Salt Marsh Vegetation Research Articles

Ecological analysis and multi-scenario simulation of Yellow River Delta wetland under clearing of Spartina alterniflora

In 2022, China released the Special Action Plan for the Control of Spartina alterniflora (2022-2025) with the goal of completely clearing S. alterniflora from China's coastal wetlands. It is crucial to conduct a thorough analysis of wetlands under artificial intervention and obtain reliable future wetland simulation results. The Yellow River Delta wetland is one of China's important wetland reserves, has faced severe impacts from S. alterniflora invasion over the past decade. This study focuses on the Yellow River Delta wetland, utilizing Landsat imagery and a combined object-oriented and pixel-based approach to achieve wetland mapping from 2013 to 2023. Through wetland analysis, we designed scenarios for natural development, ecological priority, farmland protection, and combined development. The patch generating land use simulation model was used to simulate wetland scenarios for 2030 and analyze factors influencing wetland use cover change and future conversion patterns. The results indicate that between 2013 and 2022, native vegetation was impacted by the invasion of S. alterniflora, with Suaeda glauca being the most affected. In 2023, the removal of S. alterniflora was effective, reducing its area by 42.37km2 compared to pre-removal conditions. In all three scenarios, the area of Phragmites australis increased and is expected to dominate the wetlands, while the live space of other native salt marsh vegetation has also been restored. However, the predictions indicate that S. alterniflora still poses a potential threat of expansion in the future, necessitating continuous monitoring of its dynamics. We recommend implementing zoned management of the wetland, balancing ecological restoration in coastal areas with agricultural development in the western regions.

Mass concentrations, compositions and burial fluxes of nano- and micro-plastics in a multi-species saltmarsh

Plastic pollution poses a serious threat to marine ecosystems; yet quantifying the mass concentrations of nano- and microplastics (NMPs) in saltmarsh sediments at the ocean-land interface remains a critical research gap. Here, the study employed reliable and efficient analytical techniques, namely pressurized liquid extraction and the double-shot model of thermal desorption/pyrolysis-gas chromatography-mass spectrometry, to quantify six different types of NMPs in the sediment of a multi-species saltmarsh, providing the first comprehensive assessment of NMP mass concentration and burial in this saltmarsh environment. The results demonstrate that polyethylene, polyvinyl chloride, and polypropylene dominated the NMP composition in sediments, constituting 72.6%, 17.3%, and 4.5% of the total NMPs, respectively. The measured NMPs represent an anthropogenic intrusion, constituting 0.10%–0.23% of the carbon storage in the saltmarsh. By examining the vertical concentration profiles, this study unveiled the influence of saltmarsh vegetation on NMP deposition in sediments, establishing a connection with local sedimentation patterns and the historical zonation of plant species such as Scirpus mariqueter, Phragmites australis and Spartina alterniflora. These findings underscore the crucial role of saltmarsh vegetation in facilitating NMP settling and retention, highlighting the necessity of considering vegetation dynamics in examining the emerging NMP pollution in coastal wetlands.

A unique Ruleset for Saltmarsh and Mangrove monitoring using Sentinel-2

Abstract. Mangrove and saltmarsh vegetation are two important communities in the wetland ecosystem that require continuous monitoring considering their ecological threats and status. Remote Sensing observation is one of the tools to monitor this community. However algorithms are also important for the best sensor to map it accurately. Although there is some research about eCognition-based mapping, a unique rule set is important to monitor this community. Considering this research gap, a unique threshold-based ruleset has been generated in the Random Forest Model environment. A range of vegetation indices, individual bands of Sentinel 2 and Digital Elevation Model (DEM) data were tested in the feature selection method to find the best features for a Random Forest (RF) model. Top three variables were selected and those are (a) reNDVI_A, (b) VIRE_A, and (c) SWIR1 which gave 98.37% accuracy for the test data. A similar trend was found for the other three sites when they were compared with observed data. For site 1, Mangrove was 84.73%, Saltmarsh was 60.19%, and Mixed was 70.12% accurate. A similar trend was found for other three sites with overall accuracy 87.74 % for site-2, 66.23% for site 3, and 72.98% for site 4. A unique ruleset for wetland extent estimation will help to map a wide range of areas with a very minimum level of fieldwork. It will also reduce the cost of mapping done by visual observation, measurement and extensive fieldwork. The results of this work will provide the necessary insight and motivation for ecologists, and environmentalists.

Blue carbon storage of tidal flats and salt marshes: A comparative assessment in two Chinese coastal areas

Coastal wetlands are blue carbon (C) reservoirs and play an important role in mitigating climate change by efficiently capturing and storing organic carbon (OC). However, assessments of blue C sequestration focus primarily on soil organic carbon (SOC) inventories of vegetated coastal ecosystems and often neglect the potential of tidal flats to sequestrate C. To address the issue, a comparative assessment was carried out for two representative coastal wetlands in China: the Yellow River Delta and Yancheng coastal wetlands. The study focused on distinct types of coastal ecosystems including unvegetated tidal flats and three types of salt marshes vegetated by either Spartina alterniflora, Suaeda salsa, or Phragmites australis. We combined field sampling and data synthesis to assess the OC stock of different coastal areas and evaluate the regional OC storage. The results indicated that vegetated salt marshes exhibited higher OC stocks per unit area compared to unvegetated tidal flats in both regions. Interestingly, tidal flats in the Yellow River Delta displayed comparable OC stocks to S. salsa marsh on the Yancheng coast. The regional OC storage was estimated to be 5.64 ± 0.61 Tg C for the Yellow River Delta and 9.96 ± 1.52 Tg C for the Yancheng coast. Tidal flats with low SOC stock per unit area were the primary contributors to regional OC storage, accounting for over 75 % of the total. This predominance was attributed to the extensive distribution of tidal flats along China's coast, indicating their significant potential as blue C sinks. Overall, this study provides insights into the OC storage potential of various wetland types in China and highlights the importance of considering tidal flats in estimates of blue C sequestration.

Revealing the long-term impacts of plant invasion and reclamation on native saltmarsh vegetation in the Yangtze River estuary using multi-source time series remote sensing data

Understanding the long-term dynamics of saltmarsh vegetation and their driving factors is crucial for the restoration of degraded coastal wetlands. Reclamation and plant invasion, identified as the two most significant environmental contributors to saltmarsh vegetation degradation, profoundly influence the evolution of saltmarsh vegetation. However, the long-term impacts of reclamation and plant invasion on native saltmarsh vegetation remain unclear. This study utilized multi-source time series remote sensing data to quantify the long-term impacts of Spartina alterniflora invasion and reclamation on native saltmarsh vegetation in the Yangtze River estuary from 1985 to 2020. Unlike other studies, this study generated annual saltmarsh cover data using image composite, zoning classification, object-based phenology algorithm, and random forest algorithm, which largely addressed the problem that existing studies could not capture transient change and gradual change because of insufficient observation frequency. Results showed that: (1) Reclamation had resulted in a loss of 503.93 km2 of native saltmarsh vegetation from 1985 to 2020, including 286.16 km2 of Phragmites australis community and 217.77 km2 of Scirpus spp. community; Spartina alterniflora invasion had resulted in a loss of 78.96 km2 of native saltmarsh vegetation from 1985 to 2020, including 12.48 km2 of Phragmites australis community and 66.48 km2 of Scirpus spp. community; (2) Significant differences of spatial-temporal evolution patterns of native saltmarsh vegetation were observed under different degrees of Spartina alterniflora invasion and reclamation, including irrecoverable scenario under severe plant invasion and excessive reclamation, recoverable scenario under moderate degree of reclamation and plant invasion, and competitive scenario under plant invasion and without reclamation.; (3) From a long-term remote sensing perspective, spread limitation determined by reclamation intensity was a decisive factor in the evolution of Phragmites australis community in the study area, while interspecific competition between invasive Spartina alterniflora and Scirpus spp. determined the evolution of Scirpus spp. community. This study provides a theoretical basis and baseline for the protection strategies of native saltmarsh vegetation in the study area.

Experimental characterization of littoral atmospheric acoustics: Concurrent meteorological and acoustic observations.

The aim of this work is to describe a rich set of acoustic transmission loss observations that were completed in a coastal environment. The data library, enumerated in detail and publicly posted, is comprised of pitch-catch acoustic transmission loss measurements along with concurrent high spatial resolution meteorological observations. The meteorological parameters include near-surface temperature profiles, vertical wind speed profiles in the acoustic propagation direction, and significant wave height estimates. The acoustic source is positioned on an anchored vessel such that the first several hundred meters of the acoustic range is over open water with one microphone array positioned at the shore. A second microphone array is placed several hundred meters inland along the same source-to-receiver heading. The path between the two acoustic arrays is uniform salt marsh vegetation. Observations were made during seven sessions, which represent a variety of atmospheric conditions. That variety of conditions allows for some experimental generalizations about transmission loss as a function of meteorological observations. These include (1) the relationship between vertical effective sound speed profile and transmission loss, and (2) the variability of acoustic pressure with turbulence over time and elevation.

Seasonal variations in drag coefficient of salt marsh vegetation

Understanding the seasonal variations of vegetation drag coefficients is crucial for improving wave attenuation predictions and adapting to climate impacts. This study explores the seasonal changes in drag coefficients within salt marsh vegetation, using data from a year-long series of field measurements at the Chongming Dongtan Wetland. It uncovers the complex seasonal variations of drag coefficients. Results demonstrate that incorporating a nonlinear equation for characteristic flow velocity and effective vegetation length significantly improves the precision of drag coefficient predictions, ensuring a closer match with field observations. Furthermore, it introduces a refined drag coefficient formula that incorporates adjustments for vegetation stiffness and relative submergence, offering a more accurate representation of the seasonal variability in drag forces exerted by salt marsh vegetation. This enhanced formula is crucial for accurately assessing vegetation's role in wave attenuation, providing critical insights for the design and implementation of coastal defense and wetland conservation initiatives.

Cenomanian terrestrial paleoenvironments from the Bohemian Cretaceous Basin in Central Europe and their implications for angiosperm paleoecology

In this paper, we reconstruct the vegetation communities of five terrestrial paleoenvironments from the Cretaceous (Cenomanian) Peruc-Korycany Formation of the Bohemian Cretaceous Basin in Czechia. Reconstructions are based on a synthesis of numerous studies of paleobotany, palynology, paleoecology, sedimentology and geochemistry analyses. Ordered in a transect from coastal marine settings to elevated hinterland regions, paleoenvironments and plant assemblages are reconstructed as follows: (1) Saltmarsh vegetation comprising a Frenelopsis-Classopollis assemblage; (2) Coastal freshwater swamp vegetation comprising a Cunninghamites-Taxodiaceaepollenites assemblage; (3) Meandering river floodplain vegetation comprising a Myrtophyllum-Perucipollis assemblage; (4) Braided river floodplain vegetation comprising a Eucalyptolaurus-Mauldinia assemblage; and (5) Vegetation of drier upland areas comprising fern prairies with angiosperms and Bennettitales - a Zamites-Ephedripites assemblage. Our study shows that in Cenomanian times, angiosperms were diversified, particularly in alluvial plains, where lauroid and platanoid angiosperms prevailed. Comparison of these Cenomanian paleoenvironments in Czechia with other Cenomanian paleoenvironments across Europe show a widespread dominance of angiosperms in the vegetation of alluvial plains across much of the continent. This contrasts with Barremian-Albian times when angiosperms occupied only disturbed habitats, and our findings suggest that angiosperm exchanged a ruderal (disturbed) strategy for a competitive strategy during the Albian-Cenomanian transition. Conversely, conifers dominated alluvial plains in Early Cretaceous times, while they rose to dominate saltmarshes and swamps in the Bohemian Cenomanian, exchanging a competitive strategy for a stress-tolerant strategy.

Precise mapping of coastal wetlands using time-series remote sensing images and deep learning model

Mapping coastal wetlands' spatial distribution and spatiotemporal dynamics is crucial for ecological conservation and restoration efforts. However, the high hydrological dynamics and steep environmental gradients pose challenges for precise mapping. This study developed a new method for mapping coastal wetlands using time-series remote sensing images and a deep learning model. Precise mapping and change analysis were conducted in the Liaohe Estuary Reserve in 2017 and 2022. The results demonstrated the superiority of Temporal Optimize Features (TOFs) in feature importance and classification accuracy. Incorporating TOFs into the ResNet model effectively combined temporal and spatial information, enhancing coastal wetland mapping accuracy. Comparative analysis revealed ecological restoration trends, emphasizing artificial restoration's predominant role in salt marsh vegetation rehabilitation. These findings provide essential technical support for coastal wetland ecosystem monitoring and contribute to the study of sustainability under global climate change.

Biomass distribution patterns of salt marshes: A detailed spatial analysis in central China's coastal wetlands

Wetland vegetation plays a critical role in the health of coastal ecosystems, serving pivotal roles in disaster mitigation and blue carbon sequestration. While extensive research on the effects of sea-level rise on the aboveground biomass of salt marsh vegetation, the spatial patterns of biomass distribution related to surface elevation remain less explored. This study investigates the growth patterns and spatial distribution of Spartina alterniflora in central coast of China through field surveys and the analysis of remote sensing data via Google Earth Engine. We have found a significant parabolic relationship between vegetation biomass and distance from the sea, with the optimal biomass influenced by the location of the marsh front edge. Further, we observe that biomass distribution varies with surface elevation and is influenced by geomorphological features notably creeks, which introduce significant elevation differences and local biomass fluctuations. These findings offer new insights into the spatial distribution of tidal flat vegetation, which are vital for effective coastal management and for modeling the evolution of tidal flats.

How Artificial Salt Marsh Vegetation Reduces The Threshold For Sediment Resuspension In Wave-Current Flows

Suspended sediment transport and retention within salt marshes is a key factor in their resilience against erosion associated with threats such as sea level rise and coastal squeeze. Salt marshes are vegetated intertidal wetlands found in temperate climate zones. Their presence contributes to flood protection, coastal flora and fauna, and carbon sequestration (Temmerman et al., 2013). Vegetation-induced resuspension of fine sediment helps to transport fine particles deeper into salt marshes. The interaction between waves, currents, and vegetation may resuspend sediment sooner than it would without vegetation. It has been shown in conditions with only currents (Liu et al., 2021; Tinoco & Coco, 2014) or only waves (Tinoco & Coco, 2018) that the threshold for resuspension is lower within vegetated meadows than without vegetation. However, the threshold has not yet been studied for combined wave-current conditions, which often exist in the marsh environment. Identifying this threshold will enable us to predict when in a tidal cycle sediment resuspension occurs and can be used to improve sediment transport model. We use flume experiments to methodically identify the threshold of sediment resuspension in artificial salt marsh meadows of three different area densities under combined wave-current flows.

Large-Scale Test Of Extreme Hydrodynamic Conditions Over Coastal Salt Marshes

Hard coastal structures such as dikes covered with asphalt or placed block revetments have been widely used in the past for coastal protection in densely populated deltas around the world. Nonetheless, in recent years the effectiveness of hard structures has been questioned in light of the inevitable effects of climate change and their static nature. Decades of research on how salt marshes can play a role within a comprehensive coastal protection scheme suggest that these low environmental impact structures (Maza et al., 2015) might have the capability of dissipating wave energy and hence be technically and formally considered within hybrid coastal erosion and flood protection systems (Borsje et al., 2011). However, only very few studies investigated wave attenuation by real salt marsh vegetation in large-scale laboratories (Ghodoosipour et al., 2022; Maza et al., 2015; Möller et al., 2014) and none of them addressed extreme hydrodynamic design conditions in terms of wave energy and water levels. As a result of this knowledge gap, salt marshes in The Netherlands and all around the world have never been formally considered within the coastal flood protection systems and the underlying risk assessment. With this contribution our aim is to provide an overview of the first worldwide large-scale test focused on the interaction between a salt marsh (i.e. vegetation and shallow foreshore) and extreme hydrodynamic conditions, the adopted measurement techniques and the preliminary results in terms of wave damping, erosion and removed biomass.

Quantifying Wave-Induced Hydrodynamics Near A Saltmarsh Cliff: An Experimental Piv Study

Nature-based flood defences receive increasing interest as a viable option for improving flood safety worldwide. A contemporary case is using the ability of saltmarshes to attenuate waves during storm conditions for strengthening coastal flood defences. To ensure a long-term reinforcement of flood protection, it is important to understand the erosion mechanisms of saltmarshes during storms. One of the critical locations for erosion is at the transition between the saltmarsh and the bare mudflat, often characterized by a vertical step or cliff. These cliffs vary between 0.2 to 2.0 m in height, depending on soil characteristics and local hydrodynamics. However, wave-induced hydrodynamics that controls the (mass) erosion at the saltmarsh cliff are not fully understood. Also the role of saltmarsh vegetation on these near-cliff hydrodynamics are not clearly quantified. In this research, we present high-resolution measurements of wave-induced hydrodynamics at a saltmarsh cliff performed in a scaled wave flume experiment.

Enhancing salt marshes monitoring: Estimating biomass with drone-derived habitat-specific models

Salt marshes play a vital role in biodiversity conservation, coastal protection, and carbon sequestration. Estimating aboveground biomass (AGB) is crucial for quantifying the carbon sequestration capacity of the system. However, traditional fieldwork methods are time-consuming, demanding, and detrimental to marsh ecosystems. In this study, we propose utilizing low-altitude remote sensing techniques to collect high-resolution LiDAR and multispectral (MS) data for biomass assessment. With these datasets, we characterized salt marsh vegetation habitats through the analysis of vegetation indices (VIs) variability. LiDAR high-resolution topographic information aids in evaluating habitat distribution. Moreover, the Anthocyanin Reflectance Index 2 (ARI2), combined with the Digital Surface Model, allows for the identification and separation of the two habitats with distinct dominant species (Sarcocornia spp. and Sporobolus maritimus). The analysis of the annual cycle of VIs reveals the presence of seasonality. However, the VIs for the two vegetation classes exhibit dissimilar seasonal changes, indicating distinct growth mechanisms for each. Biomass models are created for each season in the annual cycle. Habitat-specific models exhibit higher precision (up to 99%) than models that treat species uniformly. Depending on whether the marsh is considered as a whole or separated into dominant habitats, differences in biomass estimation trends are observed. This implies that the two dominant species exhibit varying behaviours throughout the year, contributing to diverse biomass production. The study reveals a seasonal pattern in the total AGB, with the highest biomass value in summer and the lowest peak in spring, with annual variation accounting for only 9% of total output. The reduced AGB value in spring may be due to increased soil salinity and stress. The use of LiDAR and MS data from an unmanned aerial vehicle (UAV) is crucial for accurately distinguishing primary marsh habitats and creating detailed biomass models, with unprecedented accuracy. This method is user-friendly, repeatable, and cost-effective, enabling the study of salt marshes, evolutionary trends, and climate change response requiring less fieldwork.

Tracking annual dynamics of carbon storage of salt marsh plants in the Yellow River Delta national nature reserve of china based on sentinel-2 imagery during 2017–2022

Coastal salt marshes play a key role in coastal carbon sequestration. Understanding the spatial distribution and annual changes of carbon storage of salt marsh plants at a local scale is helpful for accurate protection and restoration. However, the annual carbon storage of salt marsh plants has not yet been obtained in the Yellow River Delta National Nature Reserve (YRDNNR), China. Here, we developed a fast and reliable method to produce an annual map of carbon storage of herbaceous salt marsh plants from 2017 to 2022 based on multi-year in situ data and 10-meter resolution Sentinel-2 images in YRDNNR. That is, a deep belief network based on conjugate gradient (CGDBN) pixel-level classification, a generative adversarial network with a constrained factor (GAN-CF) measured sample expansion and multiple linear regression (MLR) quantitative inversion algorithm is used. The results showed that: (1) The carbon storage of herbaceous salt marsh plants in the YRDNNR increased in 2017–2018 and 2019–2021, with an average carbon storage dynamic of 4.53–8.39 Mg/ha. (2) In 2021, the area of salt marsh vegetation increased significantly by 20 % compared to 2017. Although its area decreased sharply due to the removal of invasive species (S. alterniflora) in 2022, the carbon storage per unit area of salt marsh plants remained at 7.77 Mg/ha. (3) The carbon storage of salt marsh vegetation showed a gradient change along the community succession from land to sea. Estimating annual carbon storage of salt marsh plants could provide basic data for recognizing the ‘blue carbon’ contribution of coastal plants and managing the coastal salt marsh ecosystem in Yellow River Delta.

Large-Scale Experimental Model Of Edge Treatments For Constructed Salt Marshes

Large stretches of Canada’s coastlines are lined with legacy dykes (or levees) to provide protection against coastal flooding and erosion. However, future sea-level rise presents a risk to these structures, which may result in the dykes being under designed when exposed to future water levels and wave conditions. Under certain conditions, these dykes can be augmented with a coastal saltmarsh to create a living dyke, which allows for the existing dyke to be more resilient against sea level rise without the need to retrofit the dyke with a higher crest elevation or larger armour stone. The coastal saltmarsh is able to attenuate storm waves, resulting in lower wave energy at the dyke, while also attracting and retaining sediment to combat coastal erosion. The Living Dyke project in Boundary Bay, Canada is a pilot project being used to test the living dyke concept by placing sediment and planting salt marsh vegetation in the foreshore combined with upgrades to the existing dyke. Kerr Wood Leidal Associates Ltd. prepared a preliminary design which incorporated four different edge treatment features that are to be installed at the offshore edge of a newly constructed salt marsh platform in order to attenuate wave energy and retain the placed sediment before the planted vegetation can be established. The proposed edge treatment features included a natural sand edge, a rounded gravel berm, an oyster-shell filled bag berm, and a brushwood dam. Large scale (full scale for all edge treatment feature tests except for the brushwood dam which was conducted at half-scale) physical model experiments were carried out by the National Research Council of Canada’s Ocean, Coastal and River Engineering Research Centre in their Large Wave-Current Flume to investigate the performance, including stability of the edge treatment features, wave attenuation ability, and stability of the salt marsh platform, of these edge treatment features under varying water level and wave conditions that are present at Boundary Bay.

Seasonal Variation Of Wave Attenuation Capacity Of Canadian Saltmarsh Vegetation

Nature-based Solutions (NbS) for coastal protection have been widely recognized as sustainable, economical, and eco-friendly alternatives to conventional grey structures, particularly under the threat of climate change (Temmerman et al., 2013). Living shorelines are a form of NbS, which incorporate natural elements (such as saltmarshes) that provide flood and erosion risk management benefits. Climate change impacts, such as rising sea levels and reducing sea-ice cover (Savard et al., 2016), are increasingly motivating communities in Canada to consider incorporating living shorelines in coastal protection schemes. The efficacy of wave energy dissipation by vegetation depends on both hydrodynamic conditions and plant characteristics. However, plant parameters, such as standing biomass exhibit seasonal fluctuations, leading to corresponding variations in attenuation capacity (Schulze et al., 2019). Hence, the design of NbS utilizing saltmarsh vegetation must account for seasonal variations to ensure sustained efficacy, especially within the context of Canadian regional climates, which are typically characterized by extended, stormy winters and shorter summer seasons. Few studies have quantified wave attenuation by real saltmarsh vegetation in large-scale laboratory facilities (Möller et al., 2014; Maza et al., 2015; Ghodoosipour et al., 2022), particularly for species native to the east coast of Canada. There is a knowledge gap on how seasonality affects wave attenuation by saltmarsh vegetation and how attenuation varies from the lower marsh to the higher marsh depending on species-specific plant traits. Research is needed to bridge this gap and develop technical guidance for the design of performant living shorelines in Canada.

Monitoring of chlorophyll content in local saltwort species Suaeda salsa under water and salt stress based on the PROSAIL-D model in coastal wetland

As the invasion of alien species intensifies, the native salt marsh vegetation, especially the ecosystem of Suaeda salsa (S. salsa), in Chinese coastal wetlands has been severely disrupted, significantly impeding its functionality within coastal wetland ecosystems. Chlorophyll content (Cab) is an important parameter for monitoring the growth and health status of vegetation. However, the remote sensing mechanism of Cab for different phenotypes of green and red vegetation influenced by betacyanin under different water and salt conditions is not clear. Therefore, to further clarify the remote sensing mechanism of S. salsa and improve the generality of Cab prediction for different phenotypes under different water and salt conditions, we designed a growth experiment under different groundwater levels and salt concentrations. This experiment was used to simulate the growth of S. salsa in different habitats in nature and investigate the relationship between their physicochemical parameters, spectra, and environmental stress. We propose using the specific absorption coefficient of betacyanin (Beta) to adjust PROSAIL-D to better fit the spectral characteristics of S. salsa. The relationship between Beta and Cab was utilized to further optimize the simulation accuracy of the PROSAIL-D model in different environments. Feature extraction algorithms, including differential enhancement of two-dimensional correlation spectroscopy (FD-2DCOS) and three-band models, were introduced to construct multiple spectral features for establishing a Cab prediction model for S. salsa. The research results showed that: (1) S. salsa had the best response of Cab and spectra to salinity under a higher groundwater level and showed a gradual reddening trend. (2) The spectral curves simulated by the adjusted PROSAIL-D model were more consistent with the spectral characteristics of S. salsa under different water-salt environments, and the simulation effect could be further optimized by using the relationship between Beta and Cab. (3) The FD-2DCOS analysis method we proposed could highlight the useful spectral information related to Cab better than the original 2DCOS algorithm. The final eight spectral features of (1/R701–1/R540)R540, Mean(D590–600), Mean(D660–670), Mean(D677–685), FDVI_NRG, FDVI_NIR, Skewness (D677–750) and Position(D677–750) had the best response to Cab of S. salsa, and had the least influence on LAI and soil background. (4) The particle swarm optimization random forest regression (PSO-RFR) model based on eight spectral features and adding 70% measured spectral data performed the best in predicting the actual Cab of S. salsa, with an RMSE of 2.326 μg·cm−2. Although further optimization and calibration of the adjusted PROSAIL-D model and Cab prediction model of S. salsa are needed in the future, this study extended its application to S. salsa, a special local salt marsh vegetation, and promoted the development of Cab monitoring of salt marsh vegetation in coastal wetlands.

Above- and belowground plant mercury dynamics in a salt marsh estuary in Massachusetts, USA

Abstract. Estuaries are a conduit of mercury (Hg) from watersheds to the coastal ocean, and salt marshes play an important role in coastal Hg cycling. Hg cycling in upland terrestrial ecosystems has been well studied, but processes in densely vegetated salt marsh ecosystems are poorly characterized. We investigated Hg dynamics in vegetation and soils in the Plum Island Sound estuary in Massachusetts, USA, and specifically assessed the role of marsh vegetation for Hg deposition and turnover. Monthly quantitative harvesting of aboveground biomass showed strong linear seasonal increases in Hg associated with plants, with a 4-fold increase in Hg concentration and an 8-fold increase in standing Hg mass from June (3.9 ± 0.2 µg kg−1 and 0.7 ± 0.4 µg m−2, respectively) to November (16.2 ± 2.0 µg kg−1 and 5.7 ± 2.1 µg m−2, respectively). Hg did not increase further in aboveground biomass after plant senescence, indicating physiological controls of vegetation Hg uptake in salt marsh plants. Hg concentrations in live roots and live rhizomes were 11 and 2 times higher than concentrations in live aboveground biomass, respectively. Furthermore, live belowground biomass Hg pools (Hg in roots and rhizomes, 108.1 ± 83.4 µg m−2) were more than 10 times larger than peak standing aboveground Hg pools (9.0 ± 3.3 µg m−2). A ternary mixing model of measured stable Hg isotopes suggests that Hg sources in marsh aboveground tissues originate from about equal contributions of root uptake (∼ 35 %), precipitation uptake (∼ 33 %), and atmospheric gaseous elemental mercury (GEM) uptake (∼ 32 %). These results suggest a more important role of Hg transport from belowground (i.e., roots) to aboveground tissues in salt marsh vegetation than upland vegetation, where GEM uptake is generally the dominant Hg source. Roots and soils showed similar isotopic signatures, suggesting that belowground tissue Hg mostly derived from soil uptake. Annual root turnover results in large internal Hg recycling between soils and plants, estimated at 58.6 µg m−2 yr−1. An initial mass balance of Hg indicates that the salt marsh presently serves as a small net Hg sink for environmental Hg of 5.2 µg m−2 yr−1.

Evaluating the success of vegetation restoration in rewilded salt marshes

Floodbank realignment is a common practice aimed at restoring salt marsh vegetation on previously embanked land. However, experiences indicate that it may take several years before salt marsh vegetation becomes fully established. Various challenges arising from ecogeomorphic feedback mechanisms could pose significant setbacks to vegetation recolonization. The widespread adoption of transplantation techniques for the restoration and rehabilitation of rewilded landscapes has indeed proven to be a valuable tool for accelerating plant development. In the Ria Formosa coastal lagoon (South of Portugal), a pilot plan was implemented, and two salt marsh pioneer species, Spartina maritima (syn. Sporobolus maritimus) and Sarcocornia perennis (syn. Salicornia perennis), were transplanted from a natural salt marsh to a rewilded marsh. Biodegradable 3D porous structures were installed to mimic transplant clumping, aid sedimentation, and enhance the plant's initial adjustment. Ecological, sediment, and hydrodynamic data were collected during the 12-month pilot restoration plan. The environmental profiles of the donor and restoration sites were compared to substantiate the success of the transplants in the rewilded salt marsh.Results show that although plant shoot density decreased after the transplanting, Spartina maritima acclimated well to the new environmental conditions of the restoration site, showing signs of growth and cover increase, whilst Sarcocornia perennis was not able to acclimatize and survive in the restoration site. The failure behind the Sarcocornia perennis acclimation might be related to the bed properties and topographic properties of the restoration site in the rewilded marsh. Major findings contribute to a more comprehensive understanding of how salt marsh pioneering vegetation successfully colonizes disturbed habitats, facilitated using 3D-biodegradable structures.