Evaluation of Long‐Term Response of Intertidal Creek Nekton to Phragmites australis (Common Reed) Removal in Oligohaline Delaware Bay Salt Marshes

In the oligohaline Alloway Creek watershed of the upper Delaware Bay, invasive Phragmites australis (Common reed; hereafter Phragmites) has been removed in an attempt to restore tidal marshes to pre‐invasion form and function. In order to determine the effects of Phragmites on nekton use of intertidal creeks and to evaluate the success of this restoration, intertidal creek nekton assemblages were sampled with weirs from May to November for 7 years (1999‐2005) in three marsh types: natural Spartina alterniflora (Smooth cordgrass; hereafter Spartina), sites treated for Phragmites removal (hereafter referred to as Treated), and invasive Phragmites marshes. Replicate intertidal creek collections in all three marsh types consisted primarily of resident nekton and were dominated by a relatively low number of ubiquitous intertidal species. The Treated marsh nekton assemblage was distinguished by greater abundances of most nekton, especially Fundulus heteroclitus (Mummichog). Phragmites had little impact on nekton use of intertidal creeks over this period as evidenced by similar nekton assemblages in the Spartina and Phragmites marshes for most years. Long‐term assemblage‐level analyses and nekton abundances indicated that the Treated marsh provided enhanced conditions for intertidal creek nekton. The response of intertidal creek nekton suggests that the stage of the restoration may influence the results of comparisons between the marsh types and should be considered when evaluating marsh restorations.     

Salt Marsh Restoration in Connecticut: 20 Years of Science and Management

In 1980 the State of Connecticut began a tidal marsh restoration program targeting systems degraded by tidal restrictions and impoundments. Such marshes become dominated by common reed grass (Phragmites australis) and cattail (Typha angustifolia and T. latifolia), with little ecological connection to Long Island Sound. The management and scientific hypothesis was that returning tidal action, reconnecting marshes to Long Island Sound, would set these systems on a recovery trajectory. Specific restoration targets (i.e., pre‐disturbance conditions or particular reference marshes) were considered unrealistic. However, it was expected that with time restored tides would return ecological functions and attributes characteristic of fully functioning tidal salt marshes. Here we report results of this program at nine separate sites within six marsh systems along 110 km of Long Island Sound shoreline, with restoration times of 5 to 21 years. Biotic parameters assessed include vegetation, macroinvertebrates, and use by fish and birds. Abiotic factors studied were soil salinity, elevation and tidal flooding, and soil water table depth. Sites fell into two categories of vegetation recovery: slow, ca. 0.5%, or fast, more than 5% of total area per year. Although total cover and frequency of salt marsh angiosperms was positively related to soil salinity, and reed grass stand parameters negatively so, fast versus slow recovery rates could not be attributed to salinity. Instead, rates appear to reflect differences in tidal flooding. Rapid recovery was characterized by lower elevations, greater hydroperiods, and higher soil water tables. Recovery of other biotic attributes and functions does not necessarily parallel those for vegetation. At the longest studied system (rapid vegetation recovery) the high marsh snail Melampus bidentatus took two decades to reach densities comparable with a nearby reference marsh, whereas the amphipod Orchestia grillus was well established on a slow‐recovery marsh, reed grass dominated after 9 years. Typical fish species assemblages were found in restoration site creeks and ditches within 5 years. Gut contents of fish in ditches and on the high marsh suggest that use of restored marsh as foraging areas may require up to 15 years to reach equivalence with reference sites. Bird species that specialize in salt marshes require appropriate vegetation; on the oldest restoration site, breeding populations comparable with reference marshland had become established after 15 years. Use of restoration sites by birds considered marsh generalists was initially high and was still nearly twice that of reference areas even after 20 years. Herons, egrets, and migratory shorebirds used restoration areas extensively. These results support our prediction that returning tides will set degraded marshes on trajectories that can bring essentially full restoration of ecological functions. This can occur within two decades, although reduced tidal action can delay restoration of some functions. With this success, Connecticut's Department of Environmental Protection established a dedicated Wetland Restoration Unit. As of 1999 tides have been restored at 57 separate sites along the Connecticut coast.     

Restoration of Arthropod Assemblages in a Spartina Salt Marsh following Removal of the Invasive Plant Phragmites australis

Invasive plants are one of the most serious threats to native species assemblages and have been responsible for the degradation of natural habitats worldwide. As a result, removal of invasive species and reestablishment of natural vegetation have been attempted in order to restore biodiversity and ecosystem function. This study examined how native arthropod assemblages, an abundant and functionally important group of organisms in many ecosystems, are affected by the incursion of the invasive wetland plant Phragmites australis and if the restoration of the native vegetation in brackish Spartina alterniflora marshes results in the reestablishment of the arthropod community. The invasion of Phragmites into a coastal Spartina marsh in southern New Jersey seriously altered arthropod assemblages and trophic structure by changing the abundance of trophic groups (detritivores, herbivores, carnivores) and their taxonomic composition. Herbivore assemblages shifted from the dominance of external free‐living specialists (e.g., planthoppers) in Spartina to concealed feeders in Phragmites (stem‐feeding cecidomyiids). Moreover, free‐living arthropods in Phragmites became dominated by detritivores such as Collembola and chironomids. The dominant marsh spiders, web‐building linyphiids, were significantly reduced in Phragmites habitats, likely caused by differences in the physical environment of the invaded habitats (e.g., lower stem densities). Thus, trophic structure of arthropod assemblages in Phragmites, as seen in the large shifts in feeding guilds, was significantly different from that in Spartina. Removal of Phragmites with the herbicide glyphosate resulted in the rapid return of Spartina (≤5 yrs). Moreover, return of the dominant vegetation was accompanied by the recovery of most original habitat characteristics (e.g., live and dead plant biomass, water flow rate). The arthropod assemblage associated with Spartina also quickly returned to its preinvasion state and was not distinguishable from that in uninvaded Spartina reference sites. This study provides evidence that the reestablishment of native vegetation in areas previously altered by an invasive plant can result in the rapid recovery of the native arthropod assemblage associated with the restored habitat.     

Effects of alternate flooding–drought conditions on degenerated Phragmites australis salt marsh in Northeast China

The hydrological regime is the dominant factor associated with the degradation and restoration of inland salt marshes in Northeast China. This study investigates whether alternate flooding–drought conditions could be used to actively restore degraded inland salt marshes with the native plant Phragmites australis. Pot experiments were designed to examine changes in the growth and physiology of P. australis, as well as the saline–alkaline soil characteristics, in response to different hydrological regimes, alternate flooding–drought treatments, and single treatments of moisture, flooding, and drought. After 4 months of treatments, the P. australis population that grew in alternate flooding–drought conditions exhibited substantially more biomass accumulation and less Na⁺ absorption compared with the single treatments of moisture, flooding, and drought. Photosynthesis physiology served as regulating and adaptive responses to different water regimes, with increased values after the short‐term flooding, long‐term drought, and flooding–drought cycles. In addition, the saline–alkaline soil properties changed in response to the flooding–drought cycles. The flooding–drought cycles increased organic matter and total nitrogen contents, but decreased pH, electrical conductivity, and saline ion levels. Plant growth and saline–alkaline soil were improved by flooding–drought cycles (not drought–flooding cycles), which suggests that this may be an effective approach for restoration inland salt marshes.     

敦煌阳关盐沼湿地芦苇种群小尺度空间分布格局

植物种群的空间分布格局是研究连接植物与外界环境关系的重要桥梁,是植物种群稳定性和生活史策略的表现形式。本研究以敦煌阳关盐沼湿地克隆植物芦苇(Phragmites australis)为对象,设置湿生区、轻度盐化区、重度盐化区和荒漠区采样梯度,应用Ripley K(d)函数分析法研究了芦苇种群的小尺度空间分布格局特征及生态适应对策。结果表明:(1)随着从湿生到荒漠区环境梯度的变化,芦苇种群的盖度、密度、高度、地上生物量及种群领地面积都呈现出显著下降的趋势,空斑面积呈现出显著增加的趋势,而种群领地密度则呈现出先增加后下降的趋势;(2)从湿生到荒漠生境,芦苇种群的小尺度空间拓展策略主要表现为由聚集分布为主、非聚集分布(随机分布或均匀分布)为辅,转变为随机分布为主、非随机分布(聚集分布或均匀分布)为辅的特征。研究结果明晰了干旱区内陆河湿地中芦苇种群的空间分布格局特点及其影响因素,为进一步理解克隆植物的生态适应机制提供了案例研究,为科学保护和管理干旱区内陆河湿地生态系统提供了理论依据。     

Effect of oxygen availability and salinity on EARLY LIFE HISTORY STAGES OF SALT MARSH PLANTS. I. Different germination strategies of Spartina alterniflora and Phragmites australis (Poaceae)

Gradients in oxygen availability and salinity are among the most important environmental parameters influencing zonation in salt marsh communities. The combined effects of oxygen and salinity on the germination of two salt marsh grasses, Spartina alterniflora and Phragmites australis, were studied in growth chamber experiments. Germination of both species was initiated by emergence of the shoot and completed by root emergence. Percentage S. alterniflora germination was reduced at high salinity (40 g NaCl/L) and in decreased oxygen (5 and 2.5%). In 0% oxygen shoots emerged, but roots did not. P. australis germination was reduced at a lower salinity (25 g NaCl/L) than S. alterniflora, and inhibited at 40 g NaCl/L and in anoxia. However, a combination of hypoxia (10 and 5% O2) and moderate salinity (5 and 10 g NaCl/L) increased P. australis germination. When bare areas in the salt marsh are colonized, the different germination responses of these two species to combinations of oxygen and salt concentrations are important in establishing their initial zonation. In high salinity wetlands S. alterniflora populates the lower marsh and P. australis occupies the high marsh at the upland boundary.     

退化盐沼湿地盐碱化空间变异与芦苇群落的演替关系

以苏打盐渍土区典型退化湿地为研究区,运用经典统计学和地统计学相结合的方法研究了退化湿地盐碱化指标: 土壤电导率(EC)、盐分含量(SC)、pH和钠吸附比(SAR)的空间变异特征,绘制了4种指标的空间分布图.结果表明:受结构性因素和随机性因素的共同作用,EC、pH、SC具有强空间相关性, SAR空间相关性不明显.Kriging插值结果表明:EC、pH、SC空间分布在一定范围内均存在空间上的相似性.盐碱化指标与芦苇生长指标相关分析结果表明: EC与株高、覆盖度、生物量都呈显著性相关,因此在盐碱化指标中EC是影响芦苇生长最重要因素.当pH＞10.1、EC＞0.4 mS cm-1、SC＞4604 mg kg-1时,植被由芦苇群落过渡为碱茅+芦苇群落,且随着盐碱化指标升高,芦苇所占比例减小.该研究为苏打盐渍土区植被恢复和盐碱地利用提供依据.     

Physical Evolution of Restored Breached Levee Salt Marshes in the San Francisco Bay Estuary

Since 1972 over 940 ha (2,300 ac) of leveed former salt marsh sites around San Francisco Bay have been restored to tidal action, purposely or through natural processes. The evolution of these sites can inform predictions of rates of marshplain evolution and establishment of tidal channel systems. A review of the history of 15 re‐flooded sites ranging in size from 18 to 220 ha (45 to 550 ac) and in age from 2 to 29 years indicates that marshplain vegetation with more than 50% cover was established at nine of the sites within 4 to 20 years. The remaining six sites aged 2 to approximately 20 years continue to be less than 50% vegetated. The evolution of these sites is consistent with the following simple conceptual model of the physical evolution of restored tidal marshes in subsided breached sites. Initially, deposition of estuarine sediment builds up mudflats that allow vegetation establishment once elevations are high enough for vegetation to survive. Sites that are initially lower in the tidal frame take longer to vegetate than those that are initially higher. Three factors appear to retard the time frame for vegetation establishment: limited estuarine suspended sediment supply, erosion of deposited estuarine muds by internally generated wind waves, and restricted tidal exchange. These factors affect evolution more significantly in larger sites. The comparatively short time frame for vegetation colonization and marshplain evolution experienced in earlier, smaller, and/or less subsided breached levee restorations may not necessarily be replicable by simple levee breaching on larger subsided restoration sites now being planned. Our review of the 15 sites also indicates that the formation of tidal channels within the marshes is greatly dependent on whether and how high the site was filled before breaching. Filled sites at high intertidal elevations (above approximately 0.3 m below mean higher high water) can vegetate quickly but after several decades may show little development of tidal channels.     

三种盐胁迫对互花米草和芦苇光合作用的影响北大核心CSCD

互花米草(Spartina alterniflora)的入侵给海岸带盐沼生态系统的结构和功能带来了显著影响。互花米草盐沼中的硫含量高于附近的土著芦苇(Phragmites australis)盐沼。为探讨硫元素对互花米草和芦苇竞争过程的可能影响及其作用机制,以50mmol·L–1的Na2SO4和Na2S对互花米草和芦苇进行处理,分析处理前后5天内两种植物光合气体交换和叶绿素荧光指标变化的差异,实验另设等Na+浓度的Na Cl处理作为比较。研究发现:Na2S对互花米草和芦苇光合作用影响的差异最大,Na Cl次之,Na2SO4最小。Na2S处理后,互花米草净光合速率(Pn)出现显著上升,芦苇Pn值大幅度下降。互花米草的光饱和点(Isat)上升而芦苇的Isat值无变化。表明Na2S处理对互花米草的光合能力有促进作用,但对芦苇的光合能力有抑制作用。Na Cl处理后互花米草Pn值也出现小幅上升,而芦苇Pn值略有下降。Na2SO4处理对互花米草和芦苇的Pn值均无显著影响。除Na2SO4处理的互花米草外,不同盐处理后的互花米草和芦苇非光化学淬灭(NPQ)均出现上升趋势。研究结果表明互花米草对环境硫胁迫的适应能力显著高于芦苇,暗示盐沼高硫环境尤其是硫化物有助于互花米草相对于芦苇的竞争,也很可能是其形成单一植被的重要原因之一。     

三种盐胁迫对互花米草和芦苇光合作用的影响

互花米草(Spartina alterniflora)的入侵给海岸带盐沼生态系统的结构和功能带来了显著影响。互花米草盐沼中的硫含量高于附近的土著芦苇(Phragmites australis)盐沼。为探讨硫元素对互花米草和芦苇竞争过程的可能影响及其作用机制, 以50 mmol·L^-1的Na₂SO₄和Na₂S对互花米草和芦苇进行处理, 分析处理前后5天内两种植物光合气体交换和叶绿素荧光指标变化的差异, 实验另设等Na⁺浓度的NaCl处理作为比较。研究发现: Na₂S对互花米草和芦苇光合作用影响的差异最大, NaCl次之, Na₂SO₄最小。Na₂S处理后, 互花米草净光合速率(P_n)出现显著上升, 芦苇P_n值大幅度下降。互花米草的光饱和点(I_sat)上升而芦苇的I_sat值无变化。表明Na₂S处理对互花米草的光合能力有促进作用, 但对芦苇的光合能力有抑制作用。NaCl处理后互花米草P_n值也出现小幅上升, 而芦苇P_n值略有下降。Na₂SO₄处理对互花米草和芦苇的P_n值均无显著影响。除Na₂SO₄处理的互花米草外, 不同盐处理后的互花米草和芦苇非光化学淬灭(NPQ)均出现上升趋势。研究结果表明互花米草对环境硫胁迫的适应能力显著高于芦苇, 暗示盐沼高硫环境尤其是硫化物有助于互花米草相对于芦苇的竞争, 也很可能是其形成单一植被的重要原因之一。     

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.     

基于CA模型的上海九段沙互花米草和芦苇种群扩散动态

基于1997年以来上海九段沙栽种芦苇和互花米草种群扩散格局的多年现场调查与遥感解译分析,并结合3S技术,构建了适合滩涂盐沼植物种群动态的元胞自动机（CA）模型．结果表明：该模型能较好地模拟九段沙上芦苇和互花米草种群扩散的格局和趋势,并验证了互花米草和芦苇的空间抢先占有模型以及锋面状连续扩散格局;土著植物芦苇与外来植物互花米草占据相同的生态位,而互花米草的种群扩散速度是芦苇的3—5倍,随着九段沙的不断淤涨,互花米草种群的快速扩展还将持续．构建的CA模型有助于深入研究外来物种扩散格局与其生态学过程之间的相互关系,对湿地生物多样性保护和资源管理具有重要意义．     

Responses of Plant Communities to Incremental Hydrologic Restoration of a Tide-Restricted Salt Marsh in Southern New England (Massachusetts, U.S.A.)

Hydrologic restoration of Hatches Harbor, a tide-restricted marsh on Cape Cod (Massachusetts), has resulted in significant plant community changes 7 years following the reintroduction of seawater. Since 1999, incremental increases in flow through a tide-restricting dike have facilitated the rapid decline of salt-intolerant vegetation, while encouraging the expansion of native salt marsh taxa. These changes show strong spatial gradients and are correlated with marsh surface elevation, distance from the point of seawater entry, and porewater salinity. Common reed ( Phragmites australis ) has not decreased in abundance but has migrated a considerable distance upslope. In the wake of this retreat native halophytes have proliferated. Now that maximum flow through the existing dike structure has been reached, continued recovery may be limited less by changing physicochemical conditions and more by rates of growth, seed dispersal, and seed germination of salt marsh taxa.     

Comparison of Some Characteristics Between Phragmites communis and Its Salt Tolerant Variant

R5002-12, a salt tolerant line of Phragmites communis Trin., which was obtained from ethyl methane sulfonate (EMS) treated callus selected under saline stress, was compared with its wild line in respect to their molecular biological, physiological and biochemical characterizations. Five arbitrary primers were screened which showed differences in DNA amplified polymorphism between the variant and its wild line. Some new proteins appeared in the salt tolerant plant under salt stress. Electrophoresis of peroxidase and esterase also showed some differences in isozyme expression between them. The chlorophyll content of the variant was higher than that of the original variety, whether the plants were under salt stress or not.     

丛枝真菌对互花米草和芦苇氮磷吸收的影响

互花米草(Spartina alterniflora Loisel.)是我国海滨盐沼的入侵植物,与土著种芦苇(Phragmites australis)形成了广泛的竞争;已知丛枝菌根(AMF)对不同植物的生长存在差异性影响;但其对互花米草与芦苇之间的种间关系,是否对互花米草入侵芦苇群体产生作用值得探讨.研究对两物种进行了丛枝菌根接种处理,种植模式处理和盐度处理的三因素实验.结果表明:盐度增加使得单种时芦苇、混种时互花米草的AMF侵染率显著下降(p<0.05),而混种时芦苇和单种时的互花米草AMF侵染率受盐度影响不显著(p>0.05).混种时,两种植物的丛枝菌根形成均受对方影响,并且盐度升高使两种植物之间对AMF侵染率的影响发生变化,在淡水生境下混种时,芦苇的AMF侵染率比单种时降低40.5%,互花米草的AMF侵染率比单种时提高了86.9%,均差异显著(p<0.05);在低盐度下混种时芦苇的AMF侵染率比单种时降低24.7%,差异显著(p<0.05),而对互花米草的影响不显著;在高盐度下混种对芦苇的AMF侵染率影响不显著,而使互花米草的AMF侵染率显著降低,降低率比例达78.7%.在淡水生境下,丛枝菌根对芦苇和互花米草的N、P吸收均有显著的促进作用;但是在咸水生境下生长时芦苇的N、P含量主要受盐度的显著影响(p<0.05),随盐度增加而增加;虽然在咸水生境下丛枝菌根仍旧促进芦苇的N、P吸收,但其影响远小于盐度的影响,并且促进效果受到盐度的抑制;但互花米草的N、P含量不受盐度影响.由此可见,接种AMF对这两种植物的氮磷吸收有着不同程度的促进,其作用大小与侵染程度有关,且受到盐度和种植模式的影响.     

互花米草与芦苇耐盐生理特征的比较分析

以天津滨海滩涂外来植物互花米草和本地种芦苇为研究对象,对两种植物根、茎、叶3个器官保护酶(超氧化物歧化酶(SOD)、过氧化物酶（POD）、过氧化氢酶(CAT))和膜脂过氧化产物丙二醛(MDA)、游离脯氨酸、可溶性糖以及质膜相对透性及其季节动态变化进行了测定。结果表明：（1）互花米草体内SOD、POD、CAT酶活性、游离脯氨酸、可溶性糖含量在整个生长季节较芦苇偏低;（2）游离脯氨酸和可溶性糖是互花米草和芦苇体内重要的有机渗透调节物质;(3)两种植物根、茎、叶的质膜相对透性在整个生长季节基本保持稳定,但互花米草质膜相对透过性高于芦苇。该研究有利于解释互花米草适应潮间带生存环境的部分机制,并且从生理生态学特性角度说明其竞争力高于芦苇的原因。     

芦苇耐盐变异体与野生型植株某些特性的比较

地通过细胞工程方法得到的耐盐芦苇（Ｐｈｒａｇｍｉｔｅｓ ｃｏｍｍｕｎｉｓ Ｔｒｉｎ．）变异系Ｒ５００２－１２与野生型植株进行了分子生物学和生理生化特性比较分析。筛选到５个ＲＡＰＤ引物对变异体和野生型植株的ＤＮＡＦ的随机扩增表现出不同的多态性,表明该变异体在分子水平上发生了变化。生理生化分析的结果表明,平行生长状态下的两种株系,其可溶性蛋白和同工酶的表达水平和种类不一样,变异体在ＮａＣｌ胁迫下,表达     

中国滨海沼泽湿地芦苇种子功能性状的纬度梯度变异

种子功能性状反映了植物适应环境变化的繁殖对策,这是植物在自然环境选择和遗传上的一种进化行为,对深入认识植物及种子对环境的长期适应性进化意义重大。本研究对中国滨海6个省市9个地区的滨海沼泽湿地(21°29′—40°57′ N)主要土著植物芦苇种子功能性状(包括种子大小、重量、结实率和产量)进行研究,分析其纬度变异规律。结果表明: 我国滨海湿地芦苇种子各功能性状在不同纬度差异显著,各功能性状间具有显著的相关性。芦苇种子大小(种长、种宽、种形指数、长宽比、种子表面积)和百粒重与纬度呈显著的二次函数关系,随着纬度升高先降后升,而种子结实率呈现先升后降的规律,芦苇种子数量与大小间存在着权衡关系。单位面积种子产量随着纬度升高显著增加。逐步回归分析显示,气候因素是影响不同纬度间芦苇种子功能性状差异的主要因素,土壤孔隙水的pH和盐度次之。     

Human Facilitation of Phragmites australis Invasions in Tidal Marshes: A Review and Synthesis

Efforts to manage or prevent Phragmites australis invasion in salt and brackish marshes are complicated by the lack of a general causal role for specific human activities. The pattern of invasion within a marsh differs among sites, and each may have different causal histories. A review of the literature finds three establishment/invasion patterns: (1) from stands established on ditch- or creek-bank levees toward interior portions of high marshes, (2) from stands along upland borders toward high marsh interiors, and (3) centroid spread from high marsh stands established in ostensibly random locations. Each invasion pattern seems to have different anthropogenic precursors, therefore preventing generalizations about the role of any one human activity in all sites. However, historical and experimental evidence suggests that regardless of invasion pattern, establishment is much more likely at sites where rhizomes are buried in well-drained, low salinity marsh areas. Any human activity that buries large rhizomes, increases drainage, or lowers salinity increases chances of establishing invasive clones. To integrate these patterns and improve our understanding of the rapid spread of Phragmites, recent evidence has been synthesized into a dichotomous flow chart which poses questions about current site conditions and the potential for proposed activities to change site conditions that may facilitate invasion. This simple framework could help managers assess susceptibility and take preventative measures in coastal marshes before invasion occurs or before removal becomes very expensive.     

The sedimentary flux of nutrients at a Delaware salt marsh site: A geochemical perspective

A basic geochemical approach has been used to study the diagenetic cycling and sediment-water exchange rates of essential nutrients at a site in a Delaware salt marsh. The pore water nutrients Si (OH)₄, NH₄ ⁺, PO₄ ^–3, and NO₃ ^– were analyzed and compared seasonally, and potential diffusive fluxes were calculated from the corresponding pore water concentration gradients. Concurrent direct flux measurements were also made using closed chambers deployed on the salt marsh surface under ambient and controlled conditions. The differences in these two approaches allows for estimation of nutrient production and consumption in the root zone and at the salt marsh surface. Silicate and phosphate appear to be primarily geochemically controlled, while the nitrogen species undergo dynamic seasonal redox fluctuations resulting from microbial mediation (e.g., nitrification and denitrification). Specifically: