Marsh Surface Research Articles

Anthropogenic Modifications Can Significantly Influence the Local Mean Sea Level and Affect the Survival of Salt Marshes in Shallow Tidal Systems

AbstractIn a shallow dissipative tidal system, interventions that modify the local morphology in one location of the basin may quickly affect the surrounding areas, promoting strong changes in their morphology. If the localized modification persists over time, it may produce far‐field morphological modifications at delayed times. These modifications may have an impact on the local mean sea level and on tidal range, affecting the fate of salt marshes with implications for their survival. In this study, we investigate the effect of two anthropic interventions performed between the end of the nineteenth century and the beginning of the twentieth century in the northern Venice lagoon (Italy): the construction of jetties at one inlet and the removal of reed barriers protecting a fish farm in the inner lagoon. Using a 2‐D numerical model to reproduce the hydrodynamics of different historical lagoon configurations and a zero dimensional model of marsh vertical accretion, we investigate the effect of these interventions on the salt marshes of the northern lagoon basin. Interestingly, our results show that the increased depth at the inlet induced by the jetties lowered the local mean sea level of nearby areas and increased the tidal range, producing a temporary positive feedback on the stability of the marshes in proximity of the inlet. On the contrary, in the inner lagoon areas characterized by extremely low marshes, the removal of reed barriers delimiting a fish farm may have reduced the sediment fluxes thus contributing to the drowning of large marsh surfaces.

Characterizing the Pathway and Rate of Salt Marsh Vegetation Dynamics: a Multivariate Approach

The ability of plants to enhance sedimentation is a critical factor in modeling the evolution and fate of salt marshes under future scenarios of climate change. Most eco-geomorphic models have been developed based on the changing biomass of a single species (e.g., Spartina alterniflora) through time; therefore, it still remains a challenge to predict how a vegetation cover consisting of multiple species will change through interspecific competition and facilitation under sea-level variations. In a temperate marsh of the Danish Wadden Sea, the plant species composition across a total of 402 quadrats (1 m2) was compared between 2006 and 2012 using multivariate ordination techniques. At low-elevation sites ( 80% relative proportion), the rate of vegetation change was nearly zero, due to little encroachment of other species into this already stable, dense matrix. These discussions imply that the direction and rate of multi-species interactions can be predicted by the initial environmental (i.e., marsh surface elevation, soil bulk density, distance from tidal creek) and biological conditions (i.e., plant species richness and abundance). Based on these findings, it is proposed that the evolution of salt marshes will be better understood by more explicit incorporation of multi-species interactions into future eco-geomorphic modeling efforts.

Biogeochemical characteristics and fluxes of suspended particulate organic matter in response to low‐tide rainfall

AbstractWe evaluated the effects of low‐tide rainfall on salt marsh particulate organic carbon (POC) cycling. Suspended sediment samples from intertidal creeks were collected during rain and no‐rain conditions. Bulk (carbon, nitrogen) and molecular (e.g., lignin) compositions of organic constituents in particulates were analyzed. Temporal patterns of suspended sediment concentration mimic fluctuations in rainfall intensity, but all POC constituents do not necessarily follow these patterns. For example, particulate organic matter concentrations in water column covaried with rain intensity yet organic matter (OM) contents in the particles showed trivial correlations with rain. In general, rainfall effects raised the suspended sediment and organic constituent concentrations in the water column by up to three orders of magnitude. Multivariate statistical analysis revealed that the rainfall‐entrained particulates were compositionally distinct from calm weather suspended particulates, from salt marsh surface sediment, and from creek bank surface sediment. Rainfall‐entrained particulates are depleted in bulk organic carbon and phytoplankton‐derived OM but enriched in lignin phenols. These observations indicate that rainfall‐runoff processes preferentially mobilize POC derived from Spartina alterniflora from marsh platforms and effectively transport these materials to intertidal creeks following low‐tide rainfall events. Moreover, average net transport rates by rainfall are 0.020 ± 0.002 gPOC m−2 mmRain−1, and this POC turnover rate amounts to ∼ 19% of the annual POC export from estuary to ocean. Therefore, estuarine outwelling estimates typically made under calm weather conditions represent minimum levels of POC export. Hence, low‐tide rainfall can be expected to substantially enhance the delivery of marsh‐derived POC to the coastal ocean.

Crab Burrowing Limits Surface Litter Accumulation in a Temperate Salt Marsh: Implications for Ecosystem Functioning and Connectivity

Burial of aboveground plant litter by animals reduces the amount available for surface transport and places it into a different environment, affecting decomposition rates and fluxes of organic matter to adjacent ecosystems. Here we show that in a Southwestern Atlantic salt marsh the burrowing crab Neohelice granulata buries aboveground plant litter at rates (0.5–8 g m−2 day−1) comparable to those of litter production (3 g m−2 day−1). Buried litter has a low probability (0.6%) of returning to the marsh surface. The formation of burrow excavation mounds on the marsh surface is responsible for most litter burial, whereas litter trapped in burrows was an order of magnitude lower than rates of burial under excavation mounds. Crab exclusion markedly increased surface litter accumulation (3.5-fold in just 21 days). Tides with the potential to transport significant amounts of surface litter are infrequent; hence, most litter is buried before it can be transported elsewhere or decomposes on the surface. Crab litter burial can account for the observed low levels of surface litter accumulation in this ecosystem and likely drives organic matter transformation and export. The impacts of ecosystem engineering by this crab species are therefore substantial and comparable in magnitude to the large effects found for tropical crabs and other litter-burying organisms, such as anecic earthworms.

Numerical simulations of Holocene salt-marsh dynamics under the hypothesis of large soil deformations

Abstract Salt marshes are vulnerable environments hosting complex interactions between physical and biological processes. The prediction of the elevation dynamics of a salt-marsh platform is crucial to forecast its future behavior under potential changing scenarios. An original finite-element (FE) numerical model accounting for the long-term marsh accretion and compaction linked to relative sea level rise is proposed. The accretion term considers the material sedimentation over the marsh surface, whereas the compaction reflects the progressive consolidation of the porous medium under the increasing load of the overlying younger deposits. The modeling approach is based on a 2D groundwater flow simulator coupled to a 1D vertical geomechanical module, where the soil properties may vary with the effective intergranular stress. The model takes also into account the geometric non-linearity arising from the consideration of large solid grain movements by using a Lagrangian approach with an adaptive FE mesh. The numerical experiments show the potentiality of the proposed 2D model, which consistently integrates in modeling framework the behavior of spatially distributed model parameters. High sedimentation rates and low permeabilities largely impact on the mechanism of soil compaction following the overpressure dissipation.

Does National Wetland Inventory class consistently identify vegetation and edaphic differences in Oregon tidal wetlands?

Accurately mapping, modeling, and managing the diversity of wetlands present in estuaries often relies on habitat classification systems that consistently identify differences in biotic structure or other ecosystem characteristics between classes. We used field data from four Oregon estuaries to test for differences in vegetation structure and edaphic characteristics among three tidal emergent marsh classes derived from National Wetlands Inventory (NWI) data: low marsh, high marsh, and palustrine tidal marsh. Independently of NWI class, we also evaluated the number and types of plant assemblages present and how edaphic variables, non-native plant cover, and plant species richness varied among them. Pore water salinity varied most strongly across marsh classes, with sediment carbon and nitrogen content, grain size and marsh surface elevation showing smaller differences. Cover of common vascular plant species differed between marsh classes and overall vegetation composition was somewhat distinct among marsh types. High marsh had the largest species pools. However, plot-level plant diversity was similar among marsh classes. Non-native species cover was highest in palustrine and high marshes. The marshes in the study contained a large number of plant assemblages with most occurring across more than one marsh class. The more common assemblages occurred along a continuum of tidal elevation, soil salinity, and edaphic characteristics, with varying plant richness and non-native cover. Our data suggest that NWI classes are useful for differentiating several general features of Oregon tidal marsh structure, but that more detailed information on plant assemblages found within those wetland classes would allow more precise characterization of additional wetland features such as edaphic conditions and plant diversity.

The effect of source suspended sediment concentration on the sediment dynamics of a macrotidal creek and salt marsh

Seasonal variability in the sediment dynamics of a Bay of Fundy tidal creek and salt marsh system was analyzed to better understand the ecomorphodynamics of a high suspended sediment concentration intertidal habitat. Data were collected over 62 tides for velocity, suspended sediment concentration, deposition, and grain size at four stations from the creek thalweg to the marsh surface. Five topographic surveys were also conducted throughout the 14-month study. Deposition rates per tide varied spatially from 56.4gm-2 at the creek thalweg to 15.3gm-2 at the marsh surface. Seasonal variations in deposition in the creek and marsh surface were from 38.0gm-2 to 97.7gm-2 and from 12.2gm-2 to 19.6gm-2 respectively. Deposition and erosion were greatest in late fall and winter. This seasonal change, led by higher suspended sediment concentrations, was observed in the creek and at the marsh bank but notably absent from the marsh edge and marsh surface. Sediments were predominantly deposited in floc form (76–83%). Because of high floc content, higher suspended sediment concentrations led to more rapid loss of sediment from suspension. With increasing sediment concentration, deposition increased in the tidal creek and at the marsh bank but not at the marsh edge or marsh surface. This suggests that in highly flocculated environments the water column clears fast enough that very little sediment remains in suspension when the water reaches the marsh and that the sediment concentration during marsh inundation is independent of the initial concentration in the creek.

Assessment of Plant Community Characteristics in Natural and Human-Altered Coastal Marsh Ecosystems

Salt marsh ecosystems provide many critical ecological functions, yet they are subject to considerable disturbance ranging from direct human alteration to increased inundation due to climate change. We assessed emergent salt marsh plant characteristics in the Tuckerton Peninsula, a large expanse (~ 2000 ha) of highly inundated habitat along the southern New Jersey coast, USA. Key salt marsh plant parameters were monitored in the heavily grid-ditched northern segment, Open Marsh Water Management (OMWM) altered central segment, and the shoreline altered southern segment of the peninsula in the summer months of 2011 and 2013. Plant species composition and three metrics of abundance and structure (maximum canopy height, percent areal cover, and shoot density) were examined among marsh segments, along transects within segments, seasonally by month and between years. Despite seasonal or annual variability, the northern segment of the marsh differed in plant species composition from the central and southern segments. This difference was partly due to greater percent areal cover in the northern segment of upper marsh species such as Spartina patens and Distichlis spicata. S. patens also exhibited higher shoot densities in the northern segment than the central segment. Despite the higher abundance of upper marsh species, marsh surface elevations were lower in the northern segment than in the central or southern segments, suggesting the influence of altered hydrology due to human activities. Understanding current variation in the emergent salt marsh vegetation along the peninsula will help inform future habitat change in other coastal wetlands of New Jersey and the mid-Atlantic region subject to natural and anthropogenic drivers.

Impacts of Fertilization and Tidal Inundation on Elevation Change in Microtidal, Low Relief Salt Marshes

We evaluated the importance of both tidal inundation and nutrient fertilization as drivers of elevation change in coastal salt marshes. The three sites investigated occurred along a 9-km stretch of the Atlantic Intracoastal Water Way in Central North Carolina. Despite their close geographic proximity, the sites varied in tidal range, elevation within the tidal frame, and stem height and stem density of Spartina alterniflora. Total standing aboveground biomass and marsh surface elevation change (measured by surface elevation tables; SETs) were documented during a 3-year period of nutrient fertilization and for two additional years after fertilization ceased. Measured elevation change rates in control plots varied from 0.2 to 1.2 cm year−1 and were negatively correlated with starting elevation (r 2 = 0.82, p < 0.05). Fertilization resulted in increases in both standing aboveground biomass and marsh surface elevation change. Fertilized sites gained 0.69 to 2.1 cm year−1 during the 3-year application period and 0.02 to 0.97 cm year−1 during the post application period. The magnitude of the fertilization-induced elevation response was mediated by position in the tidal frame with sites that were lower gaining less elevation relative to controls than sites that were higher. The data presented here suggest that nutrient fertilization may be an effective adaptive management strategy for helping minerogenic marshes keep pace with sea level, but that the impact of fertilization may depend on tidal inundation.

Land loss by pond expansion on the Mississippi River Delta Plain

AbstractThe world's river deltas may collapse under the combined effects of rising sea levels, subsidence, and reduced sediment supply. Saving these deltaic environments requires quantifying processes driving collapse. In the Mississippi River Delta, rapid land loss offers an important opportunity to test existing theories for marsh collapse. We use Landsat images to examine how pond expansion by edge retreat contributes to land loss over 34 years in the Atchafalaya‐Vermillion, Terrebonne, and Barataria basins of the Mississippi Delta. Tracking the area changes in ponds on the marsh surface, we find a striking consistency between pond expansion direction and the dominant wind direction and show that wind‐generated waves are capable of causing edge erosion. Expansion rate increases rapidly for ponds wider than 300 m in Terrebonne and Barataria basins. From this, we suggest that ponds in Atchafalaya‐Vermillion basin are stable, whereas ponds in Terrebonne and Barataria are unstable.

Nekton Use of Flooded Salt Marsh and an Assessment of Intertidal Creek Pools as Low-Tide Refuges

Patterns of nekton occurrence on the salt marsh surface at high tide and in an adjacent intertidal creek pool at low tide were used to investigate movements of nekton in an intertidal basin. Paired collections were made in North Inlet estuary, SC on 67 dates over 9 years. Comparisons of high- and low-tide total abundance indicated that what remained in the creek pool at low tide was representative of the nekton on the flooded marsh. Of the 64 taxa collected, the same 8 species ranked in the top 10 in both the high- and low-tide collections. Abundances of most resident species were positively correlated with the area of marsh flooded, but mummichog (Fundulus heteroclitus), the most abundant resident, was not. Abundances of young-of-the-year transient species were not related to the extent of tidal flooding. Some transient species used the flooded marsh but did not occupy the pool at low tide, and others found in the pool did not use the marsh. Differences in abundance, biomass, and length between the marsh and pool collections indicated differences in the tendency of species and life stages to retreat downstream of the pool to the subtidal channel. Proportionately more of the nekton that were present on the flooded marsh left the intertidal basin when large changes in temperature and salinity occurred between high and low tides. More transients left the basin following higher tides, but more residents did not. The results demonstrate a wide range of taxonomic and ontogenetic patterns among nekton using intertidal salt marsh basins and the underappreciated importance of intertidal creek pools as alternative low-tide refuges.

Environmental assessment of Al-Hammar Marsh, Southern Iraq.

Aim(a) To determine the spatial distributions and levels of major and minor elements, as well as heavy metals, in water, sediment, and biota (plant and fish) in Al-Hammar Marsh, southern Iraq, and ultimately to supply more comprehensive information for policy-makers to manage the contaminants input into the marsh so that their concentrations do not reach toxic levels. (b) to characterize the seasonal changes in the marsh surface water quality. (c) to address the potential environmental risk of these elements by comparison with the historical levels and global quality guidelines (i.e., World Health Organization (WHO) standard limits). (d) to define the sources of these elements (i.e., natural and/or anthropogenic) using combined multivariate statistical techniques such as Principal Component Analysis (PCA) and Agglomerative Hierarchical Cluster Analysis (AHCA) along with pollution analysis (i.e., enrichment factor analysis)MethodsWater, sediment, plant, and fish samples were collected from the marsh, and analyzed for major and minor ions, as well as heavy metals, and then compared to historical levels and global quality guidelines (WHO guidelines). Then, multivariate statistical techniques, such as PCA and AHCA, were used to determine the element sourcing.ResultsWater analyses revealed unacceptable values for almost all physio-chemical and biological properties, according to WHO standard limits for drinking water. Almost all major ions and heavy metal concentrations in water showed a distinct decreasing trend at the marsh outlet station compared to other stations. In general, major and minor ions, as well as heavy metals exhibit higher concentrations in winter than in summer. Sediment analyses using multivariate statistical techniques revealed that Mg, Fe, S, P, V, Zn, As, Se, Mo, Co, Ni, Cu, Sr, Br, Cd, Ca, N, Mn, Cr, and Pb were derived from anthropogenic sources, while Al, Si, Ti, K, and Zr were primarily derived from natural sources. Enrichment factor analysis gave results compatible with multivariate statistical techniques findings. Analysis of heavy metals in plant samples revealed that there is no pollution in plants in Al-Hammar Marsh. However, the concentrations of heavy metals in fish samples showed that all samples were contaminated by Pb, Mn, and Ni, while some samples were contaminated by Pb, Mn, and Ni.Discussion and conclusionsDecreasing of Tigris and Euphrates discharges during the past decades due to drought conditions and upstream damming, as well as the increasing stress of wastewater effluents from anthropogenic activities, led to degradation of the downstream Al-Hammar Marsh water quality in terms of physical, chemical, and biological properties. As such properties were found to consistently exceed the historical and global quality objectives. However, element concentration decreasing trend at the marsh outlet station compared to other stations indicate that the marsh plays an important role as a natural filtration and bioremediation system. Higher element concentrations in winter were due to runoff from the washing of the surrounding Sabkha during flooding by winter rainstorms. Finally, the high concentrations of heavy metals in fish samples can be attributed to bioaccumulation and biomagnification processes.

Allometry data and equations for coastal marsh plants

AbstractCoastal marshes are highly valued for ecosystem services such as protecting inland habitats from storms, sequestering carbon, removing nutrients and other pollutants from surface water, and providing habitat for fish, shellfish, and birds. Because plants largely determine the structure and function of coastal marshes, quantifying plant biomass is essential for evaluating these ecosystem services, understanding the biogeochemical processes that regulate ecosystem function, and forecasting tidal wetland responses to accelerated sea level rise. Allometry is a convenient and efficient technique for nondestructive estimation of plant biomass, and it is commonly used in studies of carbon and nitrogen cycles, energy flows, and marsh surface elevation change. We present plant allometry data and models developed for three long‐term experiments at the Smithsonian Global Change Research Wetland, a brackish marsh in the Rhode River subestuary of the Chesapeake Bay. The dataset contains 9,771 measurements of stem height, dry mass, and (in 9638 cases) stem width across 11 plant species. The vast majority of observations are for Schoenoplectus americanus (8430) and Phragmites australis (311), with fewer observations for other common species: Amaranthus cannabinus, Atriplex patula, Iva frutescens, Kosteletzkya virginica, Polygonum hydropiper, Solidago sempervirens, Spartina alterniflora, Spartina cynosuroides, and Typha angustifolia. Allometric relationships take the form of linear regressions of biomass (transformed using the Box‐Cox procedure) on either stem height and width, or on stem height alone. Allometric relationships for Schoenoplectus americanus were not meaningfully altered by elevated CO2, N enrichment, the community context, interannual variation in climate, or year, showing that a single equation can be used across a broad range of conditions for this species. Archived files include: (1) raw data used to derive allometric equations for each species, (2) reports and evaluations of the allometric equations we derived from the data, and (3) R code with which our derivations can be replicated. Methodological details of our experiments, data collection efforts, and statistical modeling are described in the metadata. The allometric equations can be used for biomass estimation in empirical and modeling studies of North American coastal wetlands, and the data can be used in ecological studies of terrestrial plant allometry.

Multiple Reoccupations after Four Paleotsunami Inundations (0.3–1.3 ka) at a Prehistoric Site in the Netarts Littoral Cell, Northern Oregon Coast, USA

Netarts Bay is the setting of one of the largest concentrations of late prehistoric Native American settlements on the tectonically active Oregon coast. A prehistoric site (35TI74) exposed by sea cliff erosion in 1998 at the south end of the Netarts littoral cell contained a stratigraphic record of activity by prehistoric Native Americans and interbedded paleotsunami deposits. The nearfield paleotsunamis were produced by great Cascadia earthquakes (Mw8.5 ± 0.5) emanating from the Cascadia Subduction Zone offshore, as previously documented in episodically buried tidal marsh surfaces at the south end of Netarts Bay and in many other estuaries in the region. The cultural deposits at 35TI74 reflect multiple reoccupations by Native Americans at this barrage creek flood plain site between paleotsunami runup events (≥7.5 m elevation) at 1.3 ka, 1.1 ka, 0.8–0.9 ka, and 0.3 ka. The conditions that led to the exposure of 35TI74 are traced to erosion of a protective beach dune ramp at the south end of the Netarts littoral cell, placing the site within reach of progressive storm‐surf erosion. The diminishing geoarchaeological record at 35TI74 represents a microcosm of the sea cliff erosional processes that threaten vulnerable prehistoric shoreline archaeological sites along much of the Pacific Northwest Coast.

Anopheles fauna of coastal Cayenne, French Guiana: modelling and mapping of species presence using remotely sensed land cover data.

Little is known about the Anopheles species of the coastal areas of French Guiana, or their spatiotemporal distribution or environmental determinants. The present study aimed to (1) document the distribution of Anopheles fauna in the coastal area around Cayenne, and (2) investigate the use of remotely sensed land cover data as proxies of Anopheles presence. To characterise the Anopheles fauna, we combined the findings of two entomological surveys that were conducted during the period 2007-2009 and in 2014 at 37 sites. Satellite imagery data were processed to extract land cover variables potentially related to Anopheles ecology. Based on these data, a methodology was formed to estimate a statistical predictive model of the spatial-seasonal variations in the presence of Anopheles in the Cayenne region. Two Anopheles species, known as main malaria vectors in South America, were identified, including the more dominant An. aquasalis near town and rural sites, and An. darlingi only found in inland sites. Furthermore, a cross-validated model of An. aquasalis presence that integrated marsh and forest surface area was extrapolated to generate predictive maps. The present study supports the use of satellite imagery by health authorities for the surveillance of malaria vectors and planning of control strategies.

Deposition of nanocomposite coatings on wood using cold discharges at atmospheric pressure

This work examines the synthesis of nanocomposite thin films on wood (sugar maple, Acer saccharum, Marsh) surfaces via a one-step process in an atmospheric pressure dielectric barrier discharge (DBD). More specifically, ZnO-SiO2 nanocomposite coatings are obtained from the atomization in the DBD reactor operated in N2/N2O (Townsend discharge) of a stable colloidal suspension. This suspension is made of crystalline ZnO nanoparticles (NPs) dispersed in hexamethyldisiloxane (HMDSO) and pentane (Pe). Scanning electron microscopy (SEM) combined with energy dispersive X-ray spectroscopy (EDS) show ZnO agglomerates well embedded into a dense SiO2 matrix. The chemical composition and the thickness of the matrix is analyzed through Fourier transform infrared spectroscopy (FT-IR) coupled to ellipsometry measurements. SEM further reveals a lumpy morphology; a feature ascribed to the intrinsic roughness of the wood samples.

Forecasting tidal marsh elevation and habitat change through fusion of Earth observations and a process model

AbstractReducing uncertainty in data inputs at relevant spatial scales can improve tidal marsh forecasting models, and their usefulness in coastal climate change adaptation decisions. The Marsh Equilibrium Model (MEM), a one‐dimensional mechanistic elevation model, incorporates feedbacks of organic and inorganic inputs to project elevations under sea‐level rise scenarios. We tested the feasibility of deriving two key MEM inputs—average annual suspended sediment concentration (SSC) and aboveground peak biomass—from remote sensing data in order to apply MEM across a broader geographic region. We analyzed the precision and representativeness (spatial distribution) of these remote sensing inputs to improve understanding of our study region, a brackish tidal marsh in San Francisco Bay, and to test the applicable spatial extent for coastal modeling. We compared biomass and SSC models derived from Landsat 8, DigitalGlobe WorldView‐2, and hyperspectral airborne imagery. Landsat 8‐derived inputs were evaluated in a MEM sensitivity analysis. Biomass models were comparable although peak biomass from Landsat 8 best matched field‐measured values. The Portable Remote Imaging Spectrometer SSC model was most accurate, although a Landsat 8 time series provided annual average SSC estimates. Landsat 8‐measured peak biomass values were randomly distributed, and annual average SSC (30 mg/L) was well represented in the main channels (IQR: 29–32 mg/L), illustrating the suitability of these inputs across the model domain. Trend response surface analysis identified significant diversion between field and remote sensing‐based model runs at 60 yr due to model sensitivity at the marsh edge (80–140 cm NAVD88), although at 100 yr, elevation forecasts differed less than 10 cm across 97% of the marsh surface (150–200 cm NAVD88). Results demonstrate the utility of Landsat 8 for landscape‐scale tidal marsh elevation projections due to its comparable performance with the other sensors, temporal frequency, and cost. Integration of remote sensing data with MEM should advance regional projections of marsh vegetation change by better parameterizing MEM inputs spatially. Improving information for coastal modeling will support planning for ecosystem services, including habitat, carbon storage, and flood protection.

Ecogeomorphic relations between marsh surface elevation and vegetation properties in a temperate multi‐species salt marsh

AbstractSalt marshes represent a fascinating example of an ecosystem whose dynamic response to climate change is chiefly governed by a two‐way bio‐physical coupling between marsh ecology and geomorphology. Relationships between vegetation biomass and marsh surface elevation, and between vegetation biomass and its physical properties that influence sedimentation rates, have been progressively formulated in the literature in order to provide mechanistic understandings and mathematical model descriptions of these ecogeomorphic feedbacks. In this study, a field survey was conducted in a temperate salt marsh grown by multiple halophyte species in order to quantify and validate these empirical relationships, yet in a location characterized by different climatic and ecological conditions from the locations where these relationships were initially derived. Regression analysis revealed that vegetation biomass can be expressed as a linearly increasing function of marsh elevation, providing therefore a direct empirical validation for such a relationship previously reported in the literature and implemented in some ecogeomorphic models. However, previously documented allometric relationships between total standing biomass and vegetation morphometrics – namely stem diameter, stem density and projected plant area per unit volume – were not confirmed by our results, which only showed an allometric scaling for stem height. These results suggest that previously documented formulations of mineral sediment trapping processes modulated by plants, which are partly derived on the basis of these allometric relationships, are not generally validated for multi‐species salt marshes. Therefore, existing models that apply these process‐based equations to study marsh evolution in a multi‐species context may not capture in detail the vegetation‐induced geomorphic work. Copyright © 2016 John Wiley &amp; Sons, Ltd.

Impact of Hurricane Sandy on salt marshes of New jersey

Hurricane Sandy, one of the largest Atlantic hurricanes on record, made landfall as an extratropical cyclone on the coast of New Jersey (29 October 2012) along a track almost perpendicular to the coast. Ten days later a northeaster caused heavy precipitation and elevated water levels along the coast. Two years of pre-storm monitoring and research in marshes of Barnegat Bay and the Delaware Estuary provided an opportunity to evaluate the impacts of Hurricane Sandy and the succeeding northeaster across the region. Peak water levels during Sandy ranged from 111 to 184 cm above the marsh surface in Barnegat Bay and 75–135 cm above the marsh surface in the Delaware Estuary. Despite widespread flooding and damage to coastal communities, the storm had modest and localized impacts on coastal marshes of New Jersey. Measurements made on the marsh platform illustrated localized responses to the storms including standing biomass removal, and changes in peak biomass the following summer. Marsh surface and elevation changes were variable within marshes and across the region. Localized elevation changes over the storm period were temporary and associated with subsurface processes. Over the long-term, there was no apparent impact of the 2012 storms, as elevations and regression slopes pre- and several months post-storm were not significant. Vegetation changes in the summer following the fall 2012 storms were also variable and localized within and among marshes. These results suggest that Hurricane Sandy and the succeeding northeaster did not have a widespread long-term impact on saline marshes in this region. Possible explanations are the dissipation of surge and wave energy from the barrier island in Barnegat Bay and the extreme water levels buffering the low-lying marsh surface from waves, winds, and currents, and carrying suspended loads past the short-statured marsh grasses to areas of taller vegetation and/or structure. These findings demonstrate that major storms that have substantial impacts on infrastructure and communities can have short-term localized effects on coastal marshes in the vicinity of the storm track.

Deriving spatial and temporal patterns of coastal marsh aggradation from hurricane storm surge marker beds

This study uses storm surge sediment beds deposited by Hurricanes Audrey (1957), Carla (1961), Rita (2005) and Ike (2008) to investigate spatial and temporal changes in marsh sedimentation on the McFaddin National Wildlife Refuge in Southeastern Texas. Fourteen sediment cores were collected along a transect extending 1230m inland from the Gulf coast. Storm-surge-deposited sediment beds were identified by texture, organic content, carbonate content, the presence of marine microfossils and 137Cs dating. The hurricane-derived sediment beds facilitate assessment of changes in marsh sedimentation from nearshore to inland locations and over decadal to annual timescales. Spatial variation along the transect reflects varying contributions from three prevailing sediment sources: flooding, overwash and organic sedimentation from marsh plants. Over about the last decade, hurricane overwash has been the predominant sediment source for nearshore locations because of large sediment inputs from Hurricanes Rita and Ike. Farther inland, hurricane inputs diminish and sedimentation is dominated by deposition from flood waters and a larger organic component. Temporal variations in sedimentation reflect hurricane activity, changes in marsh surface elevation and degree of compaction of marsh sediments, which is time-dependent. There was little to no marsh sedimentation in the period 2008–2014, firstly because no hurricanes impacted the study area and secondly because overwash sedimentation prior to 2008 had increased nearshore marsh surface elevations by up to 0.68m, reducing subsequent inputs from flooding. Marsh sedimentation rates were relatively high in the period 2005–2008, averaging 2.13cm/year and possibly reflecting sediment contributions from Hurricanes Humberto and Gustav. However, these marsh sediments are highly organic and largely uncompacted. Older, deeper marsh deposits formed between 1961 and 2005 are less organic-rich, more compacted and have an average annual sedimentation rate of 0.38cm/year, which is closely comparable to long-term sedimentation rates in similar marsh settings nearby. These results demonstrate the utility of using hurricane storm surge marker beds to investigate marsh sedimentation, provide insights into the sedimentary response of coastal marshes to hurricanes and provide useful guidance to public policy aimed at combating the effects of sea-level rise on coastal marshes along the northern Gulf of Mexico.