Development and Application of a Method to Identify Salt Marsh Vulnerability to Sea Level Rise

Wetlands are commonly assessed for ecological condition and biological integrity using a three-tiered framework of landscape-scale assessment, rapid assessment protocols, and intensive biological and physiochemical measurements. However, increased inundation resulting from accelerated sea level rise (SLR) is negatively impacting tidal marsh ecosystem functions for US Northeast coastal wetlands, yet relative vulnerability to this stressor is not incorporated in condition assessments. This article assesses tools available to measure coastal wetland vulnerability to SLR, including measurements made as part of traditional rapid condition assessments (e.g., vegetation communities, soil strength), field and remote sensing-based measurements of elevation, VDatum, and Sea Level Affecting Marshes Model (SLAMM) model outputs. A vulnerability metric that incorporates these tools was calibrated and validated using recent rates of marsh vegetation losses (1972–2011) as a surrogate for future vulnerability. The metric includes complementary measures of elevation capital, including the percentage of high vs. low marsh vegetation, Spartina alterniflora height, elevation measurements, and SLAMM outputs that collectively explained 62% of the variability in recent rates of marsh vegetation loss. Stepwise regression revealed that all three elements (elevation, vegetation measures, and SLAMM outputs) explained significant and largely unique components of vulnerability to SLR, with the greatest level of overlap found between SLAMM outputs and elevation metrics. While soil strength varied predictably with habitat zone, it did not contribute significantly to the vulnerability metric. Despite the importance of determining wetland elevation above key tidal datums of mean sea level and mean high water, we caution that VDatum was found to perform poorly in back-barrier estuaries. This factor makes it difficult to compare elevation capital among marshes that differ in tidal range and poses accuracy problems for broad-scale modeling efforts that require accurate tidal datums. Given the pervasive pattern of coastal wetland drowning occurring in the Northeastern USA and elsewhere, we advocate that compilation of regional data on marsh habitats and vulnerability to SLR is crucial as it permits agencies to target adaptation to sites based on their vulnerability or mixture of habitats, it helps match sites to appropriate interventions, and it provides a broader regional context to site-specific management actions. Without such data, adaptation actions may be implemented where action is not necessary and to the disadvantage of vulnerable sites where opportunities for successful adaptation will be missed.     

Sustainability of a Tidal Freshwater Marsh Exposed to a Long-term Hydrologic Barrier and Sea Level Rise

A 115-year-old railroad levee bisecting a tidal freshwater marsh perpendicular to the Patuxent River (Maryland) channel has created a northern, upstream marsh and a southern, downstream marsh. The main purpose of this study was to determine how this levee may affect the ability of the marsh system to gain elevation and to determine the levee’s impact on the marsh’s long-term sustainability to local relative sea level rise (RSLR). Previously unpublished data from 1989 to 1992 showed that suspended solids and short-term sediment deposition were greater in the south marsh compared to the north marsh; wetland surface elevation change data (1999 to 2009) showed significantly higher elevation gain in the south marsh compared to the north (6?±?2 vs. 0?±?2 mm year^?1, respectively). However, marsh surface accretion (2007 to 2009) showed no significant differences between north and south marshes (23?±?8 and 26?±?7 mm year^?1, respectively), and showed that shallow subsidence was an important process in both marshes. A strong seasonal effect was evident for both accretion and elevation change, with significant gains during the growing season and elevation loss during the non-growing season. Sediment transport, deposition and accretion decreased along the intertidal gradient, although no clear patterns in elevation change were recorded. Given the range in local RSLR rates in the Chesapeake Bay (2.9 to 5.8 mm year^?1), only the south marsh is keeping pace with sea level at the present time. Although one would expect the north marsh to benefit from high accretion of abundant riverine sediments, these results suggest that long-term elevation gain is a more nuanced process involving more than riverine sediments. Overall, other factors such as infrequent episodic coastal events may be important in allowing the south marsh to keep pace with sea level rise. Finally, caution should be exercised when using data sets spanning only a couple of years to estimate wetland sustainability as they may not be representative of long-term cumulative effects. Two years of data do not seem to be enough to establish long-term elevation change rates at Jug Bay, but instead a decadal time frame is more appropriate.     

Impact of Sea-level Rise and Storm Surges on a Coastal Community

A technique to evaluate the risk of storm tides (the combination of a storm surge and tide) under present and enhanced greenhouse conditions has been applied to Cairns on the north-eastern Australian coast. The technique combines a statistical model for cyclone occurrence with a state-of-the-art storm surge inundation model and involves the random generation of a large number of storm tide simulations. The set of simulations constitutes a synthetic record of extreme sea-level events that can be analysed to produce storm tide return periods. The use of a dynamic storm surge model with overland flooding capability means that the spatial extent of flooding is also implicitly modelled. The technique has the advantage that it can readily be modified to include projected changes to cyclone behaviour due to the enhanced greenhouse effect. Sea-level heights in the current climate for return periods of 50, 100, 500 and 1000 years have been determined to be 2.0 m, 2.3 m, 3.0 m and 3.4 m respectively. In an enhanced greenhouse climate (around 2050), projected increases in cyclone intensity and mean sea-level see these heights increase to 2.4 m, 2.8 m, 3.8 m and 4.2 m respectively. The average area inundated by events with a return period greater than 100 years is found to more than double under enhanced greenhouse conditions.     

Influence of Salt Marsh Size and Landscape Setting on Salt Marsh Nekton Populations

Recruitment- and predation-related effects on populations of salt marsh codominants mummichog (Fundulus heteroclitus) and pinfish (Lagodon rhomboides), were examined based on marsh size and landscape setting. Six island marshes—three small island marshes (SIM) ~40–1,000 m² and three large island marshes (LIM) ~3,000–10,000 m²—were paired with six expansive fringing marshes (EFM), each >76,000 m² in size and located within ~1.0 km of a paired SIM or LIM. Over a 2-year period, triannual collections at these sites assessed F. heteroclitus, L. rhomboides, and predator finfish populations as well as habitat characteristics. No significant population density trends were apparent for L. rhomboides young-of-year (YOY) or year-one-and-older (Y1+) cohorts based on marsh size or were any significant differences in density apparent among marsh types. F. heteroclitus YOY and Y1+ densities differed significantly among marsh types demonstrating a positive relationship between density and marsh size. Larval and juvenile F. heteroclitus abundances were significantly lower within SIM than LIM and EFM. Although larval F. heteroclitus abundances between LIM and EFM did not differ significantly, juvenile abundances did, suggesting mortality constrained LIM juvenile abundances. A significant negative relationship of F. heteroclitus to predator finfish density and a significant negative relationship of predator finfish density to low marsh area/perimeter (access restriction) estimates suggest that predation on F. heteroclitus is greater within SIM and LIM than within EFM. Habitat and landscape level attributes can affect resident nekton population regulation and these effects should be considered relative to the life history traits of targeted species when managing coastal resources.     

The Effects of Tidal Export from Salt Marsh Ditches on Estuarine Water Quality and Plankton Communities

Salt marshes are an important transition zone between terrestrial and marine ecosystems, and in their natural state, they often function to cycle or trap terrestrially derived nutrients and organic matter. Many US salt marshes were ditched during the twentieth century, potentially altering their functionality. The goal of this 4-year study was to assess the impact of water from ditches within seven salt marshes on estuarine water quality and plankton communities within four estuaries on Long Island, NY, USA. We found that concentrations of inorganic nutrients (ammonium, phosphate), dissolved and particulate organic nitrogen and carbon (POC, PON, DOC, DON), and total coliform bacteria were significantly enriched in salt marsh ditches compared to the estuaries they discharged into. In addition, concentrations of ammonium and DON became more enriched in ditches as tidal levels decreased, suggesting these constituents were generated in situ. Quantification of nitrogen sources in Flanders Bay, NY, suggested salt marsh ditches could represent a substantial source of N to this estuary during summer months. Experimental incubations demonstrated that water from salt marsh ditches was capable of significantly enhancing the growth of multiple classes of phytoplankton, with large diatoms and dinoflagellates displaying the most dramatic increases in growth. Experiments further demonstrated that salt marsh ditchwater was capable of significantly enhancing pelagic respiration rates, suggesting discharge from ditches could influence estuarine oxygen consumption. In summary, this study demonstrates that tidal draining of salt marsh ditches is capable of degrading multiple aspects of estuarine water quality.     

基于Sentinel-1A雷达影像的崇明东滩芦苇盐沼植被识别提取

为研究芦苇盐沼植物在一个生长周期不同生长季节的雷达后向散射系数变化特征,对芦苇分布信息进行提取,探究Sentinel-1A卫星数据在长江口湿地植被监测中的应用前景。以对长江河口崇明东滩南部为研究区域,利用2016年11个时相的Sentinel-1A雷达卫星影像VV（vertical transmit/vertical receive）+VH（vertical transmit/horizontal receive）双极化数据,分析潮滩地带芦苇、白茅、海三棱藨草、水体和光滩在植被生长周期内的雷达后向散射强度变化特征,对芦苇盐沼植被进行识别提取。结果表明：相较于VH极化方式,VV极化方式下不同地物的后向散射强度差异更为明显,芦苇的后向散射强度在枯叶期下显著高于其他地物;进行芦苇植被提取时,需要对植被枯萎期不同潮位状况下的雷达影像进行组合运算,芦苇提取精度可达到88.7%;对芦苇植被雷达后向散射强度和临近时相的光学遥感归一化植被指数（normalized difference vegetation index,I_NDV）进行相关性分析,发现两者呈良好的正相关关系,相关系数为0.78。     

Plasticity,Not Adaptation to Salt Level,Explains Variation Along a Salinity Gradient in a Salt Marsh Perennial

Evolutionary ecologists have long been intrigued by the fact that many plant species can inhabit a broad range of environmental conditions and that plants often exhibit dramatic differences in phenotype across environmental gradients. We investigated responses to salinity treatments in the salt marsh plant Borrichia frutescens to determine if the species is responding to variation in edaphic salt content through phenotypic plasticity or specialized trait response. We grew seedlings from fruits collected in high- and low-salt microhabitats, assigned seedlings to high- and low-salt treatments in a greenhouse, and measured traits related to salt tolerance. All traits were highly plastic in response to salinity. Plants from the two microhabitats did not differ in trait means or respond differently to the treatments. These results suggest that environmental differences between the two microhabitats are not creating genotypes adapted to high and low salt levels. In addition, despite evidence for variation in allozyme markers in this population, there was no significant genotypic variation (family effect) in any of the trait means measured across microhabitats. There was variation in plasticity for only leaf Na and leaf B concentration. The high degree of plasticity for all traits and the lack of differences among microhabitats across the salinity gradient suggest plasticity in many traits may be fixed for this species.     

长江口盐沼土壤有机质分布与矿化的空间差异

在长江口崇明东滩两类植被(互花米草、土著植被)区域分别选择一条纵向剖面,在高潮滩、中潮滩及光滩取得柱状样,利用颗粒有机碳(POC)含量、碳稳定同位素组成、土壤C/N比与颗粒组成等资料,研究盐沼有机质的分布与矿化特征。结果表明,两个纵向剖面的相同高程部位柱样之间,颗粒有机碳δ13C与POC含量的深度特征均存在显著差异;两个柱样的δ13C与POC含量的平均值均相差较大。互花米草对高潮滩柱样有机质的含量与组成均产生了明显影响,对中潮滩柱样有机质组成已有一定影响;土著植被对高潮滩柱样有机质组成的影响显著。盐沼植被对土壤有机质的分布与矿化均产生了明显影响。高潮滩柱样矿化阶段不同的有机质组分混杂,中潮滩柱样有机质的组成相对简单,矿化程度较弱。柱样粘粒含量与含水量在垂向上变化频繁,盐沼原始沉积层序对柱样的物质分布特征具有本底制约。不同高程部位柱样之间,有机质的深度分布特征以及矿化程度差异显著,盐沼碳动态受到潮滩特征性动力沉积过程的显著影响。     

Long-Term Effects of Tidal Exclusion on Salt Marsh Plain Species at Estero de Punta Banda,Baja California

Disturbance is an important factor influencing plant species composition and diversity. We addressed changes in plant composition and soil characteristics in Estero de Punta Banda, Baja California, Mexico following 22 years of disturbance by tidal exclusion. Currently, sediments in the non-tidal site are dry, 26 ± 1% moisture, and hypersaline, 143 ± 12; while those at the tidal marsh are wet, 36.2 ± 1% moisture, with 40.3 ± 2.6 salinity. The non-tidal site has lost seven species including annuals, short- and long-lived perennials, ephemerals, and parasites. Current dominants are the perennials Batis maritima and Sarcocornia pacifica. Average species richness at the non-tidal site is 4.4 ± 0.32 vs.10 ± 0.18 species per square meter at the tidal site. Average species diversity index is lower at the diked area. The general biodiversity loss that results from tidal exclusion in arid estuaries, contrasts with the species-rich communities that develop in diked humid-climate estuaries.     

Below- and Aboveground Spartina alterniflora Production in a Louisiana Salt Marsh

The monthly variations of below- and aboveground biomass of Spartina alterniflora were documented for a south Louisiana salt marsh from March 2004 to March 2005, and in March 2006 and 2007. The annual production rate above- and belowground was 1821 and 11,676 g m^?2, respectively (Smalley method), and the annual production rate per biomass belowground was 10.7 g dry weight^?1, which are highs along the latitudinal distributions of the plant’s range. The average root + rhizome/shoot ratio (R&R/S) was 2.6:1, which is lower than the R&R/S ratios of 4 to 5.1 reported for Spartina sp. marshes in the northeastern US. The belowground biomass increased from July to September and fluctuated between October and November, after which it declined until February when the growing season began. The belowground biomass was dominated by rhizomes, which declined precipitously in spring and then rose to a seasonal high in the month before declining again as the late summer rise in inflorescence began. Over half of the root biomass in a 30-cm soil profile was in the upper 10 cm, and in the 10- to 20-cm profile for rhizomes. The maximum March biomass above- and belowground was four to five times that of the minimum biomass over the four sampling years. The net standing stock (NSS) of N and P in live biomass aboveground compared to that in the belowground biomass was about 1.7 times higher and equal, respectively, but the NSS of N and P for the live + dead biomass was about six times higher belowground. The average nitrogen/phosphorous molar ratios of 16:1 aboveground is in agreement with the often tested N limitation of biomass accumulation aboveground, whereas the 37:1 belowground ratio suggests that there is an influence of P on R&R foraging for P belowground. Some implications for management and restoration are, in part, that salt marshes should be evaluated and examined using information on the plant’s physiology and production both below- and aboveground.     

压实作用下广西典型红树林区沉积速率及海平面上升对红树林迁移效应的制衡

气候变化造成的海平面上升是迫使红树林向陆迁移的主要驱动力, 而其自身通过捕沙促淤不同程度的减缓了海平面上升速率的影响。基于广西典型红树林区8根短柱的210Pb测年和含水率分析, 以考虑/未考虑沉积物压实作用为研究情景, 通过对比研究红树林区潮滩地表高程抬升速率和相对海平面上升速率的大小关系, 揭示当前海平面上升对广西红树林向陆/向海迁移的驱动机制。研究发现:未考虑压实作用下的沉积速率约是考虑压实作用下沉积速率的1.00~1.34倍(平均1.12倍), 压实作用明显;压实沉积速率介于0.16~0.78 cm/a, 其底层压实沉积速率与潮滩地表高程抬升速率相等。压实作用下, 英罗湾和丹兜海红树林区的地表高程抬升速率小于相对海平面上升速率;与未考虑压实作用得到的结论相悖。由于广西红树林海岸大都建有防波堤, 限制了红树林向陆的迁移;表明英罗湾和丹兜海的红树林正面临海平面上升的威胁。压实作用校正与否对地表高程抬升速率与相对海平面上升速率相当的区域尤为重要。     

Nature：沿海富营养化导致盐沼消失

2012年10月,Nature期刊发表了一篇题为《海富营养化促使盐沼消失》（Coastal eutrophication as a driverof salt marsh loss）的文章。文章指出,盐沼是一种具有很高生产力的沿海湿地,可以为人类提供重要的生态系统服务（例如沿岸城市的暴风雨防护、养分去除和碳封存）。尽管采取了很多保护措施,     

Ecosystem Responses of a Tidal Freshwater Marsh Experiencing Saltwater Intrusion and Altered Hydrology

Tidal freshwater marshes exist in a dynamic environment where plant productivity, subsurface biogeochemical processes, and soil elevation respond to hydrological fluctuations over tidal to multi-decadal time scales. The objective of this study was to determine ecosystem responses to elevated salinity and increased water inputs, which are likely as sea level rise accelerates and saltwater intrudes into freshwater habitats. Since June 2008, in situ manipulations in a Zizaniopsis miliacea (giant cutgrass)-dominated tidal freshwater marsh in South Carolina have raised porewater salinities from freshwater to oligohaline levels and/or subtly increased the amount of water flowing through the system. Ecosystem-level fluxes of CO₂ and CH₄ have been measured to quantify rates of production and respiration. During the first 20 months of the experiment, the major impact of elevated salinity was a depression of plant productivity, whereas increasing freshwater inputs had a greater effect on rates of ecosystem CO₂ emissions, primarily due to changes in soil processes. Net ecosystem production, the balance between gross ecosystem production and ecosystem respiration, decreased by 55% due to elevated salinity, increased by 75% when freshwater inputs were increased, and did not change when salinity and hydrology were both manipulated. These changes in net ecosystem production may impact the ability of marshes to keep up with rising sea levels since the accumulation of organic matter is critical in allowing tidal freshwater marshes to build soil volume. Thus, it is necessary to have regional-scale predictions of saltwater intrusion and water level changes relative to the marsh surface in order to accurately forecast the long-term sustainability of tidal freshwater marshes to future environmental change.     

Anammox in Tidal Marsh Sediments: The Role of Salinity,Nitrogen Loading,and Marsh Vegetation

Anammox bacteria are widespread in the marine environment, but studies of anammox in marshes and other wetlands are still scarce. In this study, the role of anammox in nitrogen removal from marsh sediments was surveyed in four vegetation types characteristic of New England marshes and in unvegetated tidal creeks. The sites spanned a salinity gradient from 0 to 20 psu. The impact of nitrogen loading on the role of anammox in marsh sediments was studied in a marsh fertilization experiment and in marshes with high nitrogen loading entering through ground water. In all locations, nitrogen removal through anammox was low compared to denitrification, with anammox accounting for less than 3% of the total N₂ production. The highest relative importance of anammox was found in the sediments of freshwater-dominated marshes, where anammox approached 3%, whereas anammox was of lesser importance in saline marsh sediments. Increased nitrogen loading, in the form of nitrate from natural or artificial sources, did not impact the relative importance of anammox, which remained low in all the nitrogen enriched locations (<1%).     

Impact of Fertilization on a Salt Marsh Food Web in Georgia

We examined the response of a salt marsh food web to increases in nutrients at 19 coastal sites in Georgia. Fertilization increased the nitrogen content of the two dominant plants, Spartina alterniflora and Juncus roemerianus, indicating that added nutrients were available to and taken up by both species. Fertilization increased Spartina cover, height, and biomass and Juncus height, but led to decreases in Juncus cover and biomass. Fertilization increased abundances of herbivores (grasshoppers) and herbivore damage, but had little effect on decomposers (fungi), and no effect on detritivores (snails). In the laboratory, herbivores and detritivores did not show a feeding preference for fertilized versus control plants of either species, nor did detritivores grow more rapidly on fertilized versus control plants, suggesting that changes in herbivore abundance in the field were driven more by plant size or appearance than by plant nutritional quality. Community patterns in control plots varied predictably among sites (i.e., 17 of 20 regression models examining variation in biological variables across sites were significant), but variation in the effects of fertilization across sites could not be easily predicted (i.e., only 6 of 20 models were significant). Natural variation among sites was typically similar or greater than impacts of fertilization when both were assessed using the coefficient of variation. Overall, these results suggest that eutrophication of salt marshes is likely to have stronger impacts on plants and herbivores than on decomposers and detritivores, and that impacts at any particular site might be hard to distinguish from natural variation among sites.     

Southern California Salt Marsh Dominance Relates to Plant Traits and Plasticity

The three most abundant tidal marsh species at Tijuana Estuary rank Salicornia virginica > Jaumea carnosa > Frankenia salina in occurrences and cover, despite being equally productive in a greenhouse study. The same abundance ranking (Sv>Jc>Fs) developed within 10 years in a restoration site that was planted with near-equal numbers per species. In this paper, we show that resistance to invasion and invasiveness also ranked Sv>Jc>Fs, helping to explain how the restored community lost diversity over time. To explain differential dominance, we assessed 20 traits (including trait ratios), expecting several traits to rank Sv>Jc>Fs, but that was not so. Nor were field abundance ranks explained by the number of superior traits, since Salicornia ranked first in only four traits; Jaumea ranked first in seven, Frankenia in three, and six traits involved ties. Instead, we found explanatory power in two traits (height and runner length) and plasticity (ability to shift trait ratios with changing conditions). We propose that Salicornia becomes dominant by growing tall (height ranked Sv>Jc = Fs) and capturing light first, and that Jaumea co-dominates by extending its runners throughout the understory. Both dominants are more plastic than the subordinate Frankenia, which allocates the greatest proportion of dry weight to roots. Our multi-trait approach explained abundance ranks where focusing on a single trait (potential productivity) could not.     

Understanding the Impacts of Climate Change: an Analysis of Inundation,Marsh Elevation,and Plant Communities in a Tidal Freshwater Marsh

Tidal freshwater marshes around the world face an uncertain future with increasing water levels, salinity intrusion, and temperature and precipitation shifts associated with climate change. Due to the characteristic abundance of both annual and perennial species in these habitats, even small increases in early growing season water levels may reduce seed germination, seedling establishment, and late-season plant cover, decreasing overall species abundance and productivity. This study looks at the distribution of tidal freshwater marsh plant species at Jug Bay, Patuxent River (Chesapeake Bay, USA), with respect to intertidal elevation, and the relationship between inundation early in the growing season and peak plant cover to better understand the potential impacts and marsh responses to increased inundation. Results show that 62% of marsh plant species are distributed at elevations around mean high water and are characterized by narrow elevation ranges in contrast with species growing at lower elevations. In addition, the frequency and duration of inundation and water depth to which the marsh was exposed to, prior to the growing season (March 15–May 15), negatively affected peak plant cover (measured in end-June to mid-July) after a threshold value was reached. For example, 36 and 55% decreases in peak plant cover were observed after duration of inundation threshold values of 25 and 36% was reached for annual and perennial species, respectively. Overall, this study suggests that plant communities of tidal freshwater marshes are sensitive to even small systematic changes in inundation, which may affect species abundance and richness as well as overall wetland resiliency to climate change.     

Nutrients and Abiotic Stress Interact to Control Ergot Plant Disease in a SW Atlantic Salt Marsh

Over the last decades, human activities have strongly affected ecosystems, with pervasive increases in nutrient loadings, abiotic stress, and altered herbivore pressure. The evaluation of how those environmental factors interact to influence plant–pathogen interactions under natural conditions becomes essential to fully understand the ecology of diseases and anticipate the possible effects of global change on natural and agricultural systems. In a SW Atlantic salt marsh, we performed a field factorial experiment to evaluate the effect of herbivory, salinity, and nutrient availability, three main limiting factors for salt marsh plant growth, on the infection of the fungus Claviceps purpurea (ergot) upon the cordgrass Spartina densiflora. Results show that herbivory has no effect but both nutrients and salinity increase fungal infection. The combined effect of salinity and nutrients is not additive but interactive. Salinity stress increases infection at ambient nutrient levels but in combination with fertilizer it buffers the higher infection produced by increased nutrient availability. Since both, nitrogen availability and salinity are factors predicted to globally increase due to human impact on ecosystems, this interaction between environmental factors and ergot infection can have strong effects on natural and productive agricultural systems.     

Vulnerability of Hampton Roads,Virginia to Storm-Surge Flooding and Sea-Level Rise

Sea-level rise will increase the area covered by hurricane storm surges in coastal zones. This research assesses how patterns of vulnerability to storm-surge flooding could change in Hampton Roads, Virginia as a result of sea-level rise. Physical exposure to storm-surge flooding is mapped for all categories of hurricane, both for present sea level and for future sea-level rise. The locations of vulnerable sub-populations are determined through an analysis and mapping of socioeconomic characteristics commonly associated with vulnerability to environmental hazards and are compared to the flood-risk exposure zones. Scenarios are also developed that address uncertainties regarding future population growth and distribution. The results show that hurricane storm surge presents a significant hazard to Hampton Roads today, especially to the most vulnerable inhabitants of the region. In addition, future sea-level rise, population growth, and poorly planned development will increase the risk of storm-surge flooding, especially for vulnerable people, thus suggesting that planning should steer development away from low-lying coastal and near-coastal zones.