Coastal environments are subject to trace metal pollution via a combination of industry and urbanised sources. The pollutants accumulate within surface sediments, especially in the quieter backwaters of estuaries. An environmental assessment of the Port Hacking estuary, southern Sydney, Australia, was undertaken using 233 surface samples. Trace metal concentrations (Ni, Cr, Cu, Zn, Pb, and As) in these samples indicated that most elements in Port Hacking were below the relevant ANZECC/ARMCANZ guideline low trigger value (ISQG-low), but a few sites exceeded this value. The low trace metal concentrations are mainly because the catchment areas have limited urban development and few discharge points. In contrast, one site in Gunnamatta Bay has Zn and Cu concentrations that exceeded the high trigger value (ISQG-high), due to moored vessels, boatyards, and stormwater outlets in this vicinity. Port Hacking is considered to be relatively unpolluted and healthy when compared with other Sydney estuaries.

The massive Qingcaosha Reservoir (QCSR) is located in the Changjiang Estuary along the northwest coast of Changxing Island. The reservoir significantly narrowed the upper reaches of the North Channel and deepened the channel near the reservoir. These topographical changes inevitably influenced hydrodynamic processes and saltwater intrusion in the estuary. A well-validated model was employed to investigate the influence of the QCSR on saltwater intrusion in the Changjiang Estuary. The model results showed that the narrowed upper reaches of the North Channel decreased the water diversion ratio and thus increased salinity in the North Channel. During the moderate tide after neap tide, the salinity decreased at the water intake of the QCSR because saltwater intrusion was obstructed at flood slack at the surface, while the salinity increase during the moderate tide after spring tide was mainly due to the intensified saltwater intrusion during spring tide. The deepening of the channel near the QCSR resulted in an increased water diversion ratio, and the salinity in the Eastern Chongming Shoal decreased by more than 0.5 psu during spring tide; however, the saltwater intrusion was enhanced due to the strengthened baroclinic force, which is proportional to the water depth. During neap tide, the salinity in the entire North Channel decreased because of a 1.4% increase in the water diversion ratio of the North Channel and the relatively weak tide.

Shipping fairways in estuaries are continuously dredged to maintain access for large vessels to major ports. However, several estuaries worldwide show adverse side effects to dredging activities, in particular affecting morphology and ecologically valuable habitats. We used physical scale experiments, field assessments of the Western Scheldt estuary (the Netherlands), and morphodynamic model runs to analyse the effects of dredging and future stresses (climate and sediment management) on a multi-channel system and its ecologically valuable intertidal flats. All methods indicate that dredging and disposal strategies are unfavourable to long-term morphology because dredging creates and propagates the imbalance between shallow and deeper parts of the estuary, causing a loss of valuable connecting channels and fixation of the tidal flats and main channel positions, while countering adverse effects by disposal strategy has limited effectiveness. Changing the disposal strategy towards main channel scour disposal can be economically and ecologically beneficial for the preservation of the multi-channel system. Further channel deepening will accelerate the adverse side effects, whereas future sea-level rise may revive the multi-channel system.

Despite being exceptional concentrations of valuable economic assets, yachts and marinas are typically overlooked in the geography of coastal risk. Focusing on the Mediterranean, which hosts the majority of the world’s yacht activity, we examine three decades of yacht insurance claims in the context of natural hazards and marina development. We find indications that yachts and marinas manifest the same generic relationships between exposure, hazard, and vulnerability observed in terrestrial coastal-risk systems. Given the fundamental importance of yachts and marinas to nautical tourism and strategies for “Blue Economy” growth, particularly in Europe, the role of yachts and marinas in the dynamics of coastal risk must be better understood—but any such insight will first require standardised, comprehensive datasets of yacht movements and marina infrastructure.

In the deep central part of the Bohai Sea off the coast of northern China, long-term observations show significantly lower dissolved oxygen (DO) concentration near the bottom in summer during 2006–2018 than during 1978–2005. The decrease in bottom DO is closely linked to changes in phytoplankton community driven by nutrient structure changes in the water column. From literature review, observations in the phytoplankton community structure indicate an increase in the abundant proportion of dinoflagellate to diatom and miniaturization since the 21st century. The new dominate species of dinoflagel-late and the pico- and nano-celled algae detritus, with slow sinking rate and long residence time, favor the efficient oxygen consumption in the water column and lead to oxygen depletion enhancement and DO concentration decrease after 2006. Analyses also suggest that water temperature, stratification, and resuspension of sediment play less significant roles in long-term variations of DO. The linkage of hypoxia formation to changes of phytoplankton community answers why hypoxia in the Bohai Sea started to occur in the recent decade while eutrophication began since the 1980s. The identified new mechanism of hypoxia formation may be applicable to other coastal seas where eutrophication has led to changes in the phytoplankton community, and should be considered in biogeochemical models.

In recent decades, international assessments of the ocean have evolved from specialized, technical evaluations of the state of the marine environment to more integrated and thematically extensive science-policy platforms. As assessment programmes such as the UN Regular Process blossom on the global stage and subsume responsibility for tracking progress on sustainable development, there is a need to consider how their processes wield influence and effectively translate knowledge into action. In the present paper, we undertake a comprehensive review of the literature on global environmental assessments (GEAs) and extract key principles that can be applied to global assessments of the marine environment. We were particularly inspired to identify how social processes could be arranged to best distill, communicate, and produce actionable knowledge. While we look to the advice of experts in the literature, we highlight specific examples from the Intergovernmental Panel on Climate Change (IPCC), Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES), and the Global Environment Outlook (GEO). From this review, knowledge coproduction, multilevel collaboration, and futures thinking emerged as the dominant principles of influential and action-oriented assessments. We conclude the paper by contextualizing how these principles may be operationalized for Global Marine Assessments in the future.

A large-scale sand ridge group is distributed in the central Jiangsu coastal area, and a deposition muddy sea bank was developed in the nearshore area. Quantitative monitoring of coastline changes is of great significance for tidal beach development and protection. The shorelines of the central coast of Jiangsu within six periods (1973–2018) were extracted in this study, and their length changes over the years were analyzed. The Digital Shoreline Analysis System (DSAS) was employed to generate a cross section perpendicular to the baseline and calculate the linear regression rate (LRR) of the shoreline, changes in end point rate (EPR), and net shoreline movement (NSM), based on which the shoreline change features were analyzed. The DSAS results indicated that the shorelines in the study area maintained fluctuating growth and presented a continuous advancing trend towards the sea. From the changes in shoreline evolution distance during 1973–2018, the advancing shorelines in the study area accounted for over 50% of the total shorelines and presented first rising and then declining trends with the period of 2003–2013 taken as the time boundary. The average shoreline change rate was 207 m/year, and the periods with the highest change degrees were 1983–1993 and 1993–2013. The shoreline change tended to be stable during 2013–2018, and only a few estuaries and ports underwent obvious erosion and sedimentation.

The growing push for open data resulted in an abundance of data for coastal researchers, which can lead to problems for individual researchers related to data discoverability. One solution is to explicitly develop services for coastal researchers to help curate data for discovery, hosting discussions around reuse, community building, and finding collaborators. To develop the idea of a coastal data curation service, we investigate aspects of the UNESCO International Coastal Atlas Network member sites that could be used to build a curation service. We develop a minimal example of a coastal data curation service, deploy this as a website, and describe the next steps to move beyond the prototype phase. We envision a coastal data curation service as a way to cultivate a community focused on coastal data discovery and reuse.

In the UK, coastal flooding and erosion are two of the primary climate-related hazards to communities, businesses, and infrastructure. To better address the ramifications of those hazards, now and into the future, the UK needs to transform its scattered, fragmented coastal data resources into a systematic, integrated portal for quality-assured, publicly accessible open data. Such a portal would support analyses of coastal risk and resilience by hosting, in addition to data layers for coastal flooding and erosion, a diverse array of spatial datasets for building footprints, infrastructure networks, land use, population, and various socio-economic measures and indicators derived from survey and census data. The portal would facilitate novel combinations of spatial data layers to yield scientifically, societally, and economically beneficial insights into UK coastal systems.

Lingding Bay (LDB), on the Pearl River Delta (PRD) of southern China, is a typical example of a large river mouth that is strongly affected by anthropogenic perturbations that have changed the boundary conditions of hydro- and sediment dynamic processes. An analysis of recent sedimentary patterns can shed light on the role of anthropogenic impacts on delta evolution. In this study, we collected surficial sediments from the LDB in December 2016 (dry season) and August 2017 (flood season) to analyze their grain size and organic geochemical compositions, with the aim of investigating recent depositional patterns in the bay and evaluating human impacts. The results reveal two major mud depocenters in the northeastern and southwestern parts of the bay, which are characterized by high values of grain-size end member 1 (EM1) and increased contributions of terrestrial organic carbon in the flood season. We propose that this sedimentary pattern is a manifestation of a system regime shift due to the strengthening of the fluvial function in fluvial-tide interactions and associated changes in the suspended sediment dispersal routine. We suggest that these changes are a result of recently intensified human activities, such as coastal land reclamation and sand mining. Coarsening of the surficial sediments in the LDB in the dry season and a marked increase in the terrestrial organic contribution at the mouth of the LDB indicates the redistribution of fine-grained sediments by waves and currents and increased mud export from the LDB in response to the shallowing of the bay.

Salt marshes are key coastal ecosystems that provide habitats for wildlife, including invertebrates, fishes, and birds. They provide ecosystem services such as protection from storm surges and waves, attenuation of flooding, sequestration of pollutants (e.g., blue carbon), and nutrient removal. They are currently under great threat from sea level rise (SLR). We collected information about trends in the horizontal extent (acreage) of New Jersey salt marshes and recent elevation changes compared with the current local rate of SLR in New Jersey, which is between 5 and 6 mm year⁻¹. We found pervasive, although variable, rates of marsh loss that resulted from both anthropogenic disturbance as well as edge erosion and interior ponding expected from SLR. Elevation trends suggest that the current rates of SLR exceed most marsh elevation gains, although some Phragmites-dominated marshes keep pace with SLR. Four potential remedies to address current coastal trends of marsh loss were described in the context of New Jersey’s regulatory and management environment: protection of marsh inland migration pathways, altered management of Phragmites, thin layer sediment placement, and living shoreline installations. Proactive steps are necessary if coastal wetland ecosystems are to be maintained over the next few decades.

Following the significant coastal changes caused by Hurricane Sandy in 2012, engineered berm-dunes were constructed along the New Jersey coastline to enhance protection from future storms. Following construction, property values on Long Beach Island, NJ, increased in three beachfront communities. The projects were financed entirely through federal disaster assistance, but the percentage of future maintenance costs must be covered by local communities. Whether communities are willing or capable of financially contributing to maintenance remains unclear because (i) some homeowners prefer ocean views over the protection afforded by the berm-dune structures, and (ii) stakeholder risk perceptions can change over time. To investigate the relationships between berm-dune geometries, values of coastal protection, and ocean view values, we developed a geoeconomic model of the natural and anthropogenic processes that shape beach and dune morphology. The model results suggest that coastal communities may exhibit significant differences in their capabilities to maintain engineered dunes depending on stakeholder wealth and risk perception. In particular, communities with strong preferences for ocean views are less likely to maintain large-scale berm-dune structures over the long term. If these structures are abandoned, the vulnerability of the coast to future storms will increase.

Protected areas (PAs) are widely applied conservation instruments. Often, they are also expected to help secure livelihoods of poor subsistence, small-scale producers, making the management of PAs often dependent on community support. The usefulness of analyzing the perceptions of PAs among local users to improve the effectiveness of PA management is increasingly recognized; however, there are few studies on spatial perceptions, for example, how users perceive the PA’s geographical boundaries or its zoning, and how these can be used in PA zoning. Here, we analyze how local stakeholders perceive two sustainable-use PAs on the Amazon coast, the changes they have brought about, and their current management. We identify and link the mental models of different user groups to formal conceptualizations of the PAs in legal instruments and identify mismatches related to what the PA means to local stakeholders and where it is located, which need to be considered when building a zoning plan. Because of the frequent research in our study area, we also discuss possible research fatigue in this region. We highlight the challenges and opportunities related to promoting spatial literacy and awareness-raising regarding PAs. We recommend adapting legal instruments to include diverse territorial representations and alternative management tools.

This study assesses the seasonal regulation of river discharge by hydropower dam-induced cascade reservoirs in the Lancang River and its effect on downstream freshwater and estuarine saltwater intrusion. There are eight main reservoirs in the Lancang River, with a total regulation capacity of 25.67 billion m³, which regulates river discharge by conserving water in the flood season and releasing water in the dry season. River discharge during the dry season from 1960 to 2009 accounted for 21% of the annual discharge before the cascade reservoirs were constructed and increased to 33% from 2010 to 2015 after the cascade reservoirs were constructed at the Jinghong hydrological station, which is the lowermost station in the Lancang River. During the 2016 extreme drought in the lower Mekong River basin, the river discharge increased by 550, 367, 1283, 969, and 524 m³/s in January, February, March, April, and May, respectively, regulated by the cascade reservoirs at the Jinghong hydrological station. Considering runoff, tides, wind, and continental shelf currents, a high-resolution three-dimensional numerical model was used to simulate the effect of regulation of river discharge by the cascade reservoirs in the Lancang River on the saltwater intrusion in the Mekong River Delta (MRD). The simulation results show that the seasonal regulation of river discharge by the cascade reservoirs in the Lancang River weakens estuarine saltwater intrusion during the dry season, especially in the sand bar areas, which is much more significant in the extreme dry season of 2016. The seasonal regulation of river discharge by the reservoirs in the Lancang River makes the seasonal distribution of downstream river discharge more uniform, favoring downstream freshwater utilization and alleviating flood disasters and saltwater intrusion in the MRD.

Deltas require sufficient sediment to maintain their land area and elevation in the face of relative sea-level rise. Understanding sediment budgets can help in managing and assessing delta resilience under future conditions. Here, we make a sediment budget for the distributary channel network of the Rhine—Meuse delta (RMD), the Netherlands, home to the Port of Rotterdam. We predict the future budget and distribution of suspended sediment to indicate the possible future state of the delta in 2050 and 2085. The influence of climate and anthropogenic effects on the fluvial and coastal boundaries was calculated for climate change scenarios, and the effects of future dredging on the budget were related to port development and accommodation of larger ships in inland ports. Suspended sediment rating curves and a 1D flow model were used to estimate the distribution of suspended sediment and projected erosion and sedimentation trends for branches. We forecast a negative sediment budget (net annual loss of sediment) for the delta as a whole, varying from −8 to −16 Mt/year in 2050 and −11 to −25 Mt/year by 2085, depending on the climate scenario and accumulated error. This sediment is unfavourably distributed: most will accrete in the northern part of the system and must consequently be removed by dredging for navigation. Meanwhile, vulnerable intertidal ecosystems will receive insufficient sediment to keep up with sea-level rise, and some channels will erode, endangering bank protection. Despite increased coastal import of sediment by estuarine processes and increased river sediment supply, extensive dredging for port development will cause a sediment deficit in the future.

Energetic swell waves, particularly when they coincide with high water levels, can present significant coastal hazards. To better understand and predict these risks, analysis of the sea levels and waves that generate these events and the resulting coastal impacts is essential. Two energetic swell events, neither of which were predicted by modelled flood forecasts, occurred in quick succession in the English Channel. The first event, on 30 January 2021, produced moderate significant wave heights at or just below the 0.25 year return period along the southwest English coast, but combined with significant swell caused overtopping at East Beach in West Bay and at Chesil Beach. The second event, on 1 February 2021, generated the highest wave energy periods measured at many locations along the southern English coastline and, at high water, caused waves to run up over the promenades at Poole Bay and Christchurch Bay and caused overtopping at Hayling Island. Both events are described in detail, and their spatial footprints are mapped through a joint return period analysis using a copula function. It is found that typical joint return period analysis of water level and significant wave height underestimates potential impacts, while a joint consideration of water level and wave power (P) describes the 31 January event better and a joint consideration of water level and energy period (T _e) best describes the 1 February event. Therefore, it is recommended that T _e and P are adopted for coastal monitoring purposes, and that future studies further explore the use of both parameters for swell monitoring.