The persistence and habitability of coral reef islands in future extreme oceanographic conditions has received increasing attention in the recent decade,concerning that the sea level rise(SLR)and more frequent and int...The persistence and habitability of coral reef islands in future extreme oceanographic conditions has received increasing attention in the recent decade,concerning that the sea level rise(SLR)and more frequent and intense storms in the context of global climate change are expected to destabilize those islands.Here,we conduct a set of wave-flume laboratory experiments focusing on the morphodynamic change of reef islands to varying ocean forcing conditions(wave height and SLR).Subsequently,a phase-resolving XBeach numerical model is adopted to simulate the monochromatic wave process and its associated sediment dynamics.The adopted model is also firstly validated by laboratory experimental results as reported in this study.It is then used to examine the impacts of island morphological factors(island width,island height,island location and island side slope)on the island migration.The combined laboratory/physical and numerical experiment outputs suggest that reef islands can accrete vertically in response to the sea level rise and the increased storminess.展开更多
Harboring polyextremotolerant microbial topsoil communities,biological soil crusts(biocrusts)occur across various climatic zones,and have been well studied in the terrestrial drylands.However,little is known about the...Harboring polyextremotolerant microbial topsoil communities,biological soil crusts(biocrusts)occur across various climatic zones,and have been well studied in the terrestrial drylands.However,little is known about the functional metabolic potential of microbial communities involved in the biogeochemical processes during the early succession of biocrusts on the tropical reef islands.We collected 26 biocrusts and bare soil samples from the Xisha Islands and Nansha Islands,and applied a functional gene array(GeoChip 5.0)to reveal nitrogen(N)cycling processes involved in these samples.Both physicochemical measurement and enzyme activity assay were utilized to characterize the soil properties.Results revealed the composition of N-cycling functional genes in biocrusts was distinct from that in bare soil.Additionally,microorganisms in biocrusts showed lower functional potential related to ammonification,denitrification,N assimilation,nitrification,N fixation,and dissimilatory nitrate reduction to ammonium compared to bare soils.Although the abundance of nifH gene was lower in biocrusts,nitrogenase activity was significantly higher compared to that in bare soils.Precipitation,soil physicochemical properties(i.e.,soil available copper,soil ammonia N and pH)and soil biological properties(i.e.,β-glucosidase,fluorescein diacetate hydrolase,alkaline protease,urease,alkaline phosphatase,catalase and chlorophyll a)correlated to the N-cycling functional genes structure.Nitrate N and ammonia N were more abundant in biocrusts than bare soil,while pH value was higher in bare soil.Our results suggested biocrusts play an important role in N-cycling in coral sand soil,and will be helpful in understanding the development and ecological functions of biocrusts on tropical reef islands.展开更多
Changes in vegetation status generally also represents changes in the ecological health of islands and reefs(IRs).However,studies are limited of drivers and trends of vegetation change of Nansha Islands,China and how ...Changes in vegetation status generally also represents changes in the ecological health of islands and reefs(IRs).However,studies are limited of drivers and trends of vegetation change of Nansha Islands,China and how they relate to climate change and human activities.To resolve this limitation,we studied changes to the Normalized Difference Vegetation Index(NDVI)vegetation-greenness index for 22 IRs of Nansha Islands during normal and extreme conditions.Trends of vegetation greenness were analyzed using Sen's slope and Mann-Kendall test at two spatial scales(pixel and island),and driving factor analyses were performed by time-lagged partial correlation analyses.These were related to impacts from human activities and climatic factors under normal(temperature,precipitation,radiation,and Normalized Difference Built-up Index(NDBI))and extreme conditions(wind speed and latitude of IRs)from 2016 to 2022.Results showed:1)among the 22 IRs,NDVI increased/decreased significantly in 15/4 IRs,respectively.Huayang Reef had the highest NDVI change-rate(0.48%/mon),and Zhongye Island had the lowest(–0.29%/mon).Local spatial patterns were in one of two forms:dotted-form,and degradation in banded-form.2)Under normal conditions,human activities(characterized by NDBI)had higher impacts on vegetation-greenness than other factors.3)Under extreme conditions,wind speed(R^(2)=0.2337,P<0.05)and latitude(R^(2)=0.2769,P<0.05)provided limited explanation for changes from typhoon events.Our results provide scientific support for the sustainable development of Nansha Islands and the United Nations‘Ocean Decade’initiative.展开更多
It is exceedingly important to estimate the stability of coral reefs. In recent years, growing construction projects have been carried out on the reef flat in the South China Sea. As a special marine geotechnical medi...It is exceedingly important to estimate the stability of coral reefs. In recent years, growing construction projects have been carried out on the reef flat in the South China Sea. As a special marine geotechnical medium, it is made of the reef debris underwent overwhelmingly long geological age. Reefs grow thickly on the carbonate platform after the Late Oligocene and have five to six main sedimentary facies. It can be used as a recorder to measure the occurrence time of recent earthquake. A model of reef body is presented to study the influence of earthquakes according to the geological structure characteristic of reefs in the Nansha Islands. Furthermore, Geo Studio is used to simulate stress and deformation situations within it under various earthquake intensities. A safety factor is calculated by the limit equilibrium method, and the possible scenarios of earthquake-induced landslides and sliding scale are defined with a Newmark sliding block method, as well as stress distribution and deformation behaviors. Therefore, the numerical results suggest that the connections between the coral reef and the earthquake are as follows:(1) the reef body has a good stability under self-gravity state;(2) after the earthquake, it may cause slope's instability and bring out slumping when the safety factor is smaller than 1(FS〈1);(3) the safety factor decreases with the increasing earthquake intensity, and fluctuates around a particular value after a while;and(4) as a new developed part of the reef, the smaller shallow landslide will be easily subject to collapse caused by the earthquake. It is concluded that it is feasible to provide a reference for evaluating the stability of coral reef using a geotechnical engineering simulation method. This can help the engineering constructions in the South China Sea.展开更多
Under the background of vigorously developing facilities of island/reef in the world,the economic value and strategic significance of the island/reef have become increasingly important.Unfortunately,they may easily be...Under the background of vigorously developing facilities of island/reef in the world,the economic value and strategic significance of the island/reef have become increasingly important.Unfortunately,they may easily become the attacking target of missiles in the war time.Therefore,aiming at the damage quantification of the targets in the island/reef under the missile attacking,a macroscopic damage assessment model for the target area is proposed in this paper.The model focuses on the construction of the assessment model framework.Firstly,the analytic hierarchy process and the grey relational analysis are applied to measure the importance of each target in the region through four indicators of the target hazard,striking urgency,damage advantage and mission relevance,respectively.Secondly,based on the damage mechanism of shock wave and fragments to target,the corresponding damage model is established,and the damage grade of each target in the evaluated area is obtained according to the damage criteria and grading standard.Finally,the model obtains the overall damage grade of the target area by employing the fuzzy comprehensive evaluation method,with synthesizing the importance and the damage grade of each target.Through the verification of an example,it demonstrates the certain feasibility of the model and provides a certain basis and reference for the subsequent research.展开更多
Coastal lagoons with small catchment basins are highly sensitive to natural processes and anthropogenic activities. To figure out the environmental changes of a coastal lagoon and its contribution to carbon burial, tw...Coastal lagoons with small catchment basins are highly sensitive to natural processes and anthropogenic activities. To figure out the environmental changes of a coastal lagoon and its contribution to carbon burial, two sediment cores were collected in Xincun Lagoon, southeastern Hainan Island and (210) ~Pb activities, grain size parameters, total organic carbon(TOC), total nitrogen(TN), total inorganic carbon(TIC) and stable carbon isotopes(δ^(13)C) were measured. The results show that in 1770–1815, the decreasing water exchange capacity with outer open water, probably caused by the shifting and narrowing of the tidal inlet, not only diminished the currents and fined the sediments in the lagoon, but also reduced the organic matter of marine sources. From 1815 to 1950, the sedimentary environment of Xincun Lagoon was frequently influenced by storm events. These extreme events resulted in the high fluctuation of sediment grain size and sorting, as well as the great variation in contributions of terrestrial(higher plants, soils) and marine sources(phytoplankton, algae, seagrass). The extremely high content of TIC, compared to TOC before 1950 could be attributed to the large-scale coverage of coral reefs. However, with the boost of seawater aquaculture activities after 1970, the health growth of coral species was severely threatened, and corresponding production and inorganic carbon burial flux reduced. The apparent enhanced inorganic carbon burial rate after 1990 might result from the concomitant carbonate debris produced by seawater aquaculture. This result is important for local government long-term coastal management and environmental planning.展开更多
To solve the durability of island and reef concrete engineering in the harsh environment of high temperature,high salt,high humidity and windy,the strength grade of concrete and the type of corrosion inhibitor were us...To solve the durability of island and reef concrete engineering in the harsh environment of high temperature,high salt,high humidity and windy,the strength grade of concrete and the type of corrosion inhibitor were used as the influence factors,while the relative dynamic elastic modulus was used as the evaluation index.In addition,the law and time variability of the deterioration of concrete,the size effect,environmental similarity and the service life model were studied.The results showed that improving the strength grade of concrete could improve the durability of concrete,and corrosion inhibitor could slightly improve the durability of concrete.Time-varying law of the deterioration of concrete conformed to the univariate quadratic polynomial.Combined with the concrete damage equivalent theory,a size effect model based on the relative dynamic elastic modulus was proposed and verified,and the size effect coefficient was also given.An environmental similarity model between simulated and practical island and reef environment was proposed.Combined with the reliability theory and the first order second moment method,a new service life model of concrete structure was proposed.The authors were convinced that the research will be advantageous to researchers.展开更多
In 2019 a Scientific Research&Demonstration Platform was deployed near islands and reefs in South China Sea by a joint research group of 7 institutes and universities in China.It is a simplified small model of a t...In 2019 a Scientific Research&Demonstration Platform was deployed near islands and reefs in South China Sea by a joint research group of 7 institutes and universities in China.It is a simplified small model of a two-module semi-submersible-type VLFS.The test on site has continued for more than one and half years since then for long-term observations to validate the developed key technologies for design and behavior predictions of floating structures deployed near islands and reefs.An integrated information system was set up to continuously collect and inspect the data of the encountered waves,structure responses,connector forces,mooring line forces,anti-corrosion status of the platform,the performance efficiencies of a floating breakwater nearby and a wave energy converter attached on the breakwater.In this paper,the status of the on-site measurements and validations of the key technologies are briefly described.展开更多
On-site measurements show that water waves near islands and reefs in South China Sea exhibit different properties of wave energy distributions with regard to wave frequencies,among which the most prominent factor is t...On-site measurements show that water waves near islands and reefs in South China Sea exhibit different properties of wave energy distributions with regard to wave frequencies,among which the most prominent factor is the interplay of swells arising from the West Pacific Ocean and the local wind waves.Observations also show that the breaking waves continuously appear,containing more energy in high frequency components,and the nonlinear characteristics of the waves are important in adjusting the energy distribution.These properties may explain the large discrepancies between the well-accepted wave spectra(for example the P-M spectrum,Neumann spectrum,ITTC spectrum etc.)and the measured wave spectra near islands and reefs in South China Sea.Therefore,a new Rational Function Spectrum is proposed in this paper to describe waves near islands and reefs which turns out to show satisfactory accuracy.It well captures wave power distributions in the form of single and double peaks,at low-and high-frequency regions,as well as nonlinear scale power law.Based on the investigation of the measured data near an island in South China Sea,the relation between the parameters used in the Rational Function Spectrum and the statistical parameters of water waves(significant wave height and wave period)is established.It is noted that the wave properties at low-and high-frequencies are controlled by the local wind velocities at the wave growth stage,but remain constant at the wave decay stage.The parameter peak frequency is only dependent on the wave period corresponding to the maximum wave height.The parameter spectral peak is determined from the wave height and the wave period.These relations help to clarify the physical meanings of the parameters used in the Rational Function Spectrum,and thus provide an alternative spectral form to describe random waves near islands and reefs.展开更多
基金The National Natural Science Foundation of China under contract Nos 51979013 and 51909013the National Key Research and Development Program of China under contract Nos 2021YFC3100502 and 2021YFB2601105the Hainan Provincial Natural Science Foundation of China under contract No.421QN0978.
文摘The persistence and habitability of coral reef islands in future extreme oceanographic conditions has received increasing attention in the recent decade,concerning that the sea level rise(SLR)and more frequent and intense storms in the context of global climate change are expected to destabilize those islands.Here,we conduct a set of wave-flume laboratory experiments focusing on the morphodynamic change of reef islands to varying ocean forcing conditions(wave height and SLR).Subsequently,a phase-resolving XBeach numerical model is adopted to simulate the monochromatic wave process and its associated sediment dynamics.The adopted model is also firstly validated by laboratory experimental results as reported in this study.It is then used to examine the impacts of island morphological factors(island width,island height,island location and island side slope)on the island migration.The combined laboratory/physical and numerical experiment outputs suggest that reef islands can accrete vertically in response to the sea level rise and the increased storminess.
基金The Strategic Priority Research Program of the Chinese Academy of Sciences under contract Nos XDA13020301 and XDA13010500the Fund of Innovation Academy of South China Sea Ecology and Environmental EngineeringChinese Academy of Sciences under contract No.ISEE2018PY01。
文摘Harboring polyextremotolerant microbial topsoil communities,biological soil crusts(biocrusts)occur across various climatic zones,and have been well studied in the terrestrial drylands.However,little is known about the functional metabolic potential of microbial communities involved in the biogeochemical processes during the early succession of biocrusts on the tropical reef islands.We collected 26 biocrusts and bare soil samples from the Xisha Islands and Nansha Islands,and applied a functional gene array(GeoChip 5.0)to reveal nitrogen(N)cycling processes involved in these samples.Both physicochemical measurement and enzyme activity assay were utilized to characterize the soil properties.Results revealed the composition of N-cycling functional genes in biocrusts was distinct from that in bare soil.Additionally,microorganisms in biocrusts showed lower functional potential related to ammonification,denitrification,N assimilation,nitrification,N fixation,and dissimilatory nitrate reduction to ammonium compared to bare soils.Although the abundance of nifH gene was lower in biocrusts,nitrogenase activity was significantly higher compared to that in bare soils.Precipitation,soil physicochemical properties(i.e.,soil available copper,soil ammonia N and pH)and soil biological properties(i.e.,β-glucosidase,fluorescein diacetate hydrolase,alkaline protease,urease,alkaline phosphatase,catalase and chlorophyll a)correlated to the N-cycling functional genes structure.Nitrate N and ammonia N were more abundant in biocrusts than bare soil,while pH value was higher in bare soil.Our results suggested biocrusts play an important role in N-cycling in coral sand soil,and will be helpful in understanding the development and ecological functions of biocrusts on tropical reef islands.
基金Under the auspices of National Key Research and Development Program of China (No.2022YFC3103103)。
文摘Changes in vegetation status generally also represents changes in the ecological health of islands and reefs(IRs).However,studies are limited of drivers and trends of vegetation change of Nansha Islands,China and how they relate to climate change and human activities.To resolve this limitation,we studied changes to the Normalized Difference Vegetation Index(NDVI)vegetation-greenness index for 22 IRs of Nansha Islands during normal and extreme conditions.Trends of vegetation greenness were analyzed using Sen's slope and Mann-Kendall test at two spatial scales(pixel and island),and driving factor analyses were performed by time-lagged partial correlation analyses.These were related to impacts from human activities and climatic factors under normal(temperature,precipitation,radiation,and Normalized Difference Built-up Index(NDBI))and extreme conditions(wind speed and latitude of IRs)from 2016 to 2022.Results showed:1)among the 22 IRs,NDVI increased/decreased significantly in 15/4 IRs,respectively.Huayang Reef had the highest NDVI change-rate(0.48%/mon),and Zhongye Island had the lowest(–0.29%/mon).Local spatial patterns were in one of two forms:dotted-form,and degradation in banded-form.2)Under normal conditions,human activities(characterized by NDBI)had higher impacts on vegetation-greenness than other factors.3)Under extreme conditions,wind speed(R^(2)=0.2337,P<0.05)and latitude(R^(2)=0.2769,P<0.05)provided limited explanation for changes from typhoon events.Our results provide scientific support for the sustainable development of Nansha Islands and the United Nations‘Ocean Decade’initiative.
基金The National Basic Research Program(973 Program)of China under contract No.2013CB956104the National Natural Science Foundation of China under contract No.41376063the Strategic Priority Research Program of the Chinese Academy of Sciences under contract No.XDA13000000
文摘It is exceedingly important to estimate the stability of coral reefs. In recent years, growing construction projects have been carried out on the reef flat in the South China Sea. As a special marine geotechnical medium, it is made of the reef debris underwent overwhelmingly long geological age. Reefs grow thickly on the carbonate platform after the Late Oligocene and have five to six main sedimentary facies. It can be used as a recorder to measure the occurrence time of recent earthquake. A model of reef body is presented to study the influence of earthquakes according to the geological structure characteristic of reefs in the Nansha Islands. Furthermore, Geo Studio is used to simulate stress and deformation situations within it under various earthquake intensities. A safety factor is calculated by the limit equilibrium method, and the possible scenarios of earthquake-induced landslides and sliding scale are defined with a Newmark sliding block method, as well as stress distribution and deformation behaviors. Therefore, the numerical results suggest that the connections between the coral reef and the earthquake are as follows:(1) the reef body has a good stability under self-gravity state;(2) after the earthquake, it may cause slope's instability and bring out slumping when the safety factor is smaller than 1(FS〈1);(3) the safety factor decreases with the increasing earthquake intensity, and fluctuates around a particular value after a while;and(4) as a new developed part of the reef, the smaller shallow landslide will be easily subject to collapse caused by the earthquake. It is concluded that it is feasible to provide a reference for evaluating the stability of coral reef using a geotechnical engineering simulation method. This can help the engineering constructions in the South China Sea.
文摘Under the background of vigorously developing facilities of island/reef in the world,the economic value and strategic significance of the island/reef have become increasingly important.Unfortunately,they may easily become the attacking target of missiles in the war time.Therefore,aiming at the damage quantification of the targets in the island/reef under the missile attacking,a macroscopic damage assessment model for the target area is proposed in this paper.The model focuses on the construction of the assessment model framework.Firstly,the analytic hierarchy process and the grey relational analysis are applied to measure the importance of each target in the region through four indicators of the target hazard,striking urgency,damage advantage and mission relevance,respectively.Secondly,based on the damage mechanism of shock wave and fragments to target,the corresponding damage model is established,and the damage grade of each target in the evaluated area is obtained according to the damage criteria and grading standard.Finally,the model obtains the overall damage grade of the target area by employing the fuzzy comprehensive evaluation method,with synthesizing the importance and the damage grade of each target.Through the verification of an example,it demonstrates the certain feasibility of the model and provides a certain basis and reference for the subsequent research.
基金Under the auspices of National Natural Science Foundation of China(No.41530962)
文摘Coastal lagoons with small catchment basins are highly sensitive to natural processes and anthropogenic activities. To figure out the environmental changes of a coastal lagoon and its contribution to carbon burial, two sediment cores were collected in Xincun Lagoon, southeastern Hainan Island and (210) ~Pb activities, grain size parameters, total organic carbon(TOC), total nitrogen(TN), total inorganic carbon(TIC) and stable carbon isotopes(δ^(13)C) were measured. The results show that in 1770–1815, the decreasing water exchange capacity with outer open water, probably caused by the shifting and narrowing of the tidal inlet, not only diminished the currents and fined the sediments in the lagoon, but also reduced the organic matter of marine sources. From 1815 to 1950, the sedimentary environment of Xincun Lagoon was frequently influenced by storm events. These extreme events resulted in the high fluctuation of sediment grain size and sorting, as well as the great variation in contributions of terrestrial(higher plants, soils) and marine sources(phytoplankton, algae, seagrass). The extremely high content of TIC, compared to TOC before 1950 could be attributed to the large-scale coverage of coral reefs. However, with the boost of seawater aquaculture activities after 1970, the health growth of coral species was severely threatened, and corresponding production and inorganic carbon burial flux reduced. The apparent enhanced inorganic carbon burial rate after 1990 might result from the concomitant carbonate debris produced by seawater aquaculture. This result is important for local government long-term coastal management and environmental planning.
基金supported by the National Natural Science Foundation of China(Grant Nos.51878350 and 11832013).
文摘To solve the durability of island and reef concrete engineering in the harsh environment of high temperature,high salt,high humidity and windy,the strength grade of concrete and the type of corrosion inhibitor were used as the influence factors,while the relative dynamic elastic modulus was used as the evaluation index.In addition,the law and time variability of the deterioration of concrete,the size effect,environmental similarity and the service life model were studied.The results showed that improving the strength grade of concrete could improve the durability of concrete,and corrosion inhibitor could slightly improve the durability of concrete.Time-varying law of the deterioration of concrete conformed to the univariate quadratic polynomial.Combined with the concrete damage equivalent theory,a size effect model based on the relative dynamic elastic modulus was proposed and verified,and the size effect coefficient was also given.An environmental similarity model between simulated and practical island and reef environment was proposed.Combined with the reliability theory and the first order second moment method,a new service life model of concrete structure was proposed.The authors were convinced that the research will be advantageous to researchers.
基金supported by the Ministry of Industry and Information Technology(Grant No.[2016]22)the Ministry of Science and Technology(Grant No.2013CB36100)+2 种基金supports of the High-tech Ships Research Program([2016]22 and[2019]357)of the Ministry of Industry and Information Technologythe State Key Fundamental Research Program(2013CB036100)and the National Key Research and Development Program(No.2017YFBO202701)of the Ministry of Scienceand Technologythe Jiangsu Province Science Foundation for Youths(BK20190151).
文摘In 2019 a Scientific Research&Demonstration Platform was deployed near islands and reefs in South China Sea by a joint research group of 7 institutes and universities in China.It is a simplified small model of a two-module semi-submersible-type VLFS.The test on site has continued for more than one and half years since then for long-term observations to validate the developed key technologies for design and behavior predictions of floating structures deployed near islands and reefs.An integrated information system was set up to continuously collect and inspect the data of the encountered waves,structure responses,connector forces,mooring line forces,anti-corrosion status of the platform,the performance efficiencies of a floating breakwater nearby and a wave energy converter attached on the breakwater.In this paper,the status of the on-site measurements and validations of the key technologies are briefly described.
基金supported by the Key Program of National Natural Science Foundation of China(Grant No.51639003)the National Natural Science Foundation of China(Grant No.51679037)+1 种基金the Ministry of Science and Technology with the Research(Grant No.2013CB36101)the Ministry of Industry and Information Technology with the Research(Grant No.[2016)22.).
文摘On-site measurements show that water waves near islands and reefs in South China Sea exhibit different properties of wave energy distributions with regard to wave frequencies,among which the most prominent factor is the interplay of swells arising from the West Pacific Ocean and the local wind waves.Observations also show that the breaking waves continuously appear,containing more energy in high frequency components,and the nonlinear characteristics of the waves are important in adjusting the energy distribution.These properties may explain the large discrepancies between the well-accepted wave spectra(for example the P-M spectrum,Neumann spectrum,ITTC spectrum etc.)and the measured wave spectra near islands and reefs in South China Sea.Therefore,a new Rational Function Spectrum is proposed in this paper to describe waves near islands and reefs which turns out to show satisfactory accuracy.It well captures wave power distributions in the form of single and double peaks,at low-and high-frequency regions,as well as nonlinear scale power law.Based on the investigation of the measured data near an island in South China Sea,the relation between the parameters used in the Rational Function Spectrum and the statistical parameters of water waves(significant wave height and wave period)is established.It is noted that the wave properties at low-and high-frequencies are controlled by the local wind velocities at the wave growth stage,but remain constant at the wave decay stage.The parameter peak frequency is only dependent on the wave period corresponding to the maximum wave height.The parameter spectral peak is determined from the wave height and the wave period.These relations help to clarify the physical meanings of the parameters used in the Rational Function Spectrum,and thus provide an alternative spectral form to describe random waves near islands and reefs.