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25 May 2020, Volume 2020 Issue 3 Previous Issue    Next Issue

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Contents 2020, 2020 (3):  0-0.  Abstract ( 264 )   PDF (311KB) ( 74 )   Save Related Articles | Metrics

Estuary and Coastal Research

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A discussion on the diversion process of tide-dominated estuary bifurcation: The North Branch estuary of the Yangtze River LU Jiayu, GE Jianzhong, DING Pingxing 2020, 2020 (3):  1-12.  doi: 10.3969/j.issn.1000-5641.201941015 Abstract ( 487 )   HTML ( 452 )   PDF (1350KB) ( 143 )   Save The North Branch estuary of the Yangtze River is a typical tide-dominated estuary with bifurcation. The hydrodynamics and diversion processes are the major factors in sediment transport and geomorphology evolution of the tide-dominated estuary. This paper is based on data from the bottom tripod system and a cross-section survey of the North Branch in April 2018, whereby the dominant flow of each channel is calculated. The results show that during the spring tide cycle, the Santiao Port and the Guyuansha south waterway are flood-dominated and the net tidal current flows landward, whereas the Guyuansha north waterway is ebb-dominated, and the net flow has a seaward direction. Moreover, a high-resolution numerical FVCOM model is used to simulate the diversion process of the North Branch estuary. The results suggest that: the cross-sectional area of Guyuansha south waterway is much bigger than that of the north waterway, and the propagation direction of the lateral tide is consistent with the orientation of the Guyuansha south waterway, which mainly has onshore movement through the Guyuansha south waterway. The spatial distribution of the flood tide flow is significantly uneven in these two waterways. Meanwhile, tidal current from the Guyuansha south waterway crosses the shallow shoal and reaches the north waterway. It produces a net flow with the seaward direction through the north waterway. The flood-tide and ebb-tide diversion ratio of the Guyuansha north waterway are 29.7% and 47.2%, respectively, during the spring tide period and 41.6% and 43.1%, respectively, during the neap tide period. The residual patterns indicate that the tidal current enters the estuary from the south waterway and exits through the north waterway. These indicators and diversion characteristics can help predict estuarine sediment transport and geomorphological evolution processes within an individual bifurcated channel. References | Related Articles | Metrics

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Numerical simulation of saltwater intrusion mitigation by building a sluice in the North Branch of the Changjiang Estuary ZHU Jianrong, LU Peiyi, TANG Chuanmin, CHEN Qing, Lü Hanghang 2020, 2020 (3):  13-22.  doi: 10.3969/j.issn.1000-5641.201941017 Abstract ( 376 )   HTML ( 142 )   PDF (1119KB) ( 135 )   Save The most prominent feature of saltwater intrusion in the Changjiang Estuary is the saltwater spillover from the North Branch into the South Branch during the dry season; the spillover is the only source of saltwater for the Dongfengxisha, Taicang, and Chenhang Reservoirs as well as the main source of saltwater for the Qingcaosha Reservoir. A three dimensional numerical saltwater intrusion model, validated on the Changjiang Estuary, was applied to simulate and analyze salinity variation both during and after construction of the sluice at the upper reaches of the North Branch; the model considered tide, climatic river discharge, and wind in January and February. The simulated results showed that the South Branch is occupied by freshwater, the phenomenon of saltwater spillover from the North Branch vanishes and the salinity in the upper reaches of the North Branch decreases substantially after building the sluice. The salinity at the water intakes of the Dongfengxisha, Taicang, and Chenhang Reservoirs approaches 0. The salinity at the water intake of the Qingcaosha Reservoir decreases significantly and is less than 0.45 and there is freshwater at all time. The operation of the sluice in the numerical experiments is adopted in two ways. One is open during ebb current, closed during flood current in the daytime, and open during flood current in the nighttime. The other is open during ebb current and closed during flood current in the daytime and nighttime. The salinity variations in the South Branch with the two operational schemes are nearly identical. This can be attributed to the fact that the saltwater intrusion in the upper reaches of the North Branch is substantially reduced by the former sluice operational scheme, and a freshwater area with salinity approaching 0.45 appears. Even though the sluice is open during day flood current, the water entering the South Branch is freshwater and the total seaward residual current in the South Branch is enhanced. Considering the numerical simulation results and operation costs, the former sluice operational scheme is recommended. The water intake time is significantly improved, not only for the Dongfengxisha, Chenhang, and Qingcaosha Reservoirs in Shanghai, but also for the Taicang Reservoir in Jiangsu; moreover, security in water supply is ensured for both places. References | Related Articles | Metrics

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Influence of water level rise on currents and saltwater intrusion in the Changjiang Estuary TANG Chuanmin, ZHU Jianrong 2020, 2020 (3):  23-31.  doi: 10.3969/j.issn.1000-5641.201941001 Abstract ( 362 )   HTML ( 231 )   PDF (1379KB) ( 147 )   Save A semi-implicit estuarine, coastal, and ocean model (ECOM-si) was used to simulate and analyze the influence of a rise in water level on runoff, tidal and wind-driven currents, and on current and saltwater intrusion under the combined effects of various dynamic factors. In a scenario where the water level rises 30 cm in the Changjiang Estuary, numerical simulation results show that seaward runoff decreases due to augmentation of the river transection area; tidal currents decrease slightly with increases in water depth; the wind-driven current by northerly winds in the dry season is enhanced, which flow landward in the North Channel and seaward in the South Channel forming horizontal circulation; and the wind-driven current in the North Branch is strengthened. After the water level rise, saltwater intrusion in the North Branch is enhanced; salinity changes slightly in the middle reaches of the South Branch; the most distinct areas of saltwater intrusion enhancement are in the North Channel and North Passage, where the salinity rise is greater than 1 in neap tide and is somewhat reduced in spring tide; the salinity rise in the northern outlet of the North Channel reaches the maximum value observed in the entire estuary; and salinity on the shoal at the river mouth of the South Passage reduces because the water level rises and the nonlinear effect weakens. The water level rise, moreover, results in a salinity increase at the water intake of the three reservoirs (Qingcaosha, Chenhang, and Dongfengxisha) in the water source of the South Branch, which reduces water intake time and affects the safety of the water supply. References | Related Articles | Metrics

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Impact of the South-to-North Water Diversion Project on saltwater intrusion and freshwater resources in the Changjiang Estuary SU Aiping, Lü Hanghang, WU Yufan 2020, 2020 (3):  32-42.  doi: 10.3969/j.issn.1000-5641.201941031 Abstract ( 531 )   HTML ( 215 )   PDF (1244KB) ( 161 )   Save The South-to-North Water Diversion Project is an interbasin water diversion project, whose impact on changes in freshwater resources in the Changjiang Estuary is of widespread interest. In this paper, we used a 3D numerical model of estuarine saltwater intrusion to study the impact on saltwater intrusion and freshwater resources in the Changjiang Estuary from both short-term and long-term perspectives. The study, moreover, was focused on the eastern and middle route water transfer schemes of the Project. The results indicate that during the neap-spring tide period in mid-to-late February, the unavailable water intake time, corresponding to salinity greater than 0.45 at the water inlets of the Dongfengxisha, Chenhang, and Qingcaosha is 7.74, 3.08, and 2.72 days, respectively. In the case of a short-term water transfer scheme at river discharge of 1 000 m3/s, saltwater intrusion is intensified, especially at the river mouths of the North Channel, North and South Passages, and in the upper reaches of the North Branch, where salinity rise is most noticeable and a large area shows a salinity rise greater than 0.5; meanwhile, the supply of freshwater in the South Branch decreases. During the neap-spring tide period in mid-to-late February, the unavailable water intake time at the water inlets of the Dongfengxisha, Chenhang and Qingcaosha Reservoirs increases by 1.43, 2.14 and 2.13 days, respectively. In the case of long-term water transfer schemes at river discharge of 1 600 m3/s, the salinity rise in the entire estuary is even more noticeable; a large area of salinity rise greater than 1 shows up on the river mouths of the North Channel, North and South Passages, and a small area of salinity rise greater than 1.5. The supply of freshwater in the South Branch also decreases. During the neap-spring tide period in mid-to-late February, the unavailable water intake time at the water inlets of Dongfengxisha, Chenhang, and Qingcaosha Reservoirs increases by 1.49, 3.08, and 3.08 days, respectively. References | Related Articles | Metrics

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Numerical simulation of erosion and deposition at the water intake channel of the outer seawall sluice in the ecological restoration project area of Chongming Dongtan Bird Habitat LU Peiyi, ZHU Jianrong, QIAN Weiwei, YUAN Lin 2020, 2020 (3):  43-54.  doi: 10.3969/j.issn.1000-5641.201941013 Abstract ( 356 )   HTML ( 162 )   PDF (1249KB) ( 96 )   Save A three-dimensional numerical model for erosion and deposition at the water intake channel of the outer seawall of Chongming Dongtan Bird Sanctuary was established based on the hydrodynamic model of the estuary coupled with the sediment module and the bottom erosion and sedimentation equation. The model’s upstream boundary condition at the sluice was specified with water flux calculated by the Weir formula, where the inner water level was calculated by the hydrodynamic model of the Suitang River. The model’s downstream boundary condition of the water level, salinity and sediment concentration were calculated by the large domain numerical model of the Changjiang Estuary. We measured bottom elevations at the water intake channel before and after the sluice opening from July 28 to July 30, 2018 and found that the calculated model elevations were in general agreement with the measured values, indicating that the model can accurately simulate erosion and sedimentation changes. The calculation results for scouring and siltation show that under natural conditions, the water intake channel becomes level after 60 days of sluice closure because of sediment deposit. Siltation is largest near the sluice and gradually decreases with distance from the sluice to the sea. After the water intake channel was naturally silted for two months, the mean erosion thickness at the water intake channel was 96 mm in the case where Suitang River accumulated up to 3.0 m of water and discharged thereafter, 133 mm in the case where Suitang River accumulated up to 3.8 m of water and discharged thereafter, and 625 mm in the case where Suitang River accumulated up to 3.0 m of water and the sluice was opened to receive tidal water. Leaving the sluice open to receive tidal water is the most effective way for scouring sediment in the water intake channel. The research results provide scientific and technical guidance for the protection and management of the ecological restoration project area in Chongming Dongtan National Nature Reserve and the scouring sediment scheme of the water intake channel. References | Related Articles | Metrics

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The development and application of a physical-biogeochemical coupling model based on FVCOM SHI Shenyang, GE Jianzhong, CHEN Jianzhong, ZHENG Xiaoqin, DING Pingxing 2020, 2020 (3):  55-67.  doi: 10.3969/j.issn.1000-5641.201941008 Abstract ( 627 )   HTML ( 161 )   PDF (1395KB) ( 517 )   Save By combining the hydrodynamic model FVCOM with the biological model ERSEM, based on FABM, this paper develops a new physical-biogeochemical model: FVCOM-FABM-ERSEM. The combined model is suitable for application to coastal areas and is one of the most comprehensive ecosystem models for the lower trophic levels of the marine food-web. Using the combined model, a one-dimensional vertical (1DV) model and a three-dimensional Changjiang Estuary model were established. The results of the 1DV model were consistent with observation data from the European L4 Station. This paper also simulates the physical and biogeochemical processes of Changjiang Estuary from 2013 to 2016 with the 3D Changjiang Estuary model. The distribution of temperature, salinity, nitrate, phosphate, and chlorophyll-a levels were all found to be consistent with observation data from cruises and MODIS data in the spring when algal blooms occur. The characteristics of the front dynamics of Changjiang Estuary were well represented. The relationship between salinity, turbidity, nutrients, and chlorophyll around the plume front was determined through modeling, indicating a significant co-occurrence effect along the front of physical and biological processes. References | Related Articles | Metrics

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Effects of silver nanoparticles on dissimilatory nitrate reduction in estuarine and tidal sediments ZHANG Mengxia, ZHENG Yanling, YIN Guoyu, DONG Hongpo, HAN Ping, GAO Juan, LIU Cheng, CHANG Yongkai, LIU Min, HOU Lijun 2020, 2020 (3):  68-77.  doi: 10.3969/j.issn.1000-5641.201941005 Abstract ( 383 )   HTML ( 297 )   PDF (906KB) ( 70 )   Save Human activity can cause accumulation of silver nanoparticles (AgNPs) in estuarine and coastal environments; however, the effects of accumulated AgNPs on nitrogen transformation remain unclear. This study investigated the effects of AgNPs on dissimilatory nitrate reduction to ammonium (DNRA) rates in Yangtze estuarine and intertidal sediments using exposure experiments with three different sizes of AgNPs (10 nm, 30 nm, and 100 nm) and three different AgNPs concentrations (0.1 mg/L, 5 mg/L, and 10 mg/L). The results showed that AgNPs inhibited DNRA rates of sediments with different salinity levels, but the inhibition did not increase significantly with time. AgNPs had relatively high inhibition in medium salinity areas depending on the physical properties of the respective sediments. Moreover, it was shown that both the size and concentration of AgNPs were important factors affecting their toxicity. When the concentration of AgNPs was ≤ 5 mg/L, the inhibition of 10 nm AgNPs on the DNRA rate was greater than those of 30 nm and 100 nm AgNPs; the strongest inhibition effects among different salinities reached 16.03% (at 0.2‰ salinity), 20.27% (at 8.0‰ salinity), and 15.36% (at 20‰ salinity). However, when the concentration of AgNPs was 10 mg/L, the inhibition of 30 nm and 100 nm AgNPs on the DNRA rate under the same salinities increased to 17.48%, 33.18%, and 26.45%, respectively; these values were larger than the inhibition of 10 nm AgNPs. There was no significant correlation between Ag+ concentration and the inhibition of AgNPs on the DNRA rate (p > 0.05), indicating the inhibitory effect of AgNPs on the DNRA rate could not be fully explained by the toxicity of Ag+. These results are of great significance to understand the influence of emerging pollutants on the estuarine nitrogen cycle. References | Related Articles | Metrics

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Response of nitrogen removal in the overlying water to sediment resuspension in the intertidal wetlands of the Yangtze Estuary ZHANG Hongli, YIN Guoyu, ZHENG Yanling, GAO Juan, GAO Dengzhou, CHANG Yongkai, LIU Cheng 2020, 2020 (3):  78-87.  doi: 10.3969/j.issn.1000-5641.201941007 Abstract ( 300 )   HTML ( 198 )   PDF (1291KB) ( 168 )   Save The 15N isotope tracer technique was used to examine the response of denitrification and anammox to sediment resuspension in the intertidal wetlands of the Yangtze Estuary. The results showed that both denitrification and anammox rates were positively correlated with the turbidity of the overlying water, which demonstrates that sediment resuspension can promote the occurrence of nitrogen removal processes in overlying water. The denitrification and anammox rates showed significant spatial differences due to the physiochemical characteristics at different sites under sediment resuspension and was mainly attributed to the sediment TOC contents. In addition, the abundance of nirS and anammox bacterial 16S rRNA genes increased with suspended sediment turbidity, which indicates that sediment resuspension could increase the abundance of nitrogen removal functional bacteria, thus promoting nitrogen removal rates. These results indicate that sediment resuspension has important influence on nitrogen transformation processes and facilitates nitrogen removal in intertidal wetlands. References | Related Articles | Metrics

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Material flux variation and mechanism analysis of different rivers originating from the Tibetan Plateau ZHANG Xiaocheng, JIANG Xuezhong 2020, 2020 (3):  88-97.  doi: 10.3969/j.issn.1000-5641.201941006 Abstract ( 305 )   HTML ( 207 )   PDF (979KB) ( 79 )   Save Many large rivers in Asia originate from the Tibetan Plateau. Changes in the rivers reflect not only changes in the Tibetan Plateau itself, but also relate closely to water resource utilization in the respective basin countries. Changes in terrestrial materials entering the sea reveal the impact of human activities on land-sea interactions in the basin. With changes in natural conditions and socio-economics, material flux from the basin has evolved over time. In this resarch, material flux was compared quantitatively by analysis of the water discharge, sediment load, and nutrient volumes for elements such as nitrogen, phosphorus, and silicon in the Yangtze, Yellow, Mekong, Indus, Ganges, and Brahmaputra Rivers. In addition, the mechanism of variation was discussed by comparison of two phases of land use and land cover in 1995 and 2015, which were extracted from remote sensed image mapping. The results revealed that the runoff of the Yangtze, Indus, and Brahmaputra Rivers decreased significantly from 1995 to 2015, but the Ganges increased over the same period. The Mekong River runoff changed slightly and fluctuated year to year. However, the sediment transportation from river to sea in the Yangtze, Yellow, and Indus Rivers reduced substantially at a statistically significant level (p < 0.05). In terms of nutrient element flux, the dissolved inorganic nitrogen (DIN) of the Yellow and Mekong Rivers showed an upward trend and the Yangtze River DIN decreased by about 26.5%. The total phosphorus and silicon flux in the Yangtze and Mekong Rivers did not change much, while the dissolved inorganic phosphorus (DIP) in the Yellow River decreased. The nitrogen and phosphorus flux was mainly affected by runoff, and the silicate flux was influenced by variations in sediment loads. Furthermore, dam construction, usage of pesticides and fertilizers, and changes in land use have changed the proportion of nutrient elements. An increase in industrial activity, agricultural development, and water conservancy facilities, resulted in a higher total nitrogen and phosphorus flux and more significant reduction in sediment loads. Understanding the material flux data of each basin is of great significance for management departments to build basins with common goals and use water resources reasonably and effectively. References | Related Articles | Metrics

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Evaluation of the effectiveness of a coastal ecological restoration project based on ecosystem services: A case study on Yingwuzhou Wetland, China WU Wei, LI Caixia, CHEN Xuechu 2020, 2020 (3):  98-108.  doi: 10.3969/j.issn.1000-5641.201941027 Abstract ( 444 )   HTML ( 173 )   PDF (692KB) ( 196 )   Save For the last three years, Yingwuzhou Wetland has been operating as the first national-level artificial coastline restoration pilot project in Shanghai; it is important for decision makers, builders, and administrators to understand the effectiveness of the project. In this paper, we study eight key indicators of ecosystem services to evaluate project performance, namely plant supply, water purification, carbon sequestration, climate regulation, wind and wave elimination, biodiversity conservation, recreation, and research and education. The results show that the total value of ecosystem services in Yingwuzhou in 2018 was 437.6×104 yuan·a–1, and the value per unit area was 18.9×104 yuan·hm–2·a–1; the proportional ranking of services can be classified as follows: Cultural Services (45.6%) > Regulation Services (41.9%) > Supporting Services (12.4%) > Provisioning Services (0.1%). The evaluation results show that the value of ecosystem services on the coastline of Yingwuzhou Wetland is significantly improved after ecological restoration; ecosystem services, moreover, are centered on culture and ecology, and the service area has localization characteristics, which has a noticeable effect on improvement of the ecological environment quality at the Jinshan coastline. The results of this study will help to visualize the effectiveness of the restoration of Yingwuzhou Wetland. The research methods can serve as a reference for the evaluation of similar ecological restoration projects in coastal zones. References | Related Articles | Metrics

Geography

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Review of driving factors for land degradation and restoration based on IPBES GUO Xiaona, CHEN Ruishan, LI Qiang, PAN Zhenzhen 2020, 2020 (3):  109-118.  doi: 10.3969/j.issn.1000-5641.201941009 Abstract ( 365 )   HTML ( 139 )   PDF (782KB) ( 112 )   Save Land degradation is one of the major global ecological problems that is endangering the health and well-being of 3.2 billion people, threatening food and water security, and reducing biodiversity. Land degradation, moreover, is triggering regional conflicts, large-scale migration and the spread of disease, and has raised widespread concerns from international organizations such as the UN, IPBES, and IPCC in recent years. Understanding the drivers of land degradation is fundamental to preventing land degradation and restoring degraded land. This paper examines the drivers of land degradation based on a land degradation and restoration assessment report from the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES). The factors that lead to land degradation can be divided into direct (human) drivers, indirect (human) drivers, and climate change. This paper elaborates on eight types of direct drivers for land degradation, namely grazing land management; cropland and agroforestry management; forests and tree plantation management; non-timber natural resource extraction; fire regime change; extractive industry and energy development; construction, industrial development, and urbanization; and invasive species. This research also explores indirect driving factors and their respective mechanisms, including: population, economy, technology, institution and management, and culture as well as mechanisms (i.e. interaction effects) that are situation-dependent, nonlinear or abruptly-changing, and remotely coupled. The research notes that climate change can also lead to various types of land degradation. Finally, this article reviews driving factors for land degradation in typical areas of China and proposes relevant preventive and response measures. An in-depth understanding of the drivers for land degradation will provide decision making support for “the governance of mountains, water, forests, cropland, lakes, and grass ecosystems” as well as the construction of “Beautiful China”. References | Related Articles | Metrics

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Evaluating service accessibility of residential care facilities in Shanghai for fulfilling basic needs CHEN Jie, WU Jianping, GUO Peijun, YAO Shenjun 2020, 2020 (3):  119-128.  doi: 10.3969/j.issn.1000-5641.201841038 Abstract ( 302 )   HTML ( 40 )   PDF (1266KB) ( 92 )   Save Appropriate assessment of the service accessibility of residential care facilities is important for making policies on the allocation of residential care resources. In accordance with policy requirements for the service of residential care facilities in Shanghai, this study modifies the traditional Two-step Floating Catchment Area (2SFCA) method by introducing a power function as a distance decay relationship, employing multi-radius service areas, using the shortest driving distance to measure the distance parameter, and introducing administrative restrictions. With the proposed method, residential care services were calculated and analyzed at the town level. Service accessibility results were then compared under two scenarios. The results show that service accessibility of Shanghai residential care facilities is far below the planning targets for 2020. Less than 1/3 of the towns had service accessibility values with at least 35 beds per thousand elderly people. Comparing the results from two scenarios studied, we found that administrative barriers resulted in lower accessibility for most towns, especially in urban areas where the elderly population density is high; consequently, this significantly enlarged the rural-urban divide. References | Related Articles | Metrics

Urban and Regional Science

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A microclimatic impact analysis on multi-dimensional indicators of urban road fabric: Empirical research on Shanghai JIANG Yunfang, HAN Xuemei, SHI Tiemao, SONG Danran 2020, 2020 (3):  129-147.  doi: 10.3969/j.issn.1000-5641.201941004 Abstract ( 350 )   HTML ( 30 )   PDF (1423KB) ( 79 )   Save Different historical backgrounds and planning ideas result in different road fabrics for a city. Road fabric patterns affect urban microclimate factors and form a unique local microclimate. In this paper, we studied the road fabric of four “city” areas in Shanghai (i.e., the old downtown area, Gubei international community, Anting new town, and new Jiangwan town) by simulating the microclimate of the four research areas using ENVI-met4.3 software; we then used the data to compare the microclimate status of urban fabric at the medium and micro levels. At the medium level, the relationship between width, orientation, spacing, connectivity, and the climate environment was analyzed. At the micro level, the effects of Near-line Rate, Height to Wide ratio (H/W) and Sky View Factor (SVF) on the distribution characteristics of microclimate factors in roads were analyzed. The comparative analysis of microclimate characteristics at the “city” scale provides useful insights for urban climate adaptability in urban design projects and spatial morphology optimization in future urbanization development. References | Related Articles | Metrics