Remote sensing composite information's trend surface analysis of Nansha Islands coral islets and reefs' top

Based on the remote sensing information feature of Nansha coral islets and reefs that controlled by the Nansha Islands local area's goological structure and growth law, by means of mathematical model and PC, the Nansha Islands coral islets and reefs' top geological data' spatial distribution and local change trend are simulated by using the trend surface system on the remote sensing composite information, and an scientific interpretation and local comparison of Nansha coral islands and islets' spatial distribution feature are made.

Physical and Mechanical Properties of Coral Sand in the Nansha Islands

Coral sand is a unique material developed in the tropical ocean environment, which is mainly composed of coral and other marine organism debris, with the CaCO3 content up to 96 %. It has special physical and mechanical properties due to its composition, structure and sedimentary environment. In this contribution, we discuss its specific gravity, porosity ratio compressibility, crushing, shearing and intensity for coral sand samples from the Nansha islands based on laboratory mechanical tests. Our results show distinct high porosity ratio, high friction angle and low intensity as compared with the quartz sand. We believe that grain crushing is the main factor that influences the deformation and strength of coral sand. Comprehensive study on the physical and mechanical properties of coral sands is significant in providing reliable scientific parameters to construction on coral islet, and thus avoids accidents in construction.

Survey of reefs based on Landsat 8 operational land imager(OLI)images in the Nansha Islands, South China Sea

A detailed survey of the reefs in the Nansha Islands＇ sea that are of strategic importance is conducive to their future development. In this study, a total of 50 Landsat 8 operational land imager（OLI） images were used to analyze the geological features and spectral characteristics of the Nansha reefs. The exposed islands/sandbanks,reef flats and sub-tidal reefs were identified with the near-infrared band, the red and green bands, and the blue band, respectively. Based on the relationships among various characteristics and bands illustrated in the OLI images, the maximum between-cluster variance threshold algorithm（OTSU method） and the mathematical morphology were employed to extract characteristic parameters of the spatial geometry of the reefs from top to bottom, which were subsequently operated by a series of post-processing methods such as vectorization,simplification and topological analysis. Among the 132 standalone reefs and 16 atolls that are identified in the study, four reefs have yet to be named in the Standard Names of Various Islands in the South China Sea and the website Nansha Islands Online（http：//www.nansha.org/）. Another 24 ones are exposed to the atmosphere even during high tides. Taiping Island with an area of 0.57 km^2 represents the largest exposed geological feature. This study demonstrated the applicability of medium-resolution satellite images to derive the coral reef information effectively and thus provided information for the related departments that are responsible to manage the coast.An improved resolution of multispectral bands with the panchromatic band in higher spatial resolution（15 m for OLI image） is expected to provide an optimum satellite based approach to map marine habitats.

Mechanical Properties and Microstructure of Portland Cement Concrete Prepared with Coral Reef Sand

The feasibility of using coral reef sand（CRS） in Portland cement concrete is investigated by testing the mechanical property and microstructure of concrete. The composition, structure and properties of the CRS are analyzed. Mechanical properties and microstructure of concrete with CRS are studied and compared to concrete with natural river sand. The relationship between the microstructure and performance of CRS concrete is established. The CRS has a porous surface with high water intake capacity, which contributes to the mechanical properties of concrete. The interfacial transition zone between the cement paste and CRS is densified compared to normal concrete with river sand. Hydration products form in the pore space of CRS and interlock with the matrix of cement paste, which increases the strength. The total porosity of concrete prepared with CRS is higher than that with natural sand. The main difference in pore size distribution is the fraction of fine pores in the range of 100 nm.

Regional hard coral distribution within geomorphic and reef flat ecological zones determined by satellite imagery of the Xisha Islands,South China Sea

Coral reefs in the Xisha Islands （also known as the Paracel Islands in English）, South China Sea, have experienced dramatic declines in coral cover. However, the current regional scale hard coral distribution of geomorphic and ecological zones, essential for reefs management in the context of global warming and ocean acidification, is not well documented. We analyzed data from field surveys, Landsat-8 and GF-1 images to map the distribution of hard coral within geomorphic zones and reef fiat ecological zones. In situ surveys conducted in June 2014 on nine reefs provided a complete picture of reef status with regard to live coral diversity, evenness of coral cover and reef health （live versus dead cover） for the Xisha Islands. Mean coral cover was 12.5% in 2014 and damaged reefs seemed to show signs of recovery. Coral cover in sheltered habitats such as lagoon patch reefs and biotic dense zones of reef flats was higher, but there were large regional differences and low diversity. In contrast, the more exposed reef slopes had high coral diversity, along with high and more equal distributions of coral cover. Mean hard coral cover of other zones was 〈10%. The total Xisha reef system was estimated to cover 1 060 km2, and the emergent reefs covered -787 km2. Hard corals of emergent reefs were considered to cover 97 km2. The biotic dense zone of the reef flat was a very common zone on all simple atolls, especially the broader northern reef flats. The total cover of live and dead coral can reach above 70% in this zone, showing an equilibrium between live and dead coral as opposed to coral and algae. This information regarding the spatial distribution of hard coral can support and inform the management of Xisha reef ecosystems.

Reconstructing Environmental Changes of a Coastal Lagoon with Coral Reefs in Southeastern Hainan Island

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.

Construction and analysis of a coral reef trophic network for Qilianyu Islands,Xisha Islands

Qilianyu Islands coral reefs(QICR),located in the northeastern part of the South China Sea,has been affected by human activities and natural disturbance.To characterize the trophic structure,ecosystem properties and keystone species of this region,a food-web model for the QICR is developed using methods involving a mass-balance approach with Ecopath with Ecosim software.Trophic levels range from 1.00 for detritus and primary producers to 3.80 for chondrichthyes.The mean trophic transfer efficiency for the entire ecosystem is 13.15%,with 55%of total energy flow originating from primary producers.A mixed trophic impact analysis indicates that coral strongly impacts most components of this ecosystem.A comparison of our QICR model with that for other coral reef ecosystems suggests that the QICR ecosystem is immature and/or is degraded.

The Effect of Climate on the Chemical Composition of the Coral Reefs around Kubbar Island—Kuwait

Thick recent carbonate sediments cover all the intertidal and subtidal zones consist of mainly different shell and coral reef debris. The chemical investigations of the coral fragments were done on controlled bases, which depend on the coral size and seasons, in order to elucidate the effect of weather parameters on the coral reefs. Geochemical investigation indicated that corals gathered from high-tide mark are mainly contaminated by copper, cobalt, and chromium and the corals gathered from low-tide mark are contaminated by lead and zinc. All the analyzed coral samples are contaminated by copper. The major contamination sights by heavy metals are related to the weather pattern around the islands. Calcium concentration in all the corals indicates a low-Magnesium calcite or aragonite composition, except for some coral samples which were gathered during October from the high-tide mark. Trace element concentration levels show high concentrations at sights of low-wave action around the island during the various seasons. Chemical analysis on the coral derbies indicates compositional variations regarding calcium and magnesium mole% between the seasons and at different locations and it is dependant on wind direction and water salinity. Some localities are iron rich others are aluminum and potassium rich. Generally, aluminum, iron, and potassium occur in lower quantities than the other elements. Therefore, all the chemical data regarding trace elements indicate relationship to weather and environmental parameters.

Sedimentology of the Redang Island Coral Reefs Environment

A study on the sedimentology of the Redang Island coral reefs environment was conducted. Sediments were collected on board UNIPERTAMA VII during the pre and post monsoon seasons. Twenty and seven sediments samples were collected using a Smith McIntyre grab on board UNI PERTAMA VII and put in labelled plastic bags then brought back to the laboratory for analysis. The sediments were analyzed for their sedimentological characteristics （mean size, skewness, standard deviation and kurtosis） using dry sieving method. Results showed that the highest mean size value of the sediments during the pre and post monsoons seasons are 2.14 ~ and 2.37 O. respectively and the lowest are -0.40 q~ and -0.10 ~, respectively. Based on the results, sediments can be classified as medium sand （34%）, poorly sorted （67%）, strongly negative skewed （36%） and extremely leptokurtic （56%） during the pre monsoon season, while during the post monsoon season sediments can be classified as medium sand （38%）, poorly sorted （73%）, strongly negative skewed （41%） and very leptokurtic （62%）. Results revealed that the sediments in the whole study area are relatively coarse. No relationship was observed between mean size and other sedimentological characteristics （R2= 0.05 pre-monsoon. R2 =0.0017 post monsoon） with seasons.

TYPE AND EVOLUTION OF LANDSCAPES OF NANSHA ISLANDS

Landscapes of the Nansha Islands may be divided into five types: tropical marine organismbreeding landscape of reef knoll like Zengmu Shoal, Wan'an Bank and so on; tropical marine organismbreeding landscape of atoll including all emerged reefs and most submerged reefs; tropical evergreen arborbush forest and phosphorous lime soil landscape of limesand Islets like Taiping Islet, Nanwei islet and so on; tropical shallow sea marine organismbreeding landscape of southern continental shelf; tropical oceanic and deepsea marine organism landscape in middle and north parts of the Nansha Islands area. These five landscape types may be also summed up as two categories, one is tropical sea landscape including those in shallow and deep sea, the other is tropical coral reef landscape including those of reef knoll, atoll and limesand islet. This paper outlines the evolutional model of landscapes of the Nansha Islands. The distribution and evolution of landscape types are related with palaeogeography and modern environmental conditions. The former shallow sea of the Nansha islands was coastal zone in the Late Pleistocene epoch. Deep sea is evolved from shallow sea due to long and slow subsidence of crust. Modern coral reefs develop on old reef top of the Late pleistocene epoch or on baserock of continental shelf in the Holocene due to the rise of sea level in postglacial. Limesand islet is in the peak of developmental stage.

The research on the remote sensing＇s information tree model of the Nansha coral islets and reef＇s spatial structure

Based on the Nansha coral islets and reef's time-space attributes,and the intension and extension of the remote sensing information, the concept model and concept system of coral islets and reef are proposed.Then twin-tree remote sensing information model for different kinds of reef is constructed by using abstracted islets and reef's primitive, and the structure recognition system for coral islets and reef type is developed.

Species composition and succession of coral reef fishes in Huaguang Reef,Xisha Islands

A list of coral reef fish species of Huaguang Reef was compiled in 2023 using hand fishing,diving fishing,underwater video,and eDNA detection,combined with historical data from 1979 and archival records from the South China Sea Fisheries Research Institute of the Chinese Academy of Fisheries Sciences for the years of 1998,1999,2003,and 2005.Successional characteristics of coral reef fishes through time were also explored.The findings revealed:(1)A total of 299 coral reef fish species were identified in Huaguang Reef,categorized into 2 classes,16 orders,and 56 families,with Perciformes exhibiting the highest species count(234),constituting 78.26%of all species.(2)In comparison to the period of 1979–2005,there was a reduction in the number of species at the order and family levels in 2023 at Huaguang Reef.Both the average taxonomic distinctness(Δt)and the variation in taxonomic distinctness(Λt)exhibited a declining trend,indicating disturbances in the fish ecosystem.(3)The proportion of herbivorous fish at Huaguang Reef remained relatively stable in 2023 compared to the 1979–2005 period.Notably,the similarity coefficient of herbivorous fish was the highest among different feeding types,signifying a degraded state of the Huaguang Reef habitat.(4)In contrast to the 1979–2005 period,a significant decline was observed in large-sized and carnivorous fish species at Huaguang Reef in 2023.The low similarity coefficients for both categories,with undiscovered fish species accounting for 58.49%and 45.76%of their respective taxa in the total list,respectively,suggested a notable impact of overfishing on coral reef fishes.The succession patterns revealed in this study provide a theoretical foundation for advancing the sustainable development of coral reef fish resources in the Xisha Islands and offer valuable insights for the protection and management of coral reef fishes.

Scleractinian coral communities of Hormuz Island in the PersianGulf

The abundance and health of scleractinian coral communities of Hormuz Island were investigated.For this purpose,we employed 20 m line intercept transects—12 in the intertidal zone and 15 subtidally to evaluate coral cover and community composition.The estimated dead coral coverage was 6.21%±0.81%,while live coral coverage was 16.93%±1.81%,considered as very poor.Totally,12 genera were recorded,of which Porites with 11.9%±1.4%live cover was the dominant,while Goniopora had the least cover(0.07%±0.08%).Based on Mann-Whitney U-test,live coral coverage,dead coral coverage,algal coverage,cover of other benthic organisms and abiotic components showed significant univariate differences between zones(p<0.05).The Spearman correlation test between the abundance of biotic and abiotic components indicated significant negative correlation of live coral and sand with zoantharian and significant positive correlation of algae and other benthic organisms with rubble.The reef health indices used for the corals indicated that,in general,the environmental conditions were not suitable,which could be attributed to both natural and anthropogenic factors,the most important of which was zoantharian’overgrowth on the scleractinian corals in this region.

Sedimentary nitrogen dynamics in a coastal reef area with relatively high nitrogen concentration

The migration and transformation of nitrogen(N)in sediments play an important role in regulating the N concentration and nutrient structures in shallow seas.However,studies of sedimentary N dynamics are rarely focused on carbonate sediments,although these account for about 40%of the continental shelf area.Thus,the regulation mechanisms of the N dynamics in the carbonate sands of coral reefs are not clear.Taking the coral reef area of Weizhou Island,which has a relatively high N concentration,as the research object,we conducted a series of flow-through reactor experiments to investigate the fluxes of different N forms at the interface of sediment and seawater and their regulation mechanism by environmental factors.The fluxes of dissolved inorganic and organic N(DIN and DON)at different stations were-0.39-0.12 mmol/(m^(2)·h) and-0.18-0.39 mmol/(m^(2)·h),respectively.Denitrification(0.11-0.25 mmol/(m^(2)·h) was closely coupled to nitrification,which was limited by the availability of organic matter and its degradation product(i.e.,NH_(4)^(+)).Thus,the excessive NO_(3)^(-) might be reduced to NH4+by dissimilatory nitrate reduction to ammonium,rather than to N_(2) by denitrification.NO_(3)^(-) reduction peaked at intermediate advection rates(96 L/(m^(2)·h)) and flow path lengths(10 cm),but the release of DON also peaked at the same condition.In addition,climate warming would significantly affect sedimentary N dynamics at Weizhou Island.These results may help address the broader issue of the N cycle in coral reef eco systems under the dual pressure of climate warming and anthropogenic activities,and these results are beneficial to coral reef protection and local ecological management.

三亚凤凰岛造礁石珊瑚迁移效果研究

造礁石珊瑚既是构成珊瑚礁生态系统中的关键功能生物,也是国家二级保护野生动物,其数量的快速衰退已引起了广泛关注,因此近年来我国对造礁石珊瑚以及珊瑚礁生态系统的保护正在逐步加强。海岸工程易对周边的珊瑚礁造成严重影响,实施保护性迁移是降低工程对造礁石珊瑚影响的重要手段。为研究海南热带海域造礁石珊瑚迁移方法以及迁移保护的效果,我们对三亚凤凰岛二期项目拆除工程影响海域内的造礁石珊瑚实施了保护性迁移及监测。迁移造礁石珊瑚个体共计16634株,包括鹿角珊瑚属、牡丹珊瑚属、滨珊瑚属等18属造礁石珊瑚种类。迁移个体分别迁移至鹿回头海域6210株与西岛海域10424株。迁移珊瑚采用了三种移植方法,分别为铆钉移植、小型移植礁体移植与直接摆放。在迁移至鹿回头和西岛两地8个月后,迁移珊瑚平均存活率均在80%以上,两地迁移珊瑚的总存活率为86.24%。调查的结果显示,铆钉移植的方法存活率最高,小型移植礁体和直接摆放的两种移植方法存活率稍低。迁移至西岛的珊瑚8个月平均生长了3.03cm,的增长率为23.31%,而鹿回头迁入的珊瑚平均生长了6.15cm,增长率为58.74%,高于迁移至西岛的珊瑚。迁移采用的三种移植方法的8个月的存活率均高于75%,并且珊瑚的生长速率较好,说明珊瑚适应迁入区环境。由以上结果来看,此次保护性迁移珊瑚数量多,涉及的珊瑚种类广,在迁移后经受过两次台风的影响,迁移结果具有一定的代表性。本研究中,珊瑚迁移的效果达到了保护受拆除工程影响的造礁石珊瑚的目的,可为未来的珊瑚迁移性保护提供重要经验。

《西沙群岛珊瑚岛(礁)地区岩土工程勘察标准》研究与编制

为适应和满足西沙群岛珊瑚岛(礁)工程建设的需要,使珊瑚岛(礁)岩土工程勘察有据可依,总结了西沙群岛岩土工程勘察项目实践经验和研究成果,通过资料收集、分析与研究,编制了《西沙群岛珊瑚岛(礁)地区岩土工程勘察标准》(DBJ46—060—2022)。介绍标准的编制背景、编制的工作流程、标准的主要内容和重点研究内容,探讨需要进一步研究的内容。

硫酸锌胶结珊瑚砂渗透特性试验及工程应用探讨

对松散珊瑚砂进行胶结处理以降低岛礁地层渗透性是促进生态岛淡水涵养的重要手段之一。为此,开展了硫酸锌胶结珊瑚砂的渗透试验,分析了不同浸泡时长、硫酸锌溶液浓度及初始干密度对胶结珊瑚砂渗透性的影响,采用干湿循环试验验证其耐久性,通过X射线衍射(X-ray diffraction,简称XRD)、扫描电镜(scanning electron microscope,简称SEM)、能量色散X射线光谱(energy dispersive spectrometer,简称EDS)及计算机断层扫描(computed tomography,简称CT)扫描研究微观胶结机制。结果表明:(1)硫酸锌胶结可将珊瑚砂渗透系数降低70.17%~95.79%;(2)干湿循环16次后,胶结处理36 h的珊瑚砂样品质量损失率不超过4%,渗透系数变化不超过1.0×10^(-3)cm/s,表明样品耐久性良好;(3)珊瑚砂和硫酸锌反应生成二水石膏与菱锌矿填充样品孔隙,使孔喉平均半径、配位数均减小,孔隙连通性显著下降。该技术可应用于岛礁吹填初期固砂防侵蚀、提高地基承载力、降低渗透性以促进地下淡水涵养和生态岛建设,具有重要的工程应用价值。

珊瑚礁海岸沉积物输运及珊瑚砂岛演变研究综述

珊瑚礁海岸沉积物的输运及珊瑚砂岛的演变研究在我国起步较晚,同时南中国海的珊瑚砂岛是我国重要的海洋空间资源,涉及国家领土主权的核心利益,开展这方面研究具有重要的学术价值和现实意义。综合分析了推移质和悬移质碳酸盐沉积物输运过程及其影响因素,重点介绍了短波、低频长波和海流对沉积物输运的驱动机制,以及粗糙珊瑚对沉积物的遮蔽效应。总结分析了珊瑚砂岛的动态演变规律及其影响因素,并重点介绍了珊瑚砂岛在长期海平面上升和短期风暴潮增强时的演变规律,并提出了今后研究需要关注的方向。

间断级配珊瑚砂地基渗流侵蚀稳定性试验研究

为解决降雨入渗导致的岛礁珊瑚砂地基沉降、塌陷等渗流侵蚀问题,利用自制渗透仪对不同D_(15)/d_(85)(D_(15)为粗粒组中小于某粒径的土颗粒累计百分含量为15%所对应的颗粒粒径,d_(85)为细粒组中小于某粒径的土颗粒累计百分含量为85%所对应的粒径)和细颗粒含量的间断级配珊瑚砂开展自上而下的单向渗透试验,厘清细颗粒迁移特征和流失的基本条件,揭示珊瑚砂渗透性变化规律,并借助微观手段对其内在机制进行分析。结果表明:(1)对于土骨架粒径为2~10 mm的珊瑚砂而言,粒径为0.25~0.50 mm的粒组是保证其渗流侵蚀稳定的关键粒组;(2)间断级配珊瑚砂地基D_(15)/d_(85)比值小于10且细颗粒含量在20%~30%之间时,渗流侵蚀稳定性较好;(3)与石英砂相比,珊瑚砂特殊的矿物成分及颗粒形貌导致其更难发生颗粒迁移,抗渗流侵蚀能力更强;(4)工程实践中,可通过提高相对密实度、优化颗粒级配或采取注浆胶结等措施提高地基渗流侵蚀稳定性。研究结果可为岛礁地基抗渗流侵蚀设计提供科学依据。

南海西沙典型珊瑚砂岛礁场地地震响应模拟与监测研究

南海珊瑚砂岛礁场地的非线性地震响应分析对中国南海岛礁建设的地震安全保障具有重要现实意义。以南海西沙某典型珊瑚砂岛礁为研究对象,建立了考虑该岛礁场地地形地貌特征及非饱和带水文地质特征的岛礁场地地震响应分析二维有限元数值模型。基于南海岛礁现场监测地震数据验证了模型的有效性,数值分析了不同输入地震信号的岛礁场地非线性地震响应规律。结果表明:①受岛礁岩盆效应影响,岛礁边缘处的PGA放大效应较为显著;沿高程方向,受地层岩性变化及地下水饱和度的影响,PGA放大因子曲线表现出明显的界面转折特征,并且松散珊瑚砂层的PGA放大效应较基岩更为显著;②岛礁场地加速度反应谱的卓越周期与输入地震动基本吻合,但岛礁场地的地表地震动显著持时与输入地震动相比均有不同幅度的延长;③全饱和与否对PGA放大因子和Arias强度有一定影响,但对PSA反应谱影响较小。研究成果可为南海西沙类似珊瑚砂岛礁场地的地震安全研究及场地抗震提供参考。