Nearshore Areas Research Articles

Influence of Geological Structure on Micro-location of Submarine Karstic Sulphur Springs near Izola (SW Slovenia)

In the Slovenian part of the Gulf of Trieste/Trst, submarine springs occur as funnel-shaped depressions in the Holocene sandy-silt marine sediment that forms the seafloor. These springs exhibit both elevated temperatures (up to 29.6 °C) and sulphur content. Based on their location, they are divided into three groups: the Izola group (three springs), the Bele skale group (two springs), and the Ronek group (seven springs). Previous investigations linked these springs to the Izola anticline, characterized by its limestone core and flysch limbs, but no detailed explanation was provided. We propose that: A) sulphur groundwater springs from the limestone (karstic aquifer) at the stratigraphic boundary with the flysch and B) springs occur in the nearshore area, where the sedimentary cover of Quaternary deposits is thin enough to be penetrated by spring waters and washed out. According to existing data, the anticline axis is NW-SE directed, and the Izola group lies approximately on the seaward extension of the axis. Therefore, this interpretation fits perfectly for the Izola group, while the Ronek and Bele skale groups are off-axis extensions and require reinterpretation. In order to resolve the micro-locations of the Ronek and Bele skale groups, we conducted a sedimentological logging of the flysch deposits and detailed geological mapping. The investigations revealed that: A) limestone outcrops occur only in the town of Izola, B) two prominent calciturbidite megabeds that occur in the flysch enable very detailed geological mapping, and C) the axis of the Izola anticline is oriented in the WNW-ESE direction, and this moderate anti-clockwise rotation of the anticline axis explains the micro locations of all springs. The Ronek and Bele skale groups are located on the southern side, and the Izola group is on the northern side of the limestone core of the Izola anticline.

Fully automatic training sample collection for detecting multi-decadal inland/seaward urban sprawl

Accurate and timely monitoring of urban sprawl using remote sensing provides valuable insights for urban management and sustainable development. While existing studies have explored methods for large-scale monitoring of urban sprawl, most of them rely on the collection of manually labeled training samples for supervised classification. Additionally, previous studies generally focused on inland urban sprawl, neglecting the process of urban sprawl towards sea areas, known as seaward urban sprawl, which has profound ecological implications for coastal ecosystems. Here we develop a fully automatic algorithm for detecting urban sprawl, named Fully Automatic Detection of Urban Sprawl (FADUS), using the time-series Landsat imagery without manually collecting training samples or existing urban maps for reference. FADUS automatically generates initial samples through a sequential binary unsupervised clustering technique and then updates them by removing the spectral outliers to obtain a high-quality training set for subsequent supervised classification. A tidal module is included in FADUS to avoid pseudo-urban changes caused by tidal fluctuations so that both inland and seaward urban sprawl can be detected. By applying the algorithm to 75 coastal cities in China, the most rapidly urbanizing region in the world, we uncovered a neglected but dramatic seaward urban sprawl process that has converted sea areas to urban space since 1985. Our results indicate that 9904.36 km2 of coastal wetlands and nearshore seawater areas have been converted to land area, of which 44.83% is currently covered by built-up area. With our method, the fully automatic detection of urban dynamics is now possible for both coastal and inland cities worldwide. Our derived map of seaward urban sprawl in China provides valuable references for coastal land-cover change monitoring, wetland protection and restoration, and integrated coastal management.

Tsunami wave characteristics in Sendai Bay, Japan, following the 2016 Mw 6.9 Fukushima earthquake

On 21 November 2016, a Mw 6.9 intraplate earthquake occurred off the Fukushima coast in Japan, triggering a moderate-size tsunami with amplifications and long oscillations along the Sendai Bay coast. Here, we apply a hybrid approach to hindcast the wave characteristics in the Sendai Bay during the 2016 tsunami event, by analyzing coastal tide records, spectral analyses, and tsunami simulations. Our analysis shows that tsunami wave on tide stations mainly carried wave periods of 3.8–22.5 min, triggered by source periods of 18.5–22.5 min. The long oscillation in Sendai Bay was due to longer period of >28.8 min, affected by the presence of edge waves and oscillation of Sendai Bay. High-energy wave was found to be significant in most oscillation periods inside the Sendai Bay and around the Oshika Peninsula. The spatial distribution of maximum spectral and simulated tsunami amplitudes also reveal that the radiated tsunami energy was entrapped in the nearshore areas, resulting in resonance amplifications in the Sendai Bay.

Effects of control strategies on the performance of floating WEC point absorbers operating attached to a breakwater by time-domain simulator

The estimation of the performance of Wave Energy Converter (WEC) arrays of the type of simple floaters operating in nearshore and coastal areas, characterized by variable bottom topography, is important for the estimation of the wave power absorption and determination of the operational characteristics of the system and could significantly contribute to the efficient design and layout of WEC farms. For this purpose, full 3D models based on Boundary Element Method have been developed, supporting the systematic use for optimization studies. Apart from WEC arrays in nearshore and coastal regions a promising possibility is the installation at the exposed side of port breakwaters with significant energy potential. In this work, the analysis of the above system is extended to the prediction of WEC performance in multichromatic incident waves under latching control strategy using a time-domain simulator, showing improvement of performance in particular conditions.

EFFECTS OF WAVE SKEWNESS AND ASYMMETRY ON THE EVOLUTION OF FIRE ISLAND, NEW YORK

Bedload transport of sediment by waves and currents is one of the key physical processes that affect the evolution of coasts, nearshore areas, and the engineering practices there. Wave skewness and asymmetry, both of which increase as waves shoal, result in a net bedload sediment flux over a wave cycle. The impacts of this mechanism on large-scale coastal and shoreline change are investigated in this study, using field observations and Coupled Ocean Atmosphere Wave Sediment Transport (COAWST), a hydrodynamic process-based numerical modeling system (Warner et al., 2010). The study site is Fire Island, New York, located at the Atlantic Coast of the USA, with a focus on the persistent shoreline shape, at the western half of this 50-km-long barrier island, that has been hypothesized to be linked to the sand deposits at the shoreface.

Wave power extraction from slanted oscillating water columns in the presence of an array of arbitrary trenches

This paper investigates the impact of arbitrary bottom topography on the efficiency of a slanted oscillating water column device located in near-shore areas. The device incorporates a turbine positioned at its opening, which harnesses the oscillation of the fluid at the free surface, created by recurrent incident waves, to propel an air volume in a uni-direction. To analyze the wave power absorption capability of the system, an eigenfunction expansion and a boundary element model based on linear water wave theory are employed. The notion is to use the anticipated amplification of scattered and reflected wave fields resulting from the existence of a sloping wall to improve the wave power absorption caused by the walls' wave reflections. The accuracy of the current study's numerical results is ratified by conducting a comparative study using the available data given by other researchers. The study demonstrates that multiple efficiencies occur in the case of the long-wave region as compared to the short-wave region. Additionally, both the shape and magnitude of the efficiency curves are influenced by the slanted design of the device's front wall and the number of trenches.

SHYTCWAVES: A STOP-MOTION HYBRID TC-INDUCED WAVES METAMODEL

Waves produced by tropical cyclones (TCs) can be estimated using numerical models and non-stationary simulations forced with vortex-type time-varying wind fields. However, dynamical simulations are time and computationally demanding at regional-scale domains since high temporal resolutions are required to correctly simulate wave propagation. Early warning systems, as well as risk induced assessments, would benefit from fast and accurate estimates of the wave climate induced by close-to-real tracks geometry. For this reason, the objective of the proposed methodology is to obtain a tool capable of estimating the spatial and temporal variability of directional wave spectra produced by TCs at regional scale in deep waters using a hybrid approach, and statistical techniques, to reduce CPU time effort. SHyTCWaves is a metamodel that provides estimates of the directional wave spectra produced by TCs, which can be used as boundary conditions for local-scale models at nearshore coastal areas, in addition to providing faster than dynamically simulated TC forecast predictions.

MONTE CARLO SIMULATION OF BARRIER-ISLAND SYSTEMS AND TSUNAMI HAZARDS

Robust characterization of the future tsunami hazard is critically important for resilient planning and engineering in coastal communities prone to tsunami inundation. The hazard from earthquake-generated tsunami waves is not only determined by the earthquake's characteristics and distance to the earthquake area, but also by the geomorphology of the nearshore and onshore areas, which can change over time. In coastal hazard assessments, a changing coastal environment is commonly taken into account by increasing the sea-level to projected values (static). However, sea-level changes and other climate-change impacts influence the entire coastal system causing morphological change (dynamic). Here, we present the modeling framework and results initially published in Weiss et al. (2022), which employs within a Monte Carlo framework the barrier island-marsh, lagoon- marsh evolution model of Lorenzo-Trueba and Mariotti (2017) and the tsunami model Geoclaw (e.g., LeVeque et al. 2011). We compare the runup of the same suite of earthquake-generated tsunamis to a barrier system for statically adjusted and dynamically adjusted sea level and bathymetry over the period from 2000 to 2100. We employ Representative Concentration Pathways 2.6 and 8.5 without and with treatment of Antarctic ice-sheet processes (e.g., Kopp et al. 2017) as different sea-level projections.

Assessing coastal outfall impact on shallow enclosed bays water quality: Field and statistical analysis

Shallow bays, valued for their environmental, economic, and social significance, face increasing threats from anthropogenic stressors, primarily wastewater discharge through coastal outfalls. The slow tidal currents in these bays hinder the effective dispersion of pollutants to deeper waters, exacerbating their impact. This study assesses the spatial effects of wastewater and brine discharges on Sulaibikhat Bay's water quality. The approach combines fieldwork, laboratory analysis, and statistical techniques to identify pollutant types, sources, and concentrations near outfalls, nearshore, and offshore areas. Throughout the study, high water temperatures were observed consistently, exceeding 30 °C in summer and 18.6 °C in winter near most outfalls, with a maximum deviation from the ambient water of 11.1 °C recorded in December. In addition to elevated electrical conductivity (EC) levels peaking at 60,700 μs/cm, these elevated temperatures significantly reduce dissolved oxygen levels and have been linked to fish kill events in the Bay. NH3-N, TSS, COD, BOD5, FC, and FS concentrations exceeded allowable limits in 56.4 %, 92.25 %, 40.30 %, 32.1 %, 70 %, and 63.36 % of samples, respectively, often reaching extreme levels. Also, the BOD5/COD ratios suggest the presence of non-biodegradable organic matter, mainly from industrial sewage, and the FC/FS levels implicate human and animal waste. These results indicate a mix of domestic, industrial, and commercial wastewater discharges and underscore the severe threat coastal outfalls pose to ecosystem health and water quality in Sulaibikhat Bay. Principal Component Analysis (PCA) and Cluster Analysis (CA) delineate two distinct environmental zones with varying characteristics and contamination levels, necessitating expanded monitoring. Finally, substantial field research, numerical modeling, and establishing a sustainable environmental management system are needed to protect this fragile ecosystem. Also, converting outfalls into offshore may mitigate the environmental status of the bay by enhancing pollutant dilution and dispersion.

EFFICIENTLY FORECASTING 2-DIMENSIONAL SPECTRA INSIDE SHELTERED PORTS USING SPECTRAL AND PHASE-RESOLVING WAVE MODELS

Ports today are grappling with the impacts of increasing ship sizes and increasingly frequent and more extreme weather events. Under these conditions, being able to predict navigation, handling, and mooring risks accurately, is becoming more crucial to safe and efficient port operations. This is especially important in ports subject to complex wave transformations. Traditionally, in order to capture the various wave transformation processes accurately from offshore to nearshore areas, the coupling of a Spectral wave (SW) and Boussinesq wave (BW) model has been required. Unfortunately, the very high computational costs of BW modelling have inhibited running such models in forecast mode. In response to this highly technical challenge, DHI have developed a transformative method for concatenating outputs from SW and BW models, enabling modelers to forecast 2D Spectra accurately, both inside and outside a sheltered port basin in a computationally efficient manner.

Bull Shark (Carcharhinus leucas) Occurrence along Beaches of South-Eastern Australia: Understanding Where, When and Why.

Unprovoked shark bites have increased over the last three decades, yet they are still relatively rare. Bull sharks are globally distributed throughout rivers, estuaries, nearshore areas and continental shelf waters, and are capable of making long distance movements between tropical and temperate regions. As this species is implicated in shark bites throughout their range, knowledge of the environmental drivers of bull shark movements are important for better predicting the likelihood of their occurrence at ocean beaches and potentially assist in reducing shark bites. Using the largest dataset of acoustically tagged bull sharks in the world, we examined the spatial ecology of 233 juvenile and large (including sub-adult and adult) bull sharks acoustically tagged and monitored over a 5.5-year period (2017-2023) using an array of real-time acoustic listening stations off 21 beaches along the coast of New South Wales, Australia. Bull sharks were detected more in coastal areas of northern NSW (<32° S) but they travelled southwards during the austral summer and autumn. Juveniles were not detected on shark listening stations until they reached 157 cm and stayed north of 31.98° S (Old Bar). Intra-specific diel patterns of occurrence were observed, with juveniles exhibiting higher nearshore presence between 20:00 and 03:00, whilst the presence of large sharks was greatest from midday through to 04:00. The results of generalised additive models revealed that large sharks were more often found when water temperatures were higher than 20 °C, after >45 mm of rain and when swell heights were between 1.8 and 2.8 m. Understanding the influence that environmental variables have on the occurrence of bull sharks in the coastal areas of NSW will facilitate better education and could drive shark smart behaviour amongst coastal water users.

Testing the applicability of marine biotic indices for ecological quality in the northern East China Sea

The northern East China Sea is currently subjected to anthropogenic disturbances during the past few decades. Using data collected in July 2019 and July 2020, the AZTI's Marine Biotic Index (AMBI), multivariate-AMBI (M-AMBI), Shannon–Wiener diversity index (H′), and BENTIX index were adopted to assess their applicability and evaluate the benthic ecological quality of the northern East China Sea. The results of the Pearson correlation between biotic indices and eutrophication environmental factors showed that H′ and M-AMBI were suitable biotic indices for evaluating the benthic ecological quality in the northern East China Sea rather than AMBI and BENTIX. The overall benthic ecological quality in the northern East China Sea was moderate to good during 2019–2020. Ecological quality showed a positive correlation with distance to mainland. However, a slow declining trend was detected for the benthic ecological quality of the northern East China Sea, especially the nearshore areas.

Importance of nanophytoplankton biomass during summer 2019 in a retreating marine-terminating glacier-fjord system, Marian Cove, West Antarctica (62°S)

The biogeochemical dynamics of fjords around Antarctica are strongly influenced by cryospheric, climatic, and oceanographic processes that occur on a seasonal scale. Furthermore, as global climate change continues, there is a growing awareness of the impact of ocean warming on glacier melting, which is expected to affect the composition of phytoplankton community structure in West Antarctica’s nearshore marine areas. In this study, we describe the role of hydrographic forcing on the short-term summer variability of the phytoplankton community in Marian Cove, an Antarctic glacial fjord (62°S). Phytoplankton and hydrographic variables were measured at five stations along the Marian Cove during summer 2019 (January–February). The highest concentrations of microphytoplankton biomass were found in the outer area of the fjord, whereas nanophytoplankton biomass displayed continued dominance during most of the summer period in Marian Cove. Hydrographic assessment showed that freshwater inputs from the glacier influenced the surface layer of the fjord, modulating phytoplankton biomass, which was dominated by nanodiatoms (Minidiscus sp., Thalassiosira spp.) and nanophytoflagellates (Cryptomonas spp., Phaeocystis sp.). Concurrent measurement of phytoplankton biomass and environmental conditions during December 2018–January 2019 indicated that a period of weak southeastern winds generated vertical stability, which led to the development of a major peak of microphytoplankton biomass in the outer cove, driven by warm, allochthonous, oceanic, nutrient-rich waters. High carbon biomass dominated by nanodiatoms and nanophytoflagellates was observed in cold, fresh, and low-light subsurface waters of the cove. Our results highlight the effects of a warming ocean, which may favor the summer resurgence of nanodiatom and nanophytoflagellate communities in Antarctic fjords due to increased glacial meltwater inputs.

A 3D BEM Model for the Hydrodynamic Analysis and Design of Heaving WEC Arrays Attached to a Breakwater

Assessment of the performance of arrays of wave energy converters (WECs) of the type of simple heaving floaters, operating in nearshore and coastal areas, is essential to estimate their power production capacity. The effective design and layout of such WEC farms can be supported by studying the system’s operational characteristics based on the wave climatology of the deployment region. Installation along the exposed side of harbor breakwaters in sea areas with substantial incoming energy potential is a promising option. In this study, a 3D hydrodynamic model based on the boundary element method (BEM) is presented and discussed, aiming to evaluate the performance of WEC arrays consisting of multiple heaving bodies attached to the exposed side of a harbor breakwater, modelled as a vertical wall, considering its reflective effects, as well as hydrodynamic interactions between the multiple floating devices. Numerical results of the predicted power performance for various configurations, including interactions of multiple WECs with the nearshore topography and the breakwater wall, as well as the effects of power take off (PTO) parameters, are presented and discussed. Finally, a case study is presented for a selected coastal site at the port of Heraklion, located in the north-central part of Crete Island in the South Aegean Sea, characterized by relatively increased wave energy potential, using long-term climatological data, illustrating the method and its applicability as a supporting tool for optimal design of WEC arrangements.

Interactions between light and wave exposure differentially affect epilithic algal biomass and productivity in two large lakes of different trophy

Light and nutrient availability determine the depth distribution of littoral attached algae, but erosional forces, such as wind waves, structure shallow, nearshore habitats. We measured the biomass and productivity of algae on cobbles (epilithon) in the wave-influenced erosional zones of two large lakes with contrasting trophic status, eutrophic Lake Erie and oligotrophic Lake Huron. We used fetch and wind speed to create an index of wave exposure for 10 sample sites and used regression models to determine the variation in algal biomass and productivity explained by physicochemical parameters. Lake Erie epilithon had greater biomass (average = 59–249 mg chlorophyll a m−2) and higher productivity (76–92 mg C m−2 hr−1) than Lake Huron epilithon (1–147 mg m−2 and 14–57 mg C m−2 hr−1, respectively). In Lake Erie, light and wave exposure had significant and opposite effects on algal biomass and productivity. Maximum algal biomass occurred between 1.5 and 3 m in Lake Erie, where the effects of waves begin to diminish and light was still relatively abundant. Conversely, Lake Huron biomass was uniformly low along the depth gradient. Although depth or wave exposure did not explain variation in biomass, Lake Huron epilithic productivity was best explained by the interaction between depth and wave exposure. Rocky nearshore areas in large lakes are dynamic habitats for attached algae, leading to high spatial variation in biomass and productivity. Understanding how physicochemical dynamics influence benthic algal biomass and productivity are necessary to predict their distributions in a changing world.

Effects of elevated temperature and microplastic exposure on growth and predatory performance of a freshwater fish

AbstractFreshwater ecosystems are increasingly exposed to co‐occurring anthropogenic stressors that can alter food web interactions and organismal life histories. We examined the individual and combined effects of climate warming and microplastic pollution on the growth rate and predatory performance of an invasive freshwater fish, the round goby (Neogobius melanostomus). In temperature‐controlled chambers, we exposed 160 juvenile gobies to one of six scenarios over 37 d, combining three environmentally relevant concentrations of microplastics (63–75 μm polyethylene microbeads) with two temperature regimes representing contemporary (18°C) and projected mean summer maxima (26°C) in their current range in the Great Lakes–St. Lawrence River basin. Exposure to elevated temperature reduced the growth and predatory performance of round gobies. Their decline in predatory performance was greatest at the highest microplastic concentration, regardless of temperature. The effects of environmentally relevant microplastic concentrations on the growth and performance of gobies were weaker than the effects of thermal stress. Given that the round goby is an abundant and widely distributed bottom‐dwelling fish in nearshore areas of the Great Lakes–St. Lawrence River basin, its responses to these co‐occurring stressors could have cascading effects on food webs.

Composition and sources of suspended particles in the Pacific Arctic region

During the 6th (2014) and 7th (2016) Chinese Arctic Expedition (CHINARE), samples of suspended particulate matter (SPM) were collected from both surface (depth: <1.0 m) and subsurface (depth: approximately between 10 and 150 m) waters over the northern shelf of the Bering Sea and in the western Arctic Ocean. To investigate the distribution and sources of organic matter in both the surface water and the vertical profile, the concentration and stable carbon isotopic composition of SPM, particulate organic carbon (POC), and particulate nitrogen (only in surface water samples) were determined, and some particle samples were selected for examination using scanning electron microscopy. Results showed apparent geographical partitioning and temporal variation in both the concentration and the composition of SPM. Higher SPM concentrations were observed in nearshore, shelf break, and sea ice edge areas; the distribution of POC concentration displayed a similar pattern, with higher values found from the northern part of the Bering Shelf to southern parts of the Chukchi Shelf. In surface water, SPM mainly comprised clay and detrital minerals with higher POC contents, lighter δ13C values, and higher POC/PN ratios, indicating organic matter predominantly derived from terrestrial sources in areas south of St. Lawrence Island and north of 73°N. The downward trend of heavier δ13C values, together with reduction in clay and detrital minerals, suggests that vertical transport of SPM is hindered by stratification, resulting in transport of terrestrial materials toward northern basin areas. In the Chukchi Slope and Canada Basin areas, extremely light δ13C values (as low as −33.41‰ PDB) were mainly observed at depths of 20–60 m, where the Polar Mixed Layer (PML) intersects with the Upper Halocline Layer (UHL). Under the condition of low sea ice extent in 2016, the POC-δ13C values were heavier in the PML than in the UHL in the Chukchi Slope and Canada Basin areas. These findings provide insights into the sources, transport, and fate of organic matter in the Pacific Arctic region, which have important implications for understanding the biogeochemical cycles and ecosystem dynamics in this remote and rapidly changing environment.

Temperature and salinity trends in the northern limit of the Canary Current Upwelling System

Thermohaline time series are crucial for detecting and quantifying abiotic changes in the marine environment, and even more so in the present global change scenario. This is particularly relevant for the Ría the Vigo and its adjacent shelf, a highly productive ecosystem at the northern limit of the Canary Current Upwelling System (CanCUS). This study analyses a 34-year time series (1987–2020) of Conductivity-Temperature-Depth (CTD) casts, the longest series available to date in the region. Long-term trends, shifts, and seasonal variability of temperature and salinity were assessed and investigated in relation to regional meteorological variability and basin-scale atmospheric teleconnection indices. Generalized Additive Models (GAM) allowed us to determine that monthly thermohaline variability can be largely explained by regional meteo-climatic variability, mainly upwelling index and river discharge. Trends and shifts in some teleconnection patterns, especially the East Atlantic (EA) pattern, may also be related to both the shift in salinity in 2013 and its long-term decrease below 50 m depth. Despite the current global warming context, no statistically significant trend was observed for either the upwelling index or temperature. The spatial analysis of sea surface temperature trends suggests that our study area has been responding to climate change differently from other surrounding near-shore areas, as the Finisterre Cape or the southern Bay of Biscay. Overall, this study highlights the importance of long-term observations to elucidate the impact of climate change in the northern limit of the CanCUS and encourages caution when extrapolating conclusions from ecosystem studies on a regional scale.

Nearshore Observations and Modeling: Synergy for Coastal Flooding Prediction

Coastal inundation has recently started to require significant attention worldwide. The increasing frequency and intensity of extreme events (sea storms, tsunami waves) are highly stressing coastal environments by endangering a large number of residential areas, ecosystems, and tourist facilities, and also leading to potential environmental risks. Predicting such events and the generated coastal flooding is thus of paramount importance and can be accomplished by exploiting the potential of different tools. An example is the combination of remote sensors, like marine radars, with numerical models. Specifically, while instruments like X-band radars are able to precisely reconstruct both wave field and bathymetry up to some kilometers off the coast, wave-resolving Boussinesq-type models can reproduce the wave propagation in the nearshore area and the consequent coastal flooding. Hence, starting from baseline simulations of wave propagation and the conversion of water elevation results into radar images, the present work illustrates the reconstruction of coastal data (wave field and seabed depth) using a specifically suited data processing method, named the “Local Method”, and the use of such coastal data to run numerical simulations of coastal inundation in different scenarios. Such scenarios were built using two different European beaches, i.e., Senigallia (Italy) and Oostende (Belgium), and three different directional spreading values to evaluate the performances in cases of either long- or short-crested waves. Both baseline and inundation simulations were run using the FUNWAVE-TVD solver. The overall validation of the methodology, in terms of maximum inundation, shows its good performance, especially in cases of short-crested wind waves. Furthermore, the application on Oostende Beach demonstrates that the present methodology might work using only open-access tools, providing an easy investigation of coastal inundation and potential low-cost integration into early warning systems.

Geological hazards in the Oujiang estuary in the Zhejiang Province, China: type, distribution, and origin

Introduction: As our understanding of the ocean and its uses continues to advance, countries worldwide with ocean access are implementing new marine strategies. For example, understanding marine geological disasters can help develop the use of ocean resources and oceanic engineering.Methods: Therefore, this study used recent data from the Oujiang Estuary, a nearshore area in China, to determine its geological hazards.Results: The geological hazards were classified as active or restricted based on topography, geomorphology, shallow seismic profile, single-channel seismic profile, and geological drilling data. Active geological hazards primarily include shallow gas and active sand waves, whereas restrictive geological hazards include irregularly buried bedrock, erosion channels, steep submarine slopes, and buried paleochannels. We also evaluated the distribution characteristics and scope, such as the vertical distribution of shallow gas based on the seismic profiles, drilling rock facies, methane, and carbon dioxide contents in the top air, and the isotope values. We found that shallow gas was vertically distributed among multiple layers. The main gas-bearing layers were the clayey silt and sandy (silt) clay layers of the early Holocene and late Pleistocene strata. The shallow gas content was relatively low in the coarse sediment layer at the bottom of the late Pleistocene succession. Generally, the Holocene and late Pleistocene deposits do not contain gas, and the gas content in the middle and late Pleistocene strata (at greater depths) is relatively low.Discussion: The combined effects of the regional geological structure, sea level changes, modern hydrodynamics, and human activities have formed the geological environment of the Oujiang Estuary.