We investigate coastal wetland ecosystem resilience to sea level rise by modelling sea level rise trajectories and the impact on vegetation communities for a coastal wetland in South Africa. The rate of sediment accretion was modelled relative to IPCC sea level rise estimates for multiple RCP scenarios. For each scenario, inundation by neap and spring tide and the 2, 4, and 8 year recurrence interval water level was modelled over a period of 200 years. When tidal variation is considered, the rate of sediment accretion exceeds rising sea levels associated with climate change, resulting in no major changes in terms of inundation. When sea level rise scenarios were modelled in conjunction with recurrence interval water levels, flooding of the coastal wetland was much greater than current levels at 1 in 4 and 1 in 8 year events. In the long term, increases in salinity may cause a reduction in Phragmites australis cover. Very small increases in depth and frequency of inundation are likely to cause an expansion of samphire species at the expense of Juncus spp. The study suggests that for this wetland, variability in flow may be a key factor in balancing wetland resilience.
The retreat of cliffs (lateral expansion) within tidal creeks results in a net loss of saltmarshes, but this retreat process can be retarded by root systems. To understand the interaction between root presence and bank sediment, quantitative measurements of two saltmarsh species root systems (Atriplex portulacoides and Juncus maritima) were carried out in a saltmarsh in Southern England, and their relationships with bank stability were examined. Computed Tomography (CT) Scanning techniques were used to investigate three-dimensional root architecture. The data obtained (e.g., root volume, diameter, and distribution patterns of roots) were examined alongside more traditional root density measurements. The volumetric percentage, ratio between horizontal (lateral) and vertical roots (H/V ratio), and root diameter distribution are discussed in relation to their influence on bank sediment erosion threshold and shear strength. The results suggest that Atriplex portulacoides is more effective than Juncus maritimus in stabilising banks. This is because root systems that provide a high resistance to flow-induced erosion are better than those that provide a high resistance to gravity-induced erosion in stabilising cliff banks. This conclusion is relevant to future saltmarsh protection and re-establishment.
In aquatic environments, suspension-feeding bivalve molluscs are exposed to a manifold of natural and anthropogenically derived particles, including micro- and nanoplastics. Plastic particles interact with feeding and digestive organs and can produce negative effects. As a result of these effects and the potential transfer of microplastics to higher trophic levels, including humans, there has been renewed interest in the ingestion of plastic particles by different species of bivalves. Many recent studies, however, have ignored the ability of bivalves to select among particles both pre- and post-ingestively. Neglecting to consider the factors that mediate particle capture, ingestion, and egestion can lead to erroneous data and conclusions. This paper outlines the current state of knowledge of particle processing by bivalves, and demonstrates how it relates to studies utilizing plastic particles. In particular, the effects of particle size, shape, and surface properties on capture, preferential ingestion, post-ingestive sorting, and egestion are summarized. The implications of particle selection for the use of bivalves as bioindicators of microplastic pollution in the environment are discussed. Only through a full understanding of the types of plastic particles ingested and egested by bivalves can internal exposure, toxic effects, and trophic transfer of microplastics be assessed adequately.
River deltas are the best place to study intense human–earth interactions and the resultant morphological changes and sedimentary records. The coastal evolution history of the Red River Delta (RRD) is examined by time-series analysis of multiple coastline locations. We find that spatiotemporal variation in seawall locations and vegetation lines are obviously site-specific due to intense human interference, while changes in 0 m isobaths are highly dependent on external stresses. Coastal erosion and deposition patterns are determined firstly by sediment inputs from different distributaries, and secondly by sediment redistribution with tides, waves, and longshore currents. The causes of chronic erosion along the Hai Hau coast include swift distributary channels, negligible sediment supply by the regional longshore current, and continuous sediment export by local wave-generated longshore and offshore currents. The area of intertidal flats decreased significantly due to land reclamation and decelerating coastal accretion. The area of mangrove forests decreased first due to human deforestation, and then increased gradually due to artificial plantation. Poorly designed coastal infrastructures may increase risks of coastal erosion and flooding disasters. More coastal sectors in the RRD may turn into erosion due to continuous decrease in riverine sediment discharges, deserving more attention on proper coastal protection and management.
The province of Fujian on China’s southeast coast is severely impacted by typhoons. Based on coastal profile monitoring and 40 years of satellite data, this paper analyzed the response of coastal profiles to natural and anthropogenic forces along the northern part of Fujian’s coast. Results indicated that the pattern of coastal evolution differed largely on cross-shore profiles and longshore coastlines. Only a few sandy coasts were severely affected by extreme weather events in summer, such as typhoons and storm surges, which may result from the wind direction relative to the coast. The cross-shore profiles changed drastically while the mean high-water coastline remained stable. In contrast, anthropogenic forces had a dual effect due to artificial sand extraction and reclamation. Artificial sand extraction usually occurred on sandy coasts, resulting in a decrease in some local surface profiles of tens of centimeters to metres in two years. Reclamation had the main impact on muddy coasts, especially in bays, causing seaward progradation during the past 40 years. The impacts of human activities on muddy coasts were far greater than natural factors. Findings from our coastal monitoring study for both sandy and muddy coasts provide an important scientific basis for practical applications, such as Fujian coastal protection, coastal zone exploitation, and utilization planning.
Remote sensing images were used to reproduce the changes in wetland vegetation since 1987, and the potential impact of policy changes and human activities on vegetation restoration and biodiversity conservation in coastal wetlands was explored based on the landscape pattern index and the human disturbance index (HDI). The results showed that the vegetation displayed a zonal distribution pattern in which, perpendicular to the coastline early in the study period, the vegetation type changed from coastal wetland to bare mud flat with Spartina alterniflora, Suaeda glauca, and Phragmites australis as well as to constructed wetlands dominated by rice. Under the influence of human activities, the number of patches (NP) and mean nearest-neighbor distance (MNN) between patches gradually increased during the study period, while the mean patch size gradually decreased. The patch density increased from 179 (1987) to 296 patches per ha (2013). Additionally, human activity in the study area intensified. The HDI increased from 0.353 (1987) to 0.471 (1987) and showed positive correlations (R2 > 80%, p < 0.01) with NP and MNN. Human activity, such as changes in land use, resulted in more fragmented vegetation patterns, and the nonzonal (intrazonal) distribution of the vegetation became more obvious in coastal wetlands.
In the present paper, tides in the port of Vancouver Harbour have been investigated with a high-resolution three-dimensional hydrodynamic model based on FVCOM (Finite Volume Community Ocean Model). The model was evaluated against field observations including tidal elevations and tidal currents, and the evaluation showed that the model was in good agreement with the observational data. Using the model, we first investigated the horizontal distributions of tides, tidal currents, and tidally induced residual circulation, and then investigated the tidal asymmetry and dynamic mechanisms of tidal flows in the harbour. The tidal residual circulation shows a strong spatial pattern, which is associated with the local coastlines and variation of topography. The tidal asymmetry in the harbour is caused by different mechanisms, not only including the traditional factors, such as residual flows, the interaction between M2 and its overtide M4, but also the interaction of principal astronomical tides of O1, K1, and M2. The momentum balance is dominated by terms of the advection and the pressure gradient in First Narrows and Second Narrows, whereas terms of the local acceleration and the Coriolis are also important in the central harbour. The spatial variations of the momentum terms are strongly associated with the local changes in coastline and topography.
Using numerical modelling, we study changes in tidal dynamics in Daya Bay (DYB) between 1989 and 2014. During this period, a total water area of 30 km2 was reclaimed and the average water depth increased by 38 cm. As DYB is a sexta-diurnal tidal resonant bay, the sexta-diurnal tides respond differently to the coastline and bathymetry changes than other tides. Taking K1, M2, M4, and M6 as examples, model results show a decrease in tidal elevation amplitude, tidal current magnitude, and tidal energy flux for K1, M2, and M4 tides. For the M6 tide, however, the model predicted an increase in tidal elevation amplitude, tidal current magnitude in some parts of the bay, and the tidal energy flowing into the bay. Land reclamation leads to the enhancement of sexta-diurnal tidal resonance and thus the magnitude of the M6 tide. Furthermore, due to the magnification of M6, tidal duration asymmetry in DYB changed from ebb-dominance to flood-dominance, and water exchange became much more active. Therefore, owing to the sexta-diurnal tidal resonance, the impact of human activities on tidal dynamics in DYB is different from that in previously reported semi-enclosed bays where large-scale land reclamation has been carried out.
To better understand the alteration of the estuarine circulation caused by estuarine dams, four major Korean estuaries were classified by using the Hansen and Rattray stratification–circulation classification scheme. The stratification and circulation parameters were calculated for both discharge and no-discharge periods from the tidally averaged salinity and velocity data obtained from these four Korean estuaries. The estuarine types of the altered Korean estuaries were compared with the previous results for natural estuaries in other countries of similar magnitude in tidal range, water depth, and discharge. This comparison revealed that the estuarine types of the altered Korean estuaries have been shifted from a partially mixed to a well-mixed type (Nakdong River Estuary), from a partially mixed to a coastal bay or a fjord type (Yeongsan River Estuary), and from a well-mixed to a well-mixed type with less tidal modulation (Geum River Estuary). The controlling factors that determined the type in natural estuaries were tide, discharge, and water depth, whereas for altered estuaries, they were the controlled river discharge and water depth. The different estuarine dam gate types with their different modes of operation (surface or bottom discharge) played an important role in the mixing and circulation of the altered estuaries.
Understanding the erosion–deposition process of sediments and the associated controlling mechanisms in subaqueous deltas is important for coastal environment protection. In this study, field observations and numerical simulations were performed for the Nanliu River subaqueous delta in Guangxi Province (Southern China) to investigate the sediment dynamic processes at the bottom boundary layer. The results show that the sediment resuspension mainly occurs during periods of spring tides and is mainly controlled by the wave action. When the seabed is free from erosion, suspended sediment settling caused by lateral transport is an important source of maintaining near bed suspended sediment concentration. It was also found that increasing the shear parameter could facilitate the formation of flocs, after which the small flocs tend to merge to large flocs. Finally, by performing a consistency analysis between the seabed erosion and deposition processes obtained from numerical simulation, and the changes of seabed level recorded by the equipment during the field observation, we determined that the local erosion coefficient was 5 × 10-5 kg/m2•s. The one-dimensional simulation is also capable of revealing the general trend at the seabed where it is first subjected to erosion and then deposition, as indicated during the field measurements.
As the most important sediment source to the north Yellow Sea (NYS), the sediment discharge from the Yellow River has substantially decreased for at least half a century. The response of the existing mud patches to this decline is not well understood. Here, we present high-resolution grain-size parameters and geochemical composition of one gravity core (B23) collected in the NYS mud patch to investigate the behavior of the mud patch variation in correspondence to the Yellow River’s sediment discharge reduction. The B23 age model is derived by 210Pb dating method, and the average sedimentation rate is estimated to be 0.49 cm/year. Results of a geochemical discrimination analysis suggest that the sediments of B23 were mainly transported from the Yellow River by the strong coastal current along the Shandong Peninsula, whereas the contributions of sediments from Yangtze and Yalu rivers are also measurable. In around 1980, the ratio of sediments from the Yellow River underwent an apparent decrease in the NYS mud. Simultaneous changes include coarsening of grain size and disaccord between East Asia Winter Monsoon intensity and content of sensitive grain size. These are all directly or indirectly due to the decline of the Yellow River’s sediment discharge.
The typhoon process has a significant influence on the distribution of heavy metals in sediments. Based on the heavy metal (V, Cr, Co, Ni, Cu, Zn, Pb, and Mn) contents in surface sediments collected under normal conditions and post-typhoon Matmo in Quanzhou Bay in 2014, the distributions, sources, and impacts of typhoon processes on heavy metals and pollution conditions were studied and discussed. The results showed that the heavy metals can be divided into two categories: Class I metals (Cu, Zn, Pb, and Mn) were mainly distributed in the estuary and significantly increased after the typhoon and Class II metals (V, Cr, Co, and Ni) were distributed in the coastal intertidal zone and estuary and remained unchanged or decreased after the typhoon. The heavy metal assessment showed that heavy metal pollution in Quanzhou Bay was serious and tended to increase after the typhoon. The increased metal supply and enhanced riverine and tida hydrodynamics after the typhoon may be the main factors influencing the variations in heavy metal content and distribution. This study provided a basis for the accurate evaluation and scientific management of heavy metal pollution caused by typhoon processes in Quanzhou Bay.
The dynamic response of marine sediment from the Yellow River under extreme sea conditions is attracting increasing academic and engineering attention because of the high occurrence frequency of geologic hazards. To simulate the dynamic response process of sediment samples under waves with a 50 year recurrence interval, we collected undisturbed sediment samples from six sites on the intertidal flats of the Yellow River Delta and performed dynamic triaxial experiments to analyze the pore-water pressure and liquefaction process. The empirical patterns of pore-water pressure generation and ranges of sediment parameters were determined, and the factors affecting sediment liquefaction were discussed. Under the cyclic loading of waves with a 50 year recurrence interval, the pore pressure response of sediments at a depth of 4 m could be generalized into three stages: rapid growth, slow growth, and stable maintenance. Moreover, the build-up of pore-water pressure was effectively represented by a logarithmic growth model. The liquefaction characteristics of sediment in the Yellow River Delta were more related to its plasticity index, mean particle size, and clay, silt, and sand contents, as well as the sedimentary history. These factors should be considered in the development of disaster assessment models in coastal environments of the Yellow River Delta.
The drag coefficient is a key parameter to quantify the wind stress over the ocean surface, which depends on the ocean surface roughness. During oil spill events, oil slicks cover the ocean surface and thus change the surface roughness by suppressing multi-scale ocean surface waves, and the drag coefficient is changed. This change has not been included in the current ocean circulation models. In this study, such change in sea surface roughness is studied by satellite remote sensing via synthetic aperture radar (SAR) data to quantify the changes in the wind effect over the oil-covered ocean surface. The concept of effective wind speed is introduced to quantify the wind work on the ocean. We investigate its influence on the wind-driven Ekman current at the ocean surface. Using observations from the Deepwater Horizon oil spill (2010) as an example, we find that the presence of oil can result in an effective wind speed of 50%~100% less than the conventional wind speed, causing overestimates by 75%~100% in the wind driven Ekman current. The effect of such bias on oil trajectory predictions is also discussed. Our results suggest that it is important to consider the effect of changes in the drag coefficient over oil-contaminated areas, especially for large-scale oil spill situations.
Mismatches in spatial scales, or spatial disconnections between causes and effects of ecosystem degradation, can reduce resilience in social–ecological systems. These mismatches can be particularly disruptive in coastal and marine areas, where multiple social and ecological systems are multi-layered. Scotland’s Western Isles have a history of local resource exploitation to meet extra-regional, larger-scale demands, which has resulted in a long process of socio-demographic decline. Salmon aquaculture is a major and expanding industry in the area, often linked to “Blue Growth”. The expansion of this industry operates within and contributes to create several scale mismatches. Combining a systems approach across nested scales with a classification of scale mismatches, this work analyses the characteristics of the Western Isles salmon aquaculture industry, and it explores effects on social–ecological resilience. An extent scale mismatch between the global stocks offish-meal species and the local capacity to respond to fluctuations is identified. The implications for this mismatch for the Western Isles are discussed. Some potential policy arrangements for incorporating matched spatial scales are considered.
Due to a long and beneficial legacy, human settlement and development is particularly concentrated in coastal zones and this concentration is expected to continue and increase in the future. Coastal dwelling, however, also entails risks from both anthropogenic and natural hazards and interactions between these. A spatially explicit ecosystem services framework combined with a vulnerability framework is used to explore human relations with the coast and to assess current and future capacities to ensure benefits of coastal migration and to address the risks that these areas pose. The spatial characteristics of some fundamental benefits — transport and settlement, fisheries and waste assimilation — of coastal dwelling and their associated environmental costs are first analysed using modern and historical examples. A variety of spatial characteristics describing human use patterns are then identified. On this basis, the implications of the variety of spatial scales in benefits and costs for effective governance are discussed with reference to historical and current marine and coastal management practice. Our analysis will attempt to demonstrate that incorporating ecosystem services in environmental management may provide a useful tool in the application of ecosystem-based management.
Marine microplastic particles (MPs, <5 mm) exhibit wide ranges of densities, sizes, and shapes, so that the entire MPs “ensemble” at every time instant can be characterized by continuous distributions of these parameters. Accordingly, this community of particles demonstrates distributions of dynamical properties, such as sinking or rising velocity, critical shear stress, and the re-suspension threshold. Moreover, all the MPs’ properties vary significantly with the time spent in marine environment and with particular conditions experienced by the particle on its journey. A brief review of the present-day numerical efforts towards prediction of MPs transport shows the prevalence of the Lagrangian particle tracking approach, especially for floating litter. In a broader context, the present practice of MPs transport modelling follows the “selective” strategy (e.g., only a certain sub-class of MPs, or specific processes, are considered, sometimes in only one- or two-dimensional setting). The heterogeneous nature of MPs, their enormous longevity and movability in marine environment, and the wide spectrum of the involved environmental processes suggest further integration (or coupling) of different models in future, as well as application of other types of models (ensemble modeling, chaos theory approaches, machine learning, etc.) to the problems of MPs transport and fate in the marine environment.
The coast is home to unique ecosystems, where complex ecological processes take place through the interaction of terrestrial, aquatic, atmospheric, and human landscapes. However, there are considerable knowledge and data gaps in achieving effective and future change-proof sustainable management of coastal zones around the world due to both technical and social barriers, as well as governance challenges. Currently, the role of Earth observation (EO) in addressing many of the recognised information gaps is small and under-utilised. While EO can provide much of the spatiotemporal information required for historical analysis and current status mapping, and offers the advantage of global coverage; its uptake can be limited by technical and methodological challenges associated mostly with lack of capacity and infrastructure, product accuracy and accessibility, costs, and institutional acceptance. While new initiatives and recent technological progress in the EO and information technology arena aim to tackle some of these issues so that EO products can be more easily used by non-EO experts, uptake is still limited. This paper discusses how EO can potentially inform transformative practices of planning in the coastal water zone, by using examples to demonstrate the EO potential in providing information relevant to decisionmaking framed by international agreements, such as the United Nations Agenda 2030, the Convention on Biological Diversity, and the Sendai Framework for Risk Reduction. By presenting evidence for how EO can contribute to innovative opportunities and data synergies at scale, the paper discusses opportunities and challenges for a more solution-led approach to sustainable coastal management.
Research on microplastics in China is progressing rapidly. Within recent years, more than 30 research institutes have conducted research on marine microplastic in estuaries, coasts, open sea, and Polar regions. Microplastics have been detected in freshwater systems (lakes, rivers, and wastewater treatment plants) and coastal and marine environments. This paper reviews the research progress of microplastics in China, providing information on topics including the methodology, quantification of microplastics in various habitats, eco-toxicological effect, biodegradation, management, and control of plastic waste and microplastics. This paper discusses the sampling and analysis of microplastic in different media, followed by spatial and temporal distribution of microplastics in marginal seas and coastal and freshwater systems. After summarizing the recent advances on toxicology research and risk assessment of microplastics, this paper provides suggestions for future study to provide baseline information for better risk assessment and improved understanding of the lifecycle of microplastics in the environment.
Land clearing, river impoundments, and other human modifications to the upland landscape and within estuarine systems can drive coastal change at local to regional scales. However, as compared with mid-latitude coasts, the impacts of human modifications along sediment-starved formerly glaciated coastal landscapes are relatively understudied. To address this gap, we present a late-Holocene record of changing sediment accumulation rates and sediment sources from sediment cores collected across a tidal flat in the Merrimack River estuary (Mass., USA). We pair sedimentology, geochronology, bulk- and stable-isotope organic geochemistry, and hydrodynamic simulations with historical data to evaluate human and natural impacts on coastal sediment fluxes. During the 17th to 19th centuries, accumulation rates increased by an order of magnitude in the central tidal flat, likely in response to enhanced delivery of terrestrial sediment resulting from upland deforestation. However, the overall increase in accumulation (0.56–2.6 mm/year) within the estuary is subtle and spatially variable across the tidal flats because of coincident anthropogenic land clearing and dam building, upland sediment storage, and estuarine hydrodynamics. This study provides insight into the response of formerly glaciated fluvialcoastal systems to human modifications, and underscores the role of estuarine environmental conditions in modifying upland signals of land-use change.