Salt Marsh Estuary Research Articles

Study on the structure and energy flow of the salt marsh wetland ecosystem in Liaohe Estuary based on the Ecopath model

Salt marshes are one of the three blue carbon ecosystems recognized by the Intergovernmental Panel on Climate Change (IPCC). However, coastal salt marshes in China are facing the risk of degradation. To reveal the status of the salt marsh wetland ecosystem in Liaohe Estuary, an Ecopath model composed of 14 functional groups was constructed based on the 2019 ecological survey data. A comprehensive analysis of the system’s food web structure, energy flow processes, and overall ecosystem characteristics was conducted. The results show that the energy flow in the Liaohe Estuary salt marsh wetland ecosystem is mainly distributed in three integrated trophic levels. The utilization rates of trophic levels II and III are low, easily causing blockages in the lower trophic levels of the ecosystem’s energy flow. The total system throughput of the Liaohe Estuary salt marsh wetland ecosystem is 49,099.039 t·km²·a−1;. The system connectivity index and the system omnivory index are 0.207 and 0.109, respectively. Compared with other wetland systems, the ecosystem has a larger scale, but the overall ecosystem characteristic index reveals lower stability and complexity of the Liaohe Estuary salt marsh wetland system.

Persistent Organic Pollutants in Tagus Estuary Salt Marshes: Patterns of Contamination and Plant Uptake.

The presence of anthropogenic compounds, including organochlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs), was studied in three salt marshes within the Tagus estuary, Portugal, along an anthropogenic pressure gradient. Results revealed differences in OCPs and PCBs among the marshes, with differing concentration levels. Specifically, one marsh, with surrounding agricultural activity, showed the highest OCP concentrations, while another, with a historical industrial past, exhibited elevated PCB levels. In contrast, a third marsh, part of a natural reserve, displayed comparatively lower concentrations of both substances. Sediment concentrations, likely influenced by agricultural practices, were found to be comparable to or higher than those observed in other Portuguese estuaries. The halophyte Spartina maritima was found to absorb OCPs, particularly in its aboveground tissues, suggesting bioaccumulation within the plant. Additionally, PCB levels appeared to be influenced by industrial history, with one marsh displaying notably higher concentrations. In conclusion, the persistence of organochlorine compounds in the salt marsh ecosystems notwithstanding the regulatory prohibitions implemented in the 1990s highlights the need for continuous monitoring and study of such sites and the necessity of remediation practices, which are imperative to mitigate ecological and health risks in these polluted salt marshes.

Above- and belowground plant mercury dynamics in a salt marsh estuary in Massachusetts, USA

Abstract. Estuaries are a conduit of mercury (Hg) from watersheds to the coastal ocean, and salt marshes play an important role in coastal Hg cycling. Hg cycling in upland terrestrial ecosystems has been well studied, but processes in densely vegetated salt marsh ecosystems are poorly characterized. We investigated Hg dynamics in vegetation and soils in the Plum Island Sound estuary in Massachusetts, USA, and specifically assessed the role of marsh vegetation for Hg deposition and turnover. Monthly quantitative harvesting of aboveground biomass showed strong linear seasonal increases in Hg associated with plants, with a 4-fold increase in Hg concentration and an 8-fold increase in standing Hg mass from June (3.9 ± 0.2 µg kg−1 and 0.7 ± 0.4 µg m−2, respectively) to November (16.2 ± 2.0 µg kg−1 and 5.7 ± 2.1 µg m−2, respectively). Hg did not increase further in aboveground biomass after plant senescence, indicating physiological controls of vegetation Hg uptake in salt marsh plants. Hg concentrations in live roots and live rhizomes were 11 and 2 times higher than concentrations in live aboveground biomass, respectively. Furthermore, live belowground biomass Hg pools (Hg in roots and rhizomes, 108.1 ± 83.4 µg m−2) were more than 10 times larger than peak standing aboveground Hg pools (9.0 ± 3.3 µg m−2). A ternary mixing model of measured stable Hg isotopes suggests that Hg sources in marsh aboveground tissues originate from about equal contributions of root uptake (∼ 35 %), precipitation uptake (∼ 33 %), and atmospheric gaseous elemental mercury (GEM) uptake (∼ 32 %). These results suggest a more important role of Hg transport from belowground (i.e., roots) to aboveground tissues in salt marsh vegetation than upland vegetation, where GEM uptake is generally the dominant Hg source. Roots and soils showed similar isotopic signatures, suggesting that belowground tissue Hg mostly derived from soil uptake. Annual root turnover results in large internal Hg recycling between soils and plants, estimated at 58.6 µg m−2 yr−1. An initial mass balance of Hg indicates that the salt marsh presently serves as a small net Hg sink for environmental Hg of 5.2 µg m−2 yr−1.

Genome assembly and population genomic data of a pulmonate snail Ellobium chinense

Ellobium chinense is an airbreathing, pulmonate gastropod species that inhabits saltmarshes in estuaries of the northwestern Pacific. Due to a rapid population decline and their unique ecological niche in estuarine ecosystems, this species has attracted special attention regarding their conservation and the genomic basis of adaptation to frequently changing environments. Here we report a draft genome assembly of E. chinense with a total size of 949.470 Mb and a scaffold N50 of 1.465 Mb. Comparative genomic analysis revealed that the GO terms enriched among four gastropod species are related to signal transduction involved in maintaining electrochemical gradients across the cell membrane. Population genomic analysis using the MSMC model for 14 re-sequenced individuals revealed a drastic decline in Korean and Japanese populations during the last glacial period, while the southern Chinese population retained a much larger effective population size (Ne). These contrasting demographic changes might be attributed to multiple environmental factors during the glacial–interglacial cycles. This study provides valuable genomic resources for understanding adaptation and historical demographic responses to climate change.

Food habits of fishes in salt marsh estuaries in the western Seto Inland Sea, Japan

Food habits of fishes in salt marsh estuaries in the western Seto Inland Sea, Japan

Nutrient enrichment undermines invasion resistance to Spartina alterniflora in a saltmarsh: Insights from modern coexistence theory

Abstract The ability of native communities to maintain invasion resistance in the face of environmental changes is crucial for biodiversity conservation. However, previous studies have primarily focused on the inhibitive effects experienced by invaders, providing limited insights into the ultimate outcome of resistance. In this study, we integrated modern coexistence theory into biotic resistance research to investigate the impact of nutrient enrichment on the resistance of Phragmites australis marshes to Spartina alterniflora invasion in the Yangtze estuary saltmarshes of China. Our results demonstrated that under non‐enriched conditions, successful invasion resistance was facilitated by stable coexistence between native and invasive species in the field. This prediction of invasion resistance aligned with the distribution dynamics of the two species in the Yangtze estuary saltmarshes over the past two decades. However, nutrient enrichment was likely to lead to a fundamental shift in their coexistence and ultimately, the failure of resistance. Synthesis and applications. Integrating modern coexistence theory into biotic resistance studies advances the assessment of invasion resistance by shifting from quantifying relative strength to predicting explicit resistance outcomes. Ecosystem managers can draw explicit conclusions about the potential establishment and impact of invaders by analysing observational or experimental data within the framework of modern coexistence theory. This information aids in identifying the most efficient strategies for addressing invasive species.

Saltmarsh vegetation alters tidal hydrodynamics of small estuaries

Saltmarshes in most estuaries in the UK and elsewhere are heavily exploited for numerous purposes including farming, fishing, and recreation. In this study, a computational model was used to investigate the impact of saltmarsh vegetation on tidal dynamics and residual currents in three distinctly different estuaries in Wales, UK, in order to understand the impacts of marsh vegetation on wider estuarine hydrodynamics. The three estuaries, Mawddach, Taf and Loughor, vary in size, tidal range, exposure, and saltmarsh coverage. Tidal constituents and residual currents were calculated using a year-long simulation of tidal dynamics. Tidal dynamics are discussed in terms of five important primary tidal constituents (M2, S2, N2, K1, O1) and two shallow water constituents (M4, MS4). The results reveal that saltmarsh vegetation reduces the amplitude of both primary and shallow water tidal constituents not only on and at the proximity of marsh platforms but also in the wider estuary, mostly confined to tidal channels and surrounding intertidal areas. Most notable changes were observed in the middle and upper estuary. Notable changes to residual current velocities were observed on marsh flat areas and in tidal channels and saltmarsh creeks which indicates that changes to marsh vegetation have the potential to alter sediment transport and hence wider estuary hydrodynamics. Our results will be useful when making decisions to restore, reclaim and realign existing saltmarshes for environmental, conservation and socioeconomic purposes, or integrate them in nature-based solutions for estuarine flood and erosion management.

Spartina alterniflora has the highest methane emissions in a St. Lawrence estuary salt marsh

Salt marshes have the ability to store large amounts of ‘blue carbon’, potentially mitigating some of the effects of climate change. Salt marsh carbon storage may be partially offset by emissions of CH4, a highly potent greenhouse gas. Sea level rise and invasive vegetation may cause shifts between different elevation and vegetation zones in salt marsh ecosystems. Elevation zones have distinct soil properties, plant traits and rhizosphere characteristics, which affect CH4 fluxes. We investigated differences in CH4 emissions between four elevation zones (mudflat, Spartina alterniflora, Spartina patens and invasive Phragmites australis) typical of salt marshes in the northern Northwest Atlantic. CH4 emissions were significantly higher from the S. alterniflora zone (17.7 ± 9.7 mg C m−2h−1) compared to the other three zones, where emissions were negligible (<0.3 mg C m−2h−1). These emissions were high for salt marshes and were similar to those typically found in oligohaline marshes with lower salinities. CH4 fluxes were significantly correlated with soil properties (salinity, water table depth, bulk density and temperature), plant traits (rhizome volume and biomass, root volume and dead biomass volume all at 0–15 cm) and CO2 fluxes. The relationships between CH4 emissions, and rhizome and root volume suggest that the aerenchyma tissues in these plants may be a major transport mechanism of CH4 from anoxic soils to the atmosphere. This may have major implications for the mitigation potential carbon sink from salt marshes globally, especially as S. alterniflora is widespread. This study shows CH4 fluxes can vary over orders of magnitude from different vegetation in the same system, therefore, specific emissions factors may need to be used in future climate models and for more accurate carbon budgeting depending on vegetation type.

Contribution of belowground plant components to salt marsh soil volume

Accumulation of belowground plant material (live roots, rhizomes, and dead material) is critical to vertical accretion of tidal salt marsh soils and their ability to maintain elevation with respect to sea-level rise. Many studies utilize a single, global relationship between soil organic carbon and belowground volume, which does not include the pore space created by belowground growth, thus does not appropriately reflect the contribution of vegetation to soil accretion. We develop factors that relate live belowground mass to the volume of live roots and rhizomes for four species in a St. Lawrence estuary salt marsh at la Pocatière, Quebec. Spartina alterniflora, Spartina patens, and invasive Phragmites australis were identified in the aboveground growth, while only tubers and roots of Cyperus esculentus were found. Cores of the top 30 cm of soil were collected and cut into 0–15 and 15–30 cm sections from the low marsh, high marsh, and S. patens marsh invaded by P. australis. The soil was washed over a 1 mm sieve, and the organic matter was retained. The live material was sorted into fractions of roots and rhizomes by species. The volume of all components was measured by displacement in water before drying to obtain mass. An overall conversion factor of 8.2 g cm−3 reflects the volumetric contribution of live belowground plant components of all species studied. The relationship varies by species, with S. alterniflora contributing the greatest volume per unit mass (8.9 g cm−3), followed by S. patens (7.9 g cm−3), then P. australis and C. esculentus, both at 5.6 g cm−3. Our results not only demonstrate that the total mass and volume of each species for each component (rhizomes, roots, and dead material) were strongly correlated but that measurements of carbon density underestimate the true volumetric contributions of salt marsh plants to the soil.

Foraging by estuarine juveniles of two paralichthyid flounders: experimental analyses of the effects of light level, turbidity, and prey type

Juvenile summer flounder Paralichthys dentatus and southern flounder P. lethostigma inhabit turbid salt marsh estuaries. Predation rates by juveniles (50-90 mm) were examined at 5 daytime light levels (6 × 1011 to 2 × 1014 quanta s-1 cm-2) and in darkness and 4 turbidity levels (clear [≤1], 11, 20, and 40 NTU) at an intermediate light level. Both species fed equally well on benthopelagic mysid shrimp and benthic spionid polychaetes at all daytime light levels tested. However, predation on mysids was significantly reduced in the dark. Consumption of polychaetes was not reduced in the dark by either species, illustrating the effectiveness of non-visual foraging methods on benthic prey. Turbidity levels tested did not affect predation on either prey type by either flounder species. Locomotor behavior was examined at the same turbidity levels. P. lethostigma spent more time swimming in the water column than P. dentatus in lower turbidity (clear-20 NTU), and both species reduced swimming at 40 NTU. It appears that both species primarily use a benthic-oriented ambush foraging strategy under high turbidity conditions. This is a particularly pronounced switch in foraging style for P. lethostigma. Estuarine turbidity is increasing due to the impacts of climate change. When turbidity is elevated enough to eliminate light sufficient for visual feeding on mysids (between darkness and the lowest light level tested), feeding on this motile prey is negatively impacted for both species. Turbidity can thus alter foraging modes and types of prey consumed, affecting nursery habitat quality and the prey base supporting these young fishes.

A Multi-year Seasonal Study of Amoeboid Protists in Surface Water at the Margin of a Hudson River Estuary Salt Marsh

Marshes bordering rivers and estuaries are productive ecosystems that interact dynamically with the adjacent water mass. This is a multi-year study (2019–2022) of seasonal changes in the density of naked amoebae in monthly samples from the surface water of the Hudson estuary near Piermont, N. Y. with relationships to key environmental variables (surface water temperature, salinity, Secchi depth representing turbidity, and enterococcus bacterial counts). During the colder months (November to March), when decayed leaves and litter from the deciduous marsh grass produced organic matter in the sediment surface, the mean abundance of active amoebae ± standard error of the mean (SEM) was higher (3.07 ± 0.99 × 10⁴/ L, N = 7). In warmer months (May to September) the abundance of amoebae was lower (1.35 ± 0.29 × 10⁴ / L, N = 10). A multivariate linear regression analysis was performed relating amoeba abundance to four major water mass variables, resulting in the following statistically significant equation (p = 0.03): AD = 0.121 × T + 0.301 × L – 0.047 × S + 0.359 × C, where: AD = active amoebae density (× 10 /L), T = temperature ( C), L = tide level (m), S = Secchi disc depth (cm) and C = bacterial enterococcus concentration (number/ml). In general, given the increasing evidence of the potential importance of amoeboid protists in aquatic ecosystems, further research is warranted on their role in food webs and the carbon biogeochemical cycle within heterotrophic estuarine and coastal waters.

Inorganic and methylated mercury dynamics in estuarine water of a salt marsh in Massachusetts, USA

Salt marsh estuaries serve as sources and sinks for nutrients and elements to and from estuarine water, which enhances and alleviates watershed fluxes to the coastal ocean. We assessed sources and sinks of mercury in the intertidal Plum Island Sound estuary in Massachusetts, the largest salt marsh estuary of New England, using 25-km spatial water sampling transects. Across all seasons, dissolved (FHg) and total (THg) mercury concentrations in estuarine water were highest and strongly enhanced in upper marshes (1.31 ± 0.20 ng L−1 and 6.56 ± 3.70 ng L−1, respectively), compared to riverine Hg concentrations (0.86 ± 0.17 ng L−1 and 0.88 ± 0.34 ng L−1, respectively). Mercury concentrations declined from upper to lower marshes and were lowest in ocean water (0.38 ± 0.10 ng L−1 and 0.56 ± 0.25 ng L−1, respectively). Conservative mixing models using river and ocean water as endmembers indicated that internal estuarine Hg sources strongly enhanced estuarine water Hg concentrations. For FHg, internal estuarine Hg contributions were estimated at 26 g yr−1 which enhanced Hg loads from riverine sources to the ocean by 44%. For THg, internal sources amounted to 251 g yr−1 and exceeded riverine sources six-fold. Proposed sources for internal estuarine mercury contributions include atmospheric deposition to the large estuarine surface area and sediment re-mobilization, although sediment Hg concentrations were low (average 23 ± 2 μg kg−1) typical of uncontaminated sediments. Soil mercury concentrations under vegetation, however, were ten times higher (average 200 ± 225 μg kg−1) than in intertidal sediments suggesting that high soil Hg accumulation might drive lateral export of Hg to the ocean. Spatial transects of methylated Hg (MeHg) showed no concentration enhancements in estuarine water and no indication of internal MeHg sources or formation. Initial mass balance considerations suggest that atmospheric deposition may either be in similar magnitude, or possibly exceed lateral tidal export which would be consistent with strong Hg accumulation observed in salt marsh soils sequestering Hg from current and past atmospheric deposition.

Variable Effects on Benthic Community From Diking to Eradicate Invasive Plants in the Yangtze Estuary Salt Marsh

The removal of invasive plants is a global concern, and ecological restoration methods have been a major research topic in recent years. In the estuarine salt marsh of the Yangtze River, dikes are typically used in ecological restoration projects to eradicate the invasive plantSpartina alterniflora. We explored ways of optimizing dike construction and of providing an effective basis for the wetland ecological control and protection of biodiversity and analyzed the effects on the macrobenthos of fully and partially dikes. The measurement of the quantitative change in macrobenthos diversity and species composition was carried out in the project area and in a control before (2013) and after (2016) dike construction. Results showed that the number of species and average density decreased significantly in the fully diked enclosed area but increased in the partially diked semi-enclosed area. Outside the project area, all site samples showed increased species richness and average density after dike construction. This study indicated that macrobenthos was negatively affected by the dike project in the inside diked area. However, when the tidewater canals were preserved to maintain the connection between the inside and outside areas, there was a positive effect on macrobenthos in the project area. We suggest that canals are preserved while diking in the salt marsh and that gates are opened regularly to maintain the water and nutrient connectedness inside and outside the dike. The diking project mostly affected mollusks and polychaetes, which are the indispensable food sources for birds and fish. The study provides valid evidence for the management of estuarine salt marsh and the protection of macrobenthos.

The role of choice experiments in natural capital accounting approaches: fast track versus simulated exchange value in the Deben Estuary saltmarshes

Natural capital accounting requires exchange rather than welfare values, but lack of data and standards have encouraged practitioners to use different approaches (e.g. simple lookup table vs spatial modeling approaches). In this paper, we demonstrate how choice modeling data can provide simulated exchange values which are more robust than simple (fast track) valuation approaches for natural capital accounting. A survey of East of England residents collected the preferences for saltmarsh management and simulated exchange values, coherently linked with the ecosystem conditions. This approach is more informative for environmental local planning purposes. We claim that expanding the set of tools available for natural capital accounting can enhance management of ecosystem services and policy decision making.

Potential eolian transfer of radioactive dusts from contaminated saltmarshes to coastal residential areas

Dust samples from a residential area next to the Dee estuary saltmarsh, north-west England, UK, were collected at two heights and analyzed to investigate the potential for transporting radioactive ...

Association of 241Am and 137Cs in finer size-fractioned saltmarsh sediments from north-west England, UK and potential health risk to coastal population

ABSTRACT This study provides an in-depth analysis of the relationship between radionuclide and particle size-class abundance through an investigation of radionuclide distribution in finer sediments within surface core samples collected from two contaminated upper saltmarsh areas of the Dee estuary and Biggar marsh in north-west England. The particle size fractionation (PSF) analysis was carried out following gravitational settling and pipette method to separate all samples into six size-fractioned groups ranging from 63 to <2 µm (very coarse silt to clay), and radioactivity analysis was performed using a well-type High Purity Germanium (HPGe) detector. The highest 241Am and 137Cs activities in PSF samples were found to be 291 ± 5 and 2071 ± 16 Bq kg−1, respectively, for the Dee estuary saltmarsh and 3832 ± 14 and 4840 ± 23 Bq kg−1, respectively, for Biggar saltmarsh and found in the clay fractions for both sites. Correlation of radioactivity concentration data of three size groups ranging from 63 to <2 µm (very coarse silt to clay) confirms a strong and increasing association of radioactivity with fine particles from coarse to fine clay-size particles. Also, examination of textural and radionuclide data of all bulk core and size-fractioned samples revealed that upper saltmarshes are made up of both contaminated and uncontaminated sediments. Furthermore, the annual outdoor external effective dose range for all short core data (0.001–0.11 mSv y−1) and for PSF sample data (0.001–0.08 mSv y−1) reveal that some values exceed the world average value of 0.07 mSv y−1as reported in UNSCEAR [43], for outdoor, which are non-negligible. Thus, the total annual external effective dose associated with existing contaminated saltmarsh sediments represents a possible health risk to saltmarsh users and coastal populations living nearby these saltmarshes.

Long‐term passive acoustics to assess spatial and temporal vocalization patterns of Atlantic common bottlenose dolphins (Tursiops truncatus) in the May River estuary, South Carolina

AbstractPassive acoustics has been used extensively to study bottlenose dolphins; yet very few studies have examined the spatial, temporal, and environmental influences on vocalization types (echolocation, burst pulse sounds, and whistles), and few are long‐term and provide high temporal resolution over multiple years. We used data from 2013 to 2018 to establish baseline acoustic patterns for bottlenose dolphins in the May River estuary, South Carolina. We deployed acoustic recorders at six stations during 2013–2014 and three stations during 2015–2018, with locations spanning the entire estuary (headwaters to the mouth). We discovered that acoustic detection of dolphins varied not only spatially, but also yearly, monthly, and tidally. Higher numbers of echolocation bouts, burst pulse sounds, and whistles were detected at the mouth as compared to the headwaters. At the mouth, vocalization detections were greatest in fall and winter for multiple years, and echolocation detection was greatest during falling and low tides. This study provides an example of another tool, long‐term passive acoustics monitoring, to better understand spatial and temporal distribution of dolphins in a typical salt marsh estuary, that can be applied to other ecosystems throughout the southeastern United States and globally.

Invasive Spartina alterniflora changes the Yangtze Estuary salt marsh from CH4 sink to source

Expansion of Spartina alterniflora salt marshes in the East China Sea coast is changing the ecosystem and thus, uncertainty has hampered methane (CH4) flux accounts in these areas. To analyse seasonal and diurnal patterns of the CH4 fluxes and their relationship with environmental factors, four plots were established in a salt marsh of the Nanhui coast in the southern fringe of the Yangtze River estuary, differing in sediment salinity and vegetation history and including one bare mudflat. Monthly studies from March 2017 to January 2018 using a chamber technique showed that CH4 fluxes from the plots ranged from −1.7 to 72.2 mg m−2 h−1. The mature Spartina sites showed higher CH4 emission, peaking in the summer. In the mudflat CH4 consumption was observed in January and the summer. The seasonal CH4 fluxes showed positive correlation (p < 0.05) with temperature, and plant development (height of vegetation), and negative correlation (p < 0.05) with water salinity. Various diurnal cycles in the CH4 fluxes were observed at different seasons. Average CH4 emissions were higher during the daytime than at night, however, without significant difference. Thus, the CH4 fluxes started to rise at noon, and the maximum CH4 flux was observed after the ebb tide (at 18:00) during nighttime. The diurnal variation in CH4 fluxes showed a significant correlation with season but not with temperature.

Methane Emissions during the Tide Cycle of a Yangtze Estuary Salt Marsh

Methane (CH4) emissions from estuarine wetlands were proved to be influenced by tide movement and inundation conditions notably in many previous studies. Although there have been several researches focusing on the seasonal or annual CH4 emissions, the short-term CH4 emissions during the tide cycles were rarely studied up to now in this area. In order to investigate the CH4 emission pattern during a tide cycle in Yangtze Estuary salt marshes, frequent fixed-point observations of methane flux were carried out using the in-situ static closed chamber technique. The results indicated that the daily average CH4 fluxes varied from 0.68 mgCH4·m−2·h−1 to 4.22 mgCH4·m−2·h−1 with the average flux reaching 1.78 mgCH4·m−2·h−1 from small tide to spring tide in summer. CH4 fluxes did not show consistent variation with both tide levels and inundation time but increased steadily during almost the whole research period. By Pearson correlation analysis, CH4 fluxes were not correlated with both tide levels (R = −0.014, p = 0.979) and solar radiation (R = 0.024, p = 0.865), but significantly correlated with ambient temperature. It is temperature rather than the tide level mainly controlling CH4 emissions during the tide cycles. Besides, CH4 fluxes also showed no significant correlation with the underground pore-water CH4 concentrations, indicating that plant-mediated transport played a more important role in CH4 fluxes compared with its production and consumption.

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.