Anthropocene Coasts最新文献

The assessment of river ecosystem health is crucial for improving river resilience, achieving ecological protection and rational utilization in the Yangtze Estuary region where there is high utilization of rivers and a high demand for quality rivers by Shanghai, the world's largest modern city. To assess the ecological health status of Yangtze Estuary rivers, this study established a river health assessment model consisting of five dimensions: water quality, river landscape, aquatic organisms, river hydrology, and human interference, and a total of ten indicators based on the ecological survey results in the summer and autumn of six river channels in Chongming Island in the Yangtze Estuary. The evaluation results reveal that the health status of rural rivers in the northwest and east of Chongming Island (S2, S3) is the best, reaching an excellent level, while the small river in the central part of Chongming Island (S6) is the worst, reaching a somewhat inferior level. Compared with rural rivers, the comprehensive evaluation results of urban rivers are good or ordinary level. The high proportion of building area on both sides of the river and the low vegetation cover are the main factors that restrict their scoring results. In contrast, rural rivers need to focus on the area of buffer zones such as forests and vegetation on both sides of the river, river connectivity, appropriate widening of narrow rivers, regular cleaning and dredging of rivers, as well as reducing human interference with the rivers. Regarding seasonal changes, the health assessment results of Chongming Island rivers in summer are better than those in autumn, and the differences between sites in summer are slightly greater than those in autumn. The seasonal differences between sites are mainly due to changes in indicators of the diversity of zooplankton, phytoplankton, and macrobenthos. To further improve the ecological health of rivers, measures of ecological restoration could be adjusted based on regular health assessment and health weakness analysis.

In AD1128, the Yellow River shifted its course from the Bohai Sea to the South Yellow Sea (SYS) due to anthropogenic dike excavation, starting the development of the Abandoned Yellow River Delta (AYRD) that lasted for more than 700 years (AD1128-1855). However, the sediment flux of the abandoned Yellow River into the sea is in a state of change due to human activities, and the growth process of the AYRD is not well understood. Here, we investigate the growth process of the AYRD and its sedimentary record characteristics over the last millennium based on three cores collected from the AYRD.

The results show that the main sediment types in the AYRD are silt, mud and sandy silt. After AD1128, the grain size components in the sediments of the AYRD showed significant stage changes with the sand content first starting to decrease. The clay content increased and remained at a high percentage in the middle to late 14th century, followed by a sharp increase from the mid-16th to the mid-17th century, due to a further increase in sediment flux from the abandoned Yellow River into the sea. A slight increase in the proportion of sand content during the final stage of the transition from subaqueous delta to terrestrial delta is a distinctive feature of the sedimentary record, and this change persists for 10 ~ 90 years in different core records.

This study further proposes a schematic model of the development of the AYRD: (a) before the 16th century, the sediments were deposited mainly in the estuary and nearshore, with rapid vertical accretion; (b) After the 16th century, the horizontal land formation was the main focus, and the rate of seaward extension increased rapidly. This model also reflects the following pattern: when the sediment flux from the river into the sea is certain, the rate of land formation is inversely proportional to the rate of vertical accretion. The dominant factors affecting the evolution of the AYRD are the sediment flux into the sea and initial submerged topography, with less influence from sea level changes. Hydrodynamic erosion by wave and tidal forces from the outer delta began to dominate after the interruption of sediment supply due to the Yellow River mouth northward to the Bohai Sea in AD1855. This study has important implications for understanding the growth and evolution of deltas under the influence of human activities.

The water’s edge is a critically important and efficient location to trade with other partners by connecting inland water channels and sea lanes and to obtain food provisions from the biologically diverse and productive sea. Human civilization has built around the ports and harbors by constructing fixed structures to support waterborne transport and enhance or sustain city functions for millennia. These artificially fixed structures are not in natural equilibrium with the environment (water and sediment). Access channels and the sea bottom adjacent to piers are often dredged to accommodate larger ships. Bottom sediment dredging is a part of port management. Where to place the dredged material is of primary concern for port authorities because of its sheer volume and the potential to be chemically contaminated. The London Convention and the London Protocol (LC/LP) are international treaties that provide a process in preventing pollution from dumping of contaminated material at sea, and finding sound alternatives such as confined disposal facilities, and using clean dredged material in wetland creation or beach nourishment, based on the precautionary approach. The Anthropocene (Anthropocene refers to the most recent period in Earth’s history when human activity started to impact significantly on the climate and ecosystems.) coast of ports, harbors, wetlands, shorelines, and beaches of the coastal megacities faces tremendous challenges in managing navigational and shoreline infrastructure in view of sea level rise and climate change. Dredged sediments are a resource and are a key to protection of shorelines. The benefits of being members of the LC/LP treaties are that there is a wealth of various national experiences on sediment management available via the network of LC/LP national experts and in the records of the LC/LP’s Meetings of Contracting Parties.

Understanding of erosion and accretion patterns over intertidal mudflats during storm periods is vital for the management and sustainable development of coastal areas. This study aimed to investigate the effect of the 2014 storm Fung-wong on the erosion and accretion patterns of the Nanhui intertidal mudflats in the Yangtze estuary, China, based on field measurements and Delft3D numerical modeling. Results show that prolonged easterly winds during the storm enhance the flood velocity, weaken the ebb velocity, and even change the current direction. The current velocity, wave heights, and bed-level changes increased by 1–1.43 times, 2.40–3.88 times, and 2.28–2.70 times than those of normal weather, respectively. The mudflats show a spatial pattern of overall erosion but increasing erosion magnitude from the high (landward) mudflat to the low (seaward) mudflat during the storm. The magnitude of bed-level change increases with increasing wind speed, but the spatial pattern of erosion and accretion remains the same. The main reason for this pattern is the longer submersion duration of the low mudflat compared with the high mudflat, so the hydrodynamic process is longer and stronger, leading to an enhancement in bed shear stress and sediment transport rate. Wind speed increases the hydrodynamic intensity but does not affect on the submersion duration over each part of the intertidal mudflat. This study is helpful to improve the understanding of physical processes during storms on intertidal mudflats and provides a reference for their protection, utilization, and management, as well as for research in related disciplines.

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.

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.