Tidal Flat Research Articles

Composition and Diversity Indices of the Fish Assemblage in the Tidal Mudflats of the Shatt Al-Arab Estuary in the Northwest Arabian Gulf

Ten thousand four hundred and thirty-five fish were collected from January 2021 to February 2022, belonging to 71 species distributed across 39 families and 20 orders. The study included the tidal zone of the Shatt al-Arab estuary in the northwest of the Arabian Gulf. Two methods used to collection the fishes; fixed gill nets and trowel nets. Various diversity indices, relative abundance, and richness were assessed. Several biodiversity indices were used to assess the area biologically and ecologically which Species diversity for Shannon and Simpson, species richness for Margalef and Menhinick, dominance for Berger-Parker, species similarity for Jaccard, numerical similarity for Bray – Curtis, and evenness for Peilou index. Nematalosa nasus had the highest relative abundance, which was recorded at 24.53%. However, the lowest relative abundance was observed for 20 species, with a value of 0.01% with only one individual. The Carangiformes had the highest percentage of 18.31% and the lowest percentage of 1.41 % for many orders only, with one species recorded. The Margalef index had its highest value on June 5.24 and its lowest on December 1.24. The Menhinick index had its highest value of 1.53 in October and its lowest value of 0.71 in November. The Shannon Index reached a peak of 2.69 in January 2021, and fell to 0.98 in September. The Simpson index recorded the highest value of 0.92 in January 2021 and the lowest value of 0.37 in September. The Peilou index reached its highest value of 0.965 in December, while its lowest value was 0.294 in September. The Jaccard index had its highest value of 0.667 between January 2021 and March, while its lowest value was 0.079 between December, June, and July. The highest value for the Bray-Curtis index occurred between July and August, reaching 0.644. In contrast, the lowest value observed was 0.005 between July and December.

The bimodal regime of ocean waves and winds over the continental shelf of Maranhão

This study analyzed surface waves and winds from ERA5 reanalysis dataset in the Western Equatorial Atlantic (WEA) Ocean in order to properly understand the long-term regime of oceanic waves over the Continental Shelf of Maranhão (CSMA), pointing to the changes that occur at the western and eastern sectors as the waves propagate to the coastal zone. A data validation with observational data collected in situ by the PNBOIA and PIRATA projects has been conducted. The parameters analyzed were significant wave height (Hs), peak period (Tp), mean wave direction (Dm), and the zonal (u10) and meridional (v10) components of wind at 10 m. The analysis covered a period of 43 years (1979–2023). The monthly climatology of the Hs, Tp and Dm found has revealed a semi-annual cycle in the waves pattern in the region. The wave direction variability executes a clockwise motion from northeast-east-southeast throughout a year. The annual climatology analysis reveals that 59 % of sea states in the region are characterized by swell conditions in the region, while wind-sea dominates in 41 % of cases, with seasonal variability. During the austral summer (autumn), swells prevail over wind-seas along the WEA, accounting for 77 % (84 %) of the cases. This coincides with the boreal winter, characterized by high storm activity, whose storms generate swells that traverse the ocean, reaching Maranhão's waters and resulting in the highest waves in the region (3.54 m in summer). In contrast, during the spring season, sea states are dominated by wind-sea conditions (70 %) due to the increase in southeast trade winds. The highest Hs observed from wind-sea conditions is 2.94 m. The largest contribution for the maxima Hs in the region is given by swells in the summer/autumn and by wind-seas in the winter/spring seasons, with swells propagating more energy and power to cause erosional processes on the eastern sector of Maranhão coast. Oppositely, in the western sector of the littoral, whose geomorphology is dominated by tidal flats, cheniers plains and mangroves, the Hs is small, indicating a depositional environment. The algorithm indicated that swells generated by tropical (extratropical) storms typically take approximately 3.5–4.5 (6−7) days to travel the distance to the CSMA, while in the equatorial zone, the arrival of swells at the CSMA averages between 3.5 and 7 days. In this study we demonstrated the CSMA region is dominated by a bimodal wave regime with a strong semi-annual cycle, which is driven by the tropical/extratropical storms propagating from the North Atlantic Ocean toward the study area and by trade winds variability.

Morphodynamics of meandering channels in non-vegetated monsoon-driven tidal flats in South Korea

To understand complex channel meandering dynamics and shape evolution in tidal flats, we analyzed tidal stream migration characteristics in the non-vegetated Gochang tidal flat over 9 years using Google Earth imagery. Large channels with tens of meters stream width migrated furthest, followed by creeks and small gullies with less than a meter of width. While annual migration speeds were fastest in large channels, normalizing by channel width revealed an opposite trend: small gullies migrated the fastest relative to their size, while large channels migrated the slowest. This unique pattern, compared to vegetated tidal flats, is likely driven by the interaction of three factors: (1) the non-vegetated Gochang flat's weak sediment cohesion, especially in the fine-grained upper intertidal zone; (2) strong hydraulic forces from typhoons and storms; and (3) the significant particle size gradient between upper and lower zones. The efficient reworking and re-deposition even in large channels highlight the importance of considering dynamic tidal migration as an advection term alongside bioturbation. This is crucial for sedimentological and biogeochemical studies, including tidal flat sedimentation rate calculations and carbon cycle research.

Coastal conversion alters topsoil carbon, nitrogen and phosphorus stocks and stoichiometric balances in subtropical coastal wetlands

The extensive conversion of coastal wetlands into agricultural and aquaculture areas has significant repercussions on soil nutrient balance. However, how coastal conversion specifically influences the dynamics and stoichiometry of topsoil carbon (C), nitrogen (N), and phosphorus (P) remains limited due to the considerable spatial variability and a lack of comprehensive field data. Here, we investigated the concentration and distribution of total C (TC), N (TN) and P (TP), along with their stoichiometric balance in four distinct coastal landscapes, including natural marshes and tidal flats, as well as converted agricultural croplands and ponds. The results revealed that converted croplands and ponds exhibited significantly higher concentrations of soil C, N and P, particularly in comparison to tidal flats. Furthermore, croplands and ponds have higher topsoil C stocks than tidal flats, but little difference or even lose stored C compared to marshes. Cropland soils showed considerably higher levels of available N (NH4+-N and NO3−-N) and available P compared to those in natural marshes and tidal flats. The distribution of soil TC, TN, and TP demonstrated greater spatial heterogeneity in natural marshes and tidal flats, while the converted areas were more uniform and became hotspots for N and P accumulation. Coastal conversion altered soil C:N:P stoichiometry, with cropland soils exhibiting a lower N:P ratio (2.9 ± 1.1), indicating that long-term application of N and P fertilizers could decrease the N:P ratio, as P is more retained in the soil than N. Furthermore, it was observed that the dynamics of C, N and P, as well as their stoichiometry, are closely linked to soil physicochemical properties, especially soil organic matter and texture. These findings highlight that coastal conversion and associated management practices markedly affected soil C, N and P dynamics in a representative wetland area of the subtropical regions, leading to a reshaping of their stoichiometric balances, particularly in the topsoil layer.

Response of macrobenthic communities to a Spartina alterniflora management project on tidal flats in Hangzhou Bay, China

Spartina alterniflora is one of the most invasive plants on Chinese tidal flats. To explore the responses of macrobenthic communities to the removal of S. alterniflora and the restoration of tidal flats, a survey of macrobenthic and sediment environmental factors was carried out in June 2022 in the mudflat recovery area (MRA) of tidal flats on the south bank of Hangzhou Bay, China. A proximate natural mudflat area (NMA), S. alterniflora area (SAA) and Scirpus mariqueter area (SMA) were selected for comparison with the MRA. A total of 48 macrobenthic species were identified, with 13, 28, 22 and 21species in the MRA, NMA, SAA and SMA, respectively. Cluster, multidimensional scaling (MDS) and SIMPER analysis suggested that the similarity between macrobenthic communities in the MRA and the NMA was high, whereas the similarity between macrobenthic communities in the MRA and SAA and the MRA and SMA was very low. The similarity between macrobenthic communities in the SAA and the SMA was high. ANOSIM analysis suggested that the differences between regions were greater than those within regions (R = 0.881). The sediment factors in the MRA were substantially different from those in the other three habitats, while the sediment factors in the SMA and the SAA were the most similar. Macrobenthos were mainly affected by the mean diameter of the sediment particles. After 1 year of natural recovery in the MRA, the macrobenthos approached the pre-project levels, but to ensure the effectiveness of the treatment project and prevent the recurrence of S. alterniflora, continuous monitoring should be carried out.

Exploring the tidal response to bathymetry evolution and present-day sea level rise in a channel–shoal environment

Abstract. Intertidal flats and salt marshes in channel–shoal environments are at severe risk of drowning under sea level rise (SLR) ultimately ceasing their function of coastal defense. Earlier studies indicated that these environments can be resilient against moderate SLR as their mean height is believed to correlate with tidal amplitude and mean sea level. Recent morphological analyses in the German Wadden Sea on the northwestern European continental shelf contradicted this assumption as mean tidal flat accretion surpassed relative SLR, indicating that nonlinear feedback between SLR, coastal morphodynamics, and tidal dynamics played a role. We explored this relationship in the German Wadden Sea's channel–shoal environment by revisiting the sensitivity of tidal dynamics to observed SLR and coastal bathymetry evolution over one nodal cycle (1997 to 2015) with a numerical model. We found a proportional response of tidal high and low water to SLR when the bathymetry was kept constant. In contrast, coastal bathymetry evolution caused a spatially varying hydrodynamic reaction with both increases and decreases in patterns of tidal characteristics within a few kilometers. An explorative assessment of potential mechanisms suggested that energy dissipation declined near the coast, which we related to a decreasing tidal prism and declining tidal energy import. Our study stresses the fact that an accurate representation of coastal morphology in hindcasts, nowcasts, and ensembles for bathymetry evolution to assess the impact of SLR is needed when using numerical models.

Burrow Morphological Characteristics of Soldier Crab (Dotilla myctiroides) on the Libong Island, Koh Libong Subdistrict, Kantang District, Trang Province, Thailand

Dotilla myctiroides, the soldier crab, digs burrows in sand flats and extracts nutrients from sediment. The present study investigated the burrow morphology of this soldier crab, at Laem Juhoi Beach, Libong Island, Koh Libong Subdistrict, Kantang District, Trang Province, Thailand. Randomly selected burrows were examined by injecting molten paraffin into them. The crab found inside a burrow was collected and measured for its carapace length. The shapes of the complete burrow casts were identified, and various morphological characteristics of the burrow casts were recorded. A total of 84 burrows were identified, all of them were the I-shaped or single-tube burrows. The burrows were categorized into two groups based on the burrow opening diameter: the <12 mm group and the ≥12 mm group. The burrow opening diameter ranged from 7.50 to 20.10 mm while the end diameter at the burrow bottom ranged from 8.40 to 21.00 mm, and the total length of the burrows ranged from 27 to 206 mm. The carapace length showed a significant correlation (p<0.05) with the burrow opening diameter in both groups. Additionally, the burrow opening with a diameter <12 mm group had significantly greater hole distances than the burrow opening with a diameter ≥12 mm group (p<0.05). The observed variations in hole distances suggest potential differences in ecological and behavioral factors that influence the burrow morphology of D. myctiroides in distinct size categories.

Effect of air exposure time on erodibility of intertidal mud flats

This study investigates the influence of air exposure time on the erodibility of intertidal mud flats, emphasizing the role of evaporation in altering sediment strength and cohesion. Through a comprehensive approach combining laboratory experiments, fieldwork, and numerical modelling, it explores the dynamic interactions between sediment properties and environmental conditions. The research reveals that drying significantly reduces sediment erodibility, with pronounced effects observed during the initial hours of air exposure. Laboratory tests demonstrate a direct correlation between drying time and increased yield stress for both artificial and field-derived mud samples. Field observations further support these results, showing spatial and temporal variations in water content and shear strength across various locations on a tidal flat. The study emphasizes the critical impact of mud content on water retention and the subsequent effect on sediment stability. The incorporation of drying time into erosion formulations within a numerical model highlights the importance of considering evaporation processes in predicting the morphological evolution of tidal flats. This research contributes to a better understanding of sediment transport dynamics in intertidal zones, offering insights into the mechanisms driving the growth and stability of mud flats. It underscores the necessity of integrating evaporation effects into cohesive sediment transport models to enhance the accuracy of predictions concerning the erosion and accretion of intertidal environments.

Biomass distribution patterns of salt marshes: A detailed spatial analysis in central China's coastal wetlands

Wetland vegetation plays a critical role in the health of coastal ecosystems, serving pivotal roles in disaster mitigation and blue carbon sequestration. While extensive research on the effects of sea-level rise on the aboveground biomass of salt marsh vegetation, the spatial patterns of biomass distribution related to surface elevation remain less explored. This study investigates the growth patterns and spatial distribution of Spartina alterniflora in central coast of China through field surveys and the analysis of remote sensing data via Google Earth Engine. We have found a significant parabolic relationship between vegetation biomass and distance from the sea, with the optimal biomass influenced by the location of the marsh front edge. Further, we observe that biomass distribution varies with surface elevation and is influenced by geomorphological features notably creeks, which introduce significant elevation differences and local biomass fluctuations. These findings offer new insights into the spatial distribution of tidal flat vegetation, which are vital for effective coastal management and for modeling the evolution of tidal flats.

Recent environmental and morphosedimentary evolution of the mining-impacted Nalón Estuary (Asturias, N Spain): Disentangling natural and anthropogenic processes

Distinguishing between natural and anthropogenic processes in sedimentary records from estuaries with legacy pollutants is an essential task, as it provides baselines to predict future environmental trajectories of coastal areas. Here, we have addressed the recent transformation history of the mining-impacted Nalón Estuary (Asturias, N Spain). Surface and core sediment records from marshes and tidal flats were examined through a broad multidisciplinary approach, involving micropaleontological (benthic foraminifera), sedimentological (grain-size), geochemical (trace metals, major element Al and total organic carbon), physical (magnetic susceptibility, frequency-dependent magnetic susceptibility and large microplastics) and radioisotopic (210Pb, 137Cs and 239+240Pu) proxies. Results suggest that the interplay between natural (high fluvial influence and extreme hydrological events) and anthropogenic (coal and mercury mining disposals) factors induced strong sedimentation-erosion processes, further shaping the recent evolution of the estuary. Short-time scale and intense sedimentation processes were revealed by overall high sediment accumulation rates, the dilution of some geological signatures and the rapid formation of a marsh in the lower estuary bay. The increasing mining fingerprints during the 20th century were shortly interrupted by the catastrophic riverine flooding of 1938. Conversely, current erosional processes by fluvial influence led to the remobilization of contaminated sedimentary materials and exposure of mining-legacy Hg levels in tidal flats from the middle sector. Fluvial activity, floodings and taphonomic biases exerted a major control on benthic foraminifera since the 19th century, although Hg ecotoxicological effects on modern assemblages at certain areas within the estuary cannot be discarded. These findings, along with the documented enhanced erosion of marshes with ‘trapped’ pollutants (Hg, coal microparticles and microplastics), highlight the importance of monitoring the environmental and geomorphic processes taking place in historically-contaminated estuaries.

Tracking dynamics characteristics of tidal flats using landsat time series and Google Earth Engine cloud platform

Tidal flats serve as vital spatial resources within coastal wetlands and play crucial roles in biological habitat preservation, environmental conservation, and human development. However, accurately delineating their extent from instantaneous remote sensing images poses challenges, owing to the dynamic interplay between seawater and land. Therefore, this study utilized the consistency of remote sensing satellites and developed a multi-feature decision approach based on the long-term remote sensing datasets and the Google Earth Engine (GEE) cloud platform for determining the spatial extent, classifying types, and mapping the spatial-temporal distribution of the tidal flats. Initially, a multi-temporal image stack was compiled from the filtered remote sensing images. Subsequently, the modified normalized difference water index (MNDWI) and automated water extraction index (AWEI) were calculated to establish the maximum and minimum water surfaces using the extreme value composite algorithm (EVCA). The Otsu algorithm and spatial overlay analysis method were then utilized to accurately delineate the spatial extent of the tidal flats. Additionally, the Normalized Difference Vegetation Index (NDVI) was utilized to accurately identify tidal flat types. Post-processing involves elevation data and mathematical morphological methods to mitigate the impact of permanent water bodies. Finally, the accuracy of the extracted spatial extent and types of tidal flats was evaluated. The efficacy and practicality of the proposed method were validated using the Zhoushan Archipelago and Landsat time series in China. The results revealed the following: (1) the acquired tidal flat information exhibited evident boundaries and accurate types, achieving an overall accuracy (OA) of 94.80 % and a Kappa coefficient of 0.89; (2) the area of tidal flats in the Zhoushan Archipelago increased from 2,182.19 ha in 1985 to 3,761.21 ha in 2020, with an average annual increase of 45.12 ha and an average annual increase rate of 1.57 %; and (3) over 35 periods, the area transformed from other land types to tidal flats amounted to 2,895.74 ha, while the area converted from tidal flats to other land types totaled 1,651.90 ha. The three islands with the most rapid growth in tidal flat area were Liuheng Island, Dachangtu Island, and Daishan Island, with changes of 675.68 ha, 380.47 ha, and 362.63 ha, respectively. This method can offer an automated, swift, and accurate approach for tidal flat extraction, demonstrating high precision and practical effectiveness, thereby providing robust technical support for coastal resource surveys.

Natural disturbance allows multiple anuran taxa to persist in a dynamic wetland complex

AbstractThe maintenance of biological diversity is frequently enhanced in a heterogenous landscape by some level of disturbance. Thus, when a landscape becomes stabilized and homogenized through the spread of an invasive plant species, there may be consequences for native biodiversity, particularly for those biotas that depend on the pre‐existing, natural disturbance regime of that landscape. At Long Point, Ontario, Canada, a sandspit in Lake Erie, the community of anuran amphibians experienced the co‐incidence of 2 major disturbance events, 1 anthropogenic and 1 natural: an intervention to remove the invasive form of the common reed (Phragmites australis australis) and a spate of extensive dune washouts caused by high water levels and storms. As a result of the unequal distribution of disturbance in the landscape, different areas were affected by only the dune washouts, only the common reed treatment, both disturbances, or neither disturbance. From May to August 2021, we explored how the disturbances affected the resident frog and toad species habitat associations in the 4 different disturbance conditions in the landscape. By means of minnow traps, acoustic surveys, and visual surveys, we determined that the dune washouts had a greater influence on resident anurans than the common reed treatment. Ranid frogs (Ranidae) tended to inhabit non‐washout sites, whereas Fowler's toads (Anaxyrus fowleri) congregated in the newly formed, sand flats and shallow, de‐vegetated pools resulting from the washouts. Neither ranid frogs nor Fowler's toads demonstrated avoidance of the sites affected by the herbicide treatment and mechanical rollover of the common reed. This evidence of species sorting, which enables multiple species to persist in a dynamic and heterogeneous landscape, suggests that wildlife management in aid of threatened species recovery may find success by encouraging natural disturbance regimes in dynamic landscapes. Future management endeavors should consider refraining from complete dune stabilization in these landscapes to allow the natural washouts to occur at a higher frequency, while ensuring the continued effectiveness of the invasive common reed eradication.

Sediment dynamic on the tidal flat sheltered by artificial engineering: A case study on eddies

Tidal flats are important ecological and terrestrial resources. With the increasing development of coastal engineering projects, it is important to understand the dynamic response of tidal flats to human activities. Hence, the time series of wave, current, and suspended sediment during the spring tide from April 30, 2013 to May 1, 2013 were recorded by three tripod observation systems placed on the upper, middle, and lower parts of the tidal flats south of a constructed harbor in Wanggang, Jiangsu, China. The results showed that eddies formed south of the reclamations during flood tides. The directions of local tidal currents changed from their original southwest to the present northwest, and the ebb tides also changed but continued to flow northeast. The sediment transport process was basically consistent with the currents. The total net sediment fluxes during the tidal cycle (mean values of two tides) on the mudflat were two orders of magnitude larger than those on the salt marsh. Most of the sediments on both the mudflat and the salt marsh were transported northward alongshore, and a small portion of the sediments was transported seaward on the mudflat but shoreward on the salt marsh. The portion of the tidal flat with an elevation >1 m was wide in the north but narrow in the south, as determined by analysis of LiDAR elevation data, which coincided with the local sediment dynamics. The sediments were transported northward from southern deep waters during flood tides, which assisted in the expansion of the tidal flats in the north. This phenomenon reflected unique local sediment dynamics that were highly constrained by reclamations and Dafeng Harbor in the north as well as seawalls in the west. The tidal flat influenced by eddies can extend up to approximately 10 km south of the Dafeng Harbor. This case study has significant implications for the protection of tidal flats and the construction of coastal artificial engineering projects.

Eating Habits and Dietary Strategies of the Glass Perchlet Fish (Ambassis macracanthus) In Benoa Bay Waters, Bali in Two Different Seasons

The Benoa Bay area and its surroundings are a center of biodiversity at the ecosystem level in the southern coastal region of Bali. This area exhibits diverse ecosystems, including mangrove ecosystems, coral reefs, seagrass beds, and tidal flats. This research aims to analyze and describe the feeding ecology of Ambassis macracanthus in the waters of Benoa Bay. The study was conducted in May, at the end of the transitional season, and in July and August, during the eastern monsoon season in Benoa Bay Waters. Modified gill nets with mesh sizes of 0.5, 1.0, 1.5, 2.0, 2.5, and 3.0 cm were used for capturing the fish. The fish were caught at three stations, which represented the characteristic conditions of the Benoa Bay Waters. Out of the 396 individuals caught during the study, only 100 were selected for examination. The average relative fullness gut index (RGI) of Ambassis macracanthus ranged from 0.39 to 0.67. The total Important Relative Index (IRI) value for the food of Ambassis macracanthus in Benoa Bay Waters was 951.27. Ambassis macracanthus in Benoa Bay Waters is an omnivorous species with a tendency towards herbivory, and 21 different organisms were found in its diet, including three classes of phytoplankton and three classes of zooplankton. The feeding strategy developed by Ambassis macracanthus in Benoa Bay Waters is generalist. This information about the fish can be used as a fundamental basis for managing fish in the waters of Benoa Bay.

Sediment dynamics and geomorphology in coastal areas affect long-term abundance of waders

Millions of migrating and wintering waders depend on coastal areas and estuaries for feeding and to replenish body reserves. These habitats are dynamic, with changing intertidal flats and sediments due to natural and climate-driven processes. The aims of this study were to examine whether physical conditions of intertidal flats such as geomorphology and sediment compositions could explain abundance of wader species, and furthermore whether changes in these conditions over time influenced changes in abundance of waders. In addition to physical structures such as datum (level), slope and sediment composition of intertidal flats, dynamic variables connected to tidal cycles such as distance of the waterline from the coast and duration of water cover were included. Penetration of the sea floor was measured as a proxy for sediment composition. The study was conducted in the Danish section of the Wadden Sea during 1981–1986 and 2008–2009 with additional data from 2020. The focus was on 12 widespread wader species. PCA analysis revealed that wader species were distributed in relation to tidal cycles such as duration of water cover and the position of waterline and to the physical structures, datum, slope and penetration, in decreasing order. With regard to the physical structures, pairwise comparisons of distribution of waders species showed that mean datum (level) was significantly different for 51 pairs of species out of 66 comparisons, mean penetration values differed for 34 pairs, and mean slope differed for 26 pairs of wader species. Long-term changes of physical structures of transects revealed that changes of densities of 10 wader species were significantly correlated with changes per year in one or more of the physical structures: seven wader species were significantly correlated with changes per year of mean datum (level) of transects (Lapwing was positively correlated while Avocet, Golden Plover, Grey Plover, Dunlin, Bar-tailed Godwit and Redshank were negatively correlated), five species with mean slope (Oystercatcher, Ringed Plover and Knut were positively correlated and Grey Plover and Redshank were negatively correlated), and three species with mean penetration values (sediment composition) of transects (Avocet and Bar-tailed Godwit were positively correlated and Lapwing was negatively correlated). The study shows that long-term changes of physical structures of intertidal flats affected abundance of wader species. The results are important for interpretation effects of erosion and accretion of coastal areas as consequences of natural and climate driven processes such as sea level rise and coastal squeeze.

Soil Organic Nitrogen Mineralization and N2O Production Driven by Changes in Coastal Wetlands

AbstractPlant invasion and land reclamation have drastically transformed the landscape of coastal wetlands globally, but their resulting effects on soil organic nitrogen (SON) mineralization and nitrous oxide (N2O) production remain unclear. In this study, we examined 21 coastal wetlands across southern China that have undergone habitat transformation from native mudflats (MFs) to Spartina alterniflora marshes (SAs), and subsequently to earthen aquaculture ponds (APs). We determined the SON net mineralization rate and the presence of pertinent enzyme‐encoding genes, namely chiA, pepA, and pepN. The SON net mineralization rate increased by 46.7% following the conversion of MFs to SAs but decreased by 33.1% in response to the transformation of SAs to APs. Nevertheless, there was no significant difference in the estimated mineralization efficiency of soil microbes among the habitat types. The results of structural equation modeling showed that N‐mineralization gene abundance played a major role in regulating SON mineralization. Although less than 20% of the SON was estimated to be labile/semi‐labile, SON mineralization was important in sustaining soil N2O production, with 5.8% of the mineralized N being fed into N2O production. Overall, our findings showed that the presence of S. alterniflora increased both SON content and mineralization rate, which would in turn promote further proliferation of this exotic plant along the coast. The conversion of S. alterniflora marshes to APs partially mitigated the positive effects of exotic plant invasion on SON turnover.

Variable responses of mineral-bound soil organic carbon to land cover change in southern China’s coastal wetlands

The formation of mineral-bound organic carbon (OC) complexes is important for the long-term preservation of soil organic carbon (SOC) in wetlands. Many coastal wetlands globally have been threatened by plant invasion and land development, but information on the effects on mineral-bound OC is limited. We measured the soil contents of Ca-OC, Fe(Al)–OC and residual OC across 21 coastal wetlands in southern China that have gone through the same sequence of land cover change, from native mudflats (MFs) to Spartina alterniflora marshes (SAs) then to earthen aquaculture ponds (APs). Residual-OC was the main component of SOC (74.1–78.2 %), followed by Fe(Al)–OC (18.4–22.8 %) and Ca-OC (<3.5 %). All three components in the soil increased when MFs were converted to SAs, but decreased in subsequent conversion of SAs to APs. Land cover change affected Fe(Al)–OC the most, but SOC storage increased more strongly with increasing Ca-OC. Nitrogen supply in the form of NH4+-N and clay content both positively affected the changes in mineral-bound OC. Our results suggest that different land cover change scenarios had different effects on the amounts of mineral-bound OC and their liability to microbial turnover, resulting in different degrees of SOC preservation and carbon emissions.

Monitoring Land Use Changes in the Yellow River Delta Using Multi-Temporal Remote Sensing Data and Machine Learning from 2000 to 2020

The Yellow River Delta (YRD), known for its vast and diverse wetland ecosystem, is the largest estuarine delta in China. However, human activities and climate change have significantly degraded the wetland ecosystem in recent decades in the YRD. Therefore, an understanding of the land use modifications is essential for the efficient management and preservation of ecosystems in this region. This study utilized time series of remote sensing data and the extreme gradient boosting method to generate land use maps of the YRD from 2000 to 2020. Several methods, including transition matrix, land use dynamic degree, and standard deviation ellipse, were employed to explore the characteristics of land use transitions. The results underscore significant spatial variations in land use over the past two decades. The most rapid increase was observed in built-up area, followed by terrestrial water and tidal flats, while unutilized land experienced the fastest decrease, followed by forest–grassland. The spatial distribution patterns of agricultural land, built-up area, terrestrial water, and forest–grassland demonstrated stronger directionality compared to other land use types. The wetlands have expanded in size and improved in structure. Unutilized land has been converted into artificial wetlands comprising ponds, reservoirs, salt ponds, shrimp and crab ponds, and natural wetlands featuring mudflats and forest–grassland. The wetland conservation efforts after 2008 have proven very effective, playing a positive role in ecological and environmental preservation, as well as in regional sustainable development.

Burrow Opening Measurements of Intertidal Macroinvertebrates from Optical Drone Images

Intertidal macroinvertebrates, such as crabs and mud shrimps, are invertebrates inhabiting the intertidal zone that are sufficiently large to be identified with the naked eye. Most intertidal macroinvertebrates typically construct burrows of various shapes in sediment to protect themselves from environmental extremes, with surface openings that reflect features of their species and body size. Especially circular burrow openings correlate with an organism’s body size; thus, measuring these openings can provide estimates of the organism’s size, weight, growth rate, and biomass. Traditional studies of these organisms have relied on field surveys, which are constrained by time, cost, and logistical limitations. This study introduces an innovative method for measuring the burrow opening diameters of intertidal macroinvertebrates using high-resolution optical images from a portable drone system. By leveraging the reflectance disparity between the sediment and burrow openings, this method facilitates the extraction and sizing of burrow openings. Our methodology was applied to three crab species known for their circular burrow opening: the red-clawed fiddler, the milky fiddler, and the ghost crab. Validation was confirmed through field data from the Mageumri and Sinduri tidal flats, South Korea. The method achieved a correlation coefficient (R2) of 0.94 and a root mean squared error (RMSE) of 1.68 mm across a diameter range of 6.21–33.59 mm. These findings suggest the potential of drone remote sensing systems as a non-invasive and efficacious approach for quantifying burrow sizes over extensive intertidal areas, thereby facilitating more accurate biomass estimations and surmounting the limitations of conventional field surveys. Future research could extend this method to additional species and further refine its precision.

Future sediment transport to the Dutch Wadden Sea under severe sea level rise and tidal range change

Future sediment transport from the North Sea coasts to the Dutch Wadden Sea for various future sea level scenarios has been studied because it influences the future sand nourishment demand for the maintenance of the coastline and because it determines bio-geomorphological development of the Wadden Sea. The present study focuses on two questions which have not yet been considered in the previous modelling studies using ASMITA: How will the transport develop around drowning of the intertidal flats in the Wadden Sea? How will tidal range change influence the future sediment exchange? By using SLR scenarios with faster acceleration and running the simulations for longer periods of time some inlets exhibited drowning, i.e., where the tidal flat volume vanishes. When drowning occurs, the sediment import rate approaches a maximum or a minimum, depending on the initial morphological state of the tidal inlet system. This maximum or minimum rate for a certain tidal inlet system depends on the SLR scenario. Theoretical analysis as well as modelling results show that tidal range change will influence the sediment import to the Wadden Sea. A tidal range increase will cause a decrease of the sediment demand in the Wadden Sea resulting into less sediment import to the Wadden Sea. It is thus important to study the tidal range development in the Wadden Sea by considering the interaction between SLR, tidal range change and morphological development in the system. It is further concluded that the empirical relation used in the previous studies is not representative of conditions in a tidal basin with fixed basin area, even though this relation has been derived from field observations in many tidal inlet systems worldwide. The equilibrium channel volume should be proportional to the tidal prism instead of to its 1.5th power.