Alterniflora Marsh Research Articles

Effective use of thin layer sediment application in Spartina alterniflora marshes is guided by elevation-biomass relationship

Thin layer application (TLA) of dredged sediments has emerged as an adaptive management option for marshes that are not increasing in elevation fast enough to keep pace with local relative sea level rise. While there have been multiple previous demonstrations of TLA, there is limited pre-and post-application monitoring data available from past projects to develop guidance concerning optimal siting, design and implementation of projects. To address this gap, we conducted a controlled TLA experiment in a Spartina alterniflora marsh adjacent to the Atlantic Intracoastal Waterway in central North Carolina. The project was informed by the results of a long-term marsh monitoring and research program which had identified the project area as particularly vulnerable to sea level rise. The experimental design included triplicate meso-scale (24m2) treatment and control cells and quarterly (during the first year) to annual monitoring efforts to document trends in marsh surface elevation and vegetative biomass. In addition, sampling was conducted to characterize porewater chemistry and sediment characteristics. Thin layer application of dredged sediments resulted in an average elevation gain of 6 cm in treatment plots. Monitoring results indicate that the gains in elevation achieved by TLA have been maintained over five growing seasons. The response of vegetative biomass to the added elevation was well-predicted by the elevation-biomass relationship of the surrounding marsh platform. Treatment cells exhibited continued increases in surface elevation after placement, while control cell elevation remained constant. These data illustrate the potential of TLA as a tool for increasing the resilience of low-lying marshes to sea level rise and illustrate the value of the surface elevation-marsh biomass relationship for providing guidance for its use in S. alterniflora-dominated marshes.

The Impact of Sea Embankment Reclamation on Greenhouse Gas GHG Fluxes and Stocks in Invasive Spartina alterniflora and Native Phragmites australis Wetland Marshes of East China

The introduction of embankment seawalls to limit the expansion of the exotic C4 perennial grass Spartina alteniflora Loisel in eastern China’s coastal wetlands has more than doubled in the past decades. Previous research focused on the impact of sea embankment reclamation on the soil organic carbon (C) and nitrogen (N) stocks in salt marshes, whereas no study attempted to assess the impact of sea embankment reclamation on greenhouse gas (GHG) fluxes in such marshes. Here we examined the impact of sea embankment reclamation on GHG stocks and fluxes of an invasive Spartina alterniflora and native Phragmites australis dominated salt marsh in the Dongtai wetlands of China’s Jiangsu province. Sea embankment reclamation significantly decreased soil total organic C by 54.0% and total organic N by 73.2%, decreasing plant biomass, soil moisture, and soil salinity in both plants’ marsh. It increased CO2 emissions by 38.2% and 13.5%, and reduced CH4 emissions by 34.5% and 37.1%, respectively, in the Spartina alterniflora and Phragmites australis marshes. The coastal embankment wall also significantly increased N2O emission by 48.9% in the Phragmites australis salt marsh and reduced emissions by 17.2% in the Spartina alterniflora marsh. The fluxes of methane CH4 and carbon dioxide CO2 were similar in both restored and unrestored sections, whereas the fluxes of nitrous oxide N2O were substantially different owing to increased nitrate as a result of N-loading. Our findings show that sea embankment reclamation significantly alters coastal marsh potential to sequester C and N, particularly in native Phragmites australis salt marshes. As a result, sea embankment reclamation essentially weakens native and invasive saltmarshes’ C and N sinks, potentially depleting C and N sinks in coastal China’s wetlands. Stakeholders and policymakers can utilize this scientific evidence to strike a balance between seawall reclamation and invasive plant expansion in coastal wetlands.

Changes of the Macrobenthos Community with Non-native Mangrove Rehabilitation (Kandelia obovata) and Salt Marsh Invasion (Spartina alterniflora) in Ximen Island, Zhejiang, China

Macrobenthos organisms are vital ecological components of intertidal wetlands. This work studied effects of non-native mangrove rehabilitation (Kandelia obovata) and salt marsh invasion (Spartina alterniflora) on macrobenthos communities in Ximen Island (Zhejiang, China). The macrobenthos communities were compared between rehabilitated K. obovata forests of five different stand ages (2-, 8-, 11-, 16-, and 60-year-old) and adjacent S. alterniflora marsh and non-vegetated mudflat. Compared to the mudflat, S. alterniflora increased the abundance, Shannon–Wiener diversity index (H’), and Margalef's richness index (d’) of macrobenthos. Gastropoda abundance was high in the S. alterniflora marsh, whereas, malacostraca biomass was low. Within mangrove forests, macrobenthos abundance was positively correlated with the stand age of mangroves (Spearman Correlation, P < 0.05), but the corresponding H’, d’ and Pielou's evenness index (J’) showed negative correlations. Gastropoda dominated over macrobenthos in the younger stands (2–11 years in age), whereas, phascolosomatidea and bivalvia were more abundant in the older stands (16 and 60 years in age). Noticeably, the highest biomass for malacostraca was recorded from the 11-year-old stand. Macrobenthos communities differed among habitats, with the divergence in community structure between the S. alterniflora marsh and mangrove stands increasing with mangrove stand age, to be significantly different for stands planted over 16 years ago. Since the 16-year-old stand exhibited similar macrobenthos features to the 60-year-old stand, we speculated that, in the case of macrobenthos, a rehabilitated K. obovata forest can reach its maturity level at a time period of about 15 years in Ximen Island.

Effects of waterlogging and salinity increase on CO2 efflux in soil from coastal marshes

Coastal marshes play a notable role in sequestering carbon in plants and soil; however, coastal ecosystems are vulnerable to global change in terms of sea-level rise and saltwater intrusion. The effects of independent and interactive hydrological treatments of waterlogging and elevated salinity on soil CO2 effluxes in Spartina alterniflora marshes were investigated based on a mesocosm approach. This study highlighted the importance of respective soil respirations during inundation (nondrainage, Rs.ND) and reaeration (drainage, Rs.D) in the marshes soils. We found that waterlogging treatments heavily suppressed Rs.ND but increased the Rs.D, regardless of salinity levels. Light salinity enhanced soil respiration, whereas high salinity inhibited soil CO2 efflux, regardless of the water table level. Waterlogging strengthened the negative effects of salinity on Rs.ND and offset the negative effects on Rs.D. The variations in soil respiration under the hydrological treatments can be mainly attributed to changes in root biomass; indigenous soil microbial biomass; and activities of sucrase, cellulase and dehydrogenase, as well as ionic concentrations and oxidation-reduction potential. The temperature sensitivity (Q10 value) of soil respiration (only for Rs.D) after drainage showed a notable decline under the conditions of waterlogging and high salinity. The effect degree of coupled hydrological treatments on soil respiration and Q10 values was similar to a single waterlogging factor before drainage and more strongly than a single factor after drainage. We suggest that the soil CO2 efflux under water flooding and reaeration, inundation duration, and salinity levels need to be considered to understand the impacts of future hydrological changes on coastal marshes.

Extreme Precipitation and Flooding Contribute to Sudden Vegetation Dieback in a Coastal Salt Marsh.

Climate extremes are becoming more frequent with global climate change and have the potential to cause major ecological regime shifts. Along the northern Gulf of Mexico, a coastal wetland in Texas suffered sudden vegetation dieback following an extreme precipitation and flooding event associated with Hurricane Harvey in 2017. Historical salt marsh dieback events have been linked to climate extremes, such as extreme drought. However, to our knowledge, this is the first example of extreme precipitation and flooding leading to mass mortality of the salt marsh foundation species, Spartina alterniflora. Here, we investigated the relationships between baseline climate conditions, extreme climate conditions, and large-scale plant mortality to provide an indicator of ecosystem vulnerability to extreme precipitation events. We identified plant zonal boundaries along an elevation gradient with plant species tolerant of hypersaline conditions, including succulents and graminoids, at higher elevations, and flood-tolerant species, including S. alterniflora, at lower elevations. We quantified a flooding threshold for wetland collapse under baseline conditions characterized by incremental increases in flooding (i.e., sea level rise). We proposed that the sudden widespread dieback of S. alterniflora following Hurricane Harvey was the result of extreme precipitation and flooding that exceeded this threshold for S. alterniflora survival. Indeed, S. alterniflora dieback occurred at elevations above the wetland collapse threshold, illustrating a heightened vulnerability to flooding that could not be predicted from baseline climate conditions. Moreover, the spatial pattern of vegetation dieback indicated that underlying stressors may have also increased susceptibility to dieback in some S. alterniflora marshes.Collectively, our results highlight a new mechanism of sudden vegetation dieback in S. alterniflora marshes that is triggered by extreme precipitation and flooding. Furthermore, this work emphasizes the importance of considering interactions between multiple abiotic and biotic stressors that can lead to shifts in tolerance thresholds and incorporating climate extremes into climate vulnerability assessments to accurately characterize future climate threats.

Effects of Ecological Restoration Using Non-Native Mangrove Kandelia obovata to Replace Invasive Spartina alterniflora on Intertidal Macrobenthos Community in Maoyan Island (Zhejiang, China)

Spartina alterniflora has extensively invaded the coastline of China, including in Maoyan Island of Zhejiang Province. Ecological restoration has been conducted using non-native mangrove Kandelia obovata to replace S. alterniflora in an attempt to restore the impacted intertidal zones. To illustrate the ecological effectiveness of the restoration projects, macrobenthos communities were studied among different habitats within the restored areas, including one non-restored S. alterniflora marsh (SA) and three differently-aged restored K. obovata stands planted in 2003, 2009, and 2011 respectively (KF14, KF8, and KF6). Besides, one unvegetated mudflat (MF) adjacent to the non-restored S. alterniflora marsh and one K. obovata forest transplanted in 2006 (RKF) at a previously barren mudflat without invasion history of S. alterniflora were set as reference sites. A total of 69 species of macrobenthos were collected from Maoyan Island, and the species richness was dominated by gastropoda (23 species), polychaeta (18 species), and malacostraca (16 species). There was no significant difference between the six sites in terms of the abundance of macrobenthos, with the average values of abundance peaking in KF6 (734.7 ind m−2) and being lowest in RKF (341.3 ind m−2). The six sites had significant differences in terms of the biomass of macrobenthos. The KF8 site contained the highest average biomass (168.3 g m−2), whereas the MF site had the lowest (54.3 g m−2). The Shannon-Wiener diversity index and Pielou’s evenness index of the macrobenthos did not exhibit significant differences among the six sites. However, the results of permutational multivariate analysis of variance (PERMANOVA) revealed significant spatial differences in the macrobenthos community structure between the sites. Since KF14 shared a similar macrobenthos community structure with RKF, while representing a strikingly different structure from SA, we infer that ecological restoration using K. obovata can restore the macrobenthos community to resemble to a normally planted K. obovata forest about 15 years after restoration.

A Mechanistic Approach for Modeling Soil Development Using Remotely Sensed Data Collected from Invaded Coasts

The invasion of the exotic species Spartina alterniflora (S. alterniflora) has profoundly influenced coastal soil development in China. Accurate assessment and monitoring of invasion-driven development in coastal soils requires the development of reliable methods to support the sustainable governance of coastal ecosystems. A space-for-time substitution method and a stratified random sampling strategy were utilized in this study to obtain soil data from 15 sites at three depth intervals (0–30, 30–60 and 60–100 cm) to obtain a total of 45 soil samples. We developed a mechanistic approach to model soil development using Sentinel-1 data. Here, soil development was represented by a comprehensive soil index, the soil quality index (SQI), which was calculated from key physical and chemical soil properties. In the structural equation model (SEM), soil, vegetation and remote-sensing data were initially assumed to be related to each other based on prior knowledge and were constructed from their corresponding observed variables. The results of the correlation analysis showed that there was a significant correlation between the invasion processes and SQI values, especially in the topsoil of the upper 30 cm. The final SEM model showed that the invasion process had great direct and positive effects on SQI in the upper 60 cm depth soil; however, vegetation (represented by a vegetation index) had a negative influence on SQI in the topmost layer. We found that Sentinel-1 data explained the large variation in the interacting ecosystem of the invasion, vegetation, and soils, with R2 values ranging between 0.45 and 0.96. The results of model performance evaluation demonstrated the efficacy of the proposed model in predicting SQI, with a ratio of performance to deviation (RPD) of 1.44 in the upper 60 cm. Our findings highlight the potential of Sentinel-1 data in monitoring the pace of soil development in constructed S. alterniflora marshes.

Estimating the gaseous carbon budget of a degraded tidal wetland

Wetlands play an important role in the global carbon cycle but are intensively disturbed by humans. Estimating the gaseous carbon budget of degraded wetlands has great significance for wetland conservation. The Shanyutan wetland is a degraded tidal wetland in Southeast China. We compared the landscape patterns of Shanyutan in 2009 and 2019 based on remote sensing images and determined the sediment CO2 flux (excluding root respiration) in various land types. We combined the sediment CO2 flux with the wetland CH4 flux, and the CH4 and CO2 fluxes of aquaculture ponds, as well as net plant carbon sequestration (NPCS) from previous studies, and calculated the gaseous carbon budget of Shanyutan for the 10-year period. Our results show that the areas of aquaculture ponds and mudflats increased over the 10-year period, whereas those of vegetated marsh and sand decreased. Determination of the sediment CO2 flux indicates that sediment CO2 flux is higher in vegetated marsh and lower in bare land, with the highest annual flux in Spartina alterniflora marsh and the lowest in sand. The gaseous carbon budget shows that aquaculture ponds and bare land are sources of atmospheric carbon, whereas vegetated marsh serves as a sink. The entire wetland was an atmospheric carbon sink in 2009, with a carbon sequestration rate of 1364.4 tC·a−1; however, it became a source in 2019 due to destruction, with a carbon efflux of 1072.6 tC·a−1. Moreover, the gaseous carbon balance in Shanyutan had a climate-warming potential, with an equivalent CO2 production of 5971.8 t·a−1 in 2009, and this potential increased ~9 times over the 10-year period. Finally, we conclude that restoring the carbon cycle of Shanyutan has considerable future economic value.

Vertical distribution of macrobenthic community of tropical saltmarshes on the Amazon coast

Saltmarshes are coastal plant formations frequently found associated with tropical and subtropical mangroves. Saltmarshes in these regions are subject to a wide array of environmental factors. This vegetation has direct and indirect effects on benthic fauna structure both above and below sediment surface. This study describes the vertical distribution of macrobenthic fauna in Amazon saltmarshes with different sediment characteristics. Four vertical stratified samples (0–10 and 10–20 cm) were collected at two different sites: (1) Furo Grande tidal channel (muddy area) and (2) Ajuruteua beach (sandy area). The saltmarsh area varied between sites, being more dense and taller in the sandy area. A total of 1959 individuals were found, belonging to 35 macrobenthic taxa, of which 23 taxa are exclusive to the muddy area. Macrobenthic fauna community distribution varies among Spartina alterniflora marshes with different sediment characteristics. Higher densities and number of taxa were generally found at near-surface layers (0–10 cm). Furthermore, this vertical distribution occurs differently depending on the site and is more prominent in sandy areas where all fauna is concentrated near the surface.

Net Ecosystem Carbon Balance in a North Carolina, USA, Salt Marsh

AbstractSalt marshes have among the highest carbon (C) burial rates of any ecosystem and often rely on C accumulation to gain elevation and persist in locations with accelerating sea level rise. Net ecosystem carbon balance (NECB), the accumulation or loss of C resulting from vertical CO2 and CH4 gas fluxes, lateral C fluxes, and sediment C inputs, varies across salt marshes; thus, extrapolation of NECB to an entire marsh is challenging. Anthropogenic nitrogen (N) inputs to salt marshes impact NECB by influencing each component of NECB, but differences in the impacts of fertilization between edge and interior marsh must be considered when scaling up. NECB was estimated for the 0.5 km2 Spartina alterniflora marsh area of Freeman Creek, NC, under control and fertilized conditions at both interior and edge berm sites. Annual CO2 fluxes were nearly balanced at control sites, but fertilization significantly increased net CO2 emissions at edge sites. Lateral C export, modeled using respiration rates, represented a significant C loss that increased with fertilization in both edge and interior marsh. Sediment C input was a significant C source in the interior, nearly doubling with fertilization, but represented a small source on the edge. When extrapolating C exchanges to the entire marsh, including edge which comprised 17% of the marsh area, the marsh displayed net loss of C despite a net C gain in the interior. Fertilization increased net C loss fivefold. Extrapolation of NECB to whole marshes requires inclusion of C fluxes for both edge and interior marsh.

Wave Attenuation by Spartina alterniflora under Macro-Tidal and Storm Surge Conditions

Salt marshes are coastal wetlands that provide many ecosystem services. They protect coasts from erosion, storm surge, and small tsunami by dissipating wave energy. Plant flexibility has been reported to reduce drag force on and wave attenuation of marsh plants. In this study, we proposed a new drag coefficient formula to account plant flexibility so that the classical theory based on rigid cylinders can be extended to predict wave decay by flexible plants. To validate this new formula, the field survey was conducted in the North Hangzhou Bay, China. The wave attenuation was measured in a Spartina alterniflora marsh under a combined macro-tidal and storm surge condition, during which strong bending motions of the plants were observed. The new formula provided better predictions of wave decay than that by the traditional drag formula when compared to the field data measured in both the present study and the earlier studies.

Distribution status, driving force, and protection suggestions of vegetation in Jiangsu Province, China

To provide support for the drawing of 1:500000 vegetation maps and vegetation protection in Jiangsu, the researchers performed a review on the history of research, distribution pattern, change and driving force of vegetation in Jiangsu Province, according to the research results and field investigation of Jiangsu vegetation in recent years. The series research work of the Jiangsu vegetation map began in 1964, and the final map was published in 2001. Vegetation in Jiangsu includes cultivited vegetation, planted and natural forests, herbaceous swamps, meadows, and sparse shrub grass. Cultivited vegetation is distributed in most flat areas, which mainly includes Zea mays , Triticum aestivum , and Oryza sativa . Natural forests are primarily distributed in Xuzhou, Lianyungang, Yili, and Ningzhen mountains. The natural forests include the coniferous forests such as Pinus massoniana , Pinus densiflora forests; the deciduous broad-leaved forests such as Quercus variabilis , Quercus acutissima , and Liquidambar formosana forests; the evergreen broad-leaved forests such as Quercus glauca and Schima superba forests; the bamboo forests such as Phyllostachys heterocycle forest; the coniferous and broad-leaved mixed forests such as Pinus massoniana and Quercus variabilis mixed forests; the evergreen and deciduous broad-leaved mixed forests such as Castanopsis sclerophylla and Quercus glauca mixed forests. Planted forests are mainly distributed in the northern Jiangsu, Lixiahe and coastal plains, including Populus spp, Platycladus orientalis , Cunninghamia lanceolate , and Pinus massoniana forests. The natural wetland vegetation is mainly distributed in the Yancheng coastal wetlands, with Phragmites communis , Spartina anglica , and Spartina alterniflora marshes. Compared with the vegetation in 1983, the area of forests represented by Pinus massoniana , Platycladus orientalis , and Robinia pseudoacacia forests decreased, and herbaceous grasslands and meadows were also drastically reduced. The salt meadows of the coastal wetlands were succeeded by Spartina anglica and Spartina alterniflora swamps, and large areas of agricultural vegetation and a part of the natural forest vegetation were transformed into towns. Human activities led by urbanization affected the distribution pattern of the vegetation in Jiangsu as the major driving force for vegetation change. According to the current situation of natural vegetation in Jiangsu, three suggestions were proposed to protect natural vegetation communities. First, ecological red line protection zones should be established in Nanjing Mufu Mountain, Zhenjiang Baohua Mountain, Lianyungang Shazhou Bay, etc., where the vegetation suffered grave human interference. Second, the development and utilization of herbs and coastal cofferdam, such as Mentha canadensis and Pseudostellaria heterophylla , should be more meticulous. Third, it is necessary to enhance the control of invasive plants, such as Spartina anglica , Solidago canadensis , and Alternanthera philoxeroides .

Effects of non-indigenous plants on food sources of intertidal macrobenthos in Yueqing Bay, China: Combining stable isotope and fatty acid analyses

Plant invasions in coastal ecosystems may substantially alter benthic community composition and food web structure. We combined analyses of stable isotopes and fatty acids (FA) to examine the effects of two non-indigenous plants (Spartina alterniflora and Kandelia candel) on the food sources of three deposit feeders (Assiminea brevicula, Cerithidea cingulata and Uca arcuata) and a carnivorous opportunistic predator (Periophthalmus modestus) in Yueqing Bay, China. A wide range of differences was found in δ13C and δ15N among the macrobenthos. The deposit feeders in K. candel mangrove forest (KC) were markedly more 13C-depleted than those in S. alterniflora marsh (SA) and unvegetated tidal flat (TF), unlike the carnivorous feeder. PERMANOVA showed that FA composition significantly differed among the macrobenthos. Diatom FA markers were higher in tissues of the deposit feeders than in the carnivorous feeder, and slightly lower in macrobenthos from the KC and SA habitats as compared with the TF. In contrast, vascular plant FA markers of macrobenthos were higher in the KC and SA than in the TF, indicating the contribution of mangrove and Spartina detritus to the consumers. The findings show that the food sources of macrobenthos were markedly affected by non-indigenous plants, through the addition of organic detritus derived from vascular plants in the diets together with a decreased contribution of diatoms, although the impacts may differ among different functional feeding groups of macrobenthos.

Enhanced Lateral Exchange of Carbon and Nitrogen in a Coastal Wetland With Invasive Spartina alterniflora

AbstractLateral movements of materials and energy in coastal wetlands, due mainly to tidal activities, have been recognized as key processes in understanding the biogeochemical cycles of ecosystems. However, our understanding of the roles of lateral movement in shaping ecosystem functions remains limited. Here we quantified the effects of lateral sediment transport on total carbon (C, inorganic + organic) and nitrogen (N) pools in plants and soils in two dominant wetland types: invasive Spartina alterniflora (Spartina) marshes and native Phragmites australis (Phragmites) marshes in coastal Shanghai of the Yangtze Estuary. We found that the accreted sediments across the water‐marsh gradients caused by lateral movement resulted in contrasting C and N contents between the two communities. The sediment load and C and N pools in the plants and soils of the Spartina marshes were significantly higher than those in the adjacent Phragmites marshes. The shifts in species composition and community structure not only altered the C and N balance but also enhanced the ecosystem net primary productivity. Our findings highlight the importance of lateral transport in altering ecosystem structure after Spartina invasion. The ecosystem C and N pools were significantly higher in the invaded ecosystems than in the native community. Our study also reveals that the plant density and structures can alter tidal hydrodynamics and the lateral transportations of sediments, which in turn influence ecosystem C and N cycle. The C accumulation processes of the native and invaded marshes were further complicated by the contrasting productivities of the ecosystems.

Comparison of Carbon, Nitrogen, and Sulfur in Coastal Wetlands Dominated by Native and Invasive Plants in the Yancheng National Nature Reserve, China

The rapid invasion of the plant Spartina alterniflora in coastal wetland areas can threaten the capacity of their soils to store carbon (C), nitrogen (N), and sulfur (S). In this study, we investigated the spatial and temporal distribution patterns of C, N and S of both soil and (native and invasive) plants in four typical coastal wetlands in the core area of the Yancheng National Nature Reserve, China. The results show that the invasive S. alterniflora greatly influenced soil properties and increased soil C, N and S storage capacity: the stock (mean ± standard error) of soil organic carbon (SOC, (3.56 ± 0.36) kg/m3), total nitrogen (TN, (0.43 ± 0.02) kg/m3), and total sulfur (TS, (0.69 ± 0.11) kg/m3) in the S. alterniflora marsh exceeded those in the adjacent bare mudflat, Suaeda salsa marsh, and Phragmites australis marsh. Because of its greater biomass, plant C ((1193.7 ± 133.6) g/m2), N ((18.8 ± 2.4) g/m2), and S ((9.4 ± 1.5) g/m2) storage of S. alterniflora was also larger than those of co-occurring native plants. More biogenic elements circulated in the soil-plant system of the S. alterniflora marsh, and their spatial and temporal distribution patterns were also changed by the S. alterniflora invasion. Soil properties changed by S. alterniflora’s invasion thereby indirectly affected the accumulation of soil C, N and S in this wetland ecosystem. The SOC, TN, and TS contents were positively correlated with soil electrical conductivity and moisture, but negatively correlated with the pH and bulk density of soil. Together, these results indicate that S. alterniflora invasion altered ecosystem processes, resulted in changes in net primary production and litter decomposition, and increased the soil C, N and S storage capacity in the invaded ecosystems in comparison to those with native tallgrass communities in the coastal wetlands of East China.

Hurricane sedimentation in a subtropical salt marsh-mangrove community is unaffected by vegetation type

Hurricanes periodically deliver sediment to coastal wetlands, such as those in the Mississippi River Delta Complex (MRDC), slowing elevation loss and improving resilience to sea-level rise. However, the amount of hurricane sediment deposited and retained in a wetland may vary depending on the dominant vegetation. In the subtropical climate of the MRDC, the black mangrove (Avicennia germinans) has been expanding and replacing salt marsh (Spartina alterniflora). Because these vegetation types differ in structure, their influence on sedimentation may also differ. We conducted a survey along 160 km of coastline to determine if the spatial deposition pattern in saline wetlands by Hurricanes Gustav and Ike in September 2008 was differentially influenced by vegetation type. Sampling was initiated two months after landfall at eighteen sites in the MRDC containing side-by-side stands of A. germinans and S. alterniflora along the shoreline, with S. alterniflora marsh landward. Average thickness of hurricane sediment across sites varied from 0.6 to 5.6 cm with an overall mean of 2.6 ± 0.4 cm. Within sites, hurricane-layer thickness varied from 1.3 cm at the shoreline to 4.8 cm in the marsh interior, but this pattern was unaffected by vegetation type. Despite greater canopy height, stem density (including pneumatophores), and leaf area, mangroves did not capture more hurricane sediment than salt marsh nor did they attenuate the delivery of sediment to the marsh interior. Data recorded at thirty-six monitoring stations in Louisiana's Coastwide Reference Monitoring System further showed that rates of accretion, as well as elevation change, in saline wetlands (S. alterniflora) of the MRDC were temporarily increased by Hurricanes Gustav and Ike. These findings agree with previous work showing the beneficial effects of hurricane sediments on coastal wetlands, but suggest that a climate-driven shift from S. alterniflora to A. germinans in the MRDC will not necessarily alter hurricane sediment capture.

Effects of salt marsh restoration on eukaryotic microbenthic communities in the Yangtze Estuary

To fight invasion of Spartina alterniflora and conserve biodiversity of migratory shorebirds, several S. alterniflora marshes and bare mudflats have been restored back to Scirpus mariqueter marshes in the Yangtze River estuary in recent years. Although it is known that changes in plant cover in salt marshes alters the physical environment, findings on its effects on benthic communities are inconsistent and site-specific. In the present study, we tested how ciliates were influenced by a recent restoration. Ciliated protozoa play a key role in wetland benthic food webs and are useful bioindicators. We investigated 3 habitats: restored S. mariqueter meadow, S. alterniflora-invaded meadow, and bare mudflats, where we quantified environmental conditions, community composition (species and traits), and 3 aspects of biodiversity (classic, taxonomic, and functional diversity) over 4 seasons. CAP and ANOSIM were used to determine the differences among samples, while RDA and GLMs were used to reveal potential driving factors. We found that, although changes in the type of vegetation due to restoration or invasion significantly modified the sediment properties and ciliate species composition, it had limited influence on functional trait composition as well as on diversity, especially on functional diversity. These results indicate that the conversion of mudflats to S. mariqueter meadow did not affect ciliate community functions at the time scale of this study. However, biomonitoring based on microbenthic communities should be included when evaluating the long-term success of coastal wetland restoration.

Effects of Spartina alterniflora invasion on spatial and temporal variations of total sulfur and inorganic sulfur fractions in sediments of salt marsh in the Min River estuary, southeast China

Abstract To investigate the effects of Spartina alterniflora invasion on spatial and temporal variations of sulfur in marsh sediments, the levels of total sulfur (TS) and inorganic sulfur (IS) fractions (Water-Soluble-S, W-S-S; Adsorbed-S, A-S; HCl-Soluble-S, H-S-S; and HCl-Volatile-S, H-V-S) were determined in Cyperus compressus marsh (before invasion, BI), S. alterniflora-C. compressus marsh (during invasion, DI) and S. alterniflora marsh (after invasion, AI) in the Min River estuary (Southeast China) by space-for-time substitution method. Results showed that the variations of sediment texture caused by S. alterniflora invasion showed great influences on the levels of TS and IS fractions in sediments at DI and AI stages. Compared with BI stage, the mean values of TS (g·kg−1) at AI and DI stages increased by 21.36% and 20.57%, while those of TIS (mg·kg−1) increased by 24.84% and 20.59%, respectively. Over all sampling seasons, significantly higher contents of W-S-S, A-S and H-S-S in sediments at AI or DI stages were observed compared to BI stage (p

Characterization of the salt marsh soils and visible-near-infrared spectroscopy along a chronosequence of Spartina alterniflora invasion in a coastal wetland of eastern China

Introduction of exotic Spartina alterniflora (S. alterniflora) is important to re-establish the structure and function of salt marsh ecosystems along the coast of China. Characterization the spatial-temporal patterns of S. alterniflora soils is thus essential for the assessment of the pace of ecosystem development. However, the determination of soil properties by traditional analysis almost impossible achieve a timely detection of soil changes that is generally required by soil monitoring tasks for demonstrating impacts of S. alterniflora invasion. This work focused on the use of visible-near-infrared spectroscopy (VNIRS) for characterizing soils and predicting key physical and chemical soil properties in S. alterniflora areas. A set of soil profiles representing a chronosequence of S. alterniflora invasion was used, comprising 45 samples from 15 sites. The results showed that approximately 20-year of S. alterniflora invasion has altered soil characteristics especially in the topsoil. Changes of soil associated with sampling horizons and ages of S. alterniflora could be distinguishable using soil variables and VNIRS, and high correlations were found between soils and spectra information. The results of predictions showed that predictive accuracy for salinity, pH, clay, the ratio of carbon to nitrogen, organic carbon and calcium carbonate were acceptable, but models for total nitrogen, bulk density, sand and silt were less satisfactory. These results suggested the possibility of VNIRS for the rapid assessment of key physical and chemical soil properties in S. alterniflora areas. This work highlights that VNIRS technique could be taken as a useful tool to investigate soil changes and explore understanding of soil development in S. alterniflora marshes.

Effects of Spartina alterniflora invasion in a seaward direction on variations of inorganic sulfur forms in marsh soils of the Minjiang River estuary, China

To explore the effects of Spartina alterniflora invasion in a seaward direction on variations of inorganic sulfur forms in marsh soils, the levels of inorganic sulfur forms (H2O-S, Adsorbed-S, HCl-Soluble-S and HCl-Volatile-S) were determined in bare flat (BF, before invasion), S. alterniflora marsh after seaward invasion for one year (SA') and S. alterniflora marsh after seaward invasion for three years (SA) in Shanyutan of the Minjiang River estuary with the method of space-for-time substitution. Results showed that the seaward invasion of S. alterniflora altered the stocks and distribution of inorganic sulfur form in marsh soils. Compared with BF, the contents of H2O-S, Adsorbed-S and HCl-Volatile-S in soils of SA increased by 52.6%, 78.2% and 21.0%, respectively, while that of HCl-Soluble-S decreased by 3.4%. In contrast, the levels of H2O-S, Adsorbed-S and HCl-Soluble-S in soils of SA' increased by 43.9%, 70.6% and 29.6%, respectively, whereas that of HCl-Volatile-S decreased by 11.6%. The contents of total inorganic sulfur (TIS) in soils of SA and SA' increased by 40.7% and 37.8%, while the stocks of TIS increased by 26.8% and 31.4%, respectively. The key factors affecting different forms of inorganic sulfur in marsh soils had changed due to the seaward invasion of S. alterniflora. In particular, the key factors affecting the variations of H2O-S contents changed from soil grain composition and bulk density in BF to soil organic matter in SA' and SA. The seaward invasion of S. alterniflora significantly increased the content of TIS in marsh soils, which was mainly contributed by H2O-S and Adsorbed-S. Thus, it was concluded that the seaward invasion of S. alterniflora significantly increased the supply capacity of available sulfur in marsh soils, which, to some extent, accelerated its seaward invasion.