Coastal Environmental Changes Research Articles

An observational study of hydrodynamic impact on water mass transport due to tidal power generation

The world's largest Sihwa Tidal Power Plant (TPP), located on the west coast of Korea, was built in 2011 for the purpose of improving water quality and producing renewable energy. After several years of actual operation, most of the original purpose was achieved, but unexpected coastal environmental changes such as tidal flat damage and sediment accumulation also occurred. In this study, in order to understand the causes of these environmental changes, field observations were conducted near TPP, and spatial and temporal variability of flow structure and water exchange process were investigated. Three-dimensional velocity data were collected along the closed line surrounding the outside of the TPP for 11 h during spring tide and analyzed according to two discharge phases: power generation phase (PGP) and drainage phase (DP). The results show that the depth-averaged maximum current velocity was more than three times greater at DP than at PGP. Jet-like flow during DP caused very high horizontal shear, whereas vertical shear was relatively weak, indicating that the horizontal and vertical flow structures were very different. The most notable result is that the mass transport patterns between PGP and DP are significantly different, i.e., during PGP, mass transport is dominated on the left side of the TPP, whereas during DP, it occurs at the front of the TPP. This means that there is a strong spatiotemporal asymmetry between the inflow from the downstream (outside of the TPP) during PGP and the outflow from the upstream (inside of the TPP) during DP. These asymmetric processes can have a significant impact on the material exchange and sediment transport near the TPP. Since observational studies on TPP are extremely rare, this study is expected to contribute to future TPP related research, such as numerical modeling.

Coastal morphodynamics and Holocene environmental changes in the Pearl River Delta, southern China: New evidence from palynological records

Coastal morphodynamics and environmental changes have been obviously altered by global warming, sea-level fluctuations, and human activities. Palynological analysis is one of the most important tools for providing information on vegetation, climate, and environmental change, which can be relatively sensitive indicators of human activity during the Holocene. However, Holocene coastal morphodynamics and palynological evidence from the Pearl River Delta and coastal areas has not been sufficiently studied. In this paper, we carry out analyses using detailed grain-size and palynological records of pollen, spores, freshwater algae, and marine dinoflagellate cysts from Borehole QZK13 in the Pearl River Estuary (PRE), southern China. The results show information relating coastal morphodynamics, vegetation evolution, climate changes, and anthropogenic activities during the Holocene based on radiocarbon chronology. In general, the PRE experienced marine transgressive processes; sea-level and the coastline tended to migrate landward between 10,700 and 4250 cal yr BP. Meanwhile, abundant arboreal pollen (mainly Castanopsis, Quercus-evergreen, Oleaceae, and Castanea) and small amounts of non-arboreal pollen (mainly Poaceae, Cyperaceae, and Artemisia) were observed in Borehole QZK13, which suggests that subtropical evergreen broadleaved forests were distributed throughout the PRE and adjacent areas, and relatively warm and moist climatic conditions were present during the early-middle Holocene. After that, there were relatively cool and wet climatic conditions, and marine regressive processes occurred in the PRE during the Late Holocene (ca. 4250–960 cal yr BP) indicated by an abrupt increase in aquatic herbs and Dicranopteris. Moreover, we hypothesize that the Neolithic “cultural fault” in the PRE is likely related to frequent storm surges induced by extreme typhoon events that occurred ca. 3000–2700 yr BP.

Longitudinal perspectives on crowding and management at a beach park in Hawai'i

This research adds to a small body of literature studying longitudinal change in coastal tourism environments. Site use and crowding at Kailua Beach Park in Hawai'i was investigated through research conducted in 2007 and 2019. Reported encounters, perceived crowding and the minimum acceptable condition all increased between these years. Overall, crowding scores were highest for respondents who reported more encounters than they think should be allowed, and the percentage of users who encountered more people than they think should be allowed has grown substantially. A significant increase of US mainland users was identified in 2019 (which mirrors broader tourism trends in Hawai'i) and local beach users are now in the minority at this site. Respondents from the USA mainland were less likely than local or international user groups to experience encounters exceeding their norm, and if their encounter norms were exceeded, USA mainland respondents generally displayed lower crowding scores. These findings have implications for norm stability, the development of appropriate standards of quality for crowding, and post-pandemic management.

Temporal change in the molluscan assemblages (bivalves and gastropods) of Frobisher Bay, Nunavut, Canada, over 50 years

Long-term studies provide an effective way to assess the ecological impacts of decades-long environmental change in Arctic coastal benthic environments, but are rarely undertaken in the Canadian Arctic. In light of this, historical datasets can be compared with modern samples to examine temporal differences in benthic community structure. Frobisher Bay, Nunavut, provides a unique opportunity to use a historical census to examine the impacts that long-term environmental changes have had on the marine benthos. Between 1967 and 1976, and in 2016, infaunal samples were collected in inner Frobisher Bay and were compared to determine how the molluscan assemblages have changed between the two time periods. Molluscan assemblages in two regions of inner Frobisher Bay (Iqaluit and Cairn Island) were examined to minimize sampling discrepancies between the two time periods. A long-term increase in mean annual air temperature and a decline in the length of the ice cover season were observed. Both regions exhibited some change in sediment composition and quality as well as in molluscan assemblage between the two time periods, and species diversity indices also indicated some change between these time periods. Both the 1967–1976 and 2016 molluscan datasets provide a baseline for future long-term studies in a changing Arctic.

A Global Assessment of Coastal Marine Heatwaves and Their Relation With Coastal Urban Thermal Changes

AbstractOcean temperature significantly influences global and regional weather and climate. Coastal marine heatwaves (MHWs) do not only profoundly impact marine ecosystems but can influence the climate of coastal regions. This study provides the first observational assessment of global coastal MHWs changes, showing a latitudinal‐dependent pattern with considerably strengthened severity of MHWs in the past four decades. Coastal MHWs have been found closely linked to remarkable changes in coastal urban thermal environments, showing consistent trends of increase in air temperature and moisture, and mostly reduced wind speed among 38 major coastal cities. These effects collectively exacerbate the thermal discomfort during the warm season. The findings demonstrate the strong coupling of coastal oceans and lands under the influence of global warming and regional interactions of ocean, land, and the atmosphere, and contribute to a global initial understanding of the characteristics and co‐variation of thermal extremes over the coastal regions.

Identification of limpets at rock coast in Lianyungang using DNA barcoding

Limpets living at the coast are of great value in both academic and applied fields. However, few studies on the status of these species at the coast of Lianyungang are available. To investigate the richness of limpets in the area, this study identified limpets mainly by using <italic>CO<italic>Ⅰ</italic></italic> (cytochrome c oxidase Ⅰ) barcoding and referring to pictures from the database of the World Register of Marine Species (WoRMS) after sample collection in four seasons. Results showed that four species of limpets were identified in this study (<italic>Siphonaria japonica</italic>, <italic>Lottia goshimai</italic>, <italic>Nipponacmea radula</italic>, <italic>Patelloida conulus</italic>). Of them, <italic>Siphonaria japonica</italic> (sample ID X-W-20) was the most common limpet with high proportion in a certain sampling season (51.4% in spring, 49.2% in summer, 49.2% in autumn, 64.3% in winter), indicating the potential usage of <italic>S</italic>. <italic>japonica</italic> to be served as the suitable biomarker in researching coastal environmental changes. Totally, three species can be accurately identified based on <italic>CO<italic>Ⅰ</italic></italic> barcoding: <italic>S</italic>. <italic>japonica</italic>, <italic>L</italic>. <italic>goshimai</italic> and <italic>N</italic>. <italic>radula</italic> (compared with sequences in NCBI database, the identity was≥99%). On the other hand, in the phylogenetic analysis, samples X-W-7 and X-W-18 were mixing in an ambiguous clade, which included <italic>P</italic>. <italic>conulus</italic> and <italic>N</italic>. <italic>schrenckii</italic>. The identification of X-W-7 and X-W-18 required other tools such as 16S rRNA barcoding (results from our unpublished data showed that the first three sequences were from <italic>P</italic>. <italic>conulus</italic> by blasting, and the identity was≥96%). Species of <italic>S</italic>. <italic>japonica</italic> and <italic>L</italic>. <italic>goshimai</italic> (firstly named by Japanese researchers in 2017) were firstly reported in Lianyungang. This study has improved the diversity of limpets for this region. According to this study, we expect that there should be more than four limpet species on this rocky intertidal shore, and this will be further verified in the future.

Empowering Fish-Farmer through Coastal Field School: Towards Sustainable Aquaculture Practice

Central Java Province is among the largest aquaculture producers in Indonesia. This hefty contribution also comes with a challenge of degraded coastal areas primarily due to mangrove conversion into ponds, land subsidence, and raising sea surface. In Demak Regency, abrasion and robs flood have adversely affected the farmers’ aquaculture ponds since the past decades. The changing coastal environment and lack of knowledge to adapt in aquaculture management led to declining production that hampered the community’s resilience in the future. To help the farmers to thrive, an initiative called Coastal Field School (CFS) was implemented in 10 villages in Demak. Principally, CFS is a participatory learning method that emphasizes problem solving and discovery based on learning toward their production systems. The entire CFS program took place in 2015 – 2020, however this study only focused on the CFS conducted in Bedono village during May 2019 – September 2019. This paper discusses the CFS impact on the farmers’ knowledge change using the indicators of farmers’ program participation level, pre-test and post-test result to determine the knowledge improvement, aquaculture management technique, and productivity rate. The test was analyzed using a paired t-test where the knowledge level of farmers increased significantly (p < 0.001). The farming productivity rate also improved by nearly 30%. It is concluded that CFS can strengthen the farmers’ resilience in the degraded coastal area in Demak.

Of marsh and mangrove: coupled biophysical and anthropogenic drivers of 20th century wetland conversion in Tampa Bay Estuary, Florida (USA)

Dense mangrove swamps currently dominate tidal wetlands of the Tampa Bay Estuary System on the central peninsular Gulf Coast of Florida (USA). Late-19th century Coast and Geodetic Survey topographical charts and Government Land Office surveys, however, depict wetland systems dominated by salt marsh—therefore suggesting mangrove dominance as a product of 20th century encroachment. To clarify the primary drivers of ecosystem change, this study integrates sedimentological, paleobotanical, and radiometric analyses of sediment cores collected in 2018 with analyses of aerial photography taken between 1940 and 1997. Results empirically ground truth the wetland conversions inferred through analytical comparisons of historical and modern mapping and establish a high-resolution chronology for coastal environmental change. These results showed that salt marsh and salt prairie habitats persisted within Tampa Bay study areas until the mid-20th century. Mangrove forest rapidly encroached the study areas over a 20 year interval, between 1960 and 1980, immediately following intensive ditching for mosquito control. The findings demonstrate how coastal geoengineering, mangrove autoecology, and sea-level rise interacted across the late-20th century to accelerate the creation of novel seascapes.

Environmental Changes and Cultural Transitions in SW Iberia during the Early-Mid Holocene

The SW coast of the Iberian Peninsula experiences a lack of palaeoenvironmental and archaeological data. With the aim to fill this gap, we contribute with a new palynological and geochemical dataset obtained from a sediment core drilled in the continental shelf of the Algarve coast. Archaeological data have been correlated with our multi-proxy dataset to understand how human groups adapted to environmental changes during the Early-Mid Holocene, with special focus on the Mesolithic to Neolithic transition. Vegetation trends indicate warm conditions at the onset of the Holocene followed by increased moisture and forest development ca. 10–7 ka BP, after which woodlands are progressively replaced by heaths. Peaks of aridity were identified at 8.2 and 7. 5 ka BP. Compositional, textural, redox state, and weathering of source area geochemical proxies indicates abrupt palaeoceanographic modifications and gradual terrestrial changes at 8.2 ka BP, while the 7.5 ka BP event mirrors a decrease in land moisture availability. Mesolithic sites are mainly composed of seasonal camps with direct access to the coast for the exploitation of local resources. This pattern extends into the Early Neolithic, when these sites coexist with seasonal and permanent occupations located in inland areas near rivers. Changes in settlement patterns and dietary habits may be influenced by changes in coastal environments caused by the sea-level rise and the impact of the 8.2 and 7.5 ka BP climate events.

14th BSGC2020 - Future Challenges for Geotechnical Engineering Preface

The Baltic Sea Region Geotechnical Conference (BSGC) series dates back to 1968, making it one of the oldest regional geotechnical conferences. The 14th Baltic Sea Region Geotechnical Conference, originally scheduled to take place in Helsinki in May 2020, had to be postponed due to COVID19 pandemic. It finally took place as virtual conference on 18th-19th January 2021, arranged in parallel with the 18th Nordic Geotechnical Meeting (NGM). The conference attracted total of 271 participants from 32 countries, successfully allowing to share insights and discuss ideas related to Future Challenges for Geotechnical Engineering, the main topic of the meeting.This 14th BSGC proceedings contain 31 technical papers presented during the conference alongside 14 interesting industry presentations. In the proceedings, the papers are divided into sections related to:• Soil and rock investigations• Digital applications in geotechnics• Environmental Geotechnics and recycling• Modelling• Design experiences and theoretical solutions• Ports and foundation engineering• Case studies and geotechnical artFurthermore, three keynote speakers presented during the 14th BSGC. The signature keynote entitled Signatures and impacts of climate change in coastal environments of the Baltic Sea and affiliations was given by Professor Tarmo Soomere, the President of Estonian Academy of Sciences. The other two keynotes were awarded jointly with 18th NGM.List of Organizing Committee, Scientific Committee are available in the pdf.

Variation of Semidiurnal Internal Tides along the Southeastern Coast of Korea Induced by Typhoons

Typhoon-induced strong winds can dramatically change the oceanic environment, occasionally resulting in sudden stratification changes. In July 2015, two consecutive typhoons, Chanhom and Nangka, passed over the Yellow and East/Japan Seas within a week. Remarkable temperature variations were observed near the southeastern coast of Korea, caused by typhoon-induced upwelling and downwelling events, which altered the energy of semidiurnal internal tides. During the typhoon-induced downwelling event, the energy of semidiurnal internal tides near the southeastern coast of Korea varied independently from the barotropic tidal forcing. Data-assimilated numerical simulation results reveal that the pycnocline, which is typically tilted toward the coast, enables the semidiurnal internal tidal energy to propagate toward shallow regions after being generated off the coast. Meanwhile, the downwelling event deepens the pycnocline near the coast and reflects and concentrates the semidiurnal internal tide energy near the bottom off the coast. A simple mechanism using the ratio between the wave characteristic slope and the bottom slope is proposed to explain the observed variations of semidiurnal internal tide energy near the coast. This paper demonstrates a case study showing that typhoon passage can modify the energetics of internal tides, which has the potential to cause unusual short-term coastal environmental changes.

Middle Holocene Coastal Environmental and Climate Change on the Southern Coast of Korea

We obtained a 15 m drill core from Deukryang Bay on the southwest coast of Korea, which is now an area of reclaimed land used for agriculture. We investigated changes in the depositional environment and hydrological climate responses to sea level changes using sedimentary facies, radiocarbon ages, grain-size analysis, total organic carbon (TOC), total sulfur (TS), and stable carbon isotopes (δ13C). Sediment deposition began at 12,000 cal yr BP and was divided into four stages based on changes from fluvial to intertidal environments related to Holocene marine transgression events. Stage 1 (&gt;10,000 cal yr BP) is represented by fluvial sediments; Stage 2 (10,000–7080 cal yr BP) is represented by the deposition of mud facies in an intertidal zone in response to sea level rise; Stage 3 (7080–3300 cal yr BP) was a period of gradually descending sea level following the Holocene maximum sea level and is characterized by gradual changes in TOC, TS, and C/S ratios compared with the mud facies of Stage 2. Stage 4 (3300 to present) was deposited in a supratidal zone and contains low TS and an abundance of TOC. Based on our TS and C/S ratio results, the south coast of Korea was mainly affected by sea level rise between 7000 and 3000 cal yr BP, during the middle Holocene. At 3000 cal yr BP, sea level began to stabilize or gradually decrease. In addition, changes in δ13C values are clearly observed since ca. 5000 cal yr BP, in particular, large hydrological changes via freshwater input are confirmed in 4000–3000 cal yr BP. We consider these shifts in freshwater input indicators of an increased influence of El Niño and La Niña conditions, related to the weakening of the East Asian Summer Monsoon (EASM) and changes in sea surface temperature (SST) of the Western Pacific Ocean during the middle Holocene climatic optimum (between 7800 and 5000 cal yr BP). The cooling periods of SST in East Asia between 8400 and 6600 cal yr BP reported from the west coast of Korea are related closely to changes in vegetation (as evidenced by δ13C) from 7700 cal yrs BP to the present in the southwest coast of Korea. We interpret the freshwater input events at 4000–3000 cal yr BP to be related to changes in SST in response to the weakening of the EASM on the southwest coast of Korea. However, additional research is needed to study the southward migration effect of the westerly jet related to SST and atmospheric circulation controlling terrestrial climate in the middle Holocene.

Cultural ecosystem services caught in a ‘coastal squeeze’ between sea level rise and urban expansion

Sea level rise and urbanization exert complex synergistic pressures on the provision of ecosystem services (ES) in coastal regions. Anticipating when and where both biophysical and cultural ES will be affected by these two types of coastal environmental change is critical for sustainable land-use planning and management. Biophysical (provisioning and regulating) services can be mapped using secondary data. We demonstrate an approach to mapping cultural ES by engaging stakeholders in iterative participatory mapping of personally and communally valuable cultural ES. We identify hotspots where highly valued cultural ES and high values for biophysical ES co-occur and generate spatially-explicit projections of sea level rise and urban expansion through 2060 to quantify impacts of the ‘coastal squeeze’ on ES. We study Johns Island, South Carolina, USA as an example of a vulnerable community in a low-lying region experiencing both rising water levels and a rapid influx of new residents and development. Our projections of environmental change through 2060 indicate that on Johns Island, cultural ES face disproportionately greater risk of decline than biophysical ES, with almost three quarters of the island’s cultural ES affected. We find that hotspots for cultural ES, such as community heritage sites and scenic vistas of oak-lined roads and marshes, rarely co-occur (only 3% area) with biophysical ES such as high values of carbon sequestration and agricultural production. This confirms the importance of engaging with local stakeholders to map cultural ES and puts them on a more level playing field with biophysical ES in decision-making contexts. Projected declines and limited overlap between biophysical and cultural ES highlight the need for tighter coordination between conservation and community planning, and for including locally valued cultural ES in assessments of threats posed by the ‘coastal squeeze’ of sea level rise and urban expansion.

Coastal environmental changes in Southeast Asia: A study from Quang Nam Province, Central Vietnam

Coastal environments are highly dynamic in nature and are sensitive to natural phenomena such as climate change and anthropogenic activities such as aquaculture or infrastructure development. At the same time, these areas are important in the economic development of the whole country, in which they are situated. Coastal areas in Vietnam are affected by a number of factors, such as climate change, sea level rise, aquaculture, pollution and tourism-related activities. This study investigated the coastal environmental changes in Quang Nam, which is a poorly developed province in Central Vietnam during the 31-year period between 1988 and 2019. For this, we analyzed spaceborne data such as Landsat series and Sentinel 2A, and digital elevation models. The coastal environmental variables analyzed were shoreline changes, changes in overall vegetation and mangrove forests, and the expansion of aquaculture ponds. In order to understand the variations in sea level heights, we analyzed HYCOM data for the period between 1994 and 2014. It has been noted that rapid shoreline erosion occurred along the Cua Dai Beach in recent years and the implementation of soft measures, such as sand bags, helped to reduce shoreline erosion to some extent. The current study also contributes to the global inventory of mangroves as most of the study area was missing in the previously available databases such as the world mangrove atlas.

Coastline extraction and land use change analysis using remote sensing (RS) and geographic information system (GIS) technology - A review of the literature.

Coastlines mapping techniques or the coastline automated analyses have been sought after. In practice, various sorts of seacoasts, for example, biological, silty, arenaceous, artificial, and bedrock coasts, have their own attributes, which force various degrees of intricacy on coastline mapping. As an extraordinary kind of complex artificial coast, aquaculture coast is shaped by the farming of aquatic organisms on silt tidal flats. With the rapid growth of coastal aquaculture in recent years, aquaculture coasts have increased in some developing countries. It has been estimated that aquaculture coasts constitute about 30% of all coastlines in mainland China. In order to identify, monitor, model, and manage the vast expanse of coastal aquaculture, effective methods of extracting aquaculture coastlines from remotely sensed imagery are desired. Secondly, with the rapid economic development in coastal areas, the development of coastal zone resources is also increasing day by day, which benefits the development of island coastal zone. Using oneself has become an important link in the development of marine economy. Due to the limited coastal resources and low environmental carrying capacity, the overexploitation and utilization of coastal resources will lead to a series of problems, such as coastal erosion, coastal migration and accumulation, island area reduction, etc., Both man-made activities and natural factors will lead to coastline changes, which will lead to corresponding changes in coastal ecological environment, thus affecting the coordinated development of coastal economy and the survival of coastal residents. Therefore, efficient, accurate and timely acquisition of coastline information and research on the spatial-temporal changes of coastline are of great significance to the protection of the living environment of coastal residents, the effective development of island and coastal resources, the coordination of sustainable economic development in coastal areas and the mitigation of marine disasters. This paper presents a review of those papers reporting coastline extraction and land use and land cover (LULC) change analysis using remote sensing (RS) and geographic information system (GIS) technology.

100 Opportunities for More Inclusive Ocean Research: Cross-Disciplinary Research Questions for Sustainable Ocean Governance and Management

In order to inform decision making and policy, research to address sustainability challenges requires cross-disciplinary approaches that are co-created with a wide and inclusive diversity of disciplines and stakeholders. As the UN Decade of Ocean Science for Sustainable Development approaches, it is therefore timely to take stock of the global range of cross-disciplinary questions to inform the development of policies to restore and sustain ocean health. We synthesized questions from major science and policy horizon scanning exercises, identifying 89 questions with relevance for ocean policy and governance. We then scanned the broad ocean science literature to examine issues potentially missed in the horizon scans and supplemented the horizon scan outcome with 11 additional questions. This resulted in an unprioritized list of 100 general questions that would require a cross-disciplinary approach to inform policy. The questions fell into broad categories including: coastal and marine environmental change, managing ocean activities, governance for sustainable oceans, ocean value, and technological and socio-economic innovation. Each question can be customized by ecosystem, region, scale, and socio-political context, and is intended to inspire discussions of salient cross-disciplinary research directions to direct scientific research that will inform policies. Governance and management responses to these questions will best be informed by drawing upon a diversity of natural and social sciences, local and traditional knowledge, and engagement of different sectors and stakeholders.

Reconstruction of 7500 years of coastal environmental change impacting seagrass ecosystem dynamics in Oyster Harbour (SW Australia)

Seagrass ecosystems, which have important functions such as coastal protection and blue carbon sequestration, are threatened by anthropogenic pressure including climate change. Long-term data series from seagrass sedimentary archives (mats) can be used to understand natural cycles of environmental change and answer key questions related to contemporary management. A 7500 yr sediment record from Posidonia australis meadows in Oyster Harbour (Albany, SW Australia) was subjected to multiproxy reconstruction by means of pigment analysis (UHPLC), analytical pyrolysis (Py-GC–MS), carbonate content, δ13C and δ15N stable isotope ratios, organic C (Corg) content, Corg/N ratio and glomalin-related soil proteins (GRSP). The study revealed a brackish lagoon (7500–7000 cal yr BP) that was transformed in an open marine environment (7000–4100 cal yr BP) due to Holocene transgression. Earliest evidence of seagrass establishment was detected around 4500 cal yr BP, and meadow extension accelerated between 4100 and 3700 cal yr BP. The meadow environment was surprisingly resistant against environmental perturbations, as the mat, composed of P. australis seagrass fibres embedded within a siliciclastic mineral matrix containing biogenic carbonates, continued to develop steadily until 190 cal yr BP (1830 CE). Then, shifts in several proxies (pigments, GRSP) showed evidence of terrestrial runoff-triggered eutrophication/turbidity (likely driven by forest clearance and agricultural activities after European settlement), but the seagrass showed resilience (no decline of the proportion of seagrass-derived Corg). By contrast, since ~1930 CE seagrass retreat is evident in the biogeochemical record: lighter δ13C values, lower lignin abundance and shifts in pigment abundance and types, affecting the balance between seagrass inputs and alternative sources, as was observed in previous studies of the area. The findings show that pigment proxies are useful early indicators of shifts in seagrass ecosystem condition, while lignocellulose and other pyrolysis products are useful proxies of more profound ecosystem alterations that influence seagrass abundance. The record indicates that the climax seagrass ecosystem condition, which prevailed for several millennia, had been impacted over the last century. Management of seagrass and coastal ecosystems should aim to avoid crossing ecological thresholds and diminish local impacts aggravating those of global change.

Coastal engineering evolution in low-lying areas and adaptation practice since the eleventh century, Jiangsu Province, China

Coastal engineering is an important measure in coping with coastal risks. With global warming and sea level rising, the sustainable adaptation of the low-lying areas becomes urgent. An in-depth understanding of the relationship between coastal engineering and environmental changes can help improve the adaptation capability for climate change. Here, we use historical documents and synthesis approach to examine coastal engineering evolution on the Jiangsu coast, the largest lowland area along China’s coastlines, and explore its response to local sea level and land use changes. The results show that coastal engineering here experienced a long-term period centered on sea-dike construction, with a shift from primary function of storm surge prevention since the eleventh century, towards a green coastal engineering approach in recent years. On the century scale, there was a close connection between local sea level change and coastal engineering change, while on the ten-year scale, population dynamics and land use changes were the key driving factors. Since the future climate and sea level change magnitude will be beyond what has been observed on the Jiangsu coast, it would be sensible to define a “critical time” that divides the near future and remote future. On such a basis, a strategic plan for the remote future may be formulated to prepare for the critical time when inevitable inundation occurs, and a second strategic plan may be adopted for the near future, to buy time for the coastal communities to make necessary preparations and at the same time to continue to use the resources. For the “near future,” a green coastal engineering approach (in combination with the experiences gained from the Jiangsu coast) should be developed to provide a low cost, high efficiency technique for coastal defense schemes. The thoughts outlined above may be applicable also to a number of low-lying coastal regions of developing countries.

A 5200-year paleoecological and geochemical record of coastal environmental changes and shoreline fluctuations in southwestern Louisiana: Implications for coastal sustainability

This study presents a 5200-year history of coastal environmental changes and shoreline fluctuations based on a multi-proxy sedimentary record developed from the eastern end of Louisiana's Chenier Plain. Palynological, loss-on ignition, grain-size, and X-ray fluorescence data for a 525 cm sedimentary core indicate five stages of ecosystem development in the Rockefeller Wildlife Refuge since the mid-Holocene. Between 5190 and 4240 cal yr BP, the relative sea-level was much lower than the present level, and our study area was occupied by a baldcypress swamp. When the Sale-Cypremont subdelta complex formed at a western position approximately 4600 years ago, our study area was transformed to a maritime forest about 4240–3440 cal yr BP, suggesting shoreline progradation. When the Mississippi River delta lobe switched to more easterly positions during the Teche, St. Bernard, Lafourche, and Plaquemine-Balize complexes, our study site was transformed back to a freshwater swamp between 3440 and 1520 cal yr BP and then to a coastal marsh between 1520 and 300 cal yr BP. After the Atchafalaya-Wax Lake subdelta complex formed at a more westerly position again, the modern-day beach form at 300 cal yr BP. These coastal ecosystem developments suggest that shoreline retreat started at ~3440 cal yr BP and persisted to the present day. In addition, evidence of at least four possible paleohurricane events was found during the late Holocene. Our multi-proxy record demonstrates that shoreline fluctuation in southwestern Louisiana was tied to the Mississippi River Delta Switch since the mid-Holocene. Shoreline progradation occurred during the Sale-Cypremont subdelta phase ~5200–3500 years ago, when the sediment supply was high. Retrogradation occurred after ~3500 cal yr BP when the Mississippi River subdelta complexes occupied more easterly position, resulting in diminished sediment supply. A significant increase in the delivery of water and total suspended sediment load from the Atchafalaya River to the Gulf of Mexico is needed in order to sustain the southwestern Louisiana coastal wetlands.

Simulation of Environmental Changes Consdering Sea-level Rise Near a Mega-scale Coastal Dike (Saemangeum [SMG] Dike, Korea)

Yoo, S.-C. and Suh, S.-W., 2020. Simulation of environmental changes considering sea-level rise near a mega-scale coastal dike (Saemangeum [SMG] dike, Korea). In: Malvárez, G. and Navas, F. (eds.), Global Coastal Issues of 2020. Journal of Coastal Research, Special Issue No. 95, pp. 309–314. Coconut Creek (Florida), ISSN 0749-0208.The construction of one of the biggest coastal dikes in Korea, the 33-km long Saemangeum (SMG) dike, was completed in 2006. Coastal environmental changes resulted in tidal asymmetry in the near field (i.e., adjacent to the dike) and the far field (i.e., up to opposite part of the Yellow Sea). Coastal hydrodynamic variations and engineering developments for gate operations (to maintain inner reservoir water quality (WQ) standards) rapidly alter coastal environments. The sea level is expected to rise by 80 cm by the end of this century, and an additional 21.4 cm of seasonal local summer sea level jump will serve as a reversing factor of WQ. This study applied the ADCIRC and EFDC models to simulate regional and local hydrodynamic and WQ changes. The far-field impacts of the SMG will occur continuously till year 2100 along the Chinese coast with M2 mordulation. The target water management level was set to elevation with respect to mean sea level (EL) as -1.5 m, which is very limited in terms of free discharge time for gate operation. According to the tidal excursion and residence time simulations, only 14% of gate operations in a month will be possible compared to the existing all-year-round condition, and only 4% will be exchangeable in summer. It is found that SMG yields alteration of tidal hydrodynamics showing overall de-amplification of ∼10 cm in the Yellow Sea (YS), especially along the west coast of Korea (WCK), as well as a slight amplification of ∼10 cm on the eastern coast of China. In addition, reducing the time for inner discharge because of the rising outer sea level directly influences WQ both in the areas near the gates and the inner water due to the increased residence time. Intensive study including long-term variations in tidal asymmetry and associated morphologies is needed to manage the hydrodynamic and/or WQ changes associated with such mega-scale coastal constructions.