Search Results (34)

Vegetated intertidal ecosystems, such as seagrass meadows, salt marshes, and macroalgal beds, are vital for biodiversity, coastal protection, and climate regulation; however, they remain highly vulnerable to anthropogenic and climate-induced stressors. This study aims to assess interannual changes in intertidal vegetation cover along the Portuguese mainland coast from 2015 to 2024 using Sentinel-2 satellite imagery calibrated with high-resolution multispectral unoccupied aerial vehicle (UAV) data, to determine the most accurate index for mapping intertidal vegetation. Among the 16 indices tested, the Atmospherically Resilient Vegetation Index (ARVI) showed the highest predictive performance. Based on a model relating intertidal vegetation cover to this index, an ARVI value greater than or equal to 0.214 was established to estimate the area covered with intertidal vegetation. Applying this threshold to time-series data revealed considerable spatial and temporal variability in vegetation cover, with estuarine systems such as the Ria de Aveiro and the Ria Formosa showing the greatest extents and marked fluctuations. At the national level, no consistent overall trend was identified for the study period. Despite limitations related to satellite image resolution and single-site validation, the results demonstrate the feasibility and utility of combining UAV data and satellite indices for long-term, large-scale monitoring of intertidal vegetation. Full article

This study examined the diffusion of nutrients (NH₄⁺, NO₃⁻, and PO₄³⁻) in the pore water of intertidal sediments in Lake Komuke (located in the northeastern part of Hokkaido on the coast of Okhotsk Sea) across nine stations, at 0 cm to 40 cm depths, from 19 May to 23 August 2015. A comparison was made between the traditional version of Fick’s first law and a modified version to understand nutrient diffusion in the intertidal flat. The novelty of this study lies in establishing a flux correction factor as a function of the activity coefficient in intertidal sediments. The outcomes of the standard and modified versions of Fick’s law exhibited observable physical differences between stations for all nutrients. However, the statistical analysis demonstrated significant differences only for NO₃⁻ and PO₄³⁻ at stations D, E, and F, suggesting that there is no statistically meaningful difference in NH₄⁺ flux. A statistical comparison of 27 pairs of fluxes obtained by the classical and modified versions of Fick’s first law indicated that 88.9% of the differences were not statistically significant between the two methods, and 11.1% were statistically significant. This shows the consistency of the modified method, firstly in reproducing the classical version of Fick’s law, and secondly in improving upon it, in a porous medium. These findings indicate that the modified version of Fick’s first law is an accurate methodology for evaluating nutrient diffusion dynamics in intertidal environments, and is potentially applicable to coastal salt marshes, with practical implications for environmental management and conservation efforts. Full article

Tidal inlets regulate the exchange of water and sediment between the open sea and adjacent basins. In many locations, engineering interventions combined with coastal protections and polders have intensified erosion and scouring. This study reports on a three-year monitoring program following the implementation of a Nature-based Solution (NbS) at a previous engineering tidal inlet in the Zwin, located along the Belgian–Dutch coast. In 2019, large-scale modifications to the intertidal zone and the opening of a dyke doubled the surface area of the tidal inlet and its associated tidal marsh. Results revealed rapid and substantial morphological adjustments: the main channel deepened, widened, and migrated eastward. Sediment balance analyses showed stability at the inlet entrance but material loss further inland. Tidal prism and cross-sectional measurements indicated a fourfold increase in tidal prism immediately after NbS implementation, triggering strong channel responses. Within a year, the channel cross-sectional area reached a new equilibrium, which remained stable in the following years. These patterns highlight active sediment transport driven by coupled hydrodynamic and morphodynamic processes. Using an extensive data set, a conceptual model is presented to illustrate how the NbS influenced tidal inlet dynamics through the interaction of flow and sedimentation processes. Full article

The intertidal zones of estuarine wetlands serve as critical components in maintaining and promoting the sustainable development of regional ecosystems. Salt marsh vegetation, a crucial element of these zones, is experiencing significant deterioration across multiple scales due to various stressors. Despite considerable attention given to the spatial patterns and temporal evolution of salt marsh vegetation, few studies have quantitatively assessed its dynamic interactions with tidal creeks. Tidal creeks serve as primary conduits for material, energy, and information exchange between intertidal zones and adjacent ecosystems. There is a complex feedback mechanism between the development of the tidal creeks and vegetation communities. We investigated the distribution patterns and successional characteristics of salt marsh vegetation at both landscape and pixel scales, with particular emphasis on coupling dynamics with tidal creeks. Our results revealed a distinct spatial gradient in vegetation distribution across the study area. While the invasion of S. alterniflora exhibited limited direct competitive effects on S. salsa, it demonstrated significant influence on tidal creek geomorphological evolution. Notably, S. salsa exhibited pronounced sensitivity to hydrological conditions, with its growth being substantially constrained by tidal creek development and associated soil modifications. Full article

The intertidal ecosystem serves as a critical transitional zone between terrestrial and marine environments, supporting diverse biodiversity and essential ecological functions. However, these systems are increasingly threatened by climate change, rising sea levels, and anthropogenic impacts. Accurately mapping intertidal ecosystems and differentiating mangroves, salt marshes, and tidal flats remains a challenge due to inconsistencies in classification frameworks. Here, we present a high-precision mapping approach for intertidal ecosystems using multi-source satellite data, including Sentinel-1, Sentinel-2, and Landsat 8/9, integrated with the Google Earth Engine (GEE) platform, to enable the detailed mapping of intertidal zones across China–ASEAN. Our findings indicate a total intertidal area of 73,461 km² in China–ASEAN, with an average width of 1.16 km. Analyses of patch area, abundance, and perimeter relationships reveal a power-law distribution with a scaling exponent of 1.52, suggesting self-organizing characteristics shaped by both natural and human pressures. Our findings offer foundational data to guide conservation and management strategies in the region’s intertidal zones and present a novel perspective to propel research on global coastal ecosystems. Full article

Mangroves are one of the world’s most productive and ecologically important ecosystems, and they are threatened by the widespread invasion of Spartina alterniflora Loisel in China. As few studies have examined the spatial pattern differences of S. alterniflora invasion and the nearby mangroves in different latitudes, we chose the Zhangjiang Estuary and the Dandou Sea, two representative mangrove–salt marsh ecotones in the north and south of the Tropic of Cancer, as the study areas for comparison. The object-based image analysis and visual interpretation methods were combined to construct fine-scale mangrove and S. alterniflora maps using high-resolution satellite imagery from 2005 to 2019. We applied spatial analysis, centroid migration, and landscape indexes to analyze the spatio–temporal distribution changes of mangroves and S. alterniflora in these two ecotones over time. We used the landscape expansion index to investigate the S. alterniflora invasion process and expansion patterns. The annual change rates of mangrove and S. alterniflora areas in the Zhangjiang Estuary showed a continuous growth trend. However, the mangrove areas in the Dandou Sea showed a fluctuating trend of increasing, decreasing, and then increasing again, while S. alterniflora areas kept rising from 2005 to 2019. Spartina alterniflora showed larger annual change rates compared with mangroves, indicating rapid S. alterniflora invasion in the intertidal zones. The opposite centroid migration directions of mangroves and S. alterniflora and the decreasing distances between the mangrove and S. alterniflora centroids indirectly revealed the fierce competition between mangroves and S. alterniflora for habitat resources. Both regions saw a decrease in mangrove patch integrality and connectivity. The integrality of mangrove patches in the Zhangjiang Estuary was always higher than those in the Dandou Sea. We observed the growth stage (2011–2014) and outbreak stage (2014–2019) of S. alterniflora expansion in the Zhangjiang Estuary and the outbreak stage (2005–2009) and plateau stage (2009–2019) of S. alterniflora expansion in the Dandou Sea. The expansion pattern of S. alterniflora varies in time and place. Since the expansion of S. alterniflora in the outbreak stage is rapid, with a large annual change rate, early warning of S. alterniflora invasion is quite important for the efficient and economical removal of the invasive plant. Continuous and accurate monitoring of S. alterniflora is highly necessary and beneficial for the scientific management and sustainable development of coastal wetlands. Full article

Salt marshes in the southern North Sea are part of the UNESCO World Heritage Site, Wadden Sea, the largest unbroken system of intertidal sand and mud flats in the world. They provide a very high nature value while significantly contributing to coastal flood and erosion risk management as a nature-based element of flood and erosion risk management systems for densely populated coastal areas. Climate change-induced sea-level rise is a significant concern: an integrated approach to salt marsh management adapted to the effects of climate change necessitates an understanding of the impact of different management strategies. This review commences with a description of the biogeomorphological conditions and processes in salt marshes for a better understanding of the natural dynamics and how they are influenced by management and climate change. Next, the impact of salt marshes on hydrodynamic processes and their role as nature-based elements of flood and erosion risk management is presented; management options and implementation methods are discussed and analysed concerning coastal flood management and nature conservation requirements. In conclusion, targeted salt marsh management needs to consider the initial conditions and the development aims of the specific site are integrated into a conceptual framework. Salt marshes have the potential to adapt to sea-level rise, thereby contributing to the long-term protection of coastal areas. Full article

Global warming is an essential factor to consider when studying tidal wetlands. The Río Piedras and Flecha de El Rompido salt marsh is one of the main wetlands in Andalusia, Spain. From the mid-1950s to the present day, Land Use Changes (LUCs) have caused significant alterations to the landscape. These changes, along with the effects of climatic variables and human activity, have led to an unprecedented impact on the environment. In this study, a patented method is used to obtain the total cubic meters of eroded soil and the average erosion prediction between 2015 and 2021 in the marshland area. Additionally, the various factors contributing to this phenomenon and the influence of intertidal processes are discussed. The results demonstrate how the enhanced integration of LIDAR technologies, digital elevation models, and Geographic Information Systems (GIS), in conjunction with regression models, has proven highly useful in describing, analyzing, and predicting the volumetric change process in the study area. In conclusion, the methodology used is helpful for any type of coastal marshes influenced by tidal processes and climate change. Full article

Tidal marshes are dynamic environments providing important ecological and economic services in coastal regions. With accelerating climate change and sea level rise (SLR), marsh mortality and wetland conversion have been observed on global coasts. For sustainable coastal management, accurate projection of SLR-induced tidal inundation and flooding requires fine-scale 3D terrain of the intertidal zones. The airborne Lidar systems, although successful in extracting terrestrial topography, suffer from high vertical uncertainties in coastal wetlands due to tidal effects. This study tests the feasibility of drone Lidar leveraging deep learning of point clouds on 3D marsh mapping. In an ocean-front, pristine estuary dominated by Spartina alterniflora, drone Lidar point clouds, and in-field marsh samples were collected. The RandLA-Net deep learning model was applied to classify the Lidar point cloud to ground, low vegetation, and high vegetation with an overall accuracy of around 0.84. With the extracted digital terrain model and digital surface model, the cm-level bare earth surfaces and marsh heights were mapped. The bare earth terrain reached a vertical accuracy (root-mean-square error, or RMSE) of 5.55 cm. At the 65 marsh samples, the drone Lidar-extracted marsh height was lower than the in-field height measurements. However, their strongly significantly linear relationship (Pearson’s r = 0.93) reflects the validity of the drone Lidar for measuring marsh canopy height. The adjusted Lidar-extracted marsh height had an RMSE of 0.12 m. This experiment demonstrates a multi-step operational procedure to deploy drone Lidar for accurate, fine-scale terrain and 3D marsh mapping, which provides essential base layers for projecting wetland inundation in various climate change and SLR scenarios. Full article

Oysters provide a suite of important ecosystem services, and recent research shows that oyster restoration rapidly enhances sedimentary organic carbon deposition. In 2012, an oyster reef enhancement project began in the GTM National Estuarine Research Reserve in Northeast FL, USA. We analyzed the spatial and downcore variability in sedimentary organic matter (OM) and particle sizes in the intertidal zone between the reefs and the marsh, along with oyster reef characteristics, to better understand physical and/or biological influences on sediment. Our data indicate that OM in the top 20 cm of sediment cores was negatively correlated with reef age. Similar decreases in particles <63 μm suggest remobilization of sediment, likely driven by the degradation of the reef structure over its approximately 9-year lifetime. Likewise, a survey of surface sediments showed that adjacent reef structural metrics were the best predictor of sediment OM and particle size. These results highlight the importance of reef structure as a control on sedimentary organic carbon deposition and stability in areas where physical energy is relatively high. This result is discussed in the context of implications for carbon budgets and biogeochemical ecosystem services of oysters as a part of living shorelines. Full article

The spatiotemporal changes of inundation frequency in the Yellow River Delta (YRD) have profound influences on sustainable ecological protection and are also closely relevant to economic development scarcity on the coast of China. However, long-term changes of inundation frequency have remained poorly characterized. Using the Google Earth Engine (GEE) cloud platform, this study processed Landsat images to explore inundation frequency changes from 1990 to 2020 in the YRD. The results indicated that (1) The existing water index combining the classification results based on the MLM (Maximum Likelihood Method) is suitable for the mapping of the long-term water bodies, especially in the coastal regions; (2) The inundation frequency showed a clearly uneven temporal–spatial distribution. The low inundation area (LIA) is mainly intertidal natural wetlands with a declining trend, while the high inundation area (HIA) is dominated by constructed wetlands with a rising trend; (3) The use frequency of artificial ponds determines the inundation frequency of the constructed wetland. The industry development has gradually matured, causing the inundation frequency from dispersion to concentration in the constructed wetland; and (4) In the natural wetland, the LIA have increased since 2010 and have accounted for 30% in 2020. The large-scale appearance of LIA occurs with the emergence of high vegetation abundance. Spartina alterniflora salt marshes with strong reproductive ability and high abundance lead to the difficulty of wetland flooding and reduce the inundation frequency. Full article

Populations of the eastern oyster (Crassostrea virginica) have been historically declining due to both natural and anthropogenic stressors. In response, oyster reefs have been created with many different approaches. This study utilized intertidal reefs constructed with oyster shells recycled from local restaurants to provide oyster settlement substrate, reef-associated faunal habitat, and a barrier to prevent marsh erosion. The objective of this study was to determine how oyster population characteristics changed over four years (2016–2019) on five different reefs within Sweetwater Lake, Galveston Bay, Texas, with a secondary objective to examine how oyster populations responded after Hurricane Harvey. Over the study period, five different reefs were sampled each summer by removing five bags per reef to determine oyster abundance and size demography. For the three years of the study (2017–2019), we also quantified oyster spat recruitment to the reefs. Oyster abundance and size (shell height) varied interactively by year and reef number, whereas oyster recruitment was significantly lower following Hurricane Harvey and then returned to pre-storm levels. Our results further highlight the importance of reef placement for breakwater-style reefs, as it appears the hydrodynamics within Sweetwater Lake influenced both oyster abundance and size among individual reefs. While the created reefs receive limited larval influx due to the narrow opening between Sweetwater Lake and Galveston Bay proper, this limited connectivity seemed to prevent mass mortality from the freshwater influx from Hurricane Harvey. Therefore, projects creating oyster reefs should consider local and regional landscape factors for the long-term success of oyster populations and robustness to natural disasters. Full article

Monitoring intertidal habitats, such as oyster reefs, salt marshes, and mudflats, is logistically challenging and often cost- and time-intensive. Remote sensing platforms, such as unoccupied aircraft systems (UASs), present an alternative to traditional approaches that can quickly and inexpensively monitor coastal areas. Despite the advantages offered by remote sensing systems, challenges remain concerning the best practices to collect imagery to study these ecosystems. One such challenge is the range of spatial resolutions for imagery that is best suited for intertidal habitat monitoring. Very fine imagery requires more collection and processing times. However, coarser imagery may not capture the fine-scale patterns necessary to understand relevant ecological processes. This study took UAS imagery captured along the Gulf of Mexico coastline in Florida, USA, and resampled the derived orthomosaic and digital surface model to resolutions ranging from 3 to 31 cm, which correspond to the spatial resolutions achievable by other means (e.g., aerial photography and certain commercial satellites). A geographic object-based image analysis (GEOBIA) workflow was then applied to datasets at each resolution to classify mudflats, salt marshes, oyster reefs, and water. The GEOBIA process was conducted within R, making the workflow open-source. Classification accuracies were largely consistent across the resolutions, with overall accuracies ranging from 78% to 82%. The results indicate that for habitat mapping applications, very fine resolutions may not provide information that increases the discriminative power of the classification algorithm. Multiscale classifications were also conducted and produced higher accuracies than single-scale workflows, as well as a measure of uncertainty between classifications. Full article

We conducted an intercontinental biogeographic survey to analyze the effects of an invasive plant species in its native and invaded ranges. Our study system included tidal wetlands colonized by Iris pseudacorus L. (yellow flag iris, Iridaceae) along salinity gradients in two estuaries in its native European (Guadalquivir Estuary) and invaded North American (San Francisco Bay-Delta Estuary) ranges. We hypothesized I. pseudacorus would impart more negative community-level impacts on plant species diversity in the invaded range compared to the native range. Our results show that the colonization of Iris pseudacorus has very different effects on the diversity of tidal plant communities in its native and invaded ranges. In the native range, I. pseudacorus promoted plant diversity by increasing evenness and species richness. On the contrary, I. pseudacorus greatly reduced plant diversity in the invaded range, being this reduction higher in those communities with higher species richness and diversity levels. In view of these results, urgent management practices are needed to control and eradicate I. pseudacorus from the inland Sacramento-San Joaquin Delta Estuary since this invasive macrophyte is reducing plant diversity at local and landscape scales. Full article

Benthic microbial communities of intertidal zones perform important biogeochemical processes and provide accessible nutrients for higher organisms. To unravel the ecosystem services of salt marsh microbial communities, we analyzed bacterial diversity and metabolic potential along the land–sea transition zone on seasonal scales on the German North Sea Island of Spiekeroog. Analysis of bacterial community was based on amplicon sequencing of 16S rRNA genes and –transcripts. Insights into potential community function were obtained by applying the gene prediction tool tax4fun2. We found that spatial variation of community composition was greater than seasonal variations. Alphaproteobacteria (15%), Gammaproteobacteria (17%) and Planctomycetes (11%) were the most abundant phyla across all samples. Differences between the DNA-based resident and RNA-based active communities were most pronounced within the Planctomycetes (17% and 5%) and Cyanobacteriia (3% and 12%). Seasonal differences were seen in higher abundance of Gammaproteobacteria in March 2015 (25%) and a cyanobacterial summer bloom, accounting for up to 70% of the active community. Taxonomy-based prediction of function showed increasing potentials for nitrification, assimilatory nitrate and sulfate reduction from sea to land, while the denitrification and dissimilatory sulfate reduction increased towards the sea. In conclusion, seasonal differences mainly occurred by blooming of individual taxa, while the overall community composition strongly corresponded to locations. Shifts in their metabolism could drive the salt marsh’s function, e.g., as a potential nitrogen sink. Full article