Spartina Patens Research Articles

Management strategies for reducing phosphorus levels in saltwater-intruded agricultural fields

As sea levels continue to rise and high tide flooding events increase in frequency, researchers and farmers alike are looking for solutions to adapt to and mitigate the effects of saltwater intrusion (SWI). Some landowners on the Lower Eastern Shore of Maryland respond to SWI by taking land out of agriculture. For example, they (1) attempt to remediate salt-damaged soils (e.g., planting switchgrass, Panicum virgatum), (2) restore native marsh grasses (e.g., planting saltmarsh hay, Spartina patens), or (3) abandon fields altogether (e.g., allow for natural recruitment). This work examines the ability of each of these land management practices to reduce phosphorus (P) levels in soils and porewater, with the overall goal to benefit both the farming community and water quality in the Chesapeake Bay. We show that remediation and restoration practices are efficient at taking up soil P and reducing porewater P concentrations through biomass P uptake. After three years of growth, we observed an increase in P uptake in biomass of Panicum virgatum (remediation species; 11–30 kg ha−1) and Spartina patens (restoration species; 4–18 kg ha−1) and a decline in available soil P pools (M3P; 30–50 % kg M3P ha−1). At all farms, under all three management strategies, the P fertility index value (FIV) in the topsoil was 33–50 % lower than baseline conditions, likely reducing the potential release of P to nearby waterways. Results from this work will help inform state-level coastal management policies and determine optimal strategies for climate resilience.

Promoting success in thin layer sediment placement: effects of sediment grain size and amendments on salt marsh plant growth and greenhouse gas exchange

Thin layer sediment placement (TLP) is used to build elevation in marshes, counteracting effects of subsidence and sea level rise. However, TLP success may vary due to plant stress associated with reductions in nutrient availability and hydrologic flushing or through the creation of acid sulfate soils. This study examined the influence of sediment grain size and soil amendments on plant growth, soil and porewater characteristics, and greenhouse gas exchange for three key U.S. salt marsh plants: Spartina alterniflora (synonym Sporobolus alterniflorus), Spartina patens (synonym Sporobolus pumilus), and Salicornia pacifica. We found that bioavailable nitrogen concentrations (measured as extractable NH4+‐N) and porewater pH and salinity were inversely related to grain size, while soil redox was more reducing in finer sediments. This suggests that utilizing finer sediments in TLP projects will result in a more reduced environment with higher nutrient availability, while larger grain sized sediments will be better flushed and oxygenated. We further found that grain size had a significant effect on vegetation biomass allocation and rates of gas exchange, although these effects were species‐specific. We found that soil amendments (biochar and compost) did not subsidize plant growth but were associated with increases in soil respiration and methane emissions. Biochar amendments were additionally ineffective in ameliorating acid sulfate conditions. This study uncovers complex interactions between sediment type and vegetation, emphasizing the limitations of soil amendments. The findings aid restoration project managers in making informed decisions regarding sediment type, target vegetation, and soil amendments for successful TLP projects.

Quantifying the role of saltmarsh as a vulnerable carbon sink: A case study from Northern Portugal

Saltmarshes play a crucial role in carbon sequestration and storage, although they are increasingly threatened by climate change-induced sea level rise (SLR). This study assessed the potential variation in Blue Carbon stocks across regional and local scales, and estimated their economic value and potential habitat loss due to SLR based on the IPCC AR6 scenarios for 2050 and 2100 in three estuarine saltmarshes in northern Portugal, the saltmarshes of the Minho, Lima and Cávado estuaries. The combined carbon stock of these saltmarshes was 38,798 ± 2880 t of organic carbon, valued at 3.96 ± 0.38 M€. Local and regional differences in carbon stocks were observed between common species, with the cordgrass Spartina patens and the reed Phragmites australis consistently showing higher values in the Lima saltmarsh in some of the parameters. Overall, the Lima saltmarsh had the highest total carbon per species cover, with S. patens showing the highest values among common species. Bolboschoenus maritimus had the highest values in the Minho saltmarsh, while the other species presented a similar carbon storage capacity. Potential habitat loss due to SLR was most evident in the Cávado saltmarsh over shorter timescales, with a significant risk of inundation even for median values of SLR, while the Lima saltmarsh was shown to be more resistant and resilient. If habitat loss directly equates to carbon loss within these saltmarshes, projected CO2 emissions may range from 22,000 to 43,449 t by 2050 and 33,000 to 130,000 t by 2100 (under the IPCC SSP5–8.5 scenario). The study shows the importance of Blue Carbon site-specific estimates, acknowledging the potential future repercussions from habitat loss due to SLR. It emphasizes the need to consider local and regional variability in Blue Carbon stocks assessments and highlights the critical importance of preserving and rehabilitating these ecosystems to ensure their continued efficacy as vital carbon sinks, thereby contributing to climate change mitigation efforts.

Plant suitability for floating treatment wetland applications in brackish waters

Brackish water bodies provide critical ecosystem services supporting human and environmental health in coastal regions. Mitigation of contaminants in brackish waters is critical. Floating treatment wetlands (FTWs) are a remediation technology typically applied to improve water quality in freshwater systems. However, the applicability of FTWs to waters with fluctuating salinity has not been determined. The goal of this study was to quantify the growth and survival of four plant species and determine which aquatic macrophytes are suited for use in FTWs deployed in brackish waters. This study trialed four species common to salt marshes of the Southeastern USA (Distichlis spicata, Juncus roemerianus, Spartina alterniflora, and Spartina patens) grown under three salinity exposures (0.5, 5.0, and 18 g⋅L−1) over 7 weeks. We also quantified macro- and micro-nutrient concentrations in these species to enable determination of how plant growth in FTWs may alter nutrient partitioning in roots and shoots. The ratios of nutrients fixed in tissues of plants grown in the salt marsh vs. those grown in FTWs shifted. The ratio of Na:Ca within tissues were higher for plants grown in the saltmarsh than those grown in the FTWs. Regarding biomass production, D. spicata and J. roemerianus grew very little, regardless of salinity exposure. J. roemerianus did not survive at 18 g⋅L−1 salinity. S. alterniflora and S. patens had the highest biomass production and final nutrient concentrations in tissues across all salinities. These trials indicated that of the four species tested, S. alterniflora and S. patens hold the most promise for FTW application in brackish settings.

Elevated temperature and nutrients lead to increased N2O emissions from salt marsh soils from cold and warm climates

Salt marshes can attenuate nutrient pollution and store large amounts of ‘blue carbon’ in their soils, however, the value of sequestered carbon may be partially offset by nitrous oxide (N2O) emissions. Global climate and land use changes result in higher temperatures and inputs of reactive nitrogen (Nr) into coastal zones. Here, we investigated the combined effects of elevated temperature (ambient + 5℃) and Nr (double ambient concentrations) on nitrogen processing in marsh soils from two climatic regions (Quebec, Canada and Louisiana, U.S.) with two vegetation types, Sporobolus alterniflorus (= Spartina alterniflora) and Sporobolus pumilus (= Spartina patens), using 24-h laboratory incubation experiments. Potential N2O fluxes increased from minor sinks to major sources following elevated treatments across all four marsh sites. One day of potential N2O emissions under elevated treatments (representing either long-term sea surface warming or short-term ocean heatwaves effects on coastal marsh soil temperatures alongside pulses of N loading) offset 15–60% of the potential annual ambient N2O sink, depending on marsh site and vegetation type. Rates of potential denitrification were generally higher in high latitude than in low latitude marsh soils under ambient treatments, with low ratios of N2O:N2 indicating complete denitrification in high latitude marsh soils. Under elevated temperature and Nr treatments, potential denitrification was lower in high latitude soil but higher in low latitude soil as compared to ambient conditions, with incomplete denitrification observed except in Louisiana S. pumilus. Overall, our findings suggest that a combined increase in temperature and Nr has the potential to reduce salt marsh greenhouse gas (GHG) sinks under future global change scenarios.

Can the marsh migrate? Factors influencing the growth of Spartina patens under upland conditions

The high elevation salt marsh plant Spartina patens can potentially cope with accelerated sea level rise by migrating inland, but the ability to do so may differ among plant ecotypes. We compared performance among ecotypes collected from three different sites within mesocosms in which we manipulated soil type, plant litter and salinity. Half of our treatment levels simulated conditions plants would encounter when expanding into terrestrial environments (i.e., upland soil, litter present and low salinity); the other half expansion into tidal creeks (i.e., marsh soil, litter absent, and high salinity). Plant litter and salinity did not significantly affect aboveground biomass or rhizome growth and only affected flowering in a three-way interaction with site. However, all three parameters were significantly affected by soil conditions and the site × soil interaction. Upland soil conditions reduced aboveground biomass, rhizome growth and flowering, as compared to marsh soil conditions, for ecotypes from some sites but not others. When just comparing plant performance in the upland soil treatment, ecotypes from some collection sites did better than others. One plausible explanation for this ecotypic variation is pre-adaptation to differences we found in organic matter content among our collection sites, with the ecotype collected from the site with the lowest organic matter content generally being least impacted by upland soil conditions. Our results indicate that S. patens ecotypes can vary in their capacity to successfully expand into uplands, and thus we suggest prioritizing conservation of such ecotypes, as well as their use in restoration efforts. Consideration of ecotypic variation might also prove useful in deciding where to focus conservation efforts for marsh migration.

Sea level rise-induced habitat loss does not alter effective migration rate for the salt marsh insect Tumidagena minuta due to large genetic effective population size

IntroductionAs anthropogenic change alters and fragments habitats, it is apparent that evolutionary change can co-occur with ecological change, though the scale and consequences of this contemporary evolution remain unclear. In coastal salt marshes of eastern North America, the flood tolerant low elevation marsh grass (Spartina alterniflora), is displacing Spartina patens, the flood intolerant high elevation marsh grass. Rising seas restrict S. patens, once occupying large areas of many hectares, to increasingly small patches, some as small as a few square meters. MethodsUsing nine microsatellite loci, we examined the genetic diversity and population structure of Tumidagena minuta, a minute, flightless planthopper and specialist herbivore of S. patens. We sampled T. minuta from S. patens habitat patches of varying radius (3–82 meters) and distances (54–1,100 meters) to test how landscape variation affects population genetic parameters associated with microevolutionary processes. We sampled and genotyped 142 T. minuta individuals across six S. patens patches in a single marsh in New Jersey, USA. ResultsWe observed high polymorphism, observing between 7 and 28 alleles per locus and an average of 13.3 alleles per locus. We observed no genetic differentiation among sampled patches (RST = −0.0109). The contemporary genetic effective population size (Ne) was estimated at approximately 360 (95% confidence interval: 208–1325) based on two-locus linkage disequilibrium. Based on an estimate of Nem = 32.4 in the finite island model, the estimated gene flow rate among these patches was 0.09 migrants per generation. DiscussionThese estimates, which are rarely produced for non-model insects, suggest that, despite rapid and precipitous decreases in habitat size and connectivity, T. minuta populations have remained large and have experienced little genetic differentiation due to drift. Ecological changes in patch size and isolation at this scale have not influenced population genetic processes like effective migration rate for T. minuta, consistent with our expectations for an insect with a large population size.

Deformation of Spartina patens and Spartina alterniflora stems under irregular wave action

ABSTRACT Physical modeling studies have endeavored to quantify the influence of plant biophysical parameters and hydrodynamics on wave-vegetation interactions and coastal protection. The accuracy with which such studies have characterized stem motion is limited by the predominant use of plant surrogates, and the few saltmarsh species considered in live vegetation studies. To address this, prototype-scale experiments were conducted in the outdoor Large Wave Canal of the Institut National de la Recherche Scientifique, Québec, in collaboration with the University of Ottawa and the National Research Council Canada, allowing novel characterization of live vegetation deformation under wave action. Two saltmarsh species were investigated (Spartina alterniflora, Spartina patens) under various irregular wave conditions (0.03 m< H s <0.28 m, T s 2.5, 10 s). Stem deformation was characterized using submerged cameras and bending angle tracking, coupled with wave height and velocity measurements. Significant differences in stem flexibility were observed between species, with S. alterniflora exhibiting more rigid stems (EI alterniflora =0.051 Nm2) than S. patens (EI patens =0.0015 Nm2; t-test; p<0.05). The two species consequexhibited different bending angles under similar hydrodynamic conditions, expected to influence their relative coastal protection capacity. These findings provide critical insight into the design of marsh construction or restoration for coastal protection.

Multi-temporal high-resolution marsh vegetation mapping using unoccupied aircraft system remote sensing and machine learning

Coastal wetlands are among the most productive ecosystems in the world and provide important ecosystem services related to improved water quality, carbon sequestration, and biodiversity. In many locations, wetlands are threatened by coastal development and rising sea levels, prompting an era of tidal wetland restoration. The creation and restoration of tidal marshes necessitate the need for ecosystem monitoring. While satellite remote sensing is a valuable monitoring tool; the spatial and temporal resolution of imagery often places operational constraints, especially in small or spatially complex environments. Unoccupied aircraft systems (UAS) are an emerging remote sensing platform that collects data with flexible on-demand capabilities at much greater spatial resolution than sensors on aircraft and satellites, and resultant imagery can be readily rendered in three dimensions through Structure from Motion (SfM) photogrammetric processing. In this study, UAS data at 5 cm resolution was collected at an engineered wetland at Poplar Island, located in Chesapeake Bay, MD United States five times throughout 2019 to 2022. The wetland is dominated by two vegetation species: Spartina alterniflora and Spartina patens that were originally planted in 2005 in low and high marsh elevation zones respectively. During each survey, UAS multispectral reflectance, canopy elevation, and texture were derived and used as input into supervised random forest classification models to classify species-specific marsh vegetation. Overall accuracy ranged from 97% to 99%, with texture and canopy elevation variables being the most important across all datasets. Random forest classifications were also applied to down-sampled UAS data which resulted in a decline in classification accuracy as spatial resolution decreased (pixels became larger), indicating the benefit of using ultra-high resolution imagery to accurately and precisely distinguish between wetland vegetation. High resolution vegetation classification maps were compared to the 2005 as-built planting plans, demonstrating significant changes in vegetation and potential instances of marsh migration. The amount of vegetation change in the high marsh zone positively correlated with interannual variations in local sea level, suggesting a feedback between vegetation and tidal inundation. This study demonstrates that UAS remote sensing has great potential to assist in large-scale estimates of vegetation changes and can improve restoration monitoring success.

Aboveground wetland vegetation growth responses to simulated sediment diversion inundation scenarios

Coastal Louisiana is experiencing extremely high rates of wetland loss, particularly within the Mississippi River Deltaic Plain. Although multiple stressors contribute to this loss, one major driver is decreased wetland elevation stemming from disconnection of recurrent sediment rich influxes of Mississippi River floodwater. The decrease in sediment delivery, in conjunction with natural subsidence processes, reduce marsh elevations and increase flooding stress on vegetation, leading to marsh collapse. River sediment diversions are large-scale restoration techniques intended to rehabilitate Louisiana's degraded coastal wetlands by mimicking historic crevasse splays, thereby stimulating land building and vegetation growth. However, such large-scale restoration techniques require an appropriate knowledge base of vegetation and soil biogeochemical responses to altered environmental conditions. In this research, monospecific sods of three foundational marsh species (Spartina patens, Spartina alterniflora, Typha latifolia) were exposed to inundation depth (20 and 40 cm), duration (8 and 16 weeks), and salinity (0 and 5 psu) treatments consistent with a range of anticipated sediment diversion scenarios in a mesocosm setting. Additionally, sods were monitored through week 20 after being removed from their experimental conditions. Both Spartina alterniflora and Typha latifolia displayed relatively consistent increases in stem densities over time across inundation depth-duration treatments, whereas Spartina patens displayed a sharp decline in stem densities at 40 cm flooding depths. Additionally, both Spartina alterniflora and Spartina patens had the least observed amount of total aboveground biomass at 40 cm flooding depths. Spartina patens sods displayed a significant loss in surface elevation with increased flooding stress through study week 20, whereas Typha latifolia demonstrated a significant gain in surface elevation. These results suggest that restoration projects increasing inundation within the limits of the depths employed herein and the anticipated duration of river diversion induced inundation are unlikely to negatively impact the aboveground growth responses of Spartina alterniflora and Typha latifolia, but could reduce stem densities and aboveground biomass of Spartina patens.

Salt marsh vegetation change during a half-century of experimental nutrient addition and climate-driven controls in Great Sippewissett Marsh

Vegetative cover was mapped annually, 1976–2022, in experimental plots in Great Sippewissett Marsh, Cape Cod, USA, chronically fertilized at different doses, and subject to changes in sea level and other climate-related variables. Dominant species within areas of higher elevation in the plots followed different decadal trajectories: rise in sea level diminished cover of Spartina patens; higher N supplies increased cover of Distichlis spicata. The opportunistic growth response of D. spicata to high N supplies unexpectedly fostered increased platform accretion, a feature that persisted for succeeding decades and led to further changes in vegetation: D. spicata functioned as an effective ecosystem engineer with long-term ecological consequences. Shrubs usually found in upper marsh margins expanded into areas where D. spicata had stimulated accretion, then shaded and excluded D. spicata, but subsequently lost cover as sea level rise continued. Increased N supply converted stands of Spartina alterniflora, the dominant low marsh species, from short to taller ecophenotypes; sea level rise had minor effects on S. alterniflora, but during 2019–2022 appeared to reach a tipping point that fostered taller S. alterniflora and bare space even in un-fertilized control plots, and in Great Sippewissett Marsh in general. Model results anticipate that—in spite of potential accretion enhanced by vegetation and ecosystem engineer effects—there will be loss of high marsh, transient increases of low marsh, followed by loss of low marsh, and eventual conversion to shallow open water by the end of the century. Dire local projections match those of the plurality of recent reports from salt marshes around the world. Proposed management strategies may only delay unfortunate outcomes rather than maintain wetlands. Concerted reductions of warming from greenhouse gases, and lower N loads seem necessary to address the coming crises in wetlands—and many other environmental threats.

Recovery of salt marsh vegetation after ice-rafting

Sediment transport on salt marsh platforms is usually brought about through storm events and high tides. At high latitudes, ice-rafting is a secondary mechanism for sediment transport, redistributing sediment from tidal flats, channels, and ponds to marshland. In January 2018, winter storm Grayson hit the North Atlantic coast, producing a large storm surge and a significant decrease in temperature. The Great Marsh in Plum Island Sound, Massachusetts, USA, experienced an unprecedented sediment deposition due to ice-rafting, burying marsh vegetation. Plant vegetation recovery was investigated in 17 sediment patches, dominated by Spartina patens, Distichlis spicata, Juncus gerardi, and S. alterniflora. The analysis was carried out considering the number of stems and stem height for each vegetation species. D. spicata firstly occupied bare patches, while S. patens, once smothered by sediment, regrew slowly. The number of stems of S. patens inside the sediment patches recovered, on average, after 2 growing seasons. The number of J. gerardi stems was not significantly affected by ice-rafted sediment deposition. S. alterniflora dynamics were different depending on physical and edaphic conditions. At some locations, S. alterniflora did not recover after sediment deposition. The deposition of the sediment layer had a positive effect on vegetation vigor, increasing stem height and maintaining high stem density. The results suggest a beneficial effect of sediment deposition not only for marsh accretion, but also for marsh vegetation growth, both of which are fundamental for marsh restoration.

Patch-level processes of vegetation underlying site-level restoration patterns in a megatidal salt marsh

Vegetation patterns during salt marsh restoration reflect underlying processes related to colonization, reproduction, and interactions of halotolerant plants. Examining both pattern and process during recovery is valuable for understanding and managing salt marsh restoration projects. We present a decade of vegetation dynamics during salt marsh restoration (2011–2020) at a study site in the Bay of Fundy with megatidal amplitudes, strong currents, cold winter temperatures, and ice. We mainly investigated reproduction (asexual and sexual) and associated spread rates of Spartina grasses, and their health-related states (stem density, canopy height, and percent flowering) which help inform the probability of processes occurring. We also estimated modes of colonization and began quantifying the effects of interspecific interactions and environmental conditions on plant state. Spartina pectinata was the only pastureland plant to survive dike-breaching and saltwater intrusion in 2010; however, it was stunted compared to reference plants. Spartina pectinata patches remained consistent initially, before decreasing in size, and disappearing by the fifth year (2015). This early dynamic may provide initial protection to a developing salt marsh before Spartina alterniflora becomes established. Spartina alterniflora first colonized the sites in year 2 (2012), likely via deposition of rhizomal material, and then spread asexually before seedlings (sexual reproduction) appeared in year 4 (2014). Vegetation cover subsequently increased greatly until near-complete in year 9 (2019). The early successional dynamics of S. pectinata and S. alterniflora occurred spatially independently of each other, and likely contributed to sediment retention, creating an improved environment for S. patens, the dominant high marsh species in our region. Spartina patens have been slowly spreading into restoration sites from high elevation areas since year 6 (2016). We expect that competition between S. alterniflora and S. patens will result in the typical distinct zonation between high and low marsh zones. A next study will use the quantified processes for spatial-explicit modeling to simulate patterns of vegetation recovery, and to evaluate different salt marsh restoration strategies for the Bay of Fundy and elsewhere. Thus, proper identification and quantification of pattern-building processes in salt marsh vegetation recovery, the focus of our present study, was an essential step.

Sand supply and dune grass species density affect foredune shape along the US Central Atlantic Coast

AbstractCoastal foredunes form via biophysical feedbacks between sand accretion and burial‐tolerant vegetation and can protect coastlines from hazards such as extreme storms and sea level rise. Predicting how coastal dunes, and the services they provide, will change in the future requires an understanding of the relative roles of the physical and ecological processes that shape their structure and function. Here we assess the relative roles of sand supply, beach morphology, and vegetation in determining foredune morphology, and its change, along a 300‐km stretch of the US Central Atlantic coast. In particular, we used the spatial variability inherent in beaches and dunes of this region to determine the relative importance of shoreline change rate (SCR; a proxy for sand supply to the beach), beach morphology, and grass density of four widespread dune grasses (Uniola paniculata, Ammophila breviligulata, Panicum amarum, and Spartina patens) to foredune morphology metrics (height, width, and aspect ratio) along the North Carolina Outer Banks barrier islands. Foredune morphology and change metrics are correlated with three main factors: multidecadal SCR (1997–2016), beach slope, and dune grass density and species identity. Multidecadal SCR and beach width explained the most variation in, and were positively correlated with, foredune height and width, and were negatively correlated with foredune aspect ratio (height divided by width). In addition, grass density and changes in grass density contributed significantly to foredune morphology change. We found a positive relationship between change in A. breviligulata density and foredune width, which aligns with previous studies on the US Atlantic and Pacific Northwest coasts. Our results demonstrate the interactive roles of beach sand supply and dune grass functional morphology in dune building processes on highly vulnerable coastlines.

Spartina alterniflora has the highest methane emissions in a St. Lawrence estuary salt marsh

Salt marshes have the ability to store large amounts of ‘blue carbon’, potentially mitigating some of the effects of climate change. Salt marsh carbon storage may be partially offset by emissions of CH4, a highly potent greenhouse gas. Sea level rise and invasive vegetation may cause shifts between different elevation and vegetation zones in salt marsh ecosystems. Elevation zones have distinct soil properties, plant traits and rhizosphere characteristics, which affect CH4 fluxes. We investigated differences in CH4 emissions between four elevation zones (mudflat, Spartina alterniflora, Spartina patens and invasive Phragmites australis) typical of salt marshes in the northern Northwest Atlantic. CH4 emissions were significantly higher from the S. alterniflora zone (17.7 ± 9.7 mg C m−2h−1) compared to the other three zones, where emissions were negligible (<0.3 mg C m−2h−1). These emissions were high for salt marshes and were similar to those typically found in oligohaline marshes with lower salinities. CH4 fluxes were significantly correlated with soil properties (salinity, water table depth, bulk density and temperature), plant traits (rhizome volume and biomass, root volume and dead biomass volume all at 0–15 cm) and CO2 fluxes. The relationships between CH4 emissions, and rhizome and root volume suggest that the aerenchyma tissues in these plants may be a major transport mechanism of CH4 from anoxic soils to the atmosphere. This may have major implications for the mitigation potential carbon sink from salt marshes globally, especially as S. alterniflora is widespread. This study shows CH4 fluxes can vary over orders of magnitude from different vegetation in the same system, therefore, specific emissions factors may need to be used in future climate models and for more accurate carbon budgeting depending on vegetation type.

Contribution of belowground plant components to salt marsh soil volume

Accumulation of belowground plant material (live roots, rhizomes, and dead material) is critical to vertical accretion of tidal salt marsh soils and their ability to maintain elevation with respect to sea-level rise. Many studies utilize a single, global relationship between soil organic carbon and belowground volume, which does not include the pore space created by belowground growth, thus does not appropriately reflect the contribution of vegetation to soil accretion. We develop factors that relate live belowground mass to the volume of live roots and rhizomes for four species in a St. Lawrence estuary salt marsh at la Pocatière, Quebec. Spartina alterniflora, Spartina patens, and invasive Phragmites australis were identified in the aboveground growth, while only tubers and roots of Cyperus esculentus were found. Cores of the top 30 cm of soil were collected and cut into 0–15 and 15–30 cm sections from the low marsh, high marsh, and S. patens marsh invaded by P. australis. The soil was washed over a 1 mm sieve, and the organic matter was retained. The live material was sorted into fractions of roots and rhizomes by species. The volume of all components was measured by displacement in water before drying to obtain mass. An overall conversion factor of 8.2 g cm−3 reflects the volumetric contribution of live belowground plant components of all species studied. The relationship varies by species, with S. alterniflora contributing the greatest volume per unit mass (8.9 g cm−3), followed by S. patens (7.9 g cm−3), then P. australis and C. esculentus, both at 5.6 g cm−3. Our results not only demonstrate that the total mass and volume of each species for each component (rhizomes, roots, and dead material) were strongly correlated but that measurements of carbon density underestimate the true volumetric contributions of salt marsh plants to the soil.

Bioinvasion by Spartina patens alters sediment biogeochemical functioning of European salt marshes

Bioinvasions pose undeniable threats and trigger changes in salt marsh ecosystem functioning. In Mediterranean and Atlantic marshes, the invasion by S. patens contributed to added competitive pressure to native middle-upper marsh species such as H. portulacoides. The introduction of a new and aggressive non-indigenous species (NIS) is a game-changer for the marsh biogeochemical functioning. In the present study we explored effects of this bioinvasion on an array of different extracellular enzymatic activities (EEA) of salt marsh sediments colonized by NIS and native plant species and its impacts on the biogeochemical functioning of a large estuarine ecosystem. In H. portulacoides there was an evident control of the extracellular enzymatic activities (EEA) by the sediment physic-chemical traits, but these relationships were weaker and fewer in number when compared to the EEA and the sediment abiotic traits in the sediments colonized by S. patens. This indicates a prevalence of a plant effect over abiotic traits in controlling EEA. Disruption in biogeochemical functioning was evident in the sediments colonized by S. patens, with clear enzymatic activity peaks during spring and summer and with significantly higher values of several EEA during autumn and winter. These led to an acceleration of necromass decomposition processes and thus to reduced marsh storage and remediation capacity. Spartina patens also showed increased phosphatase, urease, and protease activity contributing to increased release of the inorganic phosphorous and nitrogen (ammonia) into the system. Higher activity of carbon-based substrates decomposition allied to an increase in dehydrogenase activity (proxy to microbial abundance and respiration), will lead to an inevitable decrease in the carbon sink capacity of the sediments and reduction of the blue carbon storage ecosystem service. The sulfatase activity in the S. patens rhizosediments also showed a significant decrease during autumn, leading to reduced production of sulfate, sulfides and increased metal bioavailability. All these changes amount to a loss of the sink capacity of the system, in terms of eutrophication reduction through organic nitrogen and phosphorous retention, carbon sink due to the acceleration of the decomposition processes and decreased metal remediation capacity. Thus, the present work highlights the need to control this invasive species not only to prevent potential reductions in floristic diversity but also to prevent the loss of key biogeochemical services, that can impact the entire estuarine system.

Whole plant traits of coastal dune vegetation and implications for interactions with dune dynamics

AbstractCoastal dunes are important protective features against sea level rise and coastal storms. Interactions between dune plant aboveground structures and sediment trapping that allow for dune building and maintenance are well established. More recently, studies documenting belowground biomass for promoting erosion resistance in dominant dune species have been conducted, yet a knowledge gap remains regarding species‐specific characterization of whole plants, specifically with respect to roots, rhizomes, and belowground stems. Our objective was to quantify above‐ and belowground traits of four dominant dune grasses to document the potential for species‐specific effects on dune growth, maintenance, and erosion resistance. We examined above‐ and belowground traits among four prominent dune grasses of the Atlantic and Gulf Coasts of North America: Ammophila breviligulata, Panicum amarum, Spartina patens, and Uniola paniculata. Whole plant samples of each species were collected from the foredune at the US Army Engineer Research and Development Center's Field Research Facility in Duck, North Carolina, USA, and quantified for several above‐ and belowground traits (e.g., stem height, rhizome number and length, root surface area by diameter class, root tensile strength, and mycorrhizal percent infection). Belowground factors known to impact important dune processes, such as rhizome length, mycorrhizal percent infection, and root traits, differed substantially among species. When visualized in multivariate space, all species significantly differed in suites of above‐ and belowground traits. When considering belowground only, Ammophila and Spartina were similar, despite differences in biomass allocation. Species separated along axes related to mycorrhizal association, biomass allocation, and root construction. The four co‐occurring dune grass species were dissimilar in suites of plant traits. Belowground trait differences were driven by those describing root construction, biomass allocation, and mycorrhizal infection. Dissimilarity in above‐ and belowground suites of traits may demonstrate different approaches for surviving the dune environment. Incorporating belowground traits into modeling will enhance predictions of dune response to climate change through interactions between vegetation and dune dynamics that facilitate coastal resistance and resilience.

Salt marsh climate change adaptation: Using runnels to adapt to accelerating sea level rise within a drowning New England salt marsh

Sea level rise within New England is accelerating at a rate faster than the global average, leaving salt marshes particularly susceptible to degradation. Hydrological alteration is a type of climate change adaptation technique that can be used to combat the effects of sea level rise within salt marshes. Runnels (shallow channels) are a type of climate adaptation strategy used to enhance drainage in drowning marshes. In this study, we investigated the impacts of runnel installations, 3–5 years post‐implementation, on soil properties, vegetation composition, and greenhouse gas fluxes. We studied two runnel treatments (Low Elevation Runnel and High Elevation Runnel) and found that in the Low Elevation Runnel areasSpartina alterniflorastem density significantly increased in the three growing seasons after runnels were installed, and the high marsh plant,Spartina patens, persisted in the High Elevation Runnel areas. There was a significant difference in carbon dioxide uptake rates among treatments, with the unmanipulated (Reference) areas having the highest uptake rates and an increase in CO2uptake over time seen in the Low Elevation Runnel treatment. These findings highlight the potential use of a climate change adaptation strategy to combat sea level rise impacts and provide insights for future adaptation efforts.

Tidal marsh restoration at Blackwater National Wildlife Refuge, Maryland: A case study in thin-layer placement

Tidal marsh loss at Blackwater National Wildlife Refuge (NWR) has been a major concern of refuge managers in recent decades. The approximately 2,035 hectares (5,028 acres) of tidal marsh that have converted to open water in Blackwater NWR since 1938 (Scott et al. 2009) represent one of the most significant areas of marsh conversion within the Chesapeake Bay. In 2013, a suite of climate adaptation strategies focused on sea level rise was developed for Blackwater NWR and surrounding areas of Dorchester County by the Blackwater Climate Adaptation Project (BCAP). The BCAP is a collaboration of The Conservation Fund, Audubon Maryland-DC, and the U.S. Fish and Wildlife Service, assisted by the Maryland Department of Natural Resources (MD DNR), U.S. Geological Survey, and others. In 2016, the BCAP implemented a thin-layer placement (TLP) project at Shorter’s Wharf in Blackwater NWR on 16 hectares (40 acres) of subsiding and fragmenting tidal marsh dominated by Schoenoplectus americanus, Spartina alterniflora, and Spartina patens. The purpose of the project was to increase the 16 hectares’ (40 acres’) resiliency to climate-driven sea level rise and storm impacts. The project built up the marsh elevation by applying thin layers of sediment dredged from the adjacent Blackwater River. The sediment enhancement was designed to extend the longevity of the marsh and increase its resiliency by raising its surface elevation in relation to the tidal regime and to return the habitat to its prior high-marsh condition with S. patens dominating. The colonization of this site by saltmarsh sparrow would be an indicator of success in reaching this goal. Dredging operations in November and December 2016 placed approximately 19,900 cubic meters (26,000 cubic yards) of sediment on the project site. Post-restoration elevations obtained one year after material placement indicated that, although the target elevations were achieved in 78% of the surveyed placement area, the material was not distributed uniformly. Coarser material tended to stack up at the discharge location while the grain size declined and the slopes flattened toward the periphery of the discharge area. In 2017, natural vegetation had regenerated through the placed sediment with vigorous regrowth of S. americanus and S. alterniflora . This regrowth was supplemented with hand-planting of more than 200,000 plugs of S. patens. Vegetation monitoring is ongoing to determine the plant composition evolution within the placement site. Pre-dredge and post-dredge bathymetric surveys reveal 70% accretion nearly two years after dredging within the borrow area footprint.