Salt Marsh Wetlands Research Articles

Salinity effect on denitrification efficiency with reed biomass addition in salt marsh wetlands

Five simulated salt marsh wetlands with reed were constructed to investigate the effect of salinity on denitrification efficiency and its enhancement by reed biomass addition. It was found that the salinity of 7 ‰ and 10 ‰ could promote the organic carbon release of reed biomass. Results showed that the nitrate removal was highest at the salinity of 7 ‰, and would be further enhanced from 54.06 ± 12.46 % to 74.37 ± 11.53 % after the addition of reed biomass. Meanwhile, the lowest nitrous oxide emission flux was also achieved, with 0.23 mg/(m2 h) at this salinity. Microbiological analysis showed that salinity changed the microbial community. The increasing salinity increased the relative abundance of Chloroflexi and Actinobacteria, but decreased that of Proteobacteria. Main functional genera of denitrification changed from Desulfuromonas to Azoarcus and Anaeromyxbacter when the salinity increased to 15 ‰. These results will help to understand the nitrogen removal capacity of salt marsh wetlands with reed biomass addition.

Long-term Spartina alterniflora invasion simplified soil seed bank and regenerated community in a coastal marsh wetland.

The coastal wetland is easily invaded by alien species due to locating in the land and sea transitional area. As a potential driving regeneration force, the soil seed bank is vital to the community restoration and species diversity protection. To reveal the long-term Spartina alterniflora invasion impact on the soil seed banks and regenerated communities, we investigated the seed banks under the different vegetation types (S. alterniflora, Phragmites australis, Scirpus mariqueter, ruderal and unvegetated site) and soil depths (0-5 and 5-10 cm) in the coastal salt marsh wetland, Chongming island, eastern China. The results showed that the soil seed bank richness and species density under different vegetation types were higher than the aboveground vegetation, and those of 0-5 cm seed banks were higher than 5-10 cm, except for the unvegetated site. The species richness and S. alterniflora seed proportion in the seed banks under S. alterniflora communities (S.AS) were lower and larger respectively than those of other sites. The species composition between S.AS and the aboveground communities showed high similarity with aggregation phylogenetic structures in two soil depths. The seed bank variations at 0-5 and 5-10 cm depths were interpreted 3.03% and 2.25% by the aboveground communities, while 4.92% and 5.55% were interpreted by the soil microbial biomass. The SEM model explained 98.1% and 91.8% of the seed banks richness at the 0-5 cm depth and 5-10 cm depth, respectively, and explained 98.8% and 46.1% of the seed banks species density at the 0-5 cm depth and 5-10 cm depth, respectively. The aboveground vegetation biomass and abundance directly affected the 0-5 cm seed banks richness and species density, while its height and biomass only affected the 5-10 cm seed banks species density. The 0-10 cm soil depth microbial biomass indirectly affected the 0-5 cm seed banks richness and species density, while affected the 5-10 cm seed banks richness. Soil physical and chemical properties only indirectly affected the 0-5 cm seed banks species density. The results provided a reference for the ecological evaluation of the impacts of S. alterniflora invasion into the coastal salt marsh wetland of eastern China, and guidance for the protection and restoration of the native plant communities.

Coastal Wetlands Play an Important Role in the Ecological Security Pattern of the Coastal Zone

The construction of an ecological security pattern can effectively overcome the contradiction between regional human exploitation and ecological protection in the coastal zone. Taking the Xiangshan Bay (XSB) basin as an example, this study identified ecological source areas from three aspects, namely ecosystem services’ importance, ecological sensitivity, and landscape connectivity, and then constructed ecological resistance surfaces, identified ecological corridors, and constructed an ecological security pattern. The results show that the natural reserves in the XSB basin were all located in the identified primary ecological source areas, thus indicating the feasibility and reliability of the “importance–connectivity–sensitivity” ecological source identification mechanism in this study. The ecological corridor in the coastal wetland area accounts for about 40% of the total corridor length, which is the link connecting other ecological sources, revealing the important role of coastal wetlands in the coastal ecosystem. Through the ecological security pattern of the XSB basin and field investigation, we put forward suggestions such as clearing Spartina alterniflora, restoring salt marsh wetland vegetation, and strengthening follow-up monitoring for the restoration of coastal wetlands. This study is expected to provide reference and guidance for the improvement of coastal zone ecological protection and restoration.

Role of abiotic drivers on crab burrow distribution in a saltmarsh wetland

Crab burrows play an important role in saltmarsh wetlands and are a useful indicator of wetland condition. The spatiotemporal distribution of crab burrows varies considerably in tidal wetlands. However, the reasons for these variations are poorly understood, in part, due to the limited availability of comprehensive field data. Based on a two-year continuous observation at a tidal wetland in the northern Jiangsu Coast, China, this study explored the relationship between crab burrow density and environmental variables, including median grain size, water content, organic matter content, soil salinity, and elevation. Our results show that the distribution of crab burrows was unimodal across the shore in winter and spring (Nov-Apr) when air temperature was relatively low, while bimodal in summer and autumn (May-Oct) when temperature was relatively high. The density of crab burrows was larger at areas with higher water content, higher organic matter content, and lower soil salinity, while it was lower with stronger hydrodynamics and lower suspended sediment concentration. Crab burrows were more abundant in vegetated areas than in un-vegetated areas. A backward stepwise model selection was performed based on R-square and Akaike information criterion (AIC) to distinguish the main driving factors that determine crab burrow distribution. Results suggested that the principal driving factors were organic matter content and soil salinity in all the seasons, with the addition of water content in warm seasons. Overall, this study provides a comprehensive field dataset for a more in-depth understanding of crab burrow distribution and a scientific basis for sustainable management of tidal wetlands.

Analyses on Temporal and Spatial Variation Characteristics of Erosion and Deposition in the Front Edge of Salt Marsh Wetland

Analyses on Temporal and Spatial Variation Characteristics of Erosion and Deposition in the Front Edge of Salt Marsh Wetland

Future changes in habitat availability for two specialist snake species in the imperiled rocklands of South Florida, USA

AbstractRockland habitat in South Florida, USA, is a threatened ecosystem that has been lost, fragmented, or degraded because of urbanization or other anthropogenic disturbance. Furthermore, low‐lying islands and coastal areas are experiencing sea level rise (SLR) and an increased frequency and intensity of tidal flooding, putting rockland habitats there at increasing risk of ecological change. We evaluated changes in the extent of rockland habitat under various scenarios of future SLR, tidal flooding, and human development for two endemic state‐listed threatened species of snakes, the Rim Rock Crowned Snake (Tantilla oolitica) and the Key Ring‐necked Snake (Diadophis punctatus acricus). Both snakes are restricted to South Florida. We used recent and historical species' records to determine each species' habitat range. We then estimated the extent of future habitat loss due to SLR and continued human development, as well as degradation of the remaining habitat. We also asked whether the future potential drivers of habitat loss and degradation differ between the two species and across their habitat ranges. We predicted that saltwater intrusion could negatively affect rocklands by 2050, resulting in degradation of 80% of the existing habitat because of an anticipated 42 cm of SLR. Moreover, our model suggests short‐term stochastic events such as storm surge and high tides may increasingly saturate the root zone of rockland vegetation before complete inundation. Under the extreme scenario, we predict most of the rockland habitat used by these two species of snakes may be inundated by 2080. Under the extreme SLR scenario, current rocklands are likely to convert to more halophytic habitat (mangrove or salt marsh wetland) within 50–60 years. Under the low scenario, 31% of rockland habitat may be lost due to human development by 2030. Therefore, mitigation actions may help to conserve specialist species within rockland habitat threatened by human activities and climate change.

Sizes of crab burrows regulate water–salt transport of tidal marsh wetlands

In recent years, scholars have paid increased attention to the ecological role of crab burrows, particularly their impact on the hydrological processes of saltmarsh wetlands. This study aims to investigate the influence of crab burrows on soil water and salt transport and to understand the ecological significance of crab burrows in coastal wetlands from the perspective of ecohydrological processes. We combined a field sample survey and an indoor soil column infiltration experiment to analyze the differences in infiltration time, soil water content, and soil electrical conductivity (EC) between different experimental groups. Consequently, the results showed that the size of crab burrow diameter varies significantly in different areas of the coastal wetland, influenced by tidal creek and sea–land distances, with larger burrow diameters in areas around 5 m from the tidal creek. Large-diameter burrows (2.5 cm × 6) are more conducive to salt transport due to their preferential water conductivity to the underlying soil vertically, small-diameter burrows (0.5 cm × 6) could promote water infiltration uniformly and maintain good soil water retention capacity. This study's results provide insights into the hydrological connectivity and spatial distribution of salinity in coastal wetlands. Additionally, the positive impact of burrows on the water–salt environment of coastal wetland sediments may also provide new ideas for coastal wetland restoration.

The first record of Australian flatback mangrove goby Mugilogobius platynotus (Günther 1861) (Gobiidae; Tridentigerinae) from New Zealand

ABSTRACT The eastern Australian flatback mangrove goby Mugilogobius platynotus (Günther 1861) is recorded for the first time from Aotearoa, New Zealand. Three voucher specimens (two males and one female) were collected using fish traps submerged in tidal drains of a saltmarsh wetland edged by mangroves adjacent to Ngunguru River, Northland. Key characters for identification: the colour of freshly thawed specimens, meristic counts, and morphometric measurements are presented and compared with the same characters described by Larson (2001) for all Mugilogobius. We discuss this major range extension from its natural Australian distribution, concluding it is an adventive species, probably carried across the Tasman Sea into New Zealand waters by shipping, not ocean currents. Our analysis of goby species recorded from northern New Zealand mainland waters concludes seven (86%) are probably adventive and introduced from Australia. We recommend a further survey of mangrove and saltmarsh estuary habitats to discover if this new goby has established a breeding population and is expanding its current limited distribution within northern New Zealand.

Spatial Distribution of Soil Organic Carbon and Total Nitrogen in a Ramsar Wetland, Dafeng Milu National Nature Reserve

The invasion and expansion of Spartina alterniflora in coastal salt marsh wetlands have greatly affected the material cycle of the ecosystem. A total of 372 topsoil samples were collected from 124 sites representing two land-cover types by implementing an unprecedented high sampling density study in the Dafeng Milu National Nature Reserve. Classical statistics and geostatistics were used to quantify soil organic carbon (SOC) and total nitrogen (TN) spatial distribution. Redundancy analysis (RDA) was used to detect correlations between environmental factors, SOC, and TN. The results showed that SOC and TN have moderate variability. The spatial distributions of SOC and TN were similar, and the highest values were observed in the southwest of the study area. In different land cover types, the SOC and TN in the vegetation coverage areas with Spartina alterniflora as the dominant species were significantly higher than those in bare land. RDA showed that TN and aboveground biomass significantly affected the spatial distribution of SOC, while SOC and AGB dominated the spatial distribution of TN.

Salt Marsh Plant Community Structure Influences Success of Avicennia germinans During Poleward Encroachment.

Along the Florida coast, decreasing freeze events are promoting the range shift of the mangrove species Avicennia germinans northward into temperate salt marsh wetlands. Although plant species’ ranges are tightly linked with their climatic tolerances, there is considerable variability in the magnitude by which biotic factors like competition and facilitation may also influence range shifts. Changes in mangrove and marsh plant abundance can alter both the above and belowground environment, which may in turn influence ecosystem services typically associated with these systems such as storm surge abatement and carbon storage. Therefore, it is key to understand (1) how the above and belowground environment of established salt marshes influences establishment of mangroves, and (2) how above and belowground environments shift in response to mangrove encroachment. Using a semi-natural mangrove planting experiment, we investigated the impact of four distinct marsh plant community structures (Batis maritima, Spartina alterniflora, mixture of B. maritima and S. alterniflora, mudflat) on mangrove survivorship and decomposition rate. In mixed marsh plots, mangrove survivorship was 42 % higher compared to survivorship in mudflat plots, and decomposition rate was 47 % greater in mixed marsh plots compared to mudflat. However, percent cover of vegetation differed across treatments, and was highest in mixed marsh plots. High survivorship in mixed marsh plots is likely due to increased protection from physical stressors by the dense aboveground cover, and belowground plant root-driven effects such as nutrient availability and oxygen delivery. Our findings suggest that above and below ground differences in salt marsh plant community structure can have an impact on the survival of encroaching mangroves, which may have implications for predicting future mangrove encroachment and improving mangrove restoration techniques.

Effects of soil salinity characteristics on three habitats in inland salt marshes.

Understanding the effect of soil salinity on the diversity and species distribution of plant communities in inland salt marsh ecosystems could provide solutions for the management of regional saline soils and the protection of salt marsh wetland vegetation. A field experiment in succulent halophyte, Carex, and gramineous grass habitats in Ordos, Inner Mongolia (northwest China) was conducted to study the diversity and composition of plants in different saline habitats in inland salt marsh ecosystems. Results showed that plant diversity and species richness in the Carex habitat were significantly higher than the succulent halophyte habitat and the gramineous grass habitat (P < 0.05). Further, species abundance was higher in the succulent halophyte habitat and the Carex habitat than the gramineous grass habitat. Similar results were obtained when considering the abundance of constructive species. No significant differences in the abundance of dominant species and companion species between the gramineous grass habitat and the Carex habitat were found. We concluded that species abundance, species richness, species distribution, and plant diversity together explained the response of plant communities in different habitats to soil salinity, especially Na+ and SO42-. This highlights the importance of soil salinity for the maintenance of plant diversity and structural composition in inland salt marsh ecosystems.

The relationship of the main root-shoot morphological characteristics and biomass allocation of Saussurea salsa under different habitat conditions in Sugan lake wetland on the northern margin of the Qinghai-Tibet Plateau

The response analysis of plant morphological characteristics and biomass allocation in salt marsh wetland to heterogeneous habitats is helpful to explore the internal correlation between plant morphological plasticity mechanism and biomass allocation, which is of great significance for the in-depth understanding of habitat stress tolerance strategies of salt marsh plants. However, the relationship between the main root-shoot morphological indexes and biomass allocation of inland alpine arid area salt marsh plant is still unclear. According to the difference of the habitat conditions of Saussurea salsa, 3 test sample were set up, plot I (the Inland salt marsh area, 200–500 m from the lakeshore), plot II (the Oasis Wetland area, 500–1000 m from the lakeshore), plot III (the Seasonal river wetland area, 1000–1500 m from the lakeshore). The relationship between the main root-shoot morphological characteristics and biomass allocation of Saussurea salsa in the Sugan Lake salt marsh was studied in response to heterogeneous habitats. The results showed that Saussurea salsa tended to form the large and thick leaf pattern, the root morphological construction pattern with moderate root diameter (RD) and specific root length (SRL), and the root-shoot ratio (RSR) with minimum biomass allocation strategy in plot I. In plot II, the thin-leaf pattern with the largest specific leaf area (SLA) and the smallest thickness (LT) was formed. Meanwhile, the slender root morphology pattern with the smallest RD, the largest SRL and the moderate RSR was preferred. In plot III, a lobular pattern with minimum leaf area (LA) and SLA, and moderate thickness was formed. At the same time, a thick root pattern with maximum RD and minimum root length, and a maximum RSR were formed. Moreover, there was a highly significant negative correlation (p < 0.01) between SLA and RD at three plots. Besides, there appeared a less significant positive correlation (p < 0.05) between LA and LT, shoot biomass at three plots. Through the synergistic changes of morphological characteristics of aboveground and underground organs and biomass allocation strategies, the inland salt marsh plant population can maintain normal survival, growth and reproduction under harsh environment, which reflects its morphological plasticity and stress resistance mechanism under heterogeneous environment.

Environmental Isolation of Candida auris from the Coastal Wetlands of Andaman Islands, India.

Candida auris is a multidrug resistant pathogen that presents a serious global threat to human health. As C. auris is a newly emerged pathogen, several questions regarding its ecological niche remain unexplored. While species closely related to C. auris have been detected in different environmental habitats, little is known about the natural habitat(s) of C. auris Here, we explored the virgin habitats around the very isolated Andaman Islands in the Indian Ocean for evidence of C. auris We sampled coastal wetlands, including rocky shores, sandy beaches, tidal marshes, and mangrove swamps, around the Andaman group of the Andaman & Nicobar Islands, Union Territory, in India. Forty-eight samples of sediment soil and seawater were collected from eight sampling sites representing the heterogeneity of intertidal habitats across the east and west coast of South Andaman district. C. auris was isolated from two of the eight sampling sites, a salt marsh and a sandy beach. Interestingly, both multidrug-susceptible and multidrug-resistant C. auris isolates were found in the sample. Whole-genome sequencing analysis clustered the C. auris isolates into clade I, showing close similarity to other isolates from South Asia. Isolation of C. auris from the tropical coastal environment suggests its association with the marine ecosystem. The fact that viable C. auris was detected in the marine habitat confirms C. auris survival in harsh wetlands. However, the ecological significance of C. auris in salt marsh wetland and sandy beaches to human infections remains to be explored.IMPORTANCECandida auris is a recently emerged multidrug-resistant fungal pathogen capable of causing severe infections in hospitalized patients. Despite its recognition as a human pathogen a decade ago, so far the natural ecological niche(s) of C. auris remains enigmatic. A previous hypothesis suggested that C. auris might be native to wetlands, that its emergence as a human pathogen might have been linked to global warming effects on wetlands, and that its enrichment in that ecological niche was favored by the ability of C. auris for thermal tolerance and salinity tolerance. To understand the mystery of environmental niches of C. auris, we explored the coastal wetland habitat around the very isolated Andaman Islands in the Indian Ocean. C. auris was isolated from the virgin habitats of salt marsh area with no human activity and from a sandy beach. C. auris isolation from the marine wetlands suggests that prior to its recognition as a human pathogen, it existed as an environmental fungus.

Co-regulation of rainfall amount and timing on soil carbon mineralization in a typical salt marsh of the Yellow River Delta, China.

Studying the effects of rainfall regimes such as rainfall amount and timing on soil carbon mineralization is of great importance for our understanding the mechanisms underlying the stability and accumulation of soil carbon in coastal salt marshes. In this study, we examined the responses of soil carbon mineralization (CO2 and CH4 fluxes) from undisturbed soil columns to rainfall events in different seasons (dry and wet seasons) with filed experiments in a primary Suaeda salsa region in the Yellow River Delta salt-marsh wetland, which is far away from the coast and not affected by tides. The results showed that rainfall amount and timing had a significant interaction in affecting soil CO2 flux rates. During the dry season, large rainfall events significantly reduced soil CO2 flux rates but had no significant effect in the wet season, which might be closely related to the significant increase in soil water content and salinity. Rainfall amount, rainfall timing and their interactions had no significant effect on soil CH4 efflux rates. Rainfall timing and rainfall amount did not affect CH4/CO2. CH4/CO2 increased with increasing soil water content and salinity. Soil water content and soil salinity showed similar increases to increasing rainfall amount. Our results suggested that the changing rainfall regime under climate change in the future would have a great impact on soil carbon mineralization and carbon sink function by regulating soil water and salt migration in this region.

Remote Sensing Monitoring of Soil Salinization Based on SI-Brightness Feature Space and Drivers Analysis: A Case Study of Surface Mining Areas in Semi-Arid Steppe

The real-time monitoring and driving force research of soil salinization in semi-arid grassland are of great significance for regional and local ecological environment protection, management, and sustainable development. We selected a typical “mine-town-agriculture-pastureland-industry” interlaced ecologically fragile area as the study area. Based on the method of SI (Salinization Index)-Brightness feature space, we constructed a new spectral index named Semi-Arid Steppe Salinization Index (SASSI), which is more suitable for soil salinization remote sensing monitoring in semi-arid steppe. The geodetector method was used to analyze the driving forces of the temporal-spatial changes of soil salinization. The results indicated that: (1) SASSI presented a high correlation with soil surface salt content (R <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> = 0.7698), and made full use of multi-dimensional remote sensing information. SASSI can reflect the salinization status of surface soil. The indicator calculation was simple and easy to obtain, which was conducive to the quantitative analysis and monitoring of salinization. (2) The driving factors affecting the spatial distribution and change of soil salinization were water, surface mines, town, agriculture, industry, road network, and elevation. The salinized areas were mainly distributed around the wetlands of the Xilin River Basin, mining landscapes, and town landscapes. (3) The total area of salinized soil in the study area increased from 32.03 km <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> in 2002 to 150.46 km <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> in 2017. The area of salinized soil increased rapidly from 2005 to 2014, but the growth rate slowed down after 2014. The salinized soil was mainly located in the salt marsh wetland in 2002, however had spread to the whole study area in 2017. This study provides references for remote sensing monitoring of soil salinization and the impact of land use, topography and other natural factors on soil salinization in the semi-arid steppe.

苏干湖湿地土壤全盐含量空间异质性及影响因素

土壤盐分的空间异质性是影响湿地植被格局形成和演变的主要因素之一，对于认识内陆盐沼湿地盐分的空间分布及其对环境的响应机制具有重要意义。利用经典统计学、地统计学和Kriging插值等方法研究了苏干湖盐沼湿地浅层剖面0-50 cm土层全盐含量的空间异质性与地下水位埋深、植被覆盖度间的相互作用关系。结果表明：（1）苏干湖湿地0-10 cm、10-30 cm和30-50 cm土层的全盐含量均值分别为204.41、18.62、15.89 g/kg；（2）土壤全盐含量随着土层深度的增加变异性由强变弱，随机空间变异和总异质性程度由高变低，受结构性因素的影响具有强烈的空间相关性，且变程值介于5.2-8.49 km，0-10 cm、10-30 cm全盐含量具有各向异性特征，而30-50 cm的各向异性比接近于1，表现为各向同性；（3）各层土壤全盐含量具有较强的空间异质性，高、低值中心呈斑状镶嵌分布，土壤全盐含量与地下水埋深间呈正相关，与植被覆盖度间呈极显著负相关（P<0.01）。苏干湖内陆盐沼湿地土壤全盐含量空间异质性主要受植被覆盖度的影响，而地下水埋深的变化增加了其空间变异的复杂性，体现了内陆盐沼湿地土壤理化空间系统的复杂性和非均质性。;The spatial heterogeneity of soil salinity is of great significance to understand the spatial distribution of salinity in inland salt marsh wetlands and its response mechanism to the environment. In this paper, the classical statistics, geostatistical, and Kriging interpolation were used to study the interaction between the spatial heterogeneity of the total salt content in the 0-50 cm soil layer of the shallow section the Sugan Lake salt marsh and the depth of the groundwater level and the vegetation coverage. The research area was located in Sugan Lake wetland at the intersection of the Altun Mountains and the Qilian Mountains in the northwest of the Qaidam Basin (94°10'33″-94°14'43″E, 39°01'25″-39°05'32″N), and the elevation is between 2795-2808 m. The results indicates that: (1) the average values of total salt content in the soil layers of 0-10 cm, 10-30 cm and 30-50 cm in the Sugan Lake wetland are (204.41±11.8) g/kg, (18.62±0.92) g/kg, and (15.89±0.81) g/kg, respectively. (2) With the increase of soil depth, the variation of soil total salt content changes from strong to weak. Random spatial variability and total heterogeneity degree change from high to low, which has strong spatial correlation under the influence of structural factors. The range of variation is between 5.2-8.49 km. The total salt content of 0-10 cm, 10-30 cm has anisotropic characteristics, while the anisotropy ratio of 30-50 cm is close to 1, showing isotropy. (3) There is a strong spatial heterogeneity of soil total salt content in each layer, and the high and low value centers distributed in the patches. The total salt content of soil is positively correlated with groundwater depth, and highly significantly negative correlated with the vegetation coverage (P<0.01). The spatial heterogeneity of soil total salt content in inland salt marsh wetland of Sugan Lake is mainly influenced by vegetation coverage. The variation of groundwater depth increases the complexity of its spatial variability, which reflects the complexity and heterogeneity of the soil physical and chemical spatial system of inland salt marsh wetland.

Surface properties and changes in morphology of microplastics exposed &amp;lt;italic&amp;gt;in-situ&amp;lt;/italic&amp;gt; to Chinese coastal wetlands

Coastal wetlands are key areas of accumulation of microplastics. However, until now only a few studies have focused on the surface properties and morphological changes in microplastics in the real coastal wetland environment. Here, two typical biogeographic coastal soils, the Yellow River Estuary salt marsh wetland in the temperate zone and the Beibu Bay mangrove wetland in the subtropical zone, were selected for study. Polystyrene foams and polyethylene films were used and exposed within two coastal wetlands sites through in situ soil burial (underground exposure) and surface placement (above-ground exposure). The samples were sampled after 6, 12, 18 and 24 months of exposure to reveal the characteristics of the surface properties and morphological changes in microplastics in typical wetlands from the southern and northern biogeographic coastal zones. The surface morphology, microstructures and attached materials were observed using scanning electron microscopy using an energy dispersive spectrometer. Surface properties of the microplastics, i.e. the surface roughness, specific surface area, pore size distribution, functional groups and hydrophobicity, were analyzed by using atomic force microscopy, a surface area analyzer, a mercury porosimeter, Fourier transform infrared spectrometry and a contact angle meter. The surface morphology of the polystyrene foams in the Beibu Bay mangrove wetland exhibited more pits and holes than those in the Yellow River Estuary salt marsh wetland. The polystyrene foams exposed above-ground in the Beibu Bay mangrove wetland showed embrittlement and exfoliation after 18 months, while those exposed underground did not show such features. The specific surface areas of the polystyrene foams and the polyethylene films in the Yellow River Estuary salt marsh wetland were higher than those in the Beibu Bay mangrove wetland. The pore distributions on the surfaces of the two microplastic types mainly comprised macropores and mesopores. However, the porosity of the polyethylene film in the Yellow River Estuary salt marsh wetland was slightly higher than in the Beibu Bay mangrove wetland. The porosities in both regions were higher than in the original control samples. In terms of carbonyl index, rates of change in the Yellow River Estuary salt marsh wetland were higher than those in the Beibu Bay mangrove wetland. The surface hydrophobicity of the polyethylene film in the two regions declined with increasing exposure time. The changes in surface morphology of the polystyrene foams were more rapid than those in the polyethylene films, but the degree of change in specific surface area of the polyethylene films was greater than in the case of the polystyrene foams. It can be concluded that the surface properties and changes in morphology of microplastics in the coastal soil environment are related to multiple factors including the types and conditions of the wetlands, types of microplastics, exposure mode and exposure time. However, the specific mechanisms of these surface changes require further study. In summary, this study provides a scientific basis for research on the chemical processes of the micro-interfaces on the microplastic surfaces and environmental behavior and risk assessment of microplastics in the Chinese coastal zone.

Mapping properties of vegetation in a tidal salt marsh from multi-spectral satellite imagery using the SCOPE model

ABSTRACT Quantitative remote sensing of vegetation biophysical and biochemical parameters through the inversion of physical models is of great significance for monitoring vegetative growth, ecosystem function, and the global carbon and nitrogen cycles. However, mapping and comparing vegetation parameters in a tidal saltmarsh based on multi-spectral satellite imagery has been rarely documented. In this study, a coupled model (Soil-Canopy-Observation of Photochemistry and Energy fluxes, SCOPE) was used to quantitatively invert the spatial patterns of key parameters such as the leaf area index (LAI), leaf chlorophyll content (C ab), and fraction of absorbed photosynthetically active radiation (fPAR) of salt marsh vegetation from Land Remote-Sensing Satellite 8 (Landsat-8), Sentinel-2A, and RapidEye multispectral satellite imagery. The results show that RapidEye outperformed Landsat-8 and Sentinel-2A in the retrieval of LAI and C ab, with higher coefficients of determination (R 2 = 0.539 and 0.488, respectively) and lower normalized root mean square errors (NRMSE = 0.32 and 0.28, respectively). Without the red-edge band, the R 2 between the modelled and observed LAI and C ab for RapidEye decreased by 27.83% and 5.33%, respectively, while the NRMSE increased by 3.13% and 46.43%, respectively, highlighting the important role of the red-edge band in vegetation parameter retrieval. Tidal flooding resulted in poor retrieval results from Sentinel-2A. However, the accuracy of C ab inversion was significantly improved by removing the sampling sites near tidal trenches or in low-lying areas, indicating that tidal inundation exerted a notable effect on the retrieval of saltmarsh vegetation parameters when using multi-spectral images. In addition, the spatial pattern of the simulated fPAR from RapidEye is consistent with that of the gross primary productivity. This study provides an alternative method for estimating ecosystem functions in a tidal saltmarsh wetland, as well as for large-scale and high-precision monitoring of wetland restoration that is beneficial for the ecological protection of coastal zones.

Faunal mediated carbon export from mangroves in an arid area

The outwelling paradigm argues that mangrove and saltmarsh wetlands export much excess production to downstream marine systems. However, outwelling is difficult to quantify and currently 40–50% of fixed carbon is unaccounted for. Some carbon is thought outwelled through mobile fauna, including fish, which visit and feed on mangrove produce during tidal inundation or early life stages before moving offshore, yet this pathway for carbon outwelling has never been quantified. We studied faunal carbon outwelling in three arid mangroves, where sharp isotopic gradients across the boundary between mangroves and down-stream systems permitted spatial differentiation of source of carbon in animal tissue. Stable isotope analysis (C, N, S) revealed 22–56% of the tissue of tidally migrating fauna was mangrove derived. Estimated consumption rates showed that 1.4% (38 kg C ha−1 yr−1) of annual mangrove litter production was directly consumed by migratory fauna, with <1% potentially exported. We predict that the amount of faunally-outwelled carbon is likely to be highly correlated with biomass of migratory fauna. While this may vary globally, the measured migratory fauna biomass in these arid mangroves was within the range of observations for mangroves across diverse biogeographic ranges and environmental settings. Hence, this study provides a generalized prediction of the relatively weak contribution of faunal migration to carbon outwelling from mangroves and the current proposition, that the unaccounted-for 40–50% of mangrove C is exported as dissolved inorganic carbon, remains plausible.

Contemporary distribution of benthic foraminiferal assemblages in coastal wetlands of south-eastern Australia

Benthic foraminifera identified from the upper intertidal zone of coastal mangrove and saltmarsh wetlands of south-eastern Australia exhibit spatial zonation that varies with elevation and corresponds to position in the tidal frame. This study describes relationships between benthic foraminiferal assemblages and environmental variables, such as wetland elevation, pore-water salinity, substrate organic matter content and sediment grainsize. Agglutinated taxa dominated higher in the tidal frame, whereas calcareous taxa increased in both relative abundance and diversity lower in the tidal frame. Species composition varied within and between study sites, reflecting local differences in other environmental variables. Three major spatial clusters were identified in the upper intertidal zone from a dataset consisting of 111 contemporary samples: a high-to mid-elevation assemblage consisting of differing abundances of Entzia macrescens and Trochammina inflata; a mid-elevation assemblage comprised of Arenoparrella mexicana in association with Trochammina inflata and Quinqueloculina seminula; and mid-to low-elevation assemblage characterised by Cribroelphidium excavatum, Quinqueloculina seminula, Ammobaculites spp. and Miliammina fusca. Multivariate analysis correlated foraminiferal assemblages with environmental variables showing that foraminiferal distribution in the region is constrained primarily by wetland elevation, but also by pore-water salinity. Foraminiferal assemblages derived from cluster analysis correlated with vegetation zones, implying that both foraminifera and vegetation are influenced by elevation and salinity. This paper seeks to demonstrate that the consistency in spatial zonation of assemblages provides greater confidence that contemporary distribution of foraminiferal assemblages can assist with the interpretation of past depositional conditions and palaeo-environmental reconstructions, providing insights into the evolution of coastal wetlands of south-eastern Australia over the Holocene.