0.874 and 0.735 respectively in site A, B and C and Jaccard index of similarity between three study sites showed high values ranging from 41% to 69% for mangrove and mangrove associated species.

Declines of Methylmercury Along a Salinity Gradient in a Low-Lying Coastal Wetland Ecosystem at South Carolina, USA

Declines of Methylmercury Along a Salinity Gradient in a Low-Lying Coastal Wetland Ecosystem at South Carolina, USA

Key Priorities for Integrating Coastal Wetland Ecosystem Services into Law and Policy – Results of an Empirical Study in Australia

Key Priorities for Integrating Coastal Wetland Ecosystem Services into Law and Policy – Results of an Empirical Study in Australia

High-Resolution Mapping Changes in the Invasion of Spartina Alterniflora in the Yellow River Delta

The propagation of the invasive <i>Spartina alterniflora</i> (<i>S. alterniflora</i>) has seriously affected the health of coastal wetland ecosystems in China and thus requires an urgent response. In this research, we construct a feature vector set containing phenological and other time-series features based on the Google Earth Engine (GEE) platform by combining dense time-series images from the Sentinel-1 and Sentinel-2 satellites. We obtained the dataset of the annual distribution of <i>S. alterniflora</i> in the Yellow River Delta (YRD) from 2016 to 2021 by developing an object-oriented random forest classification model. The results show that <i>S. alterniflora</i> has different phenological features from other wetland plants that played an important role in its classification based on the images. A combination of multiple phenological and temporal features improved the classification accuracy of <i>S. alterniflora</i> (multi-year average OA: 95.38&#x0025;; UA: 95.01&#x0025;; PA: 95.17&#x0025;). Our results suggest that from 2016 to 2021, the growth rate of the area occupied by <i>S. alterniflora</i> was 2.17 km² per year, and a new patch of the <i>S. alterniflora</i> appeared in the south of the study area in 2018. The work here provides scientific data to support the monitoring and control of the invasive <i>S. alterniflora</i> at a large scale.

Continuous Change Mapping to Understand Wetland Quantity and Quality Evolution and Driving Forces: A Case Study in the Liao River Estuary from 1986 to 2018

Coastal wetland ecosystems, one of the most important ecosystems in the world, play an important role in regulating climate, sequestering blue carbon, and maintaining sustainable development of coastal zones. Wetland landscapes are notoriously difficult to map with satellite data, particularly in highly complex, dynamic coastal regions. The Liao River Estuary (LRE) wetland in Liaoning Province, China, has attracted major attention due to its status as Asia’s largest coastal wetland, with extensive Phragmites australis (reeds), Suaeda heteroptera (seepweed, red beach), and other natural resources that have been continuously encroached upon by anthropogenic land-use activities. Using the Continuous Change Detection and Classification (CCDC) algorithm and all available Landsat images, we mapped the spatial–temporal changes of LRE coastal wetlands (e.g., seepweed, reed, tidal flats, and shallow marine water) annually from 1986 to 2018 and analyzed the changes and driving forces. Results showed that the total area of coastal wetlands in the LRE shrank by 14.8% during the study period. The tidal flats were the most seriously affected type, with 45.7% of its total area lost. One of the main characteristics of wetland change was the concurrent disappearance and emergence of wetlands in different parts of the LRE, creating drastically different mixtures of wetland quality (e.g., wetland age composition) in addition to area change. The reduction and replacement/translocation of coastal wetlands were mainly caused by human activities related to urbanization, tourism, land reclamation, and expansion of aquaculture ponds. Our efforts in mapping annual changes of wetlands provide direct, specific, and spatially explicit information on rates, patterns, and causes of coastal wetland change, both in coverage and quality, so as to contribute to the effective plans and policies for coastal management, preservation, and restoration of coastal ecosystem services.

Impacts of Spartina alterniflora invasion on the benthic food web in the Yellow River Delta during autumn

Spartina alterniflora was introduced into the Yellow River Delta (YRD) in 1990 with the purpose of shore protection and siltation accretion. However, it spread rapidly and became a severe threat to the local coastal wetland ecosystem. To assess the impacts of S. alterniflora invasion on the benthic food web, we sampled the potential food sources of macrobenthos in November 2020, analyzed the trophic level and the benthic food web structure based on stable isotope technique. Results showed that the average δ13C values of macrobenthic food sources followed an order: sediment organic matter (SOM) > S. alterniflora > benthic microalgae > particulate organic matter (POM) > Suaeda salsa. The average δ15N values significantly differed among food sources, ranging from 1.24‰ to 9.03‰. The trophic levels of different macrobenthos ranged from 1.73 to 4.19, of which the bivalve species was the lowest one. S. alterniflora and the decayed debris were the most important food sources for macrobenthos, but without any impact on the trophic level structure of macro-benthos. In conclusion, Spartina alterniflora invasion distinctly changed the composition of food sources of macrobenthos through a "bottom-up" effect, which would probably impact the local food web structure in the YRD wetland.

Pioneer salt marsh species Scirpus mariqueter disperses quicker in summer with seed contribution from current and last year

Salt marshes are widely considered to be the most valuable ecosystems for their important ecosystem services. Considering that pioneer species often spread rapidly over large areas in a short time under suitable conditions, there is a pressing need to understand their rapid dispersal (seed and seedling) mechanism and post-germination growth and fate. Based on remotely sensed images, field surveys and manipulative experiments, the rapid dispersal mechanism of S. mariqueter, one of the key native pioneer species at the Yangtze Estuary, was investigated. The results showed that (1) the average seaward expansion rate (the area of new dispersal in current year to that of the last year) of S. mariqueter was about 61% (maximum 181.7%) from 2013 to 2019 in Chongming Dongtan, and the expansion area in summer (August) was twice as large as that in spring (May). (2) Seeds from current year facilitate the dispersal of S. mariqueter with the contribution rate up to 27%, in addition to the seeds from last year. (3) The special germination regime of leaves sprouting prior to roots largely enhanced the buoyancy of the newly germinated seedlings, allowing them to have a potential long-distance dispersal. (4) The total event processes, including seed soaking and germination (7 days), root taking (2 days), forking (6 days), were completed within 15 days, which is highly consistent with the spring tidal cycle. These results illustrated important mechanism for quick expansion of pioneer salt marsh species at a large scale. It suggests that the successful seedling establishment of salt marsh species are closely linked to windows of opportunity (WoO), which provide scientific support for the conservation and restoration of coastal wetland ecosystems.