Salt Marsh Vegetation Research Articles

Modelling wave attenuation by saltmarsh using satellite-derived vegetation properties

Saltmarshes are increasingly recognised an important asset in coastal management as they dissipate wave energy and thus reduce the potential for coastal flooding. The frontal surface area (FSA) and the drag coefficient (Cd) are parameters commonly used in wave attenuation models to express the resistance of vegetation structure to incident waves. The FSA of vegetation represents the vertical surface area facing incoming waves which is calculated as the product of height, diameter and density whereas Cd is often used as tunable parameter that represents the vegetation-wave interactions that relies on both vegetation properties and wave conditions. Despite their importance in numerical modelling, substantial uncertainty remains in obtaining these parameters in the field due to the time-intensive and relatively expensive nature of data collection. An alternative structural vegetation parameter that can be included in wave attenuation models is the leaf area index (LAI). The primary advantage of the LAI is that it can be readily derived from satellite imagery, and thus provides a low-cost, fast alternative to field data collection. However, to date, its incorporation in widely-used coastal engineering models is lacking. The aim of this paper is to verify the use of remote-sensed LAI in numerical wave models as an alternative to FSA. Here, the widely used XBeach model for simulating storm impacts on a range of coastal systems is applied to two open coast sites with extensive saltmarsh; Chesapeake Bay, USA, and Brancaster, UK. To assess the performance of wave attenuation modelling using both methods, we compared the use of remote-sensed LAI from satellite imagery and field-based FSA as inputs into the model. The LAI-based model provides similar levels of accuracy as the FSA-based model. Likewise, higher uncertainties related to plant height, diameter, and density were found in the FSA-based model than in the LAI-based model. Therefore, the LAI-based model provides the advantage of a low-cost and fast method to accurately estimate and predict wave attenuation by vegetation using numerical models such as XBeach. Our practical application in the Brancaster site exemplifies an easy and fast approach to obtaining structural parameters of saltmarsh vegetation and estimating wave attenuation between natural and artificial saltmarshes as well as between seasons.

Carbon and Nitrogen Contents Driven by Organic Matter Source within Pichavaram Wetland Sediments

Differences in grain size, total organic carbon (OC), total nitrogen (TN), OC/TN ratios, and stable isotope (δ13C and δ15N) were assessed in sediments from areas covered by mangrove and saltmarsh vegetation within Pichavaram estuary (Southeast India). The mean percentage contents of silt and clays (70 vs. 19%), OC (5.7 vs. 2.0%), and TN (0.39 vs. 0.14%) were consistently higher in the mangrove as compared to those observed in the saltmarsh tidal zone. These differences may obey the higher deposition and retention of fine particles in the presence of a mangrove root system that may facilitate the accumulation and preservation of organic matter within these sedimentary systems. Further, higher OC and TN contents were associated to higher terrestrial or mangrove-derived organic matter contribution with lighter δ13C signatures (−26.0‰) in both sedimentary tidal zones, whereas lower OC and TN contents were associated to heavier δ13C signatures. This study is in agreement with previous studies which indicate that the presence of wetland vegetation may increase the carbon and nutrient storage capacity within estuarine ecosystems, highly relevant information for the establishment of further conservation strategies for blue carbon ecosystems at global scales.

The ecology of coastal wetland ponds created by diamond mining in southern Namibia. 2. Saltmarsh vegetation

Diamond mining on the southern Namibian coastline has created multiple large coastal ponds of up to 380 000 m2 adjacent to the coastline, as the sea overtops erected seawalls or seeps into excavated areas. These ponds span ages of 1–38 years. We investigated whether the ponds offer an environment for the establishment, growth and dispersal of saltmarsh vegetation along the coast, which is otherwise devoid of natural wetlands apart from at the Orange River estuary and Lüderitz Bay. Most ponds supported saltmarshes, but they comprised only a single species, Salicornia natalensis. The abundance of this succulent, mat-forming, salt-tolerant plant was greatest around old ponds, but its health decreased with increasing age and hence salinity of the ponds. The orientation of saltmarshes around the ponds was correlated with prevailing wind direction, suggesting that wind determines dispersal of this plant along the coast. However, any saltmarsh communities that have developed will be disturbed by possible future mining activities. In addition, once mining ends, the saltmarshes will become stressed owing to rising salinities as ponds age. Nevertheless, the ponds are capable of supporting saltmarshes for up to 15 years, and new ponds will be created as mining progresses; this offers an ongoing opportunity for the ponds to serve as ‘stepping stones’ in the dispersal and establishment of S. natalensis along the coast.

Vegetation of temperate inland salt marshes on their north-western border (North German Plain)

Temperate inland salt marshes, formerly used as meadows or pastures, are priority habitats in Europe and are threatened by intensifying anthropogenic activites. They are particularly important because of their biogeographical location on the North German Plain, which is the westernmost hotspot of continental halophytic vegetation in Eurasia. In spite of their remarkably long history of floristic research, there are disproportionately few studies dealing with plant communities. They are traditionally included in the Puccinellion maritimae and Armerion maritimae alliances with a typical distribution along the North and Baltic Sea coasts. The similarity with other inland salt marshes has been overlooked. We surveyed natural and secondary sites with euhalophytic vegetation in central Germany (Saxony-Anhalt and Thuringia) in 2018 and 2020 and analysed 105 phytosociological relevés. This resulted in the identification of three main groups (alliances) containing seven associations: annual hypersaline succulent communities of the alliance Therosalicornion (Salicornietum europaeae, Halimioni pedunculatae-Puccinellietum distantis, Suaedetum maritimae), wet saline meadows of the alliance Juncion gerardi (Triglochino maritimae-Glaucetum maritimae, Scorzonero parviflorae-Juncetum gerardi variant with Glaux maritima) and saline short-grass swards of the alliance Puccinellion limosae (Puccinellietum limosae, Atriplex prostrata community). For each association we defined the typical species composition and calculated Ellenberg indicator values depending on the ecological gradients of soil salinity, nutrients and moisture. To determine possible floristic similarities between the inland and coastal salt marshes, we compared our data with data from other areas of saline vegetation: the southern Baltic Sea coast, Kujawy (Poland), Pannonian Basin (Hungary) and Transylvanian Basin (Romania). We concluded that the salt marshes in inland Germany showed a stronger relation with salt marshes of the remote Pannonian and Transylvanian Basins, and they were well separated from the Baltic salt marshes. Thus, we suggest including inland salt marshes on the North German Plain into the syntaxonomical class of continental halophytic vegetation of Festuco-Puccinellietea.

Spatiotemporal Mapping of Salt Marshes in the Intertidal Zone of China during 1985–2019

This study mapped the areal extent, identified the species composition, and analyzed the changes of salt marshes in the intertidal zone of China during the period 1985–2019. With the aid of the cloud platform of the Google Earth Engine, we selected Landsat 5/8 and Sentinel-2 images and used the support vector machine classification method to extract salt marsh information for the years of 1985, 1990, 1995, 2000, 2005, 2010, 2015, and 2019. Seven major species of salt marshes: Phragmites australis , Suaeda spp., Spartina alterniflora , Scirpus mariqueter , Tamarix chinensis , Cyperus malaccensis , and Sesuvium portulacastrum were identified. Our results showed that salt marshes are mainly distributed in Liaoning, Shandong, Jiangsu, Shanghai, and Zhejiang, with varying patterns of shrinking, expansion, or wavering in different places. The distribution of salt marshes has declined considerably from 151,324 ha in 1985 to 115,397 ha in 2019, a drop of 23.7%. During the same period, the area of native species has dropped 95.4% from 77,741 ha to 3,563 ha for Suaeda spp. and 45.1% from 60,511 ha to 33,193 ha for P. australis ; on the contrary, the area of exotic species, S. alterniflora , has exhibited a sharp rise from just 99 ha to 67,527 ha. For the past 35 years, the driving factors causing salt marsh changes are mainly land reclamation, variations in water and sand fluxes, and interspecific competition and succession of salt marsh vegetation. These results provide fundamental reference information and could form the scientific basis for formulating policies for the conservation and utilization of salt marsh resources in China.

Are saltmarshes younger than mangrove swamps?

Temperate saltmarshes and tropical mangrove swamps (mangals) are marine‐influenced, productive ecosystems that enhance nutrient transfers between land and sea and facilitate colonization of lineages between terrestrial and marine habitats. Mangals have existed since the late Cretaceous, but the time of origin of saltmarshes is less clear. On the basis of phylogenetic and fossil evidence for plants and molluscs specialized to these ecosystems, I propose that saltmarsh vegetation of angiosperms began during the latest Eocene to Early Oligocene (35–30 Ma), at least 34 m.y. after the origin of mangals. The plants that colonized saltmarshes then and later have mainly temperate origins, contrasting with the tropical‐forest origins of mangroves. Unlike the plants, the few saltmarsh‐specialized molluscs are derived from tropical lineages and reflect recent colonizations. The development of saltmarshes during the Neogene enhanced near shore productivity along temperate and Arctic coastlines.

Meta-analysis of salt marsh vegetation impacts and recovery: a synthesis following the Deepwater Horizon oil spill.

Marine oil spills continue to be a global issue, heightened by spill events such as the 2010 Deepwater Horizon spill in the Gulf of Mexico, the largest marine oil spill in US waters and among the largest worldwide, affecting over 1,000 km of sensitive wetland shorelines, primarily salt marshes supporting numerous ecosystem functions. To synthesize the effects of the oil spill on foundational vegetation species in the salt marsh ecosystem, Spartina alterniflora and Juncus roemerianus, we performed a meta‐analysis using data from 10 studies and 255 sampling sites over seven years post‐spill. We examined the hypotheses that the oil spill reduced plant cover, stem density, vegetation height, aboveground biomass, and belowground biomass, and tracked the degree of effects temporally to estimate recovery time frames. All plant metrics indicated impacts from oiling, with 20–100% maximum reductions depending on oiling level and marsh zone. Peak reductions of ~70–90% in total plant cover, total aboveground biomass, and belowground biomass were observed for heavily oiled sites at the marsh edge. Both Spartina and Juncus were impacted, with Juncus affected to a greater degree. Most plant metrics had recovery time frames of three years or longer, including multiple metrics with incomplete recovery over the duration of our data, at least seven years post‐spill. Belowground biomass was particularly concerning, because it declined over time in contrast with recovery trends in most aboveground metrics, serving as a strong indicator of ongoing impact, limited recovery, and impaired resilience. We conclude that the Deepwater Horizon spill had multiyear impacts on salt marsh vegetation, with full recovery likely to exceed 10 years, particularly in heavily oiled marshes, where erosion may preclude full recovery. Vegetation impacts and delayed recovery is likely to have exerted substantial influences on ecosystem processes and associated species, especially along heavily oiled shorelines. Our synthesis affords a greater understanding of ecosystem impacts and recovery following the Deepwater Horizon oil spill, and informs environmental impact analysis, contingency planning, emergency response, damage assessment, and restoration efforts related to oil spills.

Estimating Ground Elevation and Vegetation Characteristics in Coastal Salt Marshes Using UAV-Based LiDAR and Digital Aerial Photogrammetry

This study evaluates the skills of two types of drone-based point clouds, derived from LiDAR and photogrammetric techniques, in estimating ground elevation, vegetation height, and vegetation density on a highly vegetated salt marsh. The proposed formulation is calibrated and tested using data measured on a Spartina alterniflora-dominated salt marsh in Little Sapelo Island, USA. The method produces high-resolution (ground sampling distance = 0.40 m) maps of ground elevation and vegetation characteristics and captures the large gradients in the proximity of tidal creeks. Our results show that LiDAR-based techniques provide more accurate reconstructions of marsh vegetation (height: MAEVH = 12.6 cm and RMSEVH = 17.5 cm; density: MAEVD = 6.9 stems m−2 and RMSEVD = 9.4 stems m−2) and morphology (MAEM = 4.2 cm; RMSEM = 5.9 cm) than Digital Aerial Photogrammetry (DAP) (MAEVH = 31.1 cm; RMSEVH = 38.1 cm; MAEVD = 12.7 stems m−2; RMSEVD = 16.6 stems m−2; MAEM = 11.3 cm; RMSEM = 17.2 cm). The accuracy of the classification procedure for vegetation calculation negligibly improves when RGB images are used as input parameters together with the LiDAR-UAV point cloud (MAEVH = 6.9 cm; RMSEVH = 9.4 cm; MAEVD = 10.0 stems m−2; RMSEVD = 14.0 stems m−2). However, it improves when used together with the DAP-UAV point cloud (MAEVH = 21.7 cm; RMSEVH = 25.8 cm; MAEVD = 15.2 stems m−2; RMSEVD = 18.7 stems m−2). Thus, we discourage using DAP-UAV-derived point clouds for high-resolution vegetation mapping of coastal areas, if not coupled with other data sources.

Ecohydraulics of Surrogate Salt Marshes for Coastal Protection: Wave–Vegetation Interaction and Related Hydrodynamics on Vegetated Foreshores at Sea Dikes

Vegetation on foreshores in close vicinity to sea dikes may prove beneficial as regulating ecosystem service in the context of coastal defense, dike safety, and flood protection by reducing loads on these defense structures. Predominantly, a decrease in wave heights and bottom shear stresses is hypothesized, which calls for an inclusion in design procedures of coastal defense structures. In contrast to heterogeneous and variable salt marsh vegetation, this study uses surrogate vegetation models for systematic hydraulic experiments in a wave flume, without modeling specific plant species a priori. Froude-scale experiments are performed in order to investigate the effect of salt marsh vegetation on the wave transformation processes on the foreshore and wave run-up at sea dikes. The effect of plant and wave properties on wave transmission, energy dissipation, and wave run-up at a 1:6 sloped smooth dike are presented and discussed, focusing on the wave–vegetation–structure interaction. Vegetated foreshores can contribute to wave attenuation, where an increasing relative vegetation height hv/h results in decreased wave run-up on the dike by up to 16.5% at hv/h = 1.0.

Salt marsh vegetation and secured woody debris facilitate the recolonization of Avicennia germinans

AbstractQuestionsDoes the presence of salt marsh vegetation affect the long‐term regeneration of the pioneer mangrove species Avicennia germinans in a degraded dwarf forest? Does immobilized coarse woody debris (CWD) affect regeneration similarly? Do larger trees suppress or facilitate intraspecific saplings?LocationDwarf mangrove forest in the high intertidal zone on the Bragança peninsula in northern Brazil.MethodsThe spatial patterns of A. germinans, the herbaceous halophyte Sesuvium portulacastrum, and CWD were mapped in three sample plots (each 400 m2) during two consecutive vegetation surveys, conducted in 2011 and 2014. Inhomogeneous Poisson and Thomas point process models were used to assess the distribution of A. germinans life‐history stages (seedlings, saplings, and adult dwarf trees), conditioned on the presence of S. portulacastrum and CWD. In addition, intraspecific interactions between trees and regeneration were assessed based on crown projection mapping. Bivariate point pattern analyses were used to assess the dependence of advance regeneration on dwarf A. germinans trees and S. portulacastrum.ResultsAvicennia germinans saplings and trees were positively associated with S. portulacastrum and CWD, whereas seedlings were located around tree crowns. The density of fruit‐bearing trees was positively associated with sapling density, indicating that regeneration relied on locally dispersed propagules.ConclusionsHerbaceous vegetation and CWD have an important ecological function in degraded mangroves by retaining tidally dispersed propagules. Here, we show that herbaceous vegetation does not suppress the growth of seedlings but facilitates mangrove recolonization. Due to limited tidal dispersal, regeneration relies on local propagule supply. In addition to hydrological restoration, the observed vegetation patterns suggest that, in the absence of propagule‐retaining vegetation, restoration of high‐intertidal mangroves can be facilitated by establishing nuclei of planted trees and installing secured logs.

Algal‐Induced Biogeomorphic Feedbacks Lay the Groundwork for Coastal Wetland Development

AbstractEcosystem establishment under adverse geophysical conditions is often studied within the “windows of opportunity” framework, identifying disturbance‐free periods (e.g., calm wave climate) where species can overcome establishment thresholds. However, the role of biogeophysical interactions in this framework is less well understood. The establishment of saltmarsh vegetation on tidal flats, for example, is limited by abiotic factors such as hydrodynamics, sediment stability and drainage. On tidal flats, raised sediment ridges colonized by algal mats (Vaucheria sp.) appear to accomodate high densities of plant seedlings. Such ridges were previously found to have higher sediment strength than substratum without algae. Here, we investigate whether these measurements can be explained by geophysical factors only, or that biological (Vaucheria‐induced) processes influence tidal marsh establishment by forming stabilized bedforms. We performed two experiments under controlled mesocosm conditions, to test the hypotheses that (a) Vaucheria grows better on elevated topographic relief, that (b) the binding force of their algal filaments increases sediment strength, and that (c) Vaucheria consequently creates elevated topographic relief that further facilitates algal growth. Our experimental results confirm the existence of this algal‐induced biogeomorphic feedback cycle. These findings imply that benthic algae like Vaucheria may contribute significantly to tidal marsh formation by creating elevated and stabilized substratum. This suggests biogeophysical feedbacks can “widen” the windows of opportunity for further ecosystem establishment. Our results could be useful for the design of managed realignment projects aimed at restoring the unique ecosystem services of coastal wetlands, such as habitat biodiversity, carbon sequestration potential and nature‐based flood defense.

Salt marsh establishment in poorly consolidated muddy systems: effects of surface drainage, elevation, and plant age

AbstractConservation and restoration of salt marsh ecosystems are becoming increasingly important because of the many ecosystem services they provide. However, the processes controlling salt marsh establishment and persistence, especially on bare tidal flats in muddy areas, remain unclear. As muddy sediments typically experience a restriction of soil drainage, we expect that a surface drainage relief due to a heterogeneity topography, as might occur on the edge of tidal channels, can facilitate the establishment of salt marsh vegetation on muddy tidal flats. By means of a manipulative field experiment, using “Mega‐Marsh Organ” mesocosms, we investigated the impact of surface drainage and elevation relative to mean sea level on (1) the survival of Spartina anglica seedlings from three different age classes: 1‐yr, 3‐month, and 1‐week; and (2) the growth performance of mature S. anglica marsh tussocks. S. anglica seedling survival, especially in the establishment phase, was positively affected by better surface drainage, increases of seedling age, and higher elevation relative to mean sea level. That is, the survival rate of S. anglica seedlings at the end of 6th week increased from 0% (at surface water undrained, 1‐week, 0 cm elevation) to 94.44% (at surface water drained, 1‐yr, 90 cm elevation). In contrast, surface drainage did not affect the performance of large S. anglica marsh tussocks, as only increased elevation relative to mean sea level was shown to affect S. anglica tussock growth in terms of plant height, shoot numbers, and dry biomass. Based on our findings, we proposed a conceptual model to understand how surface drainage‐driven feedbacks in a heterogeneous topography may be reinforced to induce salt marsh establishment in muddy systems. Further testing of present hypothesized model would be beneficial for insights into salt marsh establishment on tidal mudflats.

Carbon and nitrogen pools and mobile fractions in surface soils across a mangrove saltmarsh ecotone

In the subtropics, climate change is pushing woody mangrove forests into herbaceous saltmarshes, altering soil carbon (C) and nitrogen (N) pools, with implications for coastal wetland productivity and C and N exports. We quantified total C and N pools, and mobile fractions including extractable mineral N, extractable organic C and N, and active (aerobically mineralizable) C and N, in surface soils (top 7.6 cm) of adjacent mangrove (primarily Avicennia germinans) and saltmarsh (Juncus roemerianus) vegetation zones in tidal wetlands of west-central Florida (USA). We tested whether surface-soil accumulations of C, N, and their potentially mobile fractions are greater in mangrove than in saltmarsh owing to greater accumulations in the mangrove zone of soil organic matter (SOM) and fine mineral particles (C- and N-retaining soil constituents). Extractable organic fractions were 39–45% more concentrated in mangrove than in saltmarsh surface soil, and they scaled steeply and positively with SOM and fine mineral particle (silt + clay) concentrations, which themselves were likewise greater in mangrove soil. Elevation may drive this linkage. Mangrove locations were generally at lower elevations, which tended to have greater fine particle content in the surface soil. Active C and extractable mineral N were marginally (p < 0.1) greater in mangrove soil, while active N, total N, and total C showed no statistical differences between zones. Extractable organic C and N fractions composed greater shares of total C and N pools in mangrove than in saltmarsh surface soils, which is meaningful for ecosystem function, as persistent leaching of this fraction can perpetuate nutrient limitation. The active (mineralizable) C and N fractions we observed constituted a relatively small component of total C and N pools, suggesting that mangrove surface soils may export less C and N than would be expected from their large total C and N pools.

Fifteen years of habitat, floristic and vegetation change on a pioneer sand-dune and slack system at Ainsdale, north Merseyside, UK

Changes in habitat, floristics and vegetation between 2005 and 2019 were studied on 2.9 ha of sandy foreshore near Ainsdale-on-Sea, north Merseyside. Named the ‘New Green Beach’, the site initially supported saltmarsh vegetation but, within five years, a 30-35 m-wide embryo dune ridge had formed, eventually 3.5 m high, backed by a 300 x 30 m seasonally flooded, calcareous dune-slack. The latter was colonised by pioneer slack plants, after which it rapidly developed areas of tall-herb fen and Alnus/Salix carr, while saltmarsh plants declined. During succession, species recorded as ‘rare’ became fewer in number while a higher frequency of ‘abundant’ taxa was recorded. The number of vascular plants listed annually increased from one in 2005 to 154 in 2019, though the rate of addition of new plants fell after 2010. Overall, 246 taxa were identified during the study. Only 9% of these were non-native, 17% being regionally or nationally notable, including 16 Red-listed species. Very poor statistical fits were obtained to recognised UK National Vegetation Classification vegetation types. Analysis of Ellenberg Indicator Values for salinity, nitrogen, moisture and reaction showed that the plant community became progressively adapted to low salinity, lower fertility, drier conditions and a less basic soil. The findings are discussed in relation to comparable studies elsewhere in Britain and Northern Europe. The rate of succession on the New Green Beach seems remarkably high, while evidence of declining soil fertility over time was unexpected.

Saltmarsh vegetation and social environment influence flexible seasonal vigilance strategies for two sympatric migratory curlew species in adjacent coastal habitats

BackgroundAnimals need to adjust their vigilance strategies when foraging between physically contrasting vegetated and non-vegetated habitats. Vegetated habitats may pose a greater risk for some if vegetation characteristics function as a visual obstruction but benefit others if they serve as protective shelter. Variation in group size, presence of similar species, along with variation in environmental conditions and anthropogenic disturbance can also influence vigilance investment.MethodsIn this study, we quantified the vigilance behaviour of two large-bodied, sympatric migratory curlew species—Far Eastern Curlew (Numenius madagascariensis) and Eurasian Curlew (N. arquata)—in vegetated Suaeda salsa saltmarsh and non-vegetated mudflat habitat in Liaohekou National Nature Reserve, China. We used linear mixed models to examine the effects of habitat type, season, tide time, flock size (conspecific and heterospecific), and human disturbance on curlew vigilance investment.ResultsBoth species spent a higher percentage of time under visual obstruction in S. salsa habitat compared to mudflat habitat but in response, only Far Eastern Curlew increased their percentage of vigilance time, indicating that visual obstruction in this habitat is only a concern for this species. There was no evidence that S. salsa vegetation served as a form of cryptic background colouration since neither species decreased their vigilance effect in S. salsa habitat in spring compared to the autumn migration season. The effect of curlew social environment (i.e. flock size) was habitat dependent since percentage of vigilance time by curlews in saltmarsh increased with both the number of individual curlews and number of other birds present, but not in mudflat habitat.ConclusionsWe conclude that both migratory curlew species exhibit a flexible vigilance adjustment strategy to cope with the different environmental and social conditions of adjacent and sharply contrasting coastal habitats, and that the trade-off between the risks of foraging and the abundance of prey may be a relatively common phenomenon in these and other shorebird populations.

Monitoring Impact of Salt-Marsh Vegetation Characteristics on Sedimentation: an Outlook for Nature-Based Flood Protection

Salt marshes can protect coastlines against flooding by attenuating wave energy and enhancing shoreline stabilization. However, salt-marsh functioning is threatened by human influences and sea level rise. Although it is known that protection services are mediated by vegetation, little is known about the role of vegetation structure in salt-marsh accretion. We investigated the role of vegetation presence, vegetation type and structural vegetation characteristics in sedimentation and sediment grain size. We established 56 plots on a salt marsh on the Dutch Wadden island of Texel. Plots were divided over four vegetation types contrasting in vegetation structure and varied in elevation and distance to creeks. Vegetation presence was controlled by clipping in subplots. Within each plot, we measured seven vegetation characteristics, sedimentation and the sediment grain size distribution. Furthermore, we explored the effect of the natural variation in vegetation structure on wave attenuation with a simple model approach. For this, we developed vegetation scenarios based on the field measurements of stem height, diameter and density. We found that vegetation presence increased sedimentation on average by 42%. Sedimentation was highest in Salicornia vegetation and increased with stem height and branching level. Grain size also seemed to increase with branching level. Modelled wave attenuation was 7.5 times higher with natural vegetation compared to topography only, was strongest for Spartina vegetation and most sensitive to the natural variance in stem density. Our results can be used to improve predictions of salt-marsh accretion and the implementation of salt marshes in nature-based flood defences.

Effects of the Water-Sediment Regulation Scheme on the Expansion of Spartina alterniflora at the Yellow River Estuary, China

In recent decades, the invasion of saltmarsh plant Spartina alterniflora (S. alterniflora) over a large part of coastal wetlands in China, including the Yellow River Estuary (YRE) as a regional economic hub and global ecosystem services hotspot, has caused increasing concern because of its serious threats to native ecosystems. During the same period, local authorities have implemented a Water-Sediment Regulation Scheme (WSRS) in the Yellow River for flood mitigation and delta restoration purposes. The altered hydrological regime has resulted in unintended changes to estuarine ecosystem. However, the direct consequence of the WSRS on the expansion of S. alterniflora remains unclear. In this study, quantitative relationship between the inter- and intra-annual expansion patterns of S. alterniflora represented by relevant landscape metrics and indicators that quantify the concurrent variations of river and sediment discharges as the proxy of the WSRS impacts were analysed over the period of Year 2011–2018, and the analyses were performed on the YRE as a whole and on five different zones subdivided based on the invasion sequence. The results showed that there was no significant difference in the inter-annual area variation of S. alterniflora between the years with and without WSRS. Compared with the years without WSRS (2016–2017), the intra-annual (monthly) increment of the various landscape metrics [i.e., NP (number of patches), CA (class area), LPI (largest patch index) and AI (aggregation index] were found to be significantly higher in the initial stage of peak growing season (June-July) than in the mid- and late stages (July-September) in the years with WSRS (2011–2015, 2018) in the subregion located close to the south bank of YRE as the most prominent impact zone. In addition, F (mean flow), Ff (number of high flow pulses), Tf (Julian date of maximum flow) and D (duration of WSRS) were identified as the explanatory variables for the intra-annual vegetation landscape pattern changes, and their relative contributions to resultant changes were also assessed. Our results broaden the understanding of estuarine hydrological disturbance as a potential driver regulating the saltmarsh vegetation, and also have implications for S. alterniflora invasion control at estuaries under changing environment.

Assessment of coastal salt marsh plants on the Arabian Gulf region.

Salt marshes form along coastlines and are very interesting ecosystems due to their function and services. In the future, salt marsh plants might provide food and medicine as crops irrigated via seawater in hyper-arid regions. In the Arabian Gulf, little is known about salt marsh vegetation. Therefore, a targeted search on scientific literature was performed to provide a comprehensive assessment. Hence, current knowledge of the extent and status of salt marsh in the Arabian Gulf region was reviewed, based on literature-based analysis. Then, historic trends of salt marsh publications were carefully inspected. This study provides a list of salt marsh families and their genera and species, with a total of 51 family 179 genera 316 species in the Arabian Gulf. The largest family was Chenopodiaceae followed by Poaceae, Asteraceae. Moreover, this study identified some of the gaps that could help future directions for scientific research, and help making decisions of conservation, management policies and procedures.

Erosion protection by winter state of salt marsh vegetation

The inclusion of coastal ecosystems in coastal protection strategies is highly desired, but for temperate regions it is hampered by uncertainty about the provision of relevant ecosystem services over the annual growth cycle. This flume study compared winter stages of the two salt marsh species Spartina anglica and Elymus athericus with and without above ground biomass to bare soil to assess their protection service against vertical bed erosion in the surf and swash zone. Results yielded no effect of the above ground biomass on mean erosion, even though the species responded differently with E. athericus buckling and S. anglica withstanding the hydrodynamic forcing. Equally, no significant differences were observed between species which is attributed to the comparable dry root biomass and soil bulk density of the used vegetated patches. While this similarity does not allow for establishment of quantitative relationships, the results suggest a species independent erosion protection efficiency persisting throughout the year. This has the potential to simplify the consideration of erosion protection by salt marsh in coastal protection strategies, as it alleviates the need for detailed differentiation on species or seasonal level of this ecosystem service.

Planting after shoreline cleanup treatment improves salt marsh vegetation recovery following the Deepwater Horizon oil spill

The Deepwater Horizon oil spill (2010) resulted in ~100 km of heavily oiled salt marsh shorelines with severe marsh vegetation impacts. Approximately 27 km of these shorelines had marsh cleanup treatments aimed at limiting oil spread and facilitating ecological recovery. Heavy oiling impacts and disturbance from intensive cleanup treatments left marsh shorelines largely bare of live vegetation. Following operational-scale shoreline cleanup and experimental planting of Spartina alterniflora, we compared oiling degree and vegetation recovery among three types of heavily oiled salt marsh plots over three years: oiled control (no cleanup treatment, no planting); mechanical cleanup treatment (unplanted); and mechanical treatment coupled with planting. Nearby reference plots were used to define recovery targets and determine recovery progress. Mechanical treatment with planting showed the most improvement in oiling conditions and was most effective in re-establishing vegetation cover and dominant plant species composition approaching reference conditions. In contrast, the oiled controls and mechanical treatment plots without planting were similar and showed much slower recovery trends. Vegetation planting should be considered as a shoreline treatment or restoration approach for heavily oiled salt marshes, especially where oil impacted areas are left largely unvegetated, natural recovery is delayed, marsh shorelines are at risk of erosion, and as a possible condition for the use of intensive cleanup treatments. Vegetation planting following oil spills could be incorporated into shoreline treatment operations during emergency response as shoreline stabilization and for oil removal via phytoremediation, or as emergency restoration under the Natural Resources Damage Assessment (NRDA) process, to limit the degree and duration of natural resource impacts.