Coastal Tidal Flats Research Articles

Photovoltaic Power Station Impacts on the Benthic Ecosystem and Sediment Carbon Storage in Tidal Flats in China.

Photovoltaic power is a rapidly growing component of the renewable energy sector. Photovoltaic power stations (PVPSs) on coastal tidal flats offer benefits, but the lack of information on the effects of PVPSs on benthic ecosystems and sediment carbon storage can hamper the development of eco-friendly renewable energy. We sampled the macrobenthos and sediment cores at a PVPS on a coastal tidal flat in eastern China. The biodiversity indicators and benthic ecological quality based on macrobenthos were mostly higher under the photovoltaic panels than elsewhere. These variations were primarily driven by pH, sediment grain size, and chlorophyll-a content. However, the PVPS had exerted a considerable influence on the macrobenthic community structure. Furthermore, the carbon stocks in the sediment cores from under the photovoltaic panels were similar to those in the reference sites. These results suggest that this PVPS has not had discernible short-term adverse effects on the benthic ecosystems or sediment carbon storage of the tidal flat. Nevertheless, the potentially long-term and cascading risks throughout the ecosystem warrant caution. Therefore, we recommend that policymakers adopt a cautious development strategy and implement long-term, high-frequency monitoring to ensure the sustainability of renewable energy production on coastal tidal flats.

The impact of a storm on the microtidal flat in the Yellow River Delta

Strong hydrodynamic forces generated by storms are key in shaping coastal tidal flats. Most tidal flats achieve equilibrium by adapting to hydrodynamic conditions and sediment inputs. However, high-energy wave activity during storms disrupts this equilibrium, causing rapid and significant changes, particularly in tidal flats, especially in microtidal flats, which are characterized by low tidal ranges. In this study, we conducted an 11-d field campaign on a microtidal flat in the Yellow River Delta (YRD), capturing data during both stormy and calm weather conditions. We measured tidal currents, wave activity, suspended sediment concentrations and sediment grain sizes. The results demonstrated that the tidal flat maintained equilibrium under calm conditions, with minimal fluctuations in bed level (within ±2 mm). Contrastingly, severe erosion and sediment removal during the storm significantly altered the equilibrium of the area. The storm-induced high shear stresses, ranging from 1.02 to 1.48 , along with alongshore sediment transport, resulted in an elevation change of -10 mm. Furthermore, the subsequent bed level recovery was minimal and insufficient to offset the erosion. Compared to that of the mesotidal and macrotidal flats, post-storm recovery on microtidal flats was limited due to shorter inundation periods and weaker hydrodynamic forces. Therefore, frequent storms may lead to continuous shoreline retreat on microtidal coasts. Conclusively, the present findings underscore the significant impact of storm-induced erosion on the evolutionary processes of microtidal flats and suggest that greater attention should be given to protecting these areas during storms in the Yellow River Delta. The insights can guide the development of more effective coastal protection strategies, highlighting the need for enhanced measures to mitigate erosion and promote resilience in microtidal regions.

Quantitative provenance study of sediments in the coastal tidal flats of central Jiangsu based on grain-size End-Member analysis

The coastal mudflats in central Jiangsu Province are influenced by the sediment supply from the Yangtze River and the abandoned Yellow River. However, the sources of sediment in this area have yet to be confirmed, and quantitative studies have been limited. In this study, we addressed this gap by obtaining sediment core samples with lengths of approximately 100 cm from Dongtai and Sheyang, respectively, on the central coast of Jiangsu Province in 2018. The sediment sources were identified and quantitatively evaluated using a grain-size end-member(EM) model. The findings revealed that (1) Sheyang was decomposed into five EMs, with EMs 1-3 originating from the abandoned Yellow River, EM 4 originating from the Yangtze River and the North Jiangsu radial sand ridges (NJRSR), and EM 5 originating from the NJRSR. Over a century scale, the abandoned Yellow River contributed 73.91% to sediment deposition in Sheyang, while the Yangtze River and the NJRSR contributed 26.09%. (2) Dongtai was decomposed into six EMs, with EMs 1-4 originating from the abandoned Yellow River, EM 5 originating from the Yangtze River, and EM 6 originating from the Yangtze River and the NJRSR. Over a century scale, the abandoned Yellow River contributed 70.55% to sediment deposition in Dongtai, and the Yangtze River and the NJRSR contributed 29.45%. (3) On a temporal scale, the contribution of the abandoned Yellow River to sediment deposition on the central mudflats of Jiangsu Province showed an increasing trend. Spatially, the contribution of the abandoned Yellow River to sediment deposition decreased from north to south. (4) There were significant changes in the sediment sources of Sheyang and Dongtai at the depths of 56 cm and 60 cm, respectively, which both experiencing an increased sediment supply from the abandoned Yellow River. In Dongtai, the sediment on the southern side had increased contributions from the abandoned Yellow River due to a reduction in the sediment supply from the Yangtze River. In Sheyang, the sediment on the northern side had increased contributions from the abandoned Yellow River due to the introduction of Spartina alterniflora, despite no actual changes in the sediment sources.

Experiment and Application of A Aparker Source in Seismic Exploration in Coastal Tidal Flats

We investigate a field experiment in coastal tidal flats in Jiangsu Province using a sparker source, to test the seismic data acquisition system and detect the shallow layers in the real scenarios. We also compare the geophones with 60Hz and 10Hz natural frequency in shot gather as well as in stacked profiles. We process the different data separately, and then process them together in a wide-line mode. As predicted, the fold is doubled showing a higher signal to noise ratio. Through the routine multi-domain integrated noise removal and effective data processing, the signal-to-noise ratio and resolution of the seismic data get largely improved, and thus we successfully obtain the high-quality seismic profiles. The practical experiment results are of importance for shallow geological and environmental detections, as well as for geo-hazard prevention study in the related areas.

The heterogeneity of microbial diversity and its drivers in two types of sediments from tidal flats in Beibu Gulf, China

Mudflats and sandflats are two common types of coastal tidal flats, the structure and function differences of microbial communities between them are still underappreciated. Beibu Gulf is a diurnal tidal regime located in China, the differences between the two type of tidal flats could be more distinct. In this study, we collected a total of 6 samples from Beibu Gulf, consisting of 3 sandflats samples and 3 mudflats samples, classified based on clay and silt content. Generally, the mudflats samples exhibited higher levels of NH4+_N and TOC, but lower in ORP and pH. The microbial diversity of the two types of tidal flats was investigated, revealing great differences existed and sandflats had higher microbial richness and diversity than mudflats. Furthermore, we analyzed the association between microbial communities and environmental factors, finding NH4+_N to have the highest contribution to the total variation in microbial community structure, and microbial groups such as Desulfobacterota, Campilobacterota, Chloroflexota, Calditrichota, Spirochaetota, Zixibacteria, Latescibacterota and Sva0485 group in mudflats were positively associated with NH4+_N. The functions of microbial community were predicted using metagenomic sequences and metagenome assembled genome (MAG). Mudflats contained more genes for carbon fixation. Nitrate and nitrite reduction were widely existed in mudflats and sandflats, but nitrogen fixation was only existed in mudflats, and Campilobacterota, Desulfobacterota and Gammaproteobacteria MAGs were mainly responsible for it. Sandflats composed more genes for ammonium oxidation, but no MAG was found whether in sandflats or mudflats. Microbes in mudflats exhibited a greater abundance of genes related to sulfur cycling, especially in reduction process, unique MAGs in mudflats such as Calditrichota, Chloroflexota, Desulfobacterota and Zixibacteria MAGs are responsible for sulfate and sulfite reduction. Finally, we predicted functions of ammonium related microbes in mudflats based on MAGs and found Campilobacterota and Desulfobacterota MAGs were important for high accumulation of ammonium in mudflats. This study illuminated the structural and functional differences of microbial communities in mudflats and sandflats, providing new insights into the relationship of microbial communities and environment in the tidal flat.

Tidal flat microbial communities between the Huaihe estuary and Yangtze River estuary

Tidal flats have important ecological functions and offer great economic value. Using field sampling, numerical simulation, and high-throughput sequencing, the ecological state of typical tidal flats along the eastern coast of China was investigated. The findings demonstrated that the area may be separated into subregions with notable differences in the features of microbial communities due to the variations in water quality and total pollutant discharge of seagoing rivers. With a ratio of 62%, the development of the microbial community revealed that homogenous selection predominated. In general, the formation of microbial communities follows deterministic processes, especially those of environmental selection. The wetland microbial communities are impacted by pollutants discharged into the sea from the Huaihe River and the Yangtze River. The Yangtze River's nitrogen pollutants affected the wetland zone, and denitrification dominated. The study established ecological patterns between the river and the sea and we offer suggestions for managing watersheds and safeguarding the ecology of coastal tidal flats.

Distinctive sedimentary processes on two contrasting tidal flats of the Yellow River Delta

Coastal tidal flats provide valuable ecosystems, but are highly sensitive to tidal dynamics, sea-level rise, and human activities. Tidal inundation depth and frequency are known to affect tidal flat morphodynamics. However, the causes, processes and extent remain uncertain, particularly given the associated changes in sediment availability. In this study, we monitored the hydrodynamics, sediment transport, and morphological changes on two tidal flats in the northern and southern parts of the Yellow River Delta, with contrasting tidal regimes. The data showed that longer inundation periods under diurnal tides gained additional sediment and deposition than under semi-diurnal tides, because of the associated increase in water depth and sediment availability. The wave impact increased at the site with a semi-diurnal tidal regime owing to the lower water depth, where a larger bed shear stress led to tidal flat erosion. These results indicated that the combination of tidal regime and the occurrence of powerful waves played a joint role in controlling bed erosion, sediment availability, and short-term tidal flat evolution. This has implications for coping with delta erosion by enhancing local sediment availability in diurnal tidal regions and restoring vegetation to attenuate waves in semi-diurnal regions of the Yellow River Delta.

Distribution, sources and influencing factors of organic carbon in the surface sediments of the coastal tidal flats in Jiangsu Province

Coastal tidal flats are situated in the interaction zone between the ocean and land and are vulnerable to natural changes, human activities, and global changes; these areas serve as an important mixing zone and burial area for carbon and nitrogen storage. Coastal tidal flats contribute significantly to the global carbon cycle due to their high biological productivity, high sedimentation rate, and low decomposition rate. However, there is a lack of research on the sources and influencing factors of organic carbon in surface sediments in the coastal tidal flat area of Jiangsu Province. In this study, fourteen surface sediment samples were collected from the Jiangsu coastal tidal flats, and the distribution of organic carbon was analyzed. The sources and influencing factors of sediment organic carbon were also investigated by analyzing the contents, ratios and stable isotopes of carbon and nitrogen in the sediments. The results indicated that the total organic carbon (TOC) and total nitrogen (TN) contents in the surface sediments of Jiangsu coastal tidal flats ranged from 0.09% to 0.82% and from 0.01% to 0.1%, with mean values of 0.36% and 0.04%, respectively, and that there was a significant positive correlation between TOC and TN. Moreover, the high-value areas were located mostly along the borders or in sections covered in vegetation, whereas the mudflat areas without vegetation had lower values. Considering the status of the Jiangsu coastal zone, the abandoned Yellow River estuary, Yangtze River inlet, marine benthic microalgae, C3 plants and C4 plants were selected as end members of organic carbon concentrations. The contributions of different sources were quantified using a Bayesian mixture model (MixSIAR). Among them, the abandoned Yellow River estuary and Yangtze River inlet contributed 28.1% and 19.3%, respectively, followed by marine benthic microalgae with a contribution of 26%, whereas C3 and C4 plants made limited contributions of 9% and 8.8%, respectively. Additionally, the sediment particle size, hydrodynamics, and tidal flat vegetation such as Spartina alterniflora were the key factors influencing the organic carbon distribution. In general, this study contributes to a better understanding of the biogeochemical processes and sources of organic carbon in coastal tidal flats. It also provides a solid foundation for the creation of carbon sink measures in nearshore tidal flats.

Extraction, Antioxidant Activity and Identification of Flavonoids from Root Tubers of Kosteletzkya virginica

Kosteletzkya virginica (K. virginica) is used for revegetation of salt-affected coastal tidal flats and as a raw material of biodiesel. K. virginica root tuber, a biowaste with low economic value, is rich in bioactive compounds. This study aimed to extract and identify flavonoids from K. virginica root tubers. The optimal extraction conditions were 1/25 (w/v) solid/liquid ratio, 40% ethanol concentration at 40°C for 60 min. Under these conditions, 65.2 ± 3.7 mg/g total flavonoid content was extracted from the roots, which were collected from salinized soil in late autumn of the third year. Antioxidant activity was evaluated through 1,1-diphenyl-2-picrylhydrazyl, hydroxyl radical, and superoxide anion scavenging assays. The extracted flavonoids exhibited antioxidant activity in a dose-dependent manner. Five flavonoids, glucoliquiritin apioside, licoisoflavone B, 5-methoxy-7,8-diprenyl- flavone, 7,2′-dihydroxy-6,8-dimethyl-4′,5′-methylenedioxyflavan, and 5,7,4′-trihydroxy-3′-methoxy-6,8-di-Cmethylflavanone, were identified by ultra-performance liquid chromatography–tandem mass spectrometry. Our results suggest that the flavonoids of K. virginica root tubers might be potent antioxidants and can be effectively applied as an ingredient in food and natural medicine.

Numerical Investigation on Behavior of Compressive Piles in Coastal Tidal Flat with Fill

The control centers of wind power plants are usually located in coastal tidal flat areas. A thick fill should be placed at the original ground level to ensure that the design elevation of the control centers is maintained above the water table. However, the filling would cause a long-term ground settlement and further lead to the development of the negative skin friction (NSF) of the pile foundations for the control centers. The CPTU tests were conducted to calibrate the soil properties, of which the rationalities were verified by comparisons of the pile-bearing capacities between the full-scale axial compressive tests and β-method. The numerical analysis method was then established to investigate the influence of additional ground pressures on the pile axial bearing behavior over time and the influence of NSF caused by consolidation on pile-bearing capacity. Finally, a simple procedure was further employed to investigate the evolution of the long-term pile-bearing behavior.

Salinity drives shifts in soil microbial community composition and network complexity along vegetation community succession in coastal tidal flats

The changes in soil microbial characteristics following vegetation succession in coastal tidal flats are poorly understood. Understanding the soil microbial change pattern can help us better manage tidal flat ecosystems. With increasing distance from the seaside, succession occurs in bare tidal flat, Spartina alterniflora, Suaeda salsa, Imperata cylindrica, Phragmites communis, and Sesbania cannabina. Soil samples collected at distinct vegetation succession sites were measured in terms of the contents of total soluble salt (TS) and specific ions, pH, soil organic matter and bacterial and arbuscular mycorrhizal fungi (AMF) community composition. The salt ion contents (except for bicarbonate - HCO3−) decreased as vegetation succession occurred. Compared to the bare tidal flat site, the bacterial and AMF diversity and richness increased in vegetation-covered soil. The microbial network of the late succession stages (Imperata cylindrica, Phragmites communis and Sesbania cannabina) indicated a more complicated structure with more nodes and links and higher modularity than that of the early succession stages (bare tidal flat, Spartina alterniflora and Suaeda salsa). Redundancy analysis revealed that TS, Cl−, SO42−, HCO3− and Na+ significantly influenced the bacterial and AMF (including Mg2+) community structure. TS, SO42−, Ca2+ and Mg2+ exhibited a strong negative relationship with the bacterial Shannon diversity (conducted at the operational taxonomic unit level), and the correlation coefficient ranged from −0.93 to −0.97; soil organic matter indicated a significant negative correlation with the AMF diversity, at a correlation coefficient of −0.92. The correlation between the microbial species and salt ions exhibited complexity and ion specificity. It was concluded that salinity is the key factor driving shifts in soil microbial community composition and network complexity during coastal vegetation succession considering ion-specific effects.

Tidal flat aquaculture pollution governs sedimentary antibiotic resistance gene profiles but not bacterial community based on metagenomic data

Coastal tidal flats are intersection zones between terrestrial and marine environments and are considered repositories of pollutants from anthropogenic activities (e.g., fishery and aquaculture). Specifically, the prevalence of antibiotics and antibiotic resistance genes (ARGs) in coastal aquaculture environments pose critical threats to estuarine ecosystems. However, the contribution of aquaculture to the occurrence and abundance of ARGs and community assemblies has not been fully explored in tidal flat zones. Thus, we investigated ARGs profiles, ARG-carrying host bacteria, and their associate microbial community in the Dongtai and Sheyang tidal flat aquaculture regions of Jiangsu, China using metagenomic assembly methods. The antibiotic concentrations in the sediment samples ranged from nd to 35.50 ng/g dw, and the antibiotic pollution in the Dongtai tidal flat was more severe than in the Sheyang tidal flats. Metagenomic assembly indicated that a total of 247 ARG subtypes associated with ARG 33 types were characterized across all samples and their abundance in the Dongtai region exceeded that in the Sheyang region. Meanwhile, 21 bacteria in the tidal flat aquaculture were identified as ARG-carrying pathogens, including Escherichia coli, Vibrio fluvialis, and Staphylococcus aureus. Using neutral and null modeling analysis to determine the community ecological processes, the results revealed bacterial and ARG communities were generally dominated by stochastic and deterministic processes, respectively. The above results suggested that aquaculture pollution was contributed to shape ARG profiles in tidal flats. The observed deterministic processes affecting the ARG community in tidal flat aquaculture also provides an effective foundation to control the risks of environmental antibiotic resistance through reducing aquaculture antibiotic usage.

Plant Adaptability and Vegetation Differentiation in the Coastal Beaches of Yellow-Bohai Sea in China.

To identify the key soil factors influencing the vegetation differentiation in the coastal tidal flats of the Yellow−Bohai Sea in China, this study investigated the corresponding relationship between the Spartina alterniflora (SA), Suaeda salsa (SS), and Phragmites australis (PA) communities and their respective soil factors with published data, and combined the ecological strategy for analysis. The results showed a corresponding relationship between community and soil factors. The SA community had a lower bulk density (BD) and higher soil total nitrogen (TN), and the SS community was the opposite, while the PA community had the lowest salinity and higher TN. BD, salinity and TN acted as the main soil factors driving vegetation differentiation, but the explained proportion of the three factors to vegetation differentiation changed by season and region. Considering that higher TN facilitates the competitors, salinity represents the environmental stresses, and BD is positively related to the frequency of perturbation in the specific habitat in the study area, SA, SS and PA could be recognized as C–S, S–R and C strategic species to some extent. It is likely that some coexistent mechanisms for invasive and local species will be developed, especially the SS community which seriously shrunk recently but served as an important habitat for waterfowls in tidal flat habitats.

Distribution, sources, and ecological risk assessment of polycyclic aromatic hydrocarbons (PAHs) in the tidal creek water of coastal tidal flats in the Yellow River Delta, China

The concentrations, distribution, sources and ecological risk levels of polycyclic aromatic hydrocarbons (PAHs) in tidal creek water from coastal tidal flats of the Yellow River Delta were investigated. The concentrations of 16 PAHs ranged from 0.113 to 1.533, with a mean value of 0.496 ± 0.035 μg L−1, which indicated a moderate level of pollution. The main long-term sources of PAHs in the coastal tidal flats of the Yellow River Delta were petroleum combustion and petroleum pollution. The ecological risk assessment showed that the levels of PAHs in tidal creek water of the coastal tidal flats in the Yellow River Delta corresponded to medium to high ecological risk levels, and a high probability of potential ecological risk, posing harm to aquatic organisms. Among the 7 sampling sites, site 5, site 6, and site 7 were at high ecological risk, and the other sites were at moderate ecological risk. PAH pollution in the tidal creek water near the Yellow River Estuary and farther south, in the coastal tidal wetland of Laizhou Bay, deserves special attention, especially with respect to the prevention and control of benzo[a]pyrene (BaP) pollution in the water.

Spatio-Temporal Changes and Driving Force Analysis of Wetlands in Jiaozhou Bay

Tian, Y.; Li, J.; Wang, S.; Ai, B.; Cai, H., and Wen, Z., 2022. Spatio-temporal changes and driving force analysis of wetlands in Jiaozhou Bay. Journal of Coastal Research, 38(2), 328–344. Coconut Creek (Florida), ISSN 0749-0208. Jiaozhou Bay is the largest bay-type coastal wetland with high biodiversity in Shandong Peninsula. In recent years, the wetland of Jiaozhou Bay has been reduced dramatically due to urban expansion. It is significant to study the characteristics and causes of the wetland changes in the past 40 years for the rational exploitation and sustainable development of coastal wetland resources. The types, spatial distribution, and area information of the wetland from 1983 to 2019 are obtained by artificial visual interpretation and supervised classification using ten Landsat remote sensing images, assisted by Google images. The research analyzes the conversion of land use types and the change rule of landscape pattern in the wetland, as well as the driving forces of the wetland evolution and the uncertainty factors affecting the analysis results. The results indicate that the wetland area shows an overall decreasing trend from 1983 to 2019, 77% of which are converted into nonwetland. The wetland area increases initially, followed by a decrease from 1990 to 2000, but then continues to decrease slowly from 2000 to 2019. There are many types of land use changes from coastal tidal flats to other land use types such as construction land or pond, and the landscape pattern has been gradually fragmented. The continuous increase in temperature is the main natural cause for the degradation of the wetland. Population factor is the most important driving force for the change of the wetland. The main uncertain factors affecting the analysis results are the capture time of remote sensing image, tidal level correction, wetland classification system, and method. The results provide a basis for the decision-making of wetland protection. The quantitative data will provide a reference for the construction of a multiyear wetland dataset in Jiaozhou Bay.

Spatial Distributions of Nitrogen and Phosphorus in Surface Sediments in Intertidal Flats of the Yellow River Delta, China

The spatial distributions of nitrogen (N) and phosphorus (P) in surface sediments are of great significance in studying the ecological process of nutrient cycling in intertidal flats. However, little is known about N and P’s spatial distribution in intertidal flats of the Yellow River Delta (YRD). We analyzed the N and P contents in surface sediments and Suaeda glauca density at the low-tidal level to identify the spatial distributions of nutrients and their influencing factors in coastal tidal flat sediments. The results showed that the total nitrogen (TN) and total phosphorus (TP) concentrations in this study were both lower than the background values of China’s shallow sea sediments. The spatial distributions of N and P had significantly spatial heterogeneity, while those of the nutrients at different distances from the low-tidal level to the coastline showed no significant distance effects. The spatial distribution of S. glauca in coastal tidal flats had significant location characteristics and was closely related to the distribution of TN and pH. The TN in non-estuarine intertidal flats was less than that in estuaries; in contrast, the TP was higher in non-estuaries. There are some differences of N and P between estuary and non-estuary areas.

Correlation Between Microplastics Pollution and Eutrophication in the Near Shore Waters of Dianchi Lake

Microplastics have been found in many environmental media such as sea water, coastal tidal flats, terrestrial water, sediments, and organisms. Microplastics pollution in inland freshwater lakes have received extensive attention; however, the correlation between eutrophication and microplastics pollution in freshwater lakes remains unclear. In this study, 24 sampling sites were set up in the near shore surface waters of Dianchi Lake, and the pollution characteristics of microplastics such as abundance, composition, particle size, color, and form were evaluated. Water quality parameters related to eutrophication state were analyzed, and the eutrophication indices were further calculated. Specifically, sample pre-treatment was conducted according to the method issued by National Oceanic and Atmospheric Administration (NOAA) of the United States. The color and morphological characteristics of microplastic samples were observed using a stereoscopic microscope, and counts and particle size measurements were performed using Nano Measure 1.2 software. Parts of the samples were selected, and the polymer composition analysis was performed using micro-Fourier Transform infrared (μ-FTIR) spectroscopy. The indices related to eutrophication level evaluation were tested according to the experimental standard methods issued by the Ministry of Ecology and Environment of China. The results showed that the abundance of microplastics in the near shore waters of Dianchi Lake was between 800 and 6000 n·m-3, with an average value of 2867 n·m-3. The types of polymers detected were polyethylene terephthalate (PET), polyetherurethane (PEU), polypropylene (PP), polyethylene (PE), and polyvinyl acetate (PVAc), respectively. The diameter proportion of microplastics in the range of 0.2-0.5 mm was the highest. Fiber microplastics accounted for the most observed type, followed by fragments and films. Among the 24 monitoring sites, it was found that proportions of severe, moderate, and mild eutrophication and mesotrophication sites accounted for 8.33%, 58.33%, 29.17%, and 4.17% of the total sampling sites, respectively, and the main pollutant was total nitrogen (TN). Microplastics abundances in the near shore waters of Dianchi Lake were significantly positively correlated with TN concentrations (P<0.01), whereas they were negatively correlated with chlorophyll a(Chl-a)concentrations, not reaching a significant level (P>0.05). The microplastics abundance and TN concentrations in the north bank water near the main urban area of Kunming were significantly higher than those in the other three banks. Microplastics and TN were considered to potentially have the same origin and be attributed to the tail water discharge from WWTPs.

Tidal Flat Extraction and Change Analysis Based on the RF-W Model: A Case Study of Jiaozhou Bay, East China

Coastal tidal flats are important ecological resources. As the dividing line between marine and terrestrial ecosystems, tidal flats provide a large number of ecosystem services. However, with the excessive development of coastal areas, tidal flat resources have been drastically reduced, leading to the deterioration of coastal ecosystems. There is an urgent need to acquire accurate information on the changes in tidal flat resources. This research proposes a tidal flat extraction model (RF-W model) that combines the random forest (RF) method and waterline method, which aims to improve the accuracy of tidal flat extraction. This method can effectively eliminate the shortcomings of the RF method in determining the lower boundary of tidal flats and those of the waterline method in distinguishing river channels and tidal flats. The tidal flat extraction of Qingdao Jiaozhou Bay in 2020 is performed as an example of the model. The results show that the user’s and producer’s accuracies of the RF-W model were both the highest, indicating that the improved model can accurately extract tidal flat information. Then, we used the RF-W model to extract tidal flat information for Jiaozhou Bay in seven periods (1990, 1995, 2000, 2005, 2010, 2015, and 2020) and to study the spatiotemporal changes in the tidal flats and influencing factors from 1990 to 2020. The tidal flat area of Jiaozhou Bay showed an overall downward trend before 2015, and the area decreased by 21.9 km2, with a reduction in the rate of approximately 1.1%/year. After 2015, the tidal flat area rebounded slightly. The overall change in Jiaozhou Bay showed reclamation and expansion toward the sea. The reduction in the sand content of the rivers entering the sea, reclamation and cultivation, and land development were the main factors contributing to the reduction in the tidal flat area in Jiaozhou Bay. In addition, sea level rise due to climate warming is a long-term potential factor.

In- situ and ex- situ purification effect of ecological ponds of Euryale ferox Salisb on shrimp aquaculture

This study was conducted to explore the in- situ and ex- situ purification effect of ecological ponds of Euryale ferox Salisb on shrimp aquaculture in tidal flat ponds. Nine 0.60 ha tidal flat ponds were divided into three groups randomly: (1) shrimp monoculture group, SM; (2) shrimp + E. ferox group, SE; (3) shrimp + E. ferox + tailwater group, SET. Results showed that most main water quality parameters in aquaponics groups (SE and SET) were significantly lower than those in SM group at 60, 90, and 120 days of the experiment. Total nitrogen, total phosphorus, nitrite, ammonia nitrogen, and chemical oxygen demand in SET group reduced to the same levels as those in SE group at 95 + 3 days. The concentration of nitrate in SET group reached the same levels as that in SE group until 95 + 7 days. The SET group also saved source water of 2666.6 m3 by using tailwater of shrimp aquaculture. The phytoplankton abundance and biomass in aquaponics groups (SE and SET) were significantly lower than those in SM group. The shrimp production and survival rates in the aquaponics groups (SE and SET) were significantly higher than those in SM group (P < 0.05). The profits of aquaponics groups were approximately 1.45–1.50 times higher than that of the SM group (14,290.0 USD·ha−1). The ecological and economic effects of different shrimp and E. ferox combinations revealed that the aquaponics model, especially the shrimp + E. ferox + tailwater system, is a water saving and sustainable development model that fits well with the conditions of shrimp ponds in coastal tidal flats.

Sediment Characteristics and Intertidal Beach Slopes along the Jiangsu Coast, China

Tidal flats play an important role in promoting coastal biodiversity, defense against flooding, land reclamation and recreation. Many coastal tidal flats, especially the tide-dominant ones, are muddy. However, the number of studies on the profile shape and surficial sediment distribution of muddy tidal flats is small compared to sandy beaches. Based on high spatial-resolution measurements along the tide-dominant Jiangsu Coast, China, we analyzed the morphology and sediment characteristics of the unvegetated intertidal flats along the Jiangsu Coast. The Jiangsu Coast can be divided into an eroding northern part (north coast) and an accreting southern part (south coast). The beach slope of the north coast shows a southward flattening trend, apart from some outliers related to rocky parts of the coastline. We found alternating very fine and coarse sediment (depending on the local clay content) for different locations along the north coast, which can be explained from consolidation and armoring-induced erosion resistance. In the south coast, we found gradual coarsening of bed surface sediment and gradual flattening of beach slopes to the south. This seemingly unexpected pattern is explained by the flood-dominant current causing landward sediment transport, larger tidal range in the south part, sheltering effect of the Radial Sand Ridges, and contribution of different sediment sources, viz. the Abandoned Yellow River Delta and the Radial Sand Ridges. In the cross-shore direction, the sediment grain size decreases landward. Waves are only of secondary importance for the sediment dynamics at the unvegetated tidal flats along the Jiangsu Coast.