Limited seed retention during winter inhibits vegetation establishment in spring,affecting lateral marsh expansion capacity

Coastal systems worldwide deliver vital ecosystem services, such as biodiversity, carbon sequestration, and coastal protection. Effectivity of these ecosystem services increases when vegetation is present. Understanding the mechanisms behind vegetation establishment in bio‐geomorphic systems is necessary to understand their ability to recover after erosive events and potential adaptations to climate change. In this study, we examined how seed availability affects vegetation establishment in the salt marsh–intertidal flat transition zone: the area with capacity for lateral marsh expansion. This requires vegetation establishment; therefore, seed availability is essential. In a 6‐month field experiment, we simulated a before and after winter seed dispersal at two locations, the salt‐marsh vegetation edge and the intertidal flat, and studied seed retention, the seed bank, and the seed viability of three pioneer marsh species: Salicornia procumbens, Aster tripolium, and Spartina anglica. During winter storm conditions, all supplied seeds eroded away with the sediment surface layer. After winter, supplied seeds from all three species were retained, mostly at the surface while 9% was bioturbated downwards. In the natural seed bank, A. tripolium and S. anglica were practically absent while S. procumbens occurred more frequently. The viability of S. procumbens seeds was highest at the surface, between 80% and 90%. The viability quickly decreased with depth, although viable S. procumbens seeds occurred up to 15 cm depth. Only when seeds were supplied after winter, many S. procumbens and some S. anglica individuals did establish successfully in the transition zone. Viable seed availability formed a vegetation establishment threshold, even with a local seed source. Our results suggest that, although boundary conditions such as elevation, inundation, and weather conditions were appropriate for vegetation establishment in spring, the soil surface in winter can be so dynamic that it limits lateral marsh expansion. These insights can be used for designing effective nature‐based coastal protection.     

Tidal marsh plant responses to elevated CO2, nitrogen fertilization,and sea level rise

Elevated CO₂ and nitrogen (N) addition directly affect plant productivity and the mechanisms that allow tidal marshes to maintain a constant elevation relative to sea level, but it remains unknown how these global change drivers modify marsh plant response to sea level rise. Here we manipulated factorial combinations of CO₂ concentration (two levels), N availability (two levels) and relative sea level (six levels) using in situ mesocosms containing a tidal marsh community composed of a sedge, Schoenoplectus americanus, and a grass, Spartina patens. Our objective is to determine, if elevated CO₂ and N alter the growth and persistence of these plants in coastal ecosystems facing rising sea levels. After two growing seasons, we found that N addition enhanced plant growth particularly at sea levels where plants were most stressed by flooding (114% stimulation in the + 10 cm treatment), and N effects were generally larger in combination with elevated CO₂ (288% stimulation). N fertilization shifted the optimal productivity of S. patens to a higher sea level, but did not confer S. patens an enhanced ability to tolerate sea level rise. S. americanus responded strongly to N only in the higher sea level treatments that excluded S. patens. Interestingly, addition of N, which has been suggested to accelerate marsh loss, may afford some marsh plants, such as the widespread sedge, S. americanus, the enhanced ability to tolerate inundation. However, if chronic N pollution reduces the availability of propagules of S. americanus or other flood‐tolerant species on the landscape scale, this shift in species dominance could render tidal marshes more susceptible to marsh collapse.     

Divergent selection and drift shape the genomes of two avian sister species spanning a saline–freshwater ecotone

The role of species divergence due to ecologically based divergent selection—or ecological speciation—in generating and maintaining biodiversity is a central question in evolutionary biology. Comparison of the genomes of phylogenetically related taxa spanning a selective habitat gradient enables discovery of divergent signatures of selection and thereby provides valuable insight into the role of divergent ecological selection in speciation. Tidal marsh ecosystems provide tractable opportunities for studying organisms' adaptations to selective pressures that underlie ecological divergence. Sharp environmental gradients across the saline–freshwater ecotone within tidal marshes present extreme adaptive challenges to terrestrial vertebrates. Here, we sequence 20 whole genomes of two avian sister species endemic to tidal marshes—the saltmarsh sparrow (Ammospiza caudacutus) and Nelson's sparrow (A. nelsoni)—to evaluate the influence of selective and demographic processes in shaping genome‐wide patterns of divergence. Genome‐wide divergence between these two recently diverged sister species was notably high (genome‐wide F_ST = 0.32). Against a background of high genome‐wide divergence, regions of elevated divergence were widespread throughout the genome, as opposed to focused within islands of differentiation. These patterns may be the result of genetic drift resulting from past tidal march colonization events in conjunction with divergent selection to different environments. We identified several candidate genes that exhibited elevated divergence between saltmarsh and Nelson's sparrows, including genes linked to osmotic regulation, circadian rhythm, and plumage melanism—all putative candidates linked to adaptation to tidal marsh environments. These findings provide new insights into the roles of divergent selection and genetic drift in generating and maintaining biodiversity.     

Quantifying Vegetation and Nekton Response to Tidal Restoration of a New England Salt Marsh

Tidal flow to salt marshes throughout the northeastern United States is often restricted by roads, dikes, impoundments, and inadequately sized culverts or bridge openings, resulting in altered ecological structure and function. In this study we evaluated the response of vegetation and nekton (fishes and decapod crustaceans) to restoration of full tidal flow to a portion of the Sachuest Point salt marsh, Middletown, Rhode Island. A before, after, control, impact study design was used, including evaluations of the tide‐restricted marsh, the same marsh after reintroduction of tidal flow (i.e., tide‐restored marsh), and an unrestricted control marsh. Before tidal restoration vegetation of the 3.7‐ha tide‐restricted marsh was dominated by Phragmites australis and was significantly different from the adjacent 6.3‐ha Spartina‐dominated unrestricted control marsh (analysis of similarities randomization test, p < 0.001). After one growing season vegetation of the tide‐restored marsh had changed from its pre‐restoration condition (analysis of similarities randomization test, p < 0.005). Although not similar to the unrestricted control marsh, Spartina patens and S. alterniflora abundance increased and abundance and height of Phragmites significantly declined, suggesting a convergence toward typical New England salt marsh vegetation. Before restoration shallow water habitat (creeks and pools) of the unrestricted control marsh supported a greater density of nekton compared with the tide‐restricted marsh (analysis of variance, p < 0.001), but after one season of restored tidal flow nekton density was equivalent. A similar trend was documented for nekton species richness. Nekton density and species richness from marsh surface samples were similar between the tide‐restored marsh and unrestricted control marsh. Fundulus heteroclitus and Palaemonetes pugio were the numerically dominant fish and decapod species in all sampled habitats. This study provides an example of a quantitative approach for assessing the response of vegetation and nekton to tidal restoration.     

The natural regeneration of salt marsh on formerly reclaimed land

Question: Does the vegetation of restored salt marshes increasingly resemble natural reference communities over time? Location: The Essex estuaries, southeast England. Methods: Abandoned reclamations, where coastal defences had been breached in storm events, and current salt marsh recreation schemes were surveyed giving a chronosequence of salt marsh regeneration from 2 to 107 years. The presence, abundance and height of plant species were recorded and comparisons were made with adjacent reference salt marsh communities at equivalent elevations. Results: Of the 18 paired sites surveyed, 13 regenerated marshes had fewer species than their adjacent reference marsh, three had an equal number and two had more. The plant communities of only two de‐embankment sites matched that of the reference community. 0–50 year old sites and 51–100 year old sites had fewer species per quadrat than the 101+ year sites and the reference salt marshes. There was a weak relationship between differences in species richness for regenerated and reference marshes and the time since sites were first re‐exposed to tidal inundation. Cover values for the invasive and recently evolved Spartina anglica were greater within regenerated than reference marshes. Conclusions: Salt marsh plants will colonise formerly reclaimed land relatively quickly on resumption of tidal flooding. However, even after 100 years regenerated salt marshes differ in species richness, composition and structure from reference communities.     

Drainage and Elevation as Factors in the Restoration of Salt Marsh in Britain

Intertidal restoration through realignment of flood defenses has become an important component of the U.K. coastal and estuarine management strategy. Although experimentation with recent deliberate breaches is in progress, the long‐term prognosis for salt marsh restoration can be investigated at a number of sites around Essex, southeast England where salt marshes have been reactivated (unmanaged restoration) by storm events over past centuries. These historically reactivated marshes possess higher creek densities than their natural marsh counterparts. Both geomorphology and sedimentology determine the hydrology of natural and restored salt marshes. Elevation relative to the tidal frame is known to be the primary determinant of vegetation colonization and succession. Yet vegetation surveys and geotechnical analysis at a natural marsh, where areas with good drainage exist in close proximity to areas of locally hindered drainage at the same elevation, revealed a significant inverse relationship between water saturation in the root zone and the abundance of Atriplex portulacoides, normally the physiognomic dominant on upper salt marsh in the region. Elsewhere in Essex natural and restored marshes are typified by very high sediment water contents, and this is reflected in low abundance of A. portulacoides. After a century of reestablishment no significant difference could be discerned between the vegetation composition of the storm‐reactivated marshes and their natural marsh counterparts. We conclude that vegetation composition may be restored within a century of dike breaching, but this vegetation does not provide a reliable indicator of ecological functions related to creek structure.     

Macro‐Tidal Salt Marsh Ecosystem Response to Culvert Expansion

The purpose of this paper was to examine the vegetative, sedimentary, nekton and hydrologic conditions pre‐restoration and the initial 2 years post‐restoration at a partially restricted macro‐tidal salt marsh site. Replacement of the culvert increased tidal flow by 88%. This was instrumental in altering the geomorphology of the site, facilitating the creation of new salt marsh pannes, expansion of existing pannes in the mid and high marsh zones, and expansion of the tidal creek network by incorporating relict agricultural ditches. In addition, the increase in area flooded resulted in a significant increase in nekton use, fulfilling the mandate of a federal habitat compensation program to increase and improve the overall availability and accessibility of fish habitat. The restoration of a more natural hydrological regime also resulted in the die‐off of freshwater and terrestrial vegetation along the upland edge of the marsh. Two years post‐restoration, Salicornia europea (glasswort) and Atriplex glabriuscula (marsh orache), were observed growing in these die‐back areas. Similar changes in the vegetation community structure were not observed at the reference site; however, the latter did contain higher species richness. This study represents the first comprehensive, quantitative analysis of ecological response to culvert replacement in a hypertidal ecosystem. These data will contribute to the development of long‐term data sets of pre‐ and post‐restoration, and reference marsh conditions to determine if a marsh is proceeding as expected, and to help with models that are aimed at predicting the response of marshes to tidal restoration at the upper end of the tidal spectrum.     

Will fluctuations in salt marsh–mangrove dominance alter vulnerability of a subtropical wetland to sea‐level rise?

To avoid submergence during sea‐level rise, coastal wetlands build soil surfaces vertically through accumulation of inorganic sediment and organic matter. At climatic boundaries where mangroves are expanding and replacing salt marsh, wetland capacity to respond to sea‐level rise may change. To compare how well mangroves and salt marshes accommodate sea‐level rise, we conducted a manipulative field experiment in a subtropical plant community in the subsiding Mississippi River Delta. Experimental plots were established in spatially equivalent positions along creek banks in monospecific stands of Spartina alterniflora (smooth cordgrass) or Avicennia germinans (black mangrove) and in mixed stands containing both species. To examine the effect of disturbance on elevation dynamics, vegetation in half of the plots was subjected to freezing (mangrove) or wrack burial (salt marsh), which caused shoot mortality. Vertical soil development was monitored for 6 years with the surface elevation table‐marker horizon system. Comparison of land movement with relative sea‐level rise showed that this plant community was experiencing an elevation deficit (i.e., sea level was rising faster than the wetland was building vertically) and was relying on elevation capital (i.e., relative position in the tidal frame) to survive. Although Avicennia plots had more elevation capital, suggesting longer survival, than Spartina or mixed plots, vegetation type had no effect on rates of accretion, vertical movement in root and sub‐root zones, or net elevation change. Thus, these salt marsh and mangrove assemblages were accreting sediment and building vertically at equivalent rates. Small‐scale disturbance of the plant canopy also had no effect on elevation trajectories—contrary to work in peat‐forming wetlands showing elevation responses to changes in plant productivity. The findings indicate that in this deltaic setting with strong physical influences controlling elevation (sediment accretion, subsidence), mangrove replacement of salt marsh, with or without disturbance, will not necessarily alter vulnerability to sea‐level rise.     

The effects of elevated CO2 and eutrophication on surface elevation gain in a European salt marsh

Salt marshes can play a vital role in mitigating the effects of global environmental change by dissipating incident storm wave energy and, through accretion, tracking increasing water depths consequent upon sea level rise. Atmospheric CO₂ concentrations and nutrient availability are two key variables that can affect the biological processes that contribute to marsh surface elevation gain. We measured the effects of CO₂ concentrations and nutrient availability on surface elevation change in intact mixed‐species blocks of UK salt marsh using six open‐top chambers receiving CO₂‐enriched (800 ppm) or ambient (400 ppm) air. We found more rapid surface elevation gain in elevated CO₂ conditions: an average increase of 3.4 mm over the growing season relative to ambient CO₂. Boosted regression analysis to determine the relative influence of different parameters on elevation change identified that a 10% reduction in microbial activity in elevated CO₂‐grown blocks had a positive influence on elevation. The biomass of Puccinellia maritima also had a positive influence on elevation, while other salt marsh species (e.g. Suaeda maritima) had no influence or a negative impact on elevation. Reduced rates of water use by the vegetation in the high CO₂ treatment could be contributing to elevation gain, either directly through reduced soil shrinkage or indirectly by decreasing microbial respiration rates due to lower redox levels in the soil. Eutrophication did not influence elevation change in either CO₂ treatment despite doubling aboveground biomass. The role of belowground processes (transpiration, root growth and decomposition) in the vertical adjustment of European salt marshes, which are primarily minerogenic in composition, could increase as atmospheric CO₂ concentrations rise and should be considered in future wetland models for the region. Elevated CO₂ conditions could enhance resilience in vulnerable systems such as those with low mineral sediment supply or where migration upwards within the tidal frame is constrained.     

Modeling Habitat Change in Salt Marshes After Tidal Restoration

Salt marshes continue to degrade in the United States due to indirect human impacts arising from tidal restrictions. Roads or berms with inadequate provision for tidal flow hinder ecosystem functions and interfere with self‐maintenance of habitat, because interactions among vegetation, soil, and hydrology within tidally restricted marshes prevent them from responding to sea level rise. Prediction of the tidal range that is expected after restoration relative to the current geomorphology is crucial for successful restoration of salt marsh habitat. Both insufficient (due to restriction) and excessive (due to subsidence and sea level rise) tidal flooding can lead to loss of salt marshes. We developed and applied the Marsh Response to Hydrological Modifications model as a predictive tool to forecast the success of management scenarios for restoring full tides to previously restricted areas. We present an overview of a computer simulation tool that evaluates potential culvert installations with output of expected tidal ranges, water discharges, and flood potentials. For three New England tidal marshes we show species distributions of plants for tidally restricted and nonrestricted areas. Elevation ranges of species are used for short‐term (<5 years) predictions of changes to salt marsh habitat after tidal restoration. In addition, elevation changes of the marsh substrate measured at these sites are extrapolated to predict long‐term (>5 years) changes in marsh geomorphology under restored tidal regimes. The resultant tidal regime should be designed to provide habitat requirements for salt marsh plants. At sites with substantial elevation losses a balance must be struck that stimulates elevation increases by improving sediment fluxes into marshes while establishing flooding regimes appropriate to sustain the desired plants.     

Hydrologic and edaphic constraints on Schoenoplectus acutus,Schoenoplectus californicus,and Typha latifolia in tidal marsh restoration

The demand for an improved knowledge base for planning and management of tidal marsh restoration worldwide has become more fully recognized. In the Sacramento‐San Joaquin Bay Delta, California, U.S.A., concerns have arisen about the degradation of the Delta and key ecosystem services. One restoration method proposed includes intentionally breaching levees that protect agricultural lands to re‐establish a hydrology that encourages tidal marsh development. Our research investigated relevant constraints on vegetation establishment and expansion of key tidal marsh species. We transplanted three macrophyte species (Schoenoplectus acutus, Schoenoplectus californicus, and Typha latifolia) using two transplant types (rhizomes and adults) in locations that varied in hydrologic and edaphic conditions at Liberty Island, a post‐levee breach tidal marsh restoration site. Two years of monitoring revealed that transplanted adults outperformed rhizomes. In addition, S. californicus exhibited greater survival and vegetation expansion. S. californicus vegetation expansion covered a maximum area of approximately 23 m², which is two orders of magnitude (OOM) greater than the maximum area covered by S. acutus (approximately 0.108 m²) and three OOM greater than T. latifolia (approximately 0.035 m²). Results suggest that hydrologic regime and degree of soil compaction are influential in controlling vegetation establishment and expansion. Greater vegetation expansion occurred in transplant sites characterized by a deeper surface layer of non‐compacted soil in conjunction with shorter durations of flooding. Information derived from this study is valuable to restoration planning in the Delta and other tidal marshes worldwide where these species occur, especially in terms of setting restoration goals and trajectories based on site‐specific environmental characteristics.     

Subspecies delineation amid phenotypic,geographic and genetic discordance in a songbird

Understanding the processes that drive divergence within and among species is a long‐standing goal in evolutionary biology. Traditional approaches to assessing differentiation rely on phenotypes to identify intra‐ and interspecific variation, but many species express subtle morphological gradients in which boundaries among forms are unclear. This intraspecific variation may be driven by differential adaptation to local conditions and may thereby reflect the evolutionary potential within a species. Here, we combine genetic and morphological data to evaluate intraspecific variation within the Nelson's (Ammodramus nelsoni) and salt marsh (Ammodramus caudacutus) sparrow complex, a group with populations that span considerable geographic distributions and a habitat gradient. We evaluated genetic structure among and within five putative subspecies of A. nelsoni and A. caudacutus using a reduced‐representation sequencing approach to generate a panel of 1929 SNPs among 69 individuals. Although we detected morphological differences among some groups, individuals sorted along a continuous phenotypic gradient. In contrast, the genetic data identified three distinct clusters corresponding to populations that inhabit coastal salt marsh, interior freshwater marsh and coastal brackish–water marsh habitats. These patterns support the current species‐level recognition but do not match the subspecies‐level taxonomy within each species—a finding which may have important conservation implications. We identified loci exhibiting patterns of elevated divergence among and within these species, indicating a role for local selective pressures in driving patterns of differentiation across the complex. We conclude that this evidence for adaptive variation among subspecies warrants the consideration of evolutionary potential and genetic novelty when identifying conservation units for this group.     

Soil seed bank and driftline composition along a successional gradient on a temperate salt marsh

Abstract. This study focuses on the relationship between vegetation succession and soil seed bank composition on the Schiermonnikoog (The Netherlands) salt marsh over 100 yr. The importance of driftline material in seed dispersal and the relationship with succession is also investigated. The results indicate that the majority of species have a transient or short‐term seed persistent bank. Seeds of most species are able to float over the salt marsh and become concentrated in the driftline higher up the marsh. After plants have established a seed bank forms, which disappears when vegetation is replaced by later‐successional species. Exceptions are Spergularia mar‐itima, which is still present in the seed bank of late successional stages, and Juncus gerardi and Glaux maritima, which appear in the seed bank of early successional stages, but are absent in the vegetation. Based on the results of this study constraints and possibilities for salt‐marsh restoration by de‐embankment are discussed.     

Adaptive management assists reintroduction as higher tides threaten an endangered salt marsh plant

In theory, extirpated plant species can be reintroduced and managed to restore sustainable populations. However, few reintroduced plants are known to persist for more than a few years. Our adaptive‐management case study illustrates how we restored the endangered hemiparasitic annual plant, Chloropyron maritimum subsp. maritimum (salt marsh bird's beak), to Sweetwater Marsh, San Diego Bay National Wildlife Refuge, California, United States, and used monitoring and experimentation to identify the factors limiting the reintroduced population. After extirpation in 1988, reintroduction starting that year led to a resilient, genetically diverse population in 2016 (a “boom” of approximately 14,000) that rebounded from a “bust” (62 in 2014). Multiple regressions attributed 82% of the variation in population counts to tidal amplitude, rainfall, and temperature. Populations of salt marsh bird's beak crashed when the diurnal tide range peaked during the 18.6‐year lunar nodal cycle (a rarely considered factor that periodically added approximately 12 cm to tidal ranges). We explain booms as follows: During smaller tidal amplitudes, above‐average rainfall could desalinize upper intertidal soils and stimulate salt marsh bird's beak germination. Then, moderate temperature in May favors growth to reproduction in June. In addition, salt marsh bird's beak needs a short and open canopy of native perennial plants, with roots to parasitize (not non‐native annual grass pseudohosts) and nearby upland soil for a preferred pollinator, ground‐burrowing bees. Although our reintroduced salt marsh bird's beak population is an exceptional case of persistence, this rare species‐specific environmental and biological requirement makes it vulnerable to rising sea levels and global warming.     

A casualty of climate change? Loss of freshwater forest islands on Florida's Gulf Coast

Sea level rise elicits short‐ and long‐term changes in coastal plant communities by altering the physical conditions that affect ecosystem processes and species distributions. While the effects of sea level rise on salt marshes and mangroves are well studied, we focus on its effects on coastal islands of freshwater forest in Florida's Big Bend region, extending a dataset initiated in 1992. In 2014–2015, we evaluated tree survival, regeneration, and understory composition in 13 previously established plots located along a tidal creek; 10 plots are on forest islands surrounded by salt marsh, and three are in continuous forest. Earlier studies found that salt stress from increased tidal flooding prevented tree regeneration in frequently flooded forest islands. Between 1992 and 2014, tidal flooding of forest islands increased by 22%–117%, corresponding with declines in tree species richness, regeneration, and survival of the dominant tree species, Sabal palmetto (cabbage palm) and Juniperus virginiana (southern red cedar). Rates of S. palmetto and J. virginiana mortality increased nonlinearly over time on the six most frequently flooded islands, while salt marsh herbs and shrubs replaced forest understory vegetation along a tidal flooding gradient. Frequencies of tidal flooding, rates of tree mortality, and understory composition in continuous forest stands remained relatively stable, but tree regeneration substantially declined. Long‐term trends identified in this study demonstrate the effect of sea level rise on spatial and temporal community reassembly trajectories that are dynamically re‐shaping the unique coastal landscape of the Big Bend.     

Physiological performance of intertidal coralline algae during a simulated tidal cycle

Intertidal macroalgae endure light, desiccation, and temperature variation associated with sub‐merged and emerged conditions on a daily basis. Physiological stresses exist over the course of the entire tidal cycle, and physiological differences in response to these stresses likely contribute to spatial separation of species along the shore. For example, marine species that have a high stress tolerance can live higher on the shore and are able to recover when the tide returns, whereas species with a lower stress tolerance may be relegated to living lower on the shore or in tidepools, where low tide stresses are buffered. In this study, we monitored the physiological responses of the tidepool coralline Calliarthron tuberculosum (Postels and Ruprecht) E.Y. Dawson and the nontidepool coralline Corallina vancouveriensis Yendo during simulated tidal conditions to identify differences in physiology that might underlie differences in habitat. During high tide, Corallina was more photosynthetically active than Calliarthron as light levels increased. During low tide, Corallina continued to out‐perform Calliarthron when submerged in warming tidepools, but photosynthesis abruptly halted for both species when emerged in air. Surprisingly, pigment composition did not differ, suggesting that light harvesting does not account for this difference. Additionally, Corallina was more effective at resisting desiccation by retaining water in its branches. When the tide returned, only Corallina recovered from combined temperature and desiccation stresses associated with emergence. This study broadens our understanding of intertidal algal physiology and provides a new perspective on the physiological and morphological underpinnings of habitat partitioning.     

Tidal Marsh Restoration: Trends in Vegetation Change Using a Geographical Information System (GIS)

Adequately evaluating the success of coastal tidal marsh restoration has lagged behind the actual practice of restoring tidally restricted salt marshes. A Spartina-dominated valley marsh at Barn Island Wildlife Management Area, Stonington, Connecticut, was tidally restricted in 1946 and consequently converted mostly to Typha angustifolia. With the re-introduction of tidal flooding in 1978, much of the marsh has reverted to Spartina alterniflora. Using a geographical information system (GIS), this study measures restoration success by the extent of geographical similarity between the vegetation of the restored marsh and the pre-impounded marsh. Based on geographical comparisons among different hydrologic states, pre-impounded (1946), impounded (1976), and restored (1988) tidal marsh restoration is a convergent process. Although salt marsh species currently dominate the restored system, the magnitude of actual agreement between the pre-impounded vegetation and that of the restored marsh is only moderate. Further restoration of the salt marsh vegetation may be limited by continued tidal restriction, marsh surface subsidence, and reduced accretion rates. General trends of recovery are identified using a gradient approach and the geographic pattern’ of vegetation change. In the strictest sense, if restoration refers only to vegetation types that geographically replicate preexisting types, then only 28% of the marsh has been restored. Restoration in a broader sense, however, representing the original salt marsh vegetation regardless of spatial position, amounts to 63% restored. Unrestored marsh, dominated by Typha angustifolia and Phragmites australis, remains at 37%. By emphasizing trends during vegetation recovery, this evaluation technique aims to understand the restoration process, direct future research goals, and ultimately aid in future restoration projects.     

An invasive wetland grass primes deep soil carbon pools

Understanding the processes that control deep soil carbon (C) dynamics and accumulation is of key importance, given the relevance of soil organic matter (SOM) as a vast C pool and climate change buffer. Methodological constraints of measuring SOM decomposition in the field prevent the addressing of real‐time rhizosphere effects that regulate nutrient cycling and SOM decomposition. An invasive lineage of Phragmites australis roots deeper than native vegetation (Schoenoplectus americanus and Spartina patens) in coastal marshes of North America and has potential to dramatically alter C cycling and accumulation in these ecosystems. To evaluate the effect of deep rooting on SOM decomposition we designed a mesocosm experiment that differentiates between plant‐derived, surface SOM‐derived (0–40 cm, active root zone of native marsh vegetation), and deep SOM‐derived mineralization (40–80 cm, below active root zone of native vegetation). We found invasive P. australis allocated the highest proportion of roots in deeper soils, differing significantly from the native vegetation in root : shoot ratio and belowground biomass allocation. About half of the CO₂ produced came from plant tissue mineralization in invasive and native communities; the rest of the CO₂ was produced from SOM mineralization (priming). Under P. australis, 35% of the CO₂ was produced from deep SOM priming and 9% from surface SOM. In the native community, 9% was produced from deep SOM priming and 44% from surface SOM. SOM priming in the native community was proportional to belowground biomass, while P. australis showed much higher priming with less belowground biomass. If P. australis deep rooting favors the decomposition of deep‐buried SOM accumulated under native vegetation, P. australis invasion into a wetland could fundamentally change SOM dynamics and lead to the loss of the C pool that was previously sequestered at depth under the native vegetation, thereby altering the function of a wetland as a long‐term C sink.     

Patterns of Distribution and Environmental Correlates of Macroalgal Assemblages and Sediment Chlorophyll A in Oregon Tidal Wetlands

Algae have important functional roles in estuarine wetlands. We quantified differences in macroalgal abundance, composition and diversity, and sediment chl a and pheophytin a (pheo a) among three National Wetlands Inventory (NWI) emergent marsh classes in four Oregon estuaries spanning a range of riverine to marine dominance. We also assessed the strength of macroalgal‐vascular plant associations and the degree to which environmental variables correlated with algal community metrics in marsh and woody wetlands. The frequency of occurrence of most macroalgal genera, total benthic macroalgal cover, macroalgal diversity, and sediment chl a content were several times higher in low emergent marsh than in high marsh or palustrine tidal marsh. Conversely, pheo a: chl a ratios were highest in high and palustrine marsh. Attached macroalgae (Fucus and Vaucheria) were strongly associated with plants common at lower tidal elevations such as Sarcocornia perennis and Jaumea carnosa; Ulva (an unattached alga) was not strongly associated with any common low marsh plants. In structural equation models, intertidal elevation was the most influential predictor of macroalgal cover and richness and chl a; light availability and soil salinity played secondary roles. Although common taxa such as Ulva spp. occurred across a broad range of salinities, wetlands with oligohaline soils (salinity < 5) had the lowest macroalgal diversity and lower sediment chl a. These types of baseline data on algal distributions are critical for evaluating the structural and functional impacts of future changes to coastal estuaries including sea‐level rise (SLR), altered salinity dynamics, and habitat modification.     

Ecological responses to tidal restorations of two northern New England salt marshes

Efforts are underway to restore tidal flow in New England salt marshes that were negatively impacted by tidal restrictions. We evaluated a planned tidal restoration at Mill Brook Marsh (New Hampshire) and at Drakes Island Marsh (Maine) where partial tidal restoration inadvertently occurred. Salt marsh functions were evaluated in both marshes to determine the impacts from tidal restriction and the responses following restoration. Physical and biological indicators of salt marsh functions (tidal range, surface elevations, soil water levels and salinities, plant cover, and fish use) were measured and compared to those from nonimpounded reference sites. Common impacts from tidal restrictions at both sites were: loss of tidal flooding, declines in surface elevation, reduced soil salinity, replacement of salt marsh vegetation by fresh and brackish plants, and loss of fish use of the marsh.Water levels, soil salinities and fish use increased immediately following tidal restoration. Salt-intolerant vegetation was killed within months. After two years, mildly salt-tolerant vegetation had been largely replaced in Mill Brook Marsh by several species characteristic of both high and low salt marshes. Eight years after the unplanned, partial tidal restoration at Drakes Island Marsh, the vegetation was dominated bySpartina alterniflora, a characteristic species of low marsh habitat.Hydrologic restoration that allowed for unrestricted saltwater exchange at Mill Brook restored salt marsh functions relatively quickly in comparison to the partial tidal restoration at Drakes Island, where full tidal exchange was not achieved. The irregular tidal regime at Drakes Island resulted in vegetation cover and patterns dissimilar to those of the high marsh used as a reference. The proper hydrologic regime (flooding height, duration and frequency) is essential to promote the rapid recovery of salt marsh functions. We predict that functional recovery will be relatively quick at Mill Brook, but believe that the habitat at Drakes Island will not become equivalent to that of the reference marsh unless the hydrology is further modified.Corresponding Editor: R.E. Turner Manuseript