Soil Strength Improvement by Microbial Cementation

The biologically induced cementation (BioGrout) method has been used in this study to improve engineering properties of soil. Laboratory tests have been carried out to quantify the effect of BioGrout treatment on the strength of two types of sand by using Sporosarcina pasteurii bacteria. Bearing strength and other parameters, such as colony forming units (number of bacteria), pH level, temperature, and amount of CaCO₃, have also been studied. Calcification (cementation) through precipitation of CaCO₃ on the mineral surfaces has been clearly observed from the images of a scanning electron microscope (SEM). Finally, the effect of sand material on the effectiveness of biocementation was investigated via employement of different sand types.     

金属离子种类对珊瑚砂微生物固化影响研究

选用巴斯德芽孢杆菌,对微生物诱导钙离子、镁离子以及铁离子形成碳酸盐固化松散珊瑚砂颗粒的效果进行对比研究。试验结果表明,在相同试验方法、相同注入次数的条件下,微生物诱导形成的碳酸钙和碳酸镁能将珊瑚砂松散颗粒固化成为整体,加入铁离子的试样因为反应过程的原因没有成功。通过渗透性、干密度变化、无侧限抗压强度及微观结构等方面进行对比分析,钙离子试样相对于镁离子试样,具有固化过程平稳、干密度增量大、强度高、微观颗粒包裹更好的优点。综合试验结果得出,钙离子是现阶段微生物固化珊瑚砂较为理想的金属离子。本试验首次探讨了金属离子种类对珊瑚砂微生物固化效果的影响,为微生物固化技术提供了一定理论基础,对该技术的进一步应用具有一定借鉴意义。     

Effect of different biological solutions on microbially induced carbonate precipitation and reinforcement of sand

Abstract

Sporosarcina pasteurii is widely used in the application of microbially induced carbonate precipitation (MICP) for various applications, such as ground reinforcement, erosion mitigation or stabilization of sand foreshore slopes. This study focuses on the effect of thallus resuspended by the fresh medium (RF) on urea hydrolysis, MICP, and sand reinforcement compared with untreated biological solutions (US) with high microbial concentration. The principle is investigated by tests on thallus resuspended by saline solution [NaCl (0.9%)] (RS) and supernatant (SS). The results indicate that the addition of the fresh medium is insignificant for promoting MICP and even has a slightly negative effect on urea hydrolysis and sand improvement for stationary phase bacteria. The ability of US to hydrolyze urea and MICP is derived from two sources: urease existing in the cell bodies and free urease existing in solution for lysis of partial cells, with urease in cells accounting for the majority. The preferable sand reinforcement of US is primarily due to the high amount of carbonate precipitation and formation of non-biological calcium carbonate located primarily in the pores. The results indicate that the preference of US in various engineering applications with lower cost for the realizable reinforcement.     

The influence of particle morphology on microbially induced CaCO3 clogging in granular media

Abstract

Sporosarcina pasteurii (ATCC 11859) is a nitrogen-circulating bacterium capable of precipitating calcium carbonate given a calcium source and urea. This microbially induced carbonate precipitation (MICP) is able to infill inter-granular porosity and act as a biological clogging agent, thus having a wide potential application in strengthening coastal foundations, preventing erosion by seas and rivers and in reducing sand liquefaction potential in coastal areas. A successful MICP application requires the understanding of the primary parameters that influence the microbially mediated process to achieve its engineering goals, such as injection scheme, chemical concentrations, retention times, and injection rates. However, the granular morphology has generally been oversimplified to ideal shape without enough consideration in previous studies. The following explores the critical micro-scale influence of particle morphology on mechanisms of microbially induced clogging. Spherical, non-spherical and angular particles were used as granular aggregates in permeating column experiments with the resulting permeability and calcium carbonate content of the treated aggregates examined. Microscopic examination (SEM) defines the features of the distribution of microbially precipitated calcium carbonate and the forms of clogging. The results show: (1) given a fixed duration of treatment, the calcium carbonate content for the spherical particle aggregate is significantly higher than that for near-spherical and angular particle aggregates; (2) for identical durations of treatment, the maximum permeability reduction occurs for angular particles (rather than for spherical particles with the highest carbonate content). This suggests that the microscopic distribution of calcium carbonate is significantly influenced by particle morphology, exerting a critical control in the effectiveness of clogging. SEM images indicate that the microbial calcium carbonate precipitates encapsulate the spherical particles as a near-uniform shell and occlude the pore space only by increasing the shell thickness. In contrast, the near-spherical and angular particles are only partially coated by a calcium carbonate film with scattered crystals of vaterite and calcite further clogging the void space. The polyhedral nature of the non-spherical particles tends to result in a slot-shaped pore structure which critically defines the hydraulic conductivity of the ensemble medium. As the microbial vaterite and calcite continue to accumulate on the particle surface, these slot-shaped pore structures become increasingly more tortuous – resulting in a noticeable reduction of permeability at a lower calcium carbonate content.     

Enhanced Acoustic Backscatter Due to High Abundance of Sand Dollars,Dendraster excentricus

Abstract

Detailed acoustic surveys of benthic sediments were conducted in July 1995 and September 1998 in the vicinity of Humboldt Bay, California. During these surveys, a band of enhanced acoustic backscatter was observed offshore from the bay entrance, approximately parallel to the isobaths, in water depths ranging from 16–24 m. In order to assess the cause of the increase in backscatter levels, a more comprehensive study was conducted in August and September 1999 using 100 kHz side-scan sonar, bottom grab sampling and underwater video recording. New observations indicated that a dense population of sand dollars (Dendraster excentricus) coincided with the enhanced backscatter band. Compared to the two previous acoustic studies, the central section of the band expanded westward by 180 m and the southern section of the band shifted eastward by 160 m, possibly resulting from a change in the biological or physical factors which influence the location and breadth of sand dollars.

The relationship between high sand dollar abundance and enhanced acoustic backscatter was further verified in the near shore region off Samoa Beach California, where a dense, banded population of sand dollars was previously observed. Video footage confirmed the presence of a band of sand dollars, also nominally parallel to the isobaths, in water depths of 8–15 m. A band of enhanced backscatter coincided with the dense sand dollar population. The identification of dense aggregations of sand dollars through enhanced acoustic backscatter could lead to the use of acoustic techniques to study sand dollar distributions and abundance.     

The influence of seawalls on subaerial beach volumes with receding shorelines

The results summarized herein are based on subaerial beach profiles taken on the Atlantic Ocean at Sandbridge, Virginia (USA). The shoreline has experienced an average, historic recession rate of about 2 m/yr for more than 120 years before seawall construction began in 1978. The purpose of this study is to determine whether or not the 16 walled sections increase the existing erosional trend at adjacent, non-walled beaches. Fifteen years of survey data are employed with 8–9 years of data taken before wall construction peaked in 1989. The main focus of these results is on five full wave years of monthly and post-storm survey data taken at 28 locations (16 walled, 4720 m, 62% and 12 non-walled, 2950 m, 38%) since October 1990. Three time scales (historic, seasonal, storms) and three analysis methods were used to address three questions concerning the effects of seawalls on adjacent beaches.It has been determined that volume erosion rates are not higher in front of seawalls (Question No. 1). However, the seasonal variability of the sand volume in front of walls is generally greater than at non-walled locations. Winter season waves drag more sand offshore in front of walls but also summer swell waves pile more sand up against walls in beach rebuilding.Walled beaches were found to recover about the same time as non-walled beaches for both seasonal transitions (winter to summer) and following erosional storm events (Question No. 2).At a few non-walled locations, the sand volume landward of adjacent walls was found to be eroding at a faster rate after wall construction. At some other non-walled locations, the sand volume landward remained constant or increased in time after nearby walled construction. The evidence for Sandbridge beach as a whole was considered inconclusive for Question No. 3.After wall construction, sand trapped behind the wall is not available for transport to adjacent beaches during and after storm events. The loss of this sand volume is felt to be in the initial stage of detection at Sandbridge. More full years of profile data are needed to confirm and quantify the effect. Sand is also trapped beneath the road (baseline) at non-walled locations. The study is continuing.     

Spatial partitioning between species of the phytoplankton-feeding guild on an estuarine intertidal sand flat and its implication on habitat carrying capacity

The fishery yield of Manila clams, Ruditapes philippinarum, increased considerably in the 1970s but has decreased rapidly since the middle 1980s on extensive intertidal sand flats in Ariake Sound (Kyushu, Japan). A survey conducted in 2004 on a 3.4-km² sand flat located in the central part of the Sound (Shirakawa sand flat) revealed four dominant species: two thalassinidean shrimps (Upogebia major and Nihonotrypaea japonica), which are deep-reaching burrow dwellers with strong bioturbation activities, and two bivalves (Mactra veneriformis and R. philippinarum). All four species belong to a phytoplankton (diatom)-feeding guild. In the late 1970s, the Manila clam population prevailed in high densities over the entire sand flat, whereas its distribution was restricted to the lowest quarter of the shore in 2004. In contrast, the population sizes and zones of occurrence of the other phytoplankton feeders have expanded in the absence of R. philippinarum, perhaps an indication of competitive release. After establishment, effects of the thalassinidean shrimps on sediment stability appear to have further reduced clam abundances. Across the sand flat in 2004, wet weight population biomass estimates for N. japonica, U. major, M. veneriformis, and R. philippinarum (whole body for shrimps and soft tissue for bivalves) were 304, 111, 378, and 234 tonnes, respectively. Based on Manila clam fishery yield records from Shirakawa, the carrying capacity of the Shirakawa sand flat in the late 1970s was estimated to be two times greater than the sum value for the whole phytoplankton-feeding guild in 2004. It is hypothesized that (1) the amount of phytoplankton determines the carrying capacity for the benthic community on the Shirakawa sand flat, with both phytoplankton and benthic biomass at maxima in the late 1970s, and (2) the subsequent increases in competition for space have caused further declines in the Manila clam population biomass to approximately one-eighth of its past value.     

Gradation affects basic mechanical characteristics of Chinese calcareous sand as airport subgrade of reefs

Abstract

Construction of the reefs in the South China Sea is a significant foundation to the secure stability and economic development of China. The construction of an airport runway is necessary for this realization. The calcareous sand is the main primary material in the runway construction. A certain type of calcareous sand near a certain reef of the South China Sea was studied in this paper. To investigate this specific calcareous sand, quartz sand was used as a reference for comparison. Microscopic 3-D imaging, compression and triaxial tests were conducted to test the micro, squeezing and shear properties. The effect mechanism of gradation on the calcareous sand’s compressibility and shear characteristics are discussed from a mesoscopic viewpoint using 3-D morphology. Calcareous sand particles are multiangular and flatter in comparison with quartz sand. The larger the particle sizes are, the more different the two sands’ morphologies are. The compressibility of calcareous sand is greater, and the effect of the coarse fraction (5–1?mm) content in the gradation plays the most significant role in this feature. When the coarse particles’ content is less than 25% and the mass ratio of the middle and fine particles (M) is constant, there is the worst coarse fraction content causing the calcareous sand to be most likely compressed. The worst coarse fraction content decreases with the increase in M, and an empirical formula is proposed. When the gradation, relative density and confining pressure are the same, the peak shear stress and strain of calcareous sand are all at a high level. The effect of confining pressure is manifested in calcareous sand. The shear strength and dilation of calcareous sand are also most affected by the medium coarse fraction (5–0.25?mm) content.     

Experiment Study of the Evolution of Coral Sand Particle Clouds in Water

The motion of particle clouds (i.e., sediment clouds) usually can be found in engineering applications such as wastewater discharge, land reclamation, and marine bed capping. In this paper, a series of laboratory tests are conducted on coral sand to investigate the shape feature of the single particle and the mixing processes of the coral sand particle clouds. The shape of coral sand particle is measured and quantified. The experimental results demonstrate that the shape of coral sand particles tends to be spherical as the particle size decreases, and empirical equations were established to explain the variation of D₅₀ and f_S,50 of coral sand. Compared with the silica sand, the evolution of the coral sand particle cloud still experiences three stages, but the threshold for the Reynolds number of particle clouds entering the next stage changes. Further, the normalized axial distance of the coral sand particle clouds is 58% smaller. The frontal velocity exhibits similar varying tendency for the coral sand particle cloud. Considering the difference in shape between coral sand particles and silica sand particles, a semi-empirical formula was proposed based on the original silica sand prediction formula by adding the shape factor and the experimental data of 122 µm⩽D₅₀⩽842 µm. It can predict the frontal velocity of the coral sand particle clouds.

     

中华鲎(Tachypleus tridentatus)稚鲎对不同比例泥沙类型选择行为特征

中华鲎(Tachypleus tridentatus)是保障我国医疗检测安全的重要战略生物资源,国内外中华鲎行为生态学相关研究极少。在实验室内模拟砾石底(NS)、细砂(SS)、中砂(MS)、粗砂(CS)、泥(AR)、泥沙1 (AA)、泥沙2 (AB)和沙泥(SA) 8种不同比例的泥沙类型对中华鲎行为特征的影响。结果表明,稚鲎较多时间潜藏于泥沙中,较少时间裸露于泥沙表面活动(如爬行、游泳等)。稚鲎偏好在含淤泥较多的泥沙类型中潜沙,且在泥质和泥沙质类型中埋栖时间较在沙质中埋栖时间长;在裸露于泥沙表面时,稚鲎相对偏好栖息于沙质底。泥沙环境下稚鲎用于游泳的时间比例高于砾石底。在凌晨、上午、中午、下午、夜晚5个时间段中,稚鲎在夜晚和凌晨活动较活跃。通过揭示不同比例的泥沙类型底质对中华鲎稚鲎行为特征的影响,为野外增殖放流计划的设计与实施、放流适宜地点的选择以及稚鲎人工养殖环境的优化提供科学理论依据。     

Experimental study on the coefficient of lateral pressure at rest for calcareous soils

Abstract

The coefficient of lateral pressure at rest (k₀) is a key parameter required to determine the horizontal stress distribution on subsoils. In this paper, k₀ was measured from consolidation test for calcareous and siliceous sand, and the effect of water contents on k₀ of calcareous sand was also discussed. Comparison of k₀ values measured and calculated based on empirical formulas were carried on. Results indicated that (1) the reduction rate of k₀ for calcareous sand with an increase in relative density was less than that of siliceous sand. The k₀ at low water content was generally smaller than that of siliceous sand, and it was similar to that of siliceous sand for high-water content; (2) the k₀ of calcareous sand increased with increasing initial water content initially, and then decreasing. However, the magnitude of variation was small. So the impact of water content on the k₀ of calcareous sand was limited; (3) the formulas proposed by Abdelhamid and Krizek (1976 Abdelhamid, M. S., and R. J. Krizek. 1976. At-Rest Lateral Earth Pressure of Consolidating Clay. Journal of the Geotechnical Engineering Division 102 (7): 721–738. [Google Scholar]) for estimation of the k₀ was highly applicable to calcareous fine sand.

• Highlights

• The k₀ of calcareous fine sand was investigated.

• The k₀ of calcareous and siliceous sand were compared.

• Shape parameters of sand particles for calcareous and siliceous sand were analyzed.

• Effects of related density and initial water content on the k₀ were discussed, respectively.

• The applicability of various empirical formulas for calculating k₀ of calcareous fine sand was evaluated.

     

Variations in grain‐size and sorting on two kaikoura beaches

Two exposed, high‐energy beaches on the Kaikoura coast of New Zealand are composed of sand and gravel derived from a greywacke terrain. Both beaches can be classified as mixed beaches although the sediment varies from dominantly gravel at the ends of the beach to dominantly sand at the centre, through transition zones in which sand and gravel are mixed. Sixty‐four surface samples were analysed for grain size; two sediment parameters, mean grain size (M_z) and sorting (σ_I), were calculated.

A striking feature of the cumulative frequency curves is that both unimodai and bimodal distributions include median sizes over the whole range of sampled material, even though bimodal samples display two strong modes in the sand and gravel grades. The general deficiency lof sediment dn the very coarse sand and granule classes (0 to — 2 _F ) noted by numerous authors in many parts of the world is apparent in the poorly‐sorted bimodal samples. However, the best‐sorted samples also occur in these two classes.

Mean grain size of samples ranges from medium sand (1.820) to medium pebbles (—4.7 _F ), and sorting ranges from very well sorted (0.250) to very poorly sorted (2.69 _F ). Mean erain size on the northern beach is significantly greater than on the southern beach, but values of sorting are comparable. The greater mean size on one beach compared with the other is thought to be a function of the grade of material supplied by local rivers; the similarity in sorting presumably reflects the similarity of the processes acting on the two beaches.

Mixed sand‐shingle beaches are relatively rare on a world scale but common in New Zealand. Sediment distributions along the Kaikoura beaches do not reveal a regular decrease in size away from the rivers which supply material to shore at present. Instead, the beaches are differentiated into a number of sediment zones composed of either sand, or mixed sand‐gravel, or gravel. On each beach a gravel zone is located furthest from the river outlets. Sorting generally improves toward the Kaikoura Peninsula. Explanations for these trends are not given. Variations in size and sorting across the two beaches do not show a well developed zonation because of the high level of wave energy which continually mixes the material across the beach.     

Classification of marine bioregions on the east coast of South Africa

Marine bioregional planning requires a meaningful classification and spatial delineation of the ocean environment using biological and physical characteristics. The relative inaccessibility of much of the ocean and the paucity of directly measured data spanning entire planning regions mean that surrogate data, such as satellite imagery, are frequently used to develop spatial classifications. However, due to a lack of appropriate biological data, these classifications often rely on abiotic variables, which act as surrogates for biodiversity. The aim of this study was to produce a fine-scale bioregional classification, using multivariate clustering, for the inshore and offshore marine environment off the east coast of South Africa, adjacent to the province of KwaZulu-Natal and out to the boundary of the exclusive economic zone (EEZ), 200 nautical miles offshore. We used remotely sensed data of sea surface temperature, chlorophyll a and turbidity, together with interpolated bathymetry and continental-slope data, as well as additional inshore data on sediments, seabed oxygen and bottom temperature. A multivariate k-means analysis was used to produce a fine-scale marine bioregionalisation, with three bioregions subdivided into 12 biozones. The offshore classification was primarily a pelagic bioregionalisation, whereas the inshore classification (on the continental shelf) was a coupled benthopelagic bioregionalisation, owing to the availability of benthic data for this area. The resulting classification was used as a base layer for a systematic conservation plan developed for the province, and provided the methods for subsequent planning conducted for the entire South African EEZ. Validation of the classification is currently being conducted in marine research programmes that are sampling benthic biota and habitats in a sampling design stratified according to the biozones delineated in this study.     

基于深度卷积神经网络的海洋牧场岩礁性生物图像分类

水下视频可直观记录和反映海洋牧场生物资源的现状和变动,目前亟待开展基于图像的海洋牧场生物识别分类方法研究,以充分发挥图像处理技术在海洋牧场生物群落监测领域的应用潜力。利用采集自我国北方烟威地区包含鱼礁、藻床和泥沙三种图像背景的水下视频,开展了图像增强、图像分类数据集的建立和3种分类模型的应用。对比了基于绿通道的色彩补偿和限制对比度的自适应直方图均衡等方法在海洋牧场水下图像增强上的效果。建立了北方海洋牧场常见岩礁生物图像分类数据集,包括花鲈(Lateolabraxjaponicus)、(Lizahaematocheilus)、许氏平鲉(Sebastes schlegelii)等鱼类11种、棘皮类3种和蟹类1种,共23 211张图像。基于飞桨深度学习框架和PaddleX全流程开发工具,选择AlexNet、MobileNetV3和ResNet50三种图像分类卷积神经网络进行迁移学习,并分别验证了其在含噪音水下图像上的鲁棒性。结果表明,三种模型在测试集的类准确率分别达到96.64%、94.75%和99.23%,其中ResNet50模型在含有高斯噪音的图像集验证具有更好的鲁棒性。综之,基于深度学习的计算机视觉技术在我国海洋牧场生物群落监测中具有较大应用潜力,可为我国海洋牧场监测和管理提供新的思路和方法。     

烟台近岸人工鱼礁与自然岩礁底层渔业生物群落特征对比分析

为探究烟台近岸人工鱼礁区的底层渔业群落与自然岩礁区的差异,本研究于2018年5月—2019年2月在位于山东烟台近岸的养马岛自然岩礁区、牟平人工鱼礁区及毗邻泥沙区开展4个季度的渔业调查。调查共发现渔业生物15目37科53种,自然岩礁区与人工鱼礁区的平均物种数的差异不显著,但均明显高于泥沙区(Kruskal-Wallis test, P<0.05)。两礁石区的CPUE(catch per unit effort)在各季节均显著高于泥沙区(ANOVA,P<0.05),春、夏季自然岩礁的CPUE显著高于人工鱼礁(ANOVA, P<0.05)。三个区域的优势种存在一定相似性,但各优势种的CPUE呈现出明显的区域差异,尤其对于许氏平鲉及大泷六线鱼,人工鱼礁的生境优势高于其他两个区域。多样性分析结果显示,自然岩礁区的Shannon-Wiener多样性指数H′最高,其次为人工鱼礁区和泥沙区。自然岩礁与人工鱼礁区Magalef丰富度指数D的差异不显著,但都明显高于泥沙区(ANOVA, P<0.05)。ANOSIM分析表明三个海区的群落组成在各季节均存在显著差异(P<0.05...     

底质类型对热带海草海菖蒲种子萌发和幼苗生长的影响

近几十年来,受到人类活动和气候变化的影响,全球海草床呈现退化趋势,海草床的恢复备受关注.其中,海草种子或幼苗移植由于其对供体海草床破坏和影响较小,并能保证海草的遗传多样性而备受重视.移植区的底质类型是决定海草种子或幼苗移植存活率的重要因子,然而,目前关于热带海草种子萌发和幼苗生长对不同底质类型响应的研究很有限.本研究以...     

活石（live rock）在珊瑚养殖体系中对NH4+、NO3-的去除作用

Maintaining stable water quality is one of the key processes for recirculating coral aquaculture. Traditional aquarium systems which mainly utilized a nitrification of nitrifying bacteria attached to the surface of massive artificial filter material are difficult to maintain the oligotrophic conditions necessary for coral aquaculture. This study investigated the removal effects of dissolved inorganic nitrogen(ammonia and nitrate) by live rock(LR), a key component in the "Berlin system" coral aquarium. The expression levels of bacterial functional genes, AOA3,amo A and nos Z, were measured on the exterior and interior of LR. The nitrifying and denitrifying bacterial abundance on LR was quantified and the nitrogen nutrient regulatory effects of LR were evaluated. The results demonstrated that LR mainly removed ammonium(NH_4~+) from the water with a mean efficiency of 0.141 mg/(kg·h), while the removal of nitrate(NO_3~–) was not significant. Bacterial diversity analysis showed that ammonia-oxidizing bacteria(AOB) were the most common bacteria on LR, which accounted for 0.5%–1.4% of the total bacterial population, followed by denitrifying bacteria, which accounted for 0.2% of the total population, and the ammonia-oxidizing archaea(AOA) were the least common type(0.01%). The low abundance of denitrifying bacteria may be responsible for the poor nitrate(NO_3~–) removal of LR. Thus, other biological filtration methods are needed in coral aquaria to control nitrates generated from nitrification or biological metabolism.     

Evaluation of hydraulic conductivity through particle shape and packing density characteristics of sand–silt mixtures

Abstract

This study aims to evaluate the relationship between saturated hydraulic conductivity with particle shape and packing density characteristics of silty sand soils. The article presents a series of hydraulics tests performed on three kinds of sand with different particles shapes (Chlef rounded sand, Fontainebleau sub-rounded sand and Hostun sub-angular sand) mixed with low plastic rounded Chlef silt in the range of 0–30% fines content. The sand–silt mixture samples were tested in the constant-head permeability device at a loose relative density (D_r = 18%) and a constant room temperature (T?=?20?°C). The obtained results indicate that the measured saturated hydraulic conductivity (K_s) correlates very well with the fines content (F_c), packing density in terms of [maximum void ratio “e_max,” minimum void ratio “e_min,” predicted maximum void ratio “e_max”_pr and predicted minimum void ratio “e_min”_pr] and particle shape characteristics ratios in terms of roundness ratio (R_r = R_hs/R_mixture) and sphericity ratio (S_r = S_hs/S_mixture) of the silty sand materials under consideration. Moreover, the analysis of the available data show a noticeable success in exploring the prediction of the saturated hydraulic conductivity (K_s) based on the particle shape and packing density characteristics (R_r, S_r, e_max, and e_min) of the studied sand–silt mixture samples.