Ensuring effective restoration efforts with salt marsh grass populations by assessing genetic diversity

Smooth cordgrass (Spartina alterniflora) is a foundation species that naturally occurs along the Atlantic coast of North America and is often used in restoration due to its extensive rooting capacity and ability to halt erosion. Clonal species, such as S. alterniflora, are easy to rear for transplant, but using a predominantly asexual species for restoration may lead to genetically depauperate populations. We (1) identified if genetic diversity was maintained during restoration; (2) determined if genotypes from the native populations were genetically distinct from the restored populations; and (3) evaluated if current efforts limited the number of multiple copies of the same multilocus genotypes (MLG) within restoration sites along the shorelines of the Mosquito Lagoon (ML), Florida, United States. All objectives were addressed where only one representative of an identical MLG was retained within each population. We found that allelic richness (p = 0.618) and expected heterozygosity (p = 0.527) did not significantly differ between restored and natural populations. Furthermore, pairwise F_ST estimates between naturally occurring populations ranged from 0.021 to 0.178, while estimates ranged from approximately 0 to 0.084 among restored populations. When we evaluated differentiation between natural and restored populations, average F_ST was 0.087. Finally, we found that higher numbers of samples with multiple copies of the same MLG occurred in restored populations (31.4–55.9% of samples per population) compared to natural populations (0–11.8% of samples per population). Overall, we found that current restoration efforts in the ML are effective at maintaining natural levels of genetic diversity.     

互花米草入侵对滩涂湿地甲烷排放的影响

在浙江省台州市附近滩涂湿地设置3个不同互花米草入侵密度梯度,即仅有本土植物样地、互花米草与本土植物混生样地和互花米草单优群落样地,研究互花米草入侵对滩涂湿地CH₄排放的影响.结果表明: 3个样地CH₄排放通量为0.68～5.88 mg·m^-2·h^-1,CH₄排放通量随着互花米草入侵梯度的增加而显著升高,互花米草单优群落样地CH₄排放通量分别为本土植物样地和混生样地的8.7和2.3倍.互花米草入侵显著提高了产甲烷菌数量、产甲烷潜力、甲烷氧化菌数量、甲烷氧化潜力、植物生物量、土壤有机碳含量和土壤pH,降低了土壤全氮含量.CH₄排放通量与土壤全氮呈显著负相关,与产甲烷菌数量、产甲烷潜力、甲烷氧化菌数量、甲烷氧化潜力、植物生物量和土壤pH呈显著正相关.互花米草的入侵提高了滩涂湿地植物群落生物量和土壤pH,促进了产甲烷菌数量和产甲烷潜力,从而提高了滩涂湿地的CH₄排放.     

不同发育时间的互花米草盐沼对大型底栖动物群落的影响

2004-2006年对长江口崇明东滩湿地芦苇(Phragmites australis)盐沼和不同发育时间的互花米草(Spartina alterniflora)盐沼的大型底栖动物群落特征进行分析研究.结果表明:互花米草盐沼发育初期,大型底栖动物群落以腹足类为主,物种丰富度(D=2.18)和多样性(H′=2.19)均低于芦苇盐沼(D=2.61, H′=2.29);随着时间的推移,互花米草与本地生物逐渐形成互动和稳定的格局,大型底栖动物群落组成中多毛类的种类逐渐上升(由3种变为6种),物种数和物种丰富度也上升,从而逐步形成新的大型底栖动物群落,物种丰富度(D=2.70)和多样性(H′=2.48)逐渐上升并高于芦苇盐沼(D=2.19, H′=2.09);从大型底栖动物群落的重新形成到稳定阶段,需要若干年的时间.     

废黄河口盐沼土硫酸盐还原速率的研究

本文报道了江苏省北部废黄河口滩面盐沼土中的硫酸盐还原速率。两年内,用同位素标记法测定了两块试验地的硫酸盐还原速率。结果表明,它们均有较高的还原速率。积分得大米草地和互花米草地年总还原值分别为77.75mol SO_4~(2-)·m~(-2)和110.3mol SO_4~(2-)·m~(-2)。硫酸盐还原速率高可能有3个原因:①米草地下部分向上层提供大量有机物;②SO_4~(2-)可由渗透潮水补充,不会因SO_4~(2-)亏损而影响还原率;③硫化物浓度保持在低于引起毒害的水平。硫酸盐还原主要终产物是FeS_2。FeS_2作为被还原的临时贮存库,其浓度有季节性变化。此外,还讨论了硫酸盐还原在有机碳矿化中的作用及在盐沼生态系统中能流的意义。     

江苏沿海互花米草(Spartina alterniflora Loisel)盐沼扩展过程的遥感分析

互花米草(SpartinaalternifloraLoisel)自1982年在江苏沿海栽种以来,在江苏沿海已形成了大片互花米草盐沼。本文通过对历年TM卫星相片上互花米草盐沼的识别、判读及统计,认为江苏沿海互花米草盐沼的年扩展速度在早期较慢,仅为23 4%,中期较快为89%,后期又减慢为48%。结合野外调查,绘制出了江苏沿海互花米草的分布图。此外,就互花米草盐沼对江苏沿海湿地植被演替的影响进行了讨论。     

崇明东滩自然保护区盐沼植被的时空动态

盐沼植被是滩涂湿地的重要组成部分,其动态变化直接影响着湿地的生态服务功能和价值。通过对1998~2005年间4景不同时相的LandsatTM遥感影像的解译分析,结合历史资料数据和近年来的现场调查,分析了崇明东滩鸟类自然保护区自建立以来,盐沼植被的时空演替动态过程。结果显示,随着滩涂的淤涨,东滩盐沼植被的面积从1998年的2478.32hm2增加到2005年的4687.74hm2,而互花米草(Spartina alterniflora)自人为引入至2005年,其面积已增加到1283.4hm2,其增加速率显著高于土著种芦苇(Phragmites australis)和海三棱藨草(Scirpus mariqueter),并且已在东滩保护区相当区域内形成单优势种群落。受1998年和2001年两次高滩围垦和互花米草入侵影响,崇明东滩的芦苇群落面积大大减少,虽随着滩涂的淤涨,芦苇群落的面积逐年有所增加,但增加的速度缓慢。互花米草有着更广的生态幅和竞争优势,是滩涂中扩散最快的植被,而淤涨型滩涂为其提供了可扩张的空生态位,如不加以控制和治理,其快速扩散将会对崇明东滩保护区的生态系统造成更大的威胁和影响。     

Effects of a tropical cyclone on salt marsh insect communities and post-cyclone reassembly processes

Concepts regarding effects of recurrent natural disturbances and subsequent responses of communities are central to ecology and conservation biology. Tropical cyclones constitute major disturbances producing direct effects (damage, mortality) in many coastal communities worldwide. Subsequent reassembly involves changes in composition and abundance for which the underlying mechanisms (deterministic and stochastic processes) are still not clear, especially for mobile organisms. We examined tropical cyclone-induced changes in composition and reassembly of entire insect communities in 16 Louisiana coastal salt marshes before and after Hurricane Isaac in 2012 and 2013. We used the Shannon index and multivariate permutational ANOVA to study insect resistance and resilience, β diversity partitioning to evaluate the importance of species replacement, and null models to disentangle the relative roles of different assembly processes over time after the tropical cyclone. The α diversity and species composition, overall and for different trophic levels, decreased immediately after the tropical cyclone; nonetheless, both then increased rapidly and returned to pre-cyclone states within one year. Changes in species abundance, rather than species replacement, was the primary driver, accounting for most temporal dissimilarity among insect communities. Stochastic processes, which drove community composition immediately after the tropical cyclone, decreased in importance over time. Our study indicates that rapid reformation of insect communities involved sequential landscape-level dynamics. Cyclone-resistant life cycle stages apparently survived in some, perhaps random locations within the overall salt marsh landscape. Subsequently, stochastic patterns of immigration of mobile life cycle stages resulted in rapid reformation of local communities. Post-cyclone direct regeneration of salt marsh insect communities resulted from low resistance, coupled with high landscape-level resilience via re-immigration. Our study suggests that the extent of direct regeneration of local salt marsh insect communities might change with the size of larger marsh landscapes within which they are imbedded.     

Effects of drainage and soil organic content on growth of Spartina alterniflora (Poaceae) in an artificial salt marsh mesocosm

An artificial salt marsh mesocosm was constructed using 680-L polypropylene tanks to determine the effect of soil drainage depth and organic content on growth and rhizome proliferation of the salt marsh smooth cordgrass Spartina alterniflora. Soil drainage depth had no effect on accumulation of aerial or subsurface plant tissue, but tanks that had 2.5% soil organic content supported enhanced aerial tissue and rhizome growth compared to tanks that contained sand alone. We propose a mathematical model for predicting the mass of photosynthetically significant leaf tissue without cutting and drying leaves. Implications of these findings for salt marsh creation projects are discussed.     

The environmental consequences of climatic change on British salt marsh vegetation

The present relationship between sea level and the zonation of salt marsh vegetation is discussed in terms of the salt marshes of the Essex and Kent coasts. These marshes are already decreasing in area as a result of a number of different environmental pressures, including the sinking of the land relative to the sea, at a rate of about 3 mm per year, the result of isostatic adjustment following the last glaciation. Because most British salt marshes are backed by a sea wall the marshes can not respond to rising sea levels by migrating landwards, thus increasing the impact of sea level change. In view of this and of the importance of salt marshes as protection for the sea walls themselves, a conceptual model has been developed, of the likely impact of climate change and the resulting sea level rise, on British salt marsh vegetation. The basis of this approach is the assumption that a rise in sea level will cause the drowning of certain existing vegetation zones and their subsequent replacement by new vegetation types appropriate to the changed sea level. Estimates have been made of the likely impact of rises in sea level of 0.5, 1.0 and 1.5 metres on the five major vegetation zones identified in East Anglia. The validity of this approach is discussed, together with the likely additive effect of present degenerative changes observed in the Essex salt marshes. It is estimated that over the next 60 years a sea level rise of only 0.5 m, when existing degeneration is taken to account, would cause a loss of over 40% of the present area of salt marsh in Essex and probably also in Kent. These losses would mainly effect the higher salt marsh vegetation zones which would be replaced by pioneer communities. These predictions would be greatly magnified by larger rises in sea level. The wider ecological implication of these changes and some possible remedial measures are considered. These predictions are discussed in relation to the situation in the rest of East Anglia and for Britain as a whole.     

Vegetation's importance in regulating surface elevation in a coastal salt marsh facing elevated rates of sea level rise

Rising sea levels threaten the sustainability of coastal wetlands around the globe, thus understanding how increased inundation alters the elevation change mechanisms in these systems is increasingly important. Typically, the ability of coastal marshes to maintain their position in the intertidal zone depends on the accumulation of both organic and inorganic materials, so one, if not both, of these processes must increase to keep pace with rising seas, assuming all else constant. To determine the importance of vegetation in these processes, we measured elevation change and surface accretion over a 4‐year period in recently subsided, unvegetated marshes, resulting from drought‐induced marsh dieback, in paired planted and unplanted plots. We compared soil and vegetation responses in these plots with paired reference plots that had neither experienced dieback nor subsidence. All treatments (unvegetated, planted, and reference) were replicated six times. The recently subsided areas were 6–10 cm lower in elevation than the reference marshes at the beginning of the study; thus, mean water levels were 6–10 cm higher in these areas vs. the reference sites. Surface accretion rates were lowest in the unplanted plots at 2.3 mm yr^?1, but increased in the presence of vegetation to 16.4 mm yr^?1 in the reference marsh and 26.1 mm yr^?1 in the planted plots. The rates of elevation change were also bolstered by the presence of vegetation. The unplanted areas decreased in elevation by 9.4 mm yr^?1; whereas the planted areas increased in elevation by 13.3 mm yr^?1, and the reference marshes increased by 3.5 mm yr^?1. These results highlight the importance of vegetation in the accretionary processes that maintain marsh surface elevation within the intertidal zone, and provide evidence that coastal wetlands may be able to keep pace with a rising sea in certain situations.     

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.     

密度、物种比例对盐沼植物种子萌发阶段种内、种间相互作用的影响

种间相互作用是影响湿地植物群落构建的关键因子,其形式、强度和机制可能随着生长发育的过程而发生改变。种子萌发是植物生命周期的关键环节,一定程度上决定了植物种群分布和群落结构。野外种子萌发过程受到邻近同种或异种种子间相互作用的影响,但对于种子萌发过程中种内、种间相互作用强度及其影响因素的了解仍十分有限。该研究通过培养皿萌发实验探讨了种子密度(每皿80粒、每皿160粒)及比例(单种、3:1混种、2:2混种、1:3混种)对互花米草(Spartina alterniflora)、海三棱藨草(Scirpus×mariqueter)、芦苇(Phragmites australis)种子萌发率、平均萌发时间的影响,并采用相对邻株效应(RNE)评估了这3个物种的种内、种间相互作用强度。结果表明,密度对互花米草、海三棱藨草、芦苇种子的萌发率均有一定的促进作用。与互花米草混种时,芦苇种子在占比最低(25%)处理下的平均萌发时间显著长于单种及其他混种比例处理。3种植物种子的竞争能力没有明确的等级关系,存在非传递性竞争,萌发时海三棱藨草相对互花米草具有一定的竞争优势,互花米草相对芦苇具有一定优势,而芦苇的竞争能...     

Unexpectedly high clonal diversity of two salt marsh perennials across a severe environmental gradient

In salt marsh habitats, noted for their extreme environments, a widely held assumption is that a few large clones dominate plant populations. Using a large number of polymorphic genetic markers, we were able to test this assumption for two salt marsh plants known to span extreme salinity gradients. For both species, clonal diversity was surprisingly high across populations: Simpson's diversity indices were 0.96 and 0.99. Although clonal diversity was high, there was no pattern of association between specific clones or alleles with salt microhabitat. Our findings suggest that sexual reproduction and recruitment from seeds may have been generally underappreciated as an important ecological force in the salt marsh. Furthermore, clonal diversity has implications for conservation and restoration of these critical coastal habitats, particularly with regard to buffering environmental change or disease. Recent studies also suggest that high levels of intraspecific diversity can affect a variety of community and ecosystem processes.     

Impact of surrogate selection on risk assessment for total petroleum hydrocarbons

Environmental contamination involving total petroleum hydrocarbons (TPH) is being investigated and remediated at underground storage tanks, tank farms, pipelines, and refineries across the country. Human health and environmental risk play a significant role in decision making at these sites. However, risk assessment for sites contaminated with petroleum products typically is complicated by inadequate information about the composition of TPH present at the site and the physical and chemical properties and toxicity of the components. To address these data gaps, risk assessors can select surrogate compounds to represent the movement of TPH in the environment at the site and toxicity of TPH present at the site. This article illustrates the potential impact of choice of surrogates on risk estimates, which in turn affect remediation costs.     

水淹对互花米草生长及生理的影响

研究了互花米草在不同没顶水淹时间处理下,株高、叶面积等生长指标以及叶片光合速率与色素、脯氨酸、可溶性糖和蛋白质含量等生理指标变化情况。结果表明,随着水淹时间延长,米草株高和叶面积呈下降趋势,叶片光合速率下降;叶片中自由水/束缚水、叶绿素和类胡萝卜素含量、可溶性糖在不同水淹时长处理之间也存在显著差异;但可溶性蛋白质和游离脯氨酸含量在各处理间差异无显著性。     

海洋石油污染物的微生物降解与生物修复

石油是海洋环境的主要污染物 ,已经对海洋及近岸环境造成了严重的危害。微生物降解是海洋石油污染去除的主要途径。海洋石油污染物的微生物降解受石油组分与理化性质、环境条件以及微生物群落组成等多方面因素的制约 ,N和P营养的缺乏是海洋石油污染物生物降解的主要限制因子。在生物降解研究基础上发展起来的生物修复技术在海洋石油污染治理中发展潜力巨大 ,并且取得了一系列成果。介绍了海洋中石油污染物的来源、转化过程、降解机理、影响生物降解因素及生物修复技术等方面内容 ,强调了生物修复技术在治理海洋石油污染环境中的优势和重要性 ,指出目前生物修复技术存在的问题。     

Exotic Spartina alterniflora invasion alters ecosystem–atmosphere exchange of CH4 and N2O and carbon sequestration in a coastal salt marsh in China

Coastal salt marshes are sensitive to global climate change and may play an important role in mitigating global warming. To evaluate the impacts of Spartina alterniflora invasion on global warming potential (GWP) in Chinese coastal areas, we measured CH₄ and N₂O fluxes and soil organic carbon sequestration rates along a transect of coastal wetlands in Jiangsu province, China, including open water; bare tidal flat; and invasive S. alterniflora, native Suaeda salsa, and Phragmites australis marshes. Annual CH₄ emissions were estimated as 2.81, 4.16, 4.88, 10.79, and 16.98 kg CH₄ ha^?1 for open water, bare tidal flat, and P. australis, S. salsa, and S. alterniflora marshes, respectively, indicating that S. alterniflora invasion increased CH₄ emissions by 57–505%. In contrast, negative N₂O fluxes were found to be significantly and negatively correlated (P < 0.001) with net ecosystem CO₂ exchange during the growing season in S. alterniflora and P. australis marshes. Annual N₂O emissions were 0.24, 0.38, and 0.56 kg N₂O ha^?1 in open water, bare tidal flat and S. salsa marsh, respectively, compared with ‐0.51 kg N₂O ha^?1 for S. alterniflora marsh and ?0.25 kg N₂O ha^?1 for P. australis marsh. The carbon sequestration rate of S. alterniflora marsh amounted to 3.16 Mg C ha^?1 yr^?1 in the top 100 cm soil profile, a value that was 2.63‐ to 8.78‐fold higher than in native plant marshes. The estimated GWP was 1.78, ?0.60, ?4.09, and ?1.14 Mg CO₂eq ha^?1 yr^?1 in open water, bare tidal flat, P. australis marsh and S. salsa marsh, respectively, but dropped to ?11.30 Mg CO₂eq ha^?1 yr^?1 in S. alterniflora marsh. Our results indicate that although S. alterniflora invasion stimulates CH₄ emissions, it can efficiently mitigate increases in atmospheric CO₂ and N₂O along the coast of China.     

Foliar nitrogen and larval parasitism as determinants of leafminer distribution patterns on Spartina alterniflora

ABSTRACT, 1. In northwest Florida, Hydrellia valida hew (Diptera: Ephydridae) frequently mines the leaves of salt marsh cord, grass, Spartina alterniflora . Larvae and pupae are more commonly found in shoreline plants within 3 m of the sea than in inland plants.
2. Shoreline plants contain over twice as much total foliar nitrogen as inland plants. In transects from inland to shoreline plants, leafminer density is positively correlated with total leaf nitrogen content.
3. We experimentally increased foliar nitrogen content on inland Spartina patches to levels above those of shoreline plants. Leafminer densities on experimental centres remained far below those on control edges.
4. Larval parasitism by Opius sp. (Hymenoptera: Braconidae) and Pteromalus sp. (Hymenoptera: Pteromalidae) reaches over 90%, with parasitism increasing from shoreline to inland plants. We suggest that gradients in leafminer densities are caused by differences in parasitoid abundance.