Alterniflora Marsh Research Articles

Living Shorelines: Coastal Resilience with a Blue Carbon Benefit.

Living shorelines are a type of estuarine shoreline erosion control that incorporates native vegetation and preserves native habitats. Because they provide the ecosystem services associated with natural coastal wetlands while also increasing shoreline resilience, living shorelines are part of the natural and hybrid infrastructure approach to coastal resiliency. Marshes created as living shorelines are typically narrow (< 30 m) fringing marshes with sandy substrates that are well flushed by tides. These characteristics distinguish living shorelines from the larger meadow marshes in which most of the current knowledge about created marshes was developed. The value of living shorelines for providing both erosion control and habitat for estuarine organisms has been documented but their capacity for carbon sequestration has not. We measured carbon sequestration rates in living shorelines and sandy transplanted Spartina alterniflora marshes in the Newport River Estuary, North Carolina. The marshes sampled here range in age from 12 to 38 years and represent a continuum of soil development. Carbon sequestration rates ranged from 58 to 283 g C m-2 yr-1 and decreased with marsh age. The pattern of lower sequestration rates in older marshes is hypothesized to be the result of a relative enrichment of labile organic matter in younger sites and illustrates the importance of choosing mature marshes for determination of long-term carbon sequestration potential. The data presented here are within the range of published carbon sequestration rates for S. alterniflora marshes and suggest that wide-scale use of the living shoreline approach to shoreline management may come with a substantial carbon benefit.

Reimagining South American coasts: unveiling the hidden invasion history of an iconic ecological engineer

AbstractAimThe smooth cordgrassSpartina alterniflorais an iconic ecological engineer that has inspired some of the more insightful concepts and perspectives in modern theoretical ecology and environmental management, from population to community and ecosystem scales. Although it is currently considered native over more than 100 degrees of latitude along the Atlantic coast of the Americas, we challenge the default assumption that this cordgrass is native to South America, and propose an alternative hypothesis that it was introduced in the 18th or early 19th century by human activity.LocationWorld‐wide.MethodsWe applied nine criteria that have been proposed for the recognition of non‐native species. These criteria consider the historical, biological, geographic, dispersal, ecological and evolutionary evidence that classically underpin the distinctions between native and non‐native species.ResultsOur results strongly support the hypothesis thatS. alterniflorais not native to South America. Herbarium collections, historical floristic descriptions and extensive literature reports clearly indicate thatS. alterniflorawas absent prior to the early 1800s in South America.S. alterniflorashows a reduced morphological, ecological and physiological variability along the South American coast and demonstrably increased in both regional extent and abundance over the 20th century.Main conclusionsWe conclude that what are now extensiveS. alternifloramarshes in this region were probably bare mudflats and that there have been vast unrecorded and thus overlooked shifts in bird, fish and invertebrate biodiversity, and immense shifts in algal vs. detritus production, with the concomitant trophic cascades that these changes imply. Our results change the way we perceive “natural” coastal ecosystems on the Atlantic coast of South America as a whole. Indeed, most South American coastal marshes currently are what we term “ecological mirages”– illusions that have seriously hampered our ability to recognize the nature of pre‐existing native ecosystems.

Marsh Canopy Leaf Area and Orientation Calculated for Improved Marsh Structure Mapping

An approach is presented for producing the spatiotemporal estimation of leaf area index (LAI) of a highly heterogeneous coastal marsh without reliance on user estimates of marsh leaf-stem orientation. The canopy LAI profile derivation used three years of field measured photosynthetically active radiation (PAR) vertical profiles at seven S. alterniflora marsh sites and iterative transform of those PAR attenuation profiles to best-fit light extinction coefficients (KM). KM sun zenith dependency was removed obtaining the leaf angle distribution (LAD) representing the average marsh orientation and the LAD used to calculate the LAI canopy profile. LAI and LAD reproduced measured PAR profiles with 99 percent accuracy and corresponded to field documented structures. LAI and LAD better reflect marsh structure and results substantiate the need to account for marsh orientation. The structure indexes are directly amenable to remote sensing spatiotemporal mapping and offer a more meaningful representation of wetland systems promoting biophysical function understanding.

Program Profile: The Georgia Coastal Ecosystems Long Term Ecological Research Project (GCE‐LTER)

Program Profile: The <scp>G</scp>eorgia Coastal Ecosystems Long Term Ecological Research Project (GCE‐LTER)

Structural Classification of Marshes with Polarimetric SAR Highlighting the Temporal Mapping of Marshes Exposed to Oil

Empirical relationships between field-derived Leaf Area Index (LAI) and Leaf Angle Distribution (LAD) and polarimetric synthetic aperture radar (PolSAR) based biophysical indicators were created and applied to map S. alterniflora marsh canopy structure. PolSAR and field data were collected near concurrently in the summers of 2010, 2011, and 2012 in coastal marshes, and PolSAR data alone were acquired in 2009. Regression analyses showed that LAI correspondence with the PolSAR biophysical indicator variables equaled or exceeded those of vegetation water content (VWC) correspondences. In the final six regressor model, the ratio HV/VV explained 49% of the total 77% explained LAI variance, and the HH-VV coherence and phase information accounted for the remainder. HV/HH dominated the two regressor LAD relationship, and spatial heterogeneity and backscatter mechanism followed by coherence information dominated the final three regressor model that explained 74% of the LAD variance. Regression results applied to 2009 through 2012 PolSAR images showed substantial changes in marsh LAI and LAD. Although the direct cause was not substantiated, following a release of freshwater in response to the 2010 Deepwater Horizon oil spill, the fairly uniform interior marsh structure of 2009 was more vertical and dense shortly after the oil spill cessation. After 2010, marsh structure generally progressed back toward the 2009 uniformity; however, the trend was more disjointed in oil impact marshes.

Microbial Community Composition and Extracellular Enzyme Activities Associated with Juncus roemerianus and Spartina alterniflora Vegetated Sediments in Louisiana Saltmarshes.

Saltmarshes are typically dominated by perennial grasses with large underground rhizome systems that can change local sediment conditions and be important in shaping the sediment microbial community. Factors such as salinity that control plant zonation in saltmarshes are also likely to influence the microbial community, but little is known as to whether microbial communities share distribution patterns with plants in these systems. To determine the extent to which microbial assemblages are influenced by saltmarsh plant communities, as well as to examine patterns in microbial community structure at local and regional scales, we sampled sediments at three saltmarshes in Louisiana, USA. All three systems exhibit a patchy distribution of Juncus roemerianus stands within a Spartina alterniflora marsh. Sediment samples were collected from the interior of several J. roemerianus stands as well as from the S. alterniflora matrix. Samples were assayed for extracellular enzyme activity and DNA extracted to determine microbial community composition. Denaturing gradient gel electrophoresis of rRNA gene fragments was used to determine regional patterns in bacterial, archaeal, and fungal assemblages, while Illumina sequencing was used to examine local, vegetation-driven, patterns in community structure at one site. Both enzyme activity and microbial community structure were primarily influenced by regional site. Within individual saltmarshes, bacterial and archaeal communities differed between J. roemerianus and S. alterniflora vegetated sediments, while fungal communities did not. These results highlight the importance of the plant community in shaping the sediment microbial community in saltmarshes but also demonstrate that regional scale factors are at least as important.

Invasion chronosequence of Spartina alterniflora on methane emission and organic carbon sequestration in a coastal salt marsh

Spartina alterniflora was intentionally introduced to China in 1979 for the purpose of sediment stabilization and dike protection, and has continuously replaced native plants or invaded bare mudflats in the coastal marsh. To evaluate the spatial variation of CH4 emission and soil organic carbon (SOC) storage along the invasion chronosequence, we selected four sites including bare mudflat (Control, as first year invasion), and marshes invaded by S. alterniflora in 2002 (SA-1), 1999 (SA-2) and 1995 (SA-3), respectively, in Sheyang county, Jiangsu, China and set up the marsh mesocosm system for flux measurement. The mean accumulation rate of SOC in the 0–30 cm layer exponentially increased with the invasion time, ranging from 1.08 (over the first 9 years) to 2.35 Mg Cha−1yr−1 (over the period of 12–16 years). The cumulative CH4 emission during the growth season was 20.5, 75.4, 81.0 and 92.2 kg CH4ha−1 in Control, SA-1, SA-2 and SA-3, respectively, and there was a binomial relationship between CH4 emission and invasion time. Cumulative CH4 emission was logarithmically increased with SOC concentration; however the ratio of CH4 emission to SOC concentration was inversely correlated with the invasion time in the S. alterniflora marsh, suggesting that the less increased SOC in the S. alterniflora marsh was converted into CH4. The net global warming potential (GWP) was estimated at 733 kg CO2-eq ha−1yr−1 in the tidal mudflat and reduced to −1273 (SA-1) to −2233 kg CO2-eq ha−1yr−1 (SA-3) in the S. alterniflora marsh. Our results indicated that S. alterniflora invasion effectively sequestrated atmospheric CO2 and mitigated GWP in the coastal marsh of China.

The expansion of Spartina alterniflora marsh in response to tidal flat reclamation, central Jiangsu coast, eastern China

The central Jiangsu coast is typical of China's coastal muddy silt with an average tidal range of 4 m. The shoreline has been gradually advancing seaward as the coast was supplied by a large amount sediment from ancient Yangtze River and Yellow River. As a result, a lot of land resources are fostered in the coast. Therefore tidal flat reclamation activities gradually intensified to the demand of economic development. A large- scale reclamation plan in Jiangsu coast has been implemented since the 21 st century and Spartina alterniflora marsh has become the main target of tidal flat reclamation. Thus how Spartina alterniflora marsh will expand during the reclamation period is worthy of study. Thirteen phases of satellite imageries from 2001 to 2013 and field observation data are analyzed to quantify the expansion rate of Spartina alterniflora marsh in association with the reclamation activities. The result shows that Spartina alterniflora expansion during 2001- 2013 can be divided into three periods. During 2001- 2007,the Spartina alterniflora area outside the seawall was relatively large and the influence on the tidal flat sedimentary environment by reclamation did not hamper its expansion. As a result,both the annually increased Spartina alterniflora area and the expansion rate keep pace with reclamation. During 2008- 2010, the Spartina alterniflora area outside the seawall decreased significantly; nevertheless, the mean annual expansion rate of the Spartina alterniflora marsh was still relatively high. During 2011- 2013, the area of Spartina alterniflora marsh became small because of the reclamation activities during 2001-2007 and 2008-2010 periods. Spartina alterniflora expansion became stabilized. As such, the pattern of the marsh expansion differs in response to the reclamation rate and stages. If a sufficiently wide marsh can be maintained during reclamation, then the marsh will continue to grow. The underlying mechanism is that the Spartina alterniflora marsh is influenced by the generation of seedling and the sediment types and bed elevation, while reclamation will affect all these factors. The relationship between marsh expansion and reclamation rate for the period of 2001- 2007 indicates that, for sustainable reclamation on the Jiangsu coast, a width of 0.9-1 km for the Spartina alterniflora marsh should be maintained.

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 CO2 eq ha(-1) yr(-1) in open water, bare tidal flat, P. australis marsh and S. salsa marsh, respectively, but dropped to -11.30 Mg CO2 eq 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.

Weak Correlation Between Methane Production and Abundance of Methanogens Across Three Brackish Marsh Zones in the Min River Estuary, China

Methane production is influenced by the abundance of methanogens and the availability of substrates. Sulfate-reducing bacteria (SRB) also play an important role in the anaerobic decomposition of organic matter. However, the relationships between methane production and abundance of methanogen and pore water substrates in estuarine brackish marshes are poorly characterized, and even to our knowledge, no published research has explored the relationship between methane production rate and pore water dimethyl sulfide (DMS) concentration. We investigated methane production rate, abundances of methanogens and SRB, sediment organic carbon contents, and concentrations of pore water substrates (acetate and DMS) and terminal electron acceptors (SO4 2−, NO3 −, and Fe3+) at a brackish marsh landscape dominated by Phragmites australis marsh, Cyperus malaccensis marsh, and Spartina alterniflora marsh in the Min River estuary, southeast China. The average rates of methane production over the entire 30 cm of the sediment profile (5 cm sampling interval) in the three marshes were 0.142, 0.058, and 0.067 μg g−1 day−1, respectively. The abundance of both methanogens and SRB in the sediment of the P. australis marsh with the highest sediment organic carbon content was higher than in the C. malaccensis and S. alterniflora marshes. Mean pore water DMS concentrations over the entire 30 cm of the sediment profile under the S. alterniflora marsh were higher than those in the C. malaccensis marsh and P. australis marsh. Methane production rate correlated weakly with the abundance of methanogens across the three marsh zones together, but did not correlate with the concentrations of pore water acetate and DMS. Our results suggest that the abundance of methanogens is controlled by sediment organic carbon supply, and further, methane production is affected by the abundance of methanogens in the subtropical estuarine brackish marshes.

互花米草生物量变化对盐沼沉积物有机碳的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 互花米草生物量变化对盐沼沉积物有机碳的影响 DOI: 10.5846/stxb201404090685 作者: 作者单位: 南京大学,南京大学,南京大学,南京大学,盐城工学院 环境科学与工程学院,青岛海洋地质研究所 作者简介: 通讯作者: 中图分类号: 基金项目: 江苏省自然科学基金重点研究专项(BK2011012); 海洋公益性行业科研专项经费项目(2010418006); 海洋沉积与环境地质国家海洋局重点实验室开放基金(MASEG201205); 国土资源部海洋油气资源和环境地质重点实验室基金项目(MRE201408) The response of organic carbon content to biomass dynamics in Spartina alterniflora marsh Author: Affiliation: Nanjing University,Nanjing University,Nanjing University,Nanjing University,School of Environmental Science and Engineering, Yancheng Institute of Technology, Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:以江苏王港典型互花米草(Spartina alterniflora)盐沼湿地为研究对象,分析光滩及互花米草滩沉积物中有机碳的水平和垂向分布特征,了解互花米草生物量的季节动态变化,探讨二者之间的相互关系,在此基础上研究互花米草生物量分布和季节变化对沉积物中有机碳(TOC)含量的影响。结果表明,互花米草枯落物中的有机碳数量在两个月内衰减了40%,而表层沉积物中TOC含量及其中互花米草来源TOC所占比例的变化,均与互花米草地表枯落物量的季节变化存在两个月的"相位差",这与枯落物快速分解时间大致吻合,说明枯落物是表层沉积物中TOC的重要来源。高达60%的互花米草地下生物量分布在0-20cm深度内,该深度范围内沉积物中TOC含量较高,且TOC主要来源于互花米草。此外,不同深度TOC含量与地下生物量之间存在良好的正相关关系,说明地下生物量是影响沉积物TOC含量的重要因子。研究区互花米草年固碳能力为2274g m-2 a-1,盐沼沉积物中TOC埋藏速率达到了470 g m-2 a-1,是地表一个重要的碳汇;同时研究区每年向近岸水域输出大量的TOC,是近岸海域生态系统的一个重要碳源。 Abstract:Spartina alterniflora (C4) was introduced to the coastal region of Jiangsu Province as an exotic species in 1982. This perennial grass then gradually invaded regions previously occupied by native C3 plants. Much research has focused on variation of the ecosystem carbon cycle and has demonstrated that this S. alterniflora invasion has increased the carbon accumulation rate. However, the impact of plant biomass (both aboveground and belowground) on the organic carbon content of salt marsh sediments requires further study. To explore the response of organic carbon content to the biomass dynamics in an S. alterniflora marsh, the contents of total organic carbon (TOC), total nitrogen (TN), and stable carbon isotope composition (δ13C) of sediments, in an S. alterniflora marsh as well as the bare flat, were investigated by analysis of coral and surface sediments, together with the biomass variations of S. alterniflora. The sediment water content, grain size, and δ13C of coastal water and S. alterniflora were also determined. The Litterbag method was used to measure the S. alterniflora litter decomposition rate. The results indicate that the organic carbon of newer litter rapidly decomposed in the first 2 months, and then remained stable. The seasonal variation of the TOC content of surface sediments in the S. alterniflora marsh was significant, and a 2-month phase shift was not only observed in the TOC content variations and surface litter mass but was also recorded for the proportion of organic carbon derived from S. alterniflora and surface litter mass. However, this phase-shift phenomenon did not exist on the bare flat, indicating that the litter is a dominant source of the organic carbon in surface sediments. The results show that 60% and 33% of belowground biomass was observed in the top 20 cm and at 20-40 cm depths, respectively. Compared with the bare flat, the vertical changes of TOC content in the S. alterniflora marsh showed a different distribution pattern. That is to say, the TOC content of sediments at depths < 20 cm was significantly higher than those at depths > 20 cm, and had an increasing trend from depth 20 cm to the surface. A similar variation was observed for the proportion of organic carbon derived from S. alterniflora in the top 20 cm of sediments. Furthermore, there was a remarkably positive relationship between the belowground biomass of S. alterniflora and TOC content. This suggests that belowground biomass plays an important role in TOC variation along the profiles. The greatest and least plant organic carbon storages in the S. alterniflora marsh were observed in October and April, respectively. The average carbon fixation of S. alterniflora, with quantity 2274 g·m-2·a-1, was 460% that of terrestrial vegetation in China. Similarly, the burial rate of organic carbon of S. alterniflora marsh sediments, with quantity 470 g·m-2·a-1, was significantly greater than the average value of coastal salt marshes in China. Thus, the S. alterniflora salt marsh fixed large amounts of carbon dioxide from the air, and enhanced the organic carbon accumulation of the sediment. 参考文献 相似文献 引证文献

Plant effects on burrowing crab morphology in a Chinese salt marsh: Native vs. exotic plants

Burrowing crabs are conspicuous components of many salt marshes yet factors influencing burrow morphology have received little attention. We studied the effects of marsh plants on crab burrows and found significant variation of crab burrow morphology along a successional gradient from mudflat to vegetated marshes (either exotic Spartina alterniflora or native Phragmites australis marsh). Mudflat soil had lower water content, but higher bulk density than vegetated marshes. Burrows in vegetated marshes had more openings and branching and higher width–depth ratios, but smaller openings and lower depth, length, and total volume than on mudflats. S. alterniflora marshes had less rhizome biomass, but higher fine root biomass than P.australis marshes found at higher elevations, and burrows in S. alterniflora marshes were shallower, shorter, had smaller volumes, but had larger surface openings than P.australis marshes. Young S. alterniflora marshes had higher aboveground biomass, but lower stem density, rhizome and fine root biomass, and burrows were deeper, longer, and larger than in old S. alterniflora marshes. These data suggest that plant properties influence burrow morphologies and that burrow morphologies change during salt marsh succession due to changing root distributions and soil properties.

Effects of Tidewater and Crab Burrowing on H2S Emission and Sulfur Storage in Spartina alterniflora Marsh

Aiming to uncover the effects of tidewater and crab burrowing on sulfur cycling of Spartina alterniflora marsh, a field experiment was carried out at Jiangsu Yancheng Wetland National Nature Reserve. H2S flux, plant sulfur storage and total sulfur of sediments in S. alterniflora marsh were measured under different tidewater and crab burrows treatments. Results showed that crab burrows significantly increased H2S emission from S. alterniflora marsh, while no significant effect on H2S emission by tidewater was detected. Both tidewater and crab burrows had no significant effects on plant sulfur storage except that the crab burrows significantly decreased it in the seeding season. Tidewater only significantly impacted total sulfur in sediments of 0–30 cm depth, while those in soil of 0–20 and 40–50 cm depths were significantly affected by crab burrows. Total sulfur in sediments affected by tidewater and crab burrows exhibited a seasonal variation. The findings of this study indicated that both tidewater and crab burrowing were key disturbing factors affecting sulfur cycling in S. alterniflora marsh but in different aspects.

Abundance and Diet of Predatory Fishes in Phragmites, Treated Phragmites, and Natural Spartina Marshes in Delaware Bay

Abundance and diet of larger predatory fishes in Phragmites marsh creeks were compared with those in natural Spartina alterniflora marshes and Phragmites marshes exposed to herbicides and burning (treated marshes). The most abundant fishes (n = 3,107) caught in gill nets from June to November 2001 and May to November 2002 were Morone americana (white perch; 82 %) and Ictalurus punctatus (channel catfish; 6 %). Annual abundance of species varied inconsistently across habitats. Morone americana caught in Phragmites marshes had lower percent piscivory and gut fullness than those caught in Spartina or treated marsh creeks, perhaps due to reduced fish prey availability. The diet in Phragmites marshes also showed comparatively higher occurrences and dry weights of the dominant marsh surface fish Fundulus heteroclitus (mummichog). With the few exceptions noted for M. americana, larger, piscivorous fishes appeard to function similarly in all three habitats, perhaps because their relatively large home ranges may cross habitat boundaries. More research, at broader spatial scales, is needed to link the effects of marsh restoration on piscivorous fish behavior and movement.

Distribution and deposition characteristics of carbon and nitrogen in sediments in a semi-closed bay area, southeast China

In this study, we analyzed carbon and nitrogen parameters (e.g., total organic carbon (TOC), total nitrogen (TN), stable isotopes of organic matter (δ13C, δ15N), and carbon–nitrogen ratio (C/N)), grain-size parameters and deposition rate, as well as their variations in the surface layer and on the profile of the sediment cores in various ecological zones of Luoyuan Bay. The results showed that the sedimentary type of Luoyuan Bay was clay silt. The TOC, TN, δ13C, and δ15N were in the range of 0.450–0.955%, 0.054–0.101%, −23.75 to −19.47‰, and 3.57–6.72‰, respectively; the C/N was in the range of 8.80–13.78. The grain-size parameters of the Spartina alterniflora marsh and transition zone were similar, whereas a similarity in the carbon and nitrogen parameters between the transition zone and mudflat was observed. The correlation of TOC and TN was different between the fresh organic matter and the obsolete organic matter. The particle size was not the main factor that controlled the TOC and TN contents in the sediments; the δ13C indicated the organic matter was dominated by marine sources. The average deposition rates in the Spartina alterniflora marsh, transition zone, and mudflat were 2.47, 2.79, 1.16gcm−2y−1, respectively. In the Spartina alterniflora marsh, the TOC and TN content increased by 96% and 104%, respectively, from 1955 to the present. Compared with the mudflat, the TOC and TN content in the layer between the surface and the 40-cm depth of the Spartina alterniflora marsh were 26% and 13% higher, respectively. The introduction of Spartina alterniflora and the metabolism of their roots had a significant effect on the carbon and nitrogen deposition in the layer at 0–40cm depth. The carbon sequestration rate of the salt marsh wetland in Luoyuan Bay was comparable to the carbon sequestration of global marshes. The deposition rates of TOC and TN in the Spartina alterniflora marsh and transition zone were greater than twice that in the mudflat.

Marsh Dieback, loss, and recovery mapped with satellite optical, airborne polarimetric radar, and field data

Landsat Thematic Mapper and Satellite Pour l'Observation de la Terre (SPOT) satellite based optical sensors, NASA Uninhabited Aerial Vehicle synthetic aperture radar (UAVSAR) polarimetric SAR (PolSAR), and field data captured the occurrence and the recovery of an undetected dieback that occurred between the summers of 2010, 2011, and 2012 in the Spartina alterniflora marshes of coastal Louisiana. Field measurements recorded the dramatic biomass decrease from 2010 to 2011 and a biomass recovery in 2012 dominated by a decrease of live biomass, and the loss of marsh as part of the dieback event. Based on an established relationship, the near-infrared/red vegetation index (VI) and site-specific measurements delineated a contiguous expanse of marsh dieback encompassing 6649.9ha of 18,292.3ha of S. alterniflora marshes within the study region. PolSAR data were transformed to variables used in biophysical mapping, and of this variable suite, the cross-polarization HV (horizontal send and vertical receive) backscatter was the best single indicator of marsh dieback and recovery. HV backscatter exhibited substantial and significant changes over the dieback and recovery period, tracked measured biomass changes, and significantly correlated with the live/dead biomass ratio. Within the context of regional trends, both HV and VI indicators started higher in pre-dieback marshes and exhibited substantially and statistically higher variability from year to year than that exhibited in the non-dieback marshes. That distinct difference allowed the capturing of the S. alterniflora marsh dieback and recovery; however, these changes were incorporated in a regional trend exhibiting similar but more subtle biomass composition changes.

Responses of CH4 emissions to nitrogen addition and Spartina alterniflora invasion in Minjiang River estuary, southeast of China

The nitrogen (N) input and Spartina alterniflora invasion in the tidal marsh of the southeast of China are increasingly serious. To evaluate CH4 emissions in the tidal marsh as affected by the N inputs and S. alterniflora invasion, we measured CH4 emissions from plots with vegetated S. alterniflora and native Cyperus malaccensis, and fertilized with exogenous N at the rate of 0 (N0), 21 (N1) and 42 (N2) g N/(m2·yr), respectively, in the Shanyutan marsh in the Minjiang River estuary, the southeast of China. The average CH4 fluxes during the experiment in the C. malaccensis and S. alterniflora plots without N addition were 3.67 mg CH4/(m2·h) and 7.79 mg CH4/(m2·h), respectively, suggesting that the invasion of S. alterniflora into the Minjiang River estuary stimulated CH4 emission. Exogenous N had positive effects on CH4 fluxes both in native and in invaded tidal marsh. The mean CH4 fluxes of N1 and N2 treatments increased by 31.05% and 123.50% in the C. malaccensis marsh, and 63.88% and 7.55% in the S. alterniflora marsh, respectively, compared to that of N0 treatment. The CH4 fluxes in the two marshes were positively correlated with temperature and pH, and negatively correlated with electrical conductivity and redox potential (Eh) at different N addition treatments. While the relationships between CH4 fluxes and environmental variables (especially soil temperature, pH and Eh at different depths) tended to decrease with N additions. Significant temporal variability in CH4 fluxes were observed as the N was gradually added to the native and invaded marshes. In order to better assess the global climatic role of tidal marshes as affected by N addition, much more attention should be paid to the short-term temporal variability in CH4 emission.

Heavy metal contamination and ecological risk in Spartina alterniflora marsh in intertidal sediments of Bohai Bay, China

To investigate the effects of Spartina alterniflora on heavy metals pollution of intertidal sediments, sediment cores of a S. alterniflora salt marsh and a mudflat in Bohai Bay, China were analyzed. The results showed that S. alterniflora caused higher total C and P, but lower bulk density and electrical conductivity. The levels of Cd, Cu and Pb were higher in S. alterniflora sediment. Both Cd and Zn were higher than the probable effect level at both sites, indicating their toxicological importance. The geo-accumulation and potential ecological risk indexes revealed higher metal contamination in S. alterniflora sediment. Multivariate analysis implied that anthropogenic activities altered mobility and bioavailability of heavy metals. The percentage of mobile heavy metals was higher in S. alterniflora sediment, indicating improvement of conversion from the immobilized fraction to the mobilized fraction. These findings indicate that S. alterniflora may facilitate accumulation of heavy metals and increase their bioavailability and mobility.

Differences in burrow morphology of crabs between Spartina alterniflora marsh and mangrove habitats

Density and morphology of crab burrows were compared using resin casts between exotic Spartina alterniflora marsh (SPA) and four mangrove habitats (Avicennia marina forest, AM; Kandelia obovata forest, KO; Aegiceras corniculatum forest, AC; Mudflat, MF) at a subtropical mangrove estuary, Yunxiao, China. Five burrow-morphological parameters (density, opening diameter, depth, branching and total burrow volume per m2) were measured. The results showed that there were significant differences in the morphology (depth and volume) of crab burrows between SPA and mangrove habitats. The depth (ANOVA, d.f.=27, F=24.212, P=0.000) and total burrow volume (ANOVA, d.f.=23, F=3.666, P=0.022) per m2 in SPA were significantly lower than those in the other four mangrove habitats. Correlation analysis indicated significant negative correlation between burrow depth and root density. We concluded that over-dense roots and subterranean stems of Spartina alterniflora impeded crabs excavating burrows extensively, both in the vertical and horizontal directions. Consequently, the invasion of Spartina alterniflora weakened the ecosystem engineering effects of mangrove crabs. The burrows in KO and AM had significantly higher burrow complexity than those in the other three habitats. We speculated that mangrove root was the main environmental variable resulting in the varied complexity of crab burrows. Higher root density or lower root density both impede crabs constructing complex burrows, while intermediate root density contributes to the development of higher borrow complexity.

Climate Drivers of Spartina alterniflora Saltmarsh Production in Georgia, USA

Tidal wetlands are threatened by global changes related not only to sea level rise but also to altered weather patterns. To predict consequences of these changes on coastal communities, it is necessary to understand how temporally varying abiotic conditions drive wetland production. In 2000–2011, we conducted annual surveys of Spartina alterniflora biomass in tidal marshes at nine sites in and around the Altamaha river estuary on the coast of Georgia, USA. End of the year live biomass was assessed in the creekbank and midmarsh zones to estimate annual net primary production (ANPP). River discharge was the most important driver of S. alterniflora ANPP, especially in creekbank vegetation. Increased river discharge reduces water column salinity, and this was most likely the proximate driver of increased production. In the midmarsh zone, the patterns were less distinct, although river discharge was again the best predictor, but maximum temperature had similar predictive ability. In contrast to results from terrestrial grasslands, we found no consistent evidence for a sharply delimited critical period for any climate driver in the tidal marsh, which indicates that plant growth was responsive to abiotic drivers at any time during the growing season. Results were broadly consistent across multiple sites within a geographic region. Our results differ from previous analyses of production in S. alterniflora marshes, which either identified oceanic drivers of S. alterniflora production or were unable to identify any drivers, likely because the low-latitude sites we studied were hotter and more affected by river discharge than those in previous studies.