珊瑚礁岩土的工程地质特性研究进展

文章综述了珊瑚礁岩土工程的研究意义、珊瑚礁岩土的组成、钙质砂的物理性质、钙质砂的静力学特性、珊瑚礁岩土中的桩基工程、珊瑚礁混凝土等方面的研究现状。得出：1）颗粒易破碎是钙质砂最重要的特性,直接影响着钙质砂的其他力学性能,而影响钙质砂颗粒破碎的主要因素有围压、有效应力、颗粒级配、初始孔隙比、颗粒强度、颗粒形状等;2）生物颗粒的易破碎以及成桩过程对钙质砂结构的扰动,导致钙质砂中的桩基承载力远低于普通石英砂;3）在以珊瑚砂为原料的混凝土工程中,利用抗硫酸盐水泥拌养的珊瑚混凝土,其强度和耐久性相对较好。最后指出：加强对钙质砂颗粒破碎发生机理的研究以及建立破碎模型、加强对新型珊瑚礁钢筋混凝土和新型桩基的研究、开展珊瑚礁岩土工程的灾害预防与处理以及工程后期的养护等,是珊瑚礁岩土工程进一步研究的方向。     

珊瑚礁生态修复的理论与实践

南海乃至全球的珊瑚礁生态系统都处于快速退化中,珊瑚礁的生态修复因此成为社会关注的热点内容,但相关理论与技术仍在探索之中。保护珊瑚礁的生态环境、避免对珊瑚礁进一步的破坏无疑是最关键的策略。对于已退化珊瑚礁的修复,初步有以下认识：1）珊瑚移植是重要的技术手段,可通过对移植后的珊瑚进行损伤组织修复、重建免疫系统、改变共生体虫黄藻系群结构等增强移植珊瑚适应新环境的能力。2）园艺式养殖、养殖箱培养等是提供珊瑚移植对象的相对有效途径;人工鱼礁则是协助珊瑚建立发育基底的重要手段;营造和维持适合珊瑚生长的环境有助于提高珊瑚礁生态修复成效。3）可借助水流扩散、幼虫附着和变态行为的化学诱导、微地形对幼虫附着的帮助等可促进珊瑚浮浪幼虫的传播和存活。4）通过杂交等手段改变珊瑚及其共生虫黄藻的基因类型,提升珊瑚对环境的耐受能力和恢复潜力等技术则仍处于实验室试验阶段。     

珊瑚砂高压力下一维蠕变分形破碎及颗粒形状分析

珊瑚砂是一种含钙极高的海洋生物成因材料,具有高棱角性、形状不规则、易破碎等特点。通过珊瑚砂的高压一维蠕变试验,研究颗粒破碎引起颗粒分布曲线和形状因子的演化规律。借助于高速动态图像的激光粒度粒形仪器,从统计学的角度分析试验前后颗粒形状随压力演化的关系,发现颗粒的形状因子,如长宽比、球形度和凹凸度等,随压力增加而逐渐增加。不同粒径的颗粒形状因子均向一个窄幅范围趋近,说明颗粒破碎具有无尺度性和自相似性的分形特性,分形维数随压力增加而逐渐增大,且趋近分形破碎极限。采用Hardin和Einav的方法计算相对破碎量,发现在两种计算方法下相对破碎量与压力呈幂函数关系,且幂指数相同。相对破碎量随时间增加的现象并不明显,说明在高压力下颗粒破碎主要为压缩破碎,且颗粒细化滑移填充孔隙引起的变形是造成蠕变的主要原因。     

海南岛西北部海域珊瑚礁造礁石珊瑚种类组成与分布

调查了海南岛西北部海域造礁石珊瑚种类的多样性及分布.结果表明:共发现50种造礁石珊瑚和1种多孔螅.海南岛西北部造礁石珊瑚优势种为澄黄滨珊瑚(Porites lutea)和丛生盔形珊瑚(Galaxea fascicularis),与历史资料相比优势种发生明显变化;海南岛西北部海域造礁石珊瑚覆盖率急剧下降,是由自然因素和人为活动共同造成;海南岛西北部海域是北部湾、琼州海峡和南海的重要交汇点,可能是造礁石珊瑚幼虫扩散的重要通道,对华南沿岸造礁石珊瑚资源自然恢复起到重要作用.因此,未来的海洋管理应该加强对珊瑚礁的保护力度,开发利用与环境保护并重,这样才能有效保护海南岛西北部海域的珊瑚礁.     

珊瑚颗粒力学特性应变率效应试验研究

珊瑚单颗粒破碎特性与珊瑚砂高压缩性、剪缩性及良好蠕变性等宏观力学行为密切相关。珊瑚颗粒的应变率效应对于不同形式荷载作用下珊瑚砂强度与变形特性研究具有重要意义。对约300颗珊瑚颗粒进行0.1～50 mm/min位移速率下的单颗粒破碎试验,探讨加载应变速率对颗粒破碎强度、破碎模式、破碎能量及破碎分形的影响。结果表明,珊瑚颗粒破碎强度服从Weibull分布规律,且特征破碎强度随应变率的提高非线性增大;随着加载速率的增大,颗粒主劈裂破坏往往先于棱角的局部碎裂和表面研磨,相应的荷载?位移曲线呈现出由峰前“多峰”向峰后“多峰”现象转变;珊瑚颗粒破碎能量密度和破碎分形维数同样具有明显的应变率效应,且均与对数应变率呈线性正相关关系,表征能量耗散和破碎程度均随加载应变率的增大而增大。     

广西涠洲岛海域珊瑚礁现状及其保护策略研究

通过对2005年涠洲岛珊瑚礁生态调查,结合对以往资料和数据的分析,对比1984年和1964年2次调查结果,掌握涠洲岛珊瑚礁的现状.同时讨论了涠洲岛珊瑚礁区面临的生存威胁,提出保护和管理涠洲岛珊瑚礁的建议,以期建立可持续的生态旅游开发与新型的生态保护生态管理体系.     

Assessment of the distribution of sponge chips in the sediment of East Pacific Ocean reefs

Sponges are one of the principal agents of bioerosion and sediment production in coral reefs. They generate small carbonate chips that can be found in the sediments, and we investigated whether these could provide a means for assessment of bioerosion applicable to reef monitoring. We tested this hypothesis on samples from 12 Mexican coral reefs distributed along the Pacific coast, where boring sponges were particularly abundant, and quantified the amount of chips in samples of superficial sediment in three grain‐size fractions: fine (<44 μm), medium (44–210 μm) and coarse (>210 μm). The grain‐size distribution varied among reefs, with the majority of the sediment of most reefs being composed of coarse sands, and the medium and fine fractions dominating only at La Entrega and Playa Blanca. All the reefs presented clear evidence of bioerosion by sponges, with the characteristic chips present in the sediment, although at most sites the percentage of chips was very low (from 1% to 3% of the total sediment). Only at La Entrega and Playa Blanca did they constitute a significant fraction of the total sediment (18% and 16%, respectively). While not statistically significant, there was an interesting trend between sponge chips versus sponge abundance that suggests that quantification of the chips in the sediment could be used as a proxy for sponge erosion of the entire community, which cannot be estimated in by laboratory experiments. However, while this methodology could provide an integrated approach to monitor sponge bioerosion, more studies are necessary due to the influence of environmental factors on the transport and deposition of these chips.     

Off‐reef planktivorous reef fishes respond positively to decadal‐scale no‐take marine reserve protection and negatively to benthic habitat change

The effects of no‐take marine reserve (NTMR) protection and changes in benthic habitat on fusiliers (family Caesionidae) were investigated at four small Philippine offshore islands on time scales of 10–31 years. Fusiliers are highly mobile, schooling, medium‐sized planktivorous fish that generally feed “off‐reef.” For these reasons, and given the small size of the NTMRs (3.6–37.5 ha) in this study, it was predicted that fusilier density would be unlikely to show clear effects of NTMR protection, or to respond to changes in benthic habitat. In contrast to predictions, clear NTMR effects were observed on fusilier density at three of the four NTMRs, with durations of protection from 14 to 31 years. Furthermore, the study provided strong evidence that benthic variables, specifically cover of live hard coral and dead substratum, affect the density of fusiliers. This effect of benthic habitat on density was highlighted by several major environmental disturbances that caused shifts in the benthic habitat from live hard coral to dead substratum. For two of the three most abundant species of fusiliers individually, and for all three of them combined (Pterocaesio pisang + Caesio caerulaurea + Pterocaesio digramma/tessellata), as live hard coral cover decreased, fish density decreased. It is hypothesized that these “off‐reef” daytime feeders may have such a strong association with live hard coral cover because they use this habitat as nocturnal sleeping sites. Multivariate analyses indicated that, across all sites and times sampled, cover of live hard coral and dead substratum accounted for 38% of the variation in fish assemblage structure. These results are important as there are very few reports in the published literature of strong effects of NTMR protection or changes in benthic habitat on the density and assemblage structure of fusiliers.     

Borehole image-based evaluation of coral reef porosity distribution characteristics

In this study, we used digital borehole image camera to obtain images of porosity distribution in coral reefs in South China Sea, and developed an effective evaluation system for such distributions. First, the original images are preprocessed, allowing the pore regions to be automatically detected. The depth and sectional functions are established to measure five parameters: pore count, pore radius, radius concentration rate, total pore area ratio, and fractal dimension count. These are used to calculate the characteristic values of porosity distributions, and their fuzzy relationships are used to build the evaluation model, determine the Hamming distances between distributions, and establish the relationships between the characteristics and coral rock classifications. Test results from applying the method on a deep borehole image segment show the results to be consistent with other methods, and the following conclusions can be reached: (1) the porosity evaluation model is a viable way to analyze porosity distribution characteristics; (2) the resulting classification method is viable; and (3) porosity distribution analysis on coral reefs has important implications.     

海南岛龙湾港滨珊瑚重金属含量的年际变化

采用等离子体原子发射光谱(ICP AES)技术,测定了1986—1997年海南省琼海市龙湾港(19°20′N、110°39′E)滨珊瑚中的Fe、Cu、Al、Ba、Zn、Mn、Cd、Ni 、Cr重金属含量。结果表明,1993 年珊瑚中 Fe的含量高出其平均值的1.03倍,受到了较明显的Fe污染。另外,珊瑚中的Fe含量在1994、1995年,Cu在1986年,Mn在1993年,Zn在1995年的含量高出各自平均值的0 5~1倍,受到相应重金属的轻微污染。然而,与广东省电白县大放鸡岛滨珊瑚、南沙珊瑚礁沉积物中的重金属含量相比,龙湾港在近12年中海洋珊瑚受重金属的污染不显著。运用多元统计的分析方法,探讨了重金属之间、重金属与降雨量和径流量之间的相关性,并对重金属的污染来源提出一些看法。