Research on Pressure Tight Sampling Technique of Deep-Sea Shallow Sediment—A New Approach to Gas Hydrate Investigation

Analyzed and calculated are pressure changes and body deformation of the sample inside of the corer in the process of sampling of deep-sea shallow sediment with a non-piston corer for gas hydrate investigation, Two conclusions are drawn： （1） the stress increments associated with the corer through the sampling process do not affect the stabilization of the gas hydrate; （2） the body deformation of the sample is serious and the ＂incremental filling ratio＂ （IFR） is less than unit, For taking samples with in-situ pressure and structure, combining with the design theories of the pressure tight corer, we have designed a kind of piston corer, named the gas hydrate pressure tight piston corer, Several tests on the sea have been conducted. Test results indicate that the piston corer has a good ability of taking sediment samples on the seafloor and maintaining their original in-situ pressure, meeting the requirement of exploration of gas hydrate in deep-sea shallow sediment layers.

Numerical Simulation of Mechanical Compaction of Deepwater Shallow Sediments

To study the compaction law and overpressure evolution in deepwater shallow sediments, a large-strain compaction model that considers material nonlinearity and moving boundary is formulated. The model considers the dependence of permeability and material properties on void ratio. The modified Cam-Clay model is selected as the constitutive relations of the sediments, and the deactivation/reactivation method is used to capture the moving top surface during the deposition process. A one-dimensional model is used to study the compaction law of the shallow sediments. Results show that the settlement of the shallow sediments is large under their own weight during compaction. The void ratio decreases strictly with burial depth and decreases more quickly near the seafloor than in the deeper layers. The generation of abnormal pressure in the shallow flow sands is closely related to the compaction law of shallow sediments. The two main factors that affect the generation of overpressure in the sands are deposition rate and permeability of overlying clay sediments. Overpressure increases with an increase in deposition rate and a decrease in the permeability of the overlying clay sediment. Moreover, an upper limit for the overpressure exists. A two-dimensional model is used to study the differential compaction of the shallow sediments. The pore pressure will still increase due to the inflow of the pore fluid from the neighboring clay sediment even though the deposition process is interrupted.

Leak-Off Mechanism and Pressure Prediction for Shallow Sediments in Deepwater Drilling

Deepwater sediments are prone to loss circulation in drilling due to a low overburden gradient. How to predict the magnitude of leak-off pressure more accurately is an important issue in the protection of drilling safety and the reduction of drilling cost in deep water. Starting from the mechanical properties of a shallow formation and based on the basic theory of rock-soil mechanics, the stress distribution around a borehole was analyzed. It was found that the rock or soil on a borehole is in the plastic yield state before the effective tensile stress is generated, and the effective tangential and vertical stresses increase as the drilling fluid density increases; thus, tensile failure will not occur on the borehole wall. Based on the results of stress calculation, two mechanisms and leak-off pressure prediction models for shallow sediments in deepwater drilling were put forward, and the calculated values of these models were compared with the measured value of shallow leak-off pressure in actual drilling. The results show that the MHPS(minimum horizontal principle stress) model and the FIF(fracturing in formation) model can predict the lower and upper limits of leak-off pressure. The PLC(permeable lost circulation) model can comprehensively analyze the factors influencing permeable leakage and provide a theoretical basis for leak-off prevention and plugging in deepwater drilling.

Geochemical Forms of Phosphorus in Sediments of Three Large, Shallow Lakes of China

A sequential extraction method for the fractionation of phosphorus (P) in lake sediments was used to analyze phosphorus fractions of sediments taken from three large, shallow, eutrophic freshwater lakes of China-Taihu Lake, Chaohu Lake,and Longgan Lake. All three lakes are located in the lower reaches of the Changjiang River (Yangtze River). In Taihu Lake and Chaohu Lake, algae blooms occurred every year, while Longgan Lake was a macrophyte-dominated lake. Results showed that exchangeable phosphorus fractions were much higher in the eutrophic lake sediments than in the macrophyte-flourishing lake sediment. Also, the ratio of Fe:P in the sediments of the algae-predominant lakes was generally much lower than that in the macrophyte-predominant lakes. Thus, the geochemical fractions of phosphorus in sediments had a closer relationship with the type of aquatic vegetation.

Characterizing Constituents of Sediment Phosphorus Fractionation in a Freshwater Shallow Lake System

[Objective] This study aimed to characterize constituents of phosphorus(P)fractionation as well as reciprocities among factors in sediments of a freshwater shallow lake. [Method] Surface sediment was discretely sampled at 24 sites through Van Veen grabs. Based on a modified sequential extraction scheme, P fractionation was determined as Fe/Al bound P(Fe/Al-P), Ca bound P(Ca-P), solute and reductive P(S/R-P) and organic P(OP). Curve estimation and Pearson product-moment correlation were employed for statistical analysis. [Result] Total P(TP) content ranged from 443 to 774 mg/kg. Inorganic P(IP) was the major component of TP,of which Ca-P was dominated with an average of 51%±9.7%. Average contents of P fractionation were in the following order: Ca-P(51%) > OP(29%) > S/R-P(8%) >Fe/Al-P(7%). The molar ratio of Fe to P was 11- 20, close to the threshold value of P leaching. [Conclusion] In freshwater shallow lakes, IP and Ca-P were prone to be relatively high, whereas Fe/Al-P was low compared with deep lakes. Occurrence of spatially monotonic gradient indicated the primary causation of anthropogenic sources. Imminent sediment P liberation was also expected. Close associations among TP, Fe/Al-P and Ca-P, implying that anthropogenic P was mainly bound to metals in particulates. Significant correlations of TOC and P fractionation highlighted endogenous mechanism and authigenic origin in sediments.

Experimental Study on the Effect of Sediment Composition Ratio on Shallow Water Delta

1 Introduction Shallow water delta in the middle-newborn Stratum Widely developed with huge oil and gas in China(Hu Shengwu et al.,2013).The control factors on the deltadevelopment like Climate,sea level,tectonic subsidence,sediment supply(flow,type),the geometric characteristics of the upstream river,the energy(wave,

MIXED FINITE ELEMENT METHODS FOR THE SHALLOW WATER EQUATIONS INCLUDING CURRENT AND SILT SEDIMENTA-TION (Ⅰ)-THE CONTINUOUS-TIME CASE

An initial-boundary value problem for shallow equation system consisting of water dynamics equations,silt transport equation, the equation of bottom topography change,and of some boundary and initial conditions is studied, the existence of its generalized solution and semidiscrete mixed finite element(MFE) solution was discussed, and the error estimates of the semidiscrete MFE solution was derived.The error estimates are optimal.

MIXED FINITE ELEMENT METHODS FOR THE SHALLOW WATER EQUATIONS INCLUDING CURRENT AND SILT SEDIMENTATION (Ⅱ)——THE DISCRETE-TIME CASE ALONG CHARACTERISTICS

The mixed finite element(MFE) methods for a shallow water equation system consisting of water dynamics equations,silt transport equation,and the equation of bottom topography change were derived.A fully discrete MFE scheme for the discrete_time along characteristics is presented and error estimates are established.The existence and convergence of MFE solution of the discrete current velocity,elevation of the bottom topography,thickness of fluid column,and mass rate of sediment is demonstrated.

外源钾铝对不同镁肥在砖红壤中淋溶的影响

研究海南浅海沉积物发育砖红壤中高钾与高铝共存对不同镁肥淋洗的影响,可为该缺镁土壤上合理施用镁肥提供理论依据。采集浅海沉积物发育砖红壤,设置4个钾铝处理:不加钾铝(–K–Al)、高钾(+K)、高铝(+Al)、高钾高铝共存(+K+Al),通过室内土柱模拟试验研究了一水硫酸镁、白云石、氢氧化镁、氧化镁、钙镁磷肥的淋失特征。结果表明:不同处理第1次淋溶液中镁浓度最大(125.47~898.81 mg/L),第2次骤降(8.79~157.64 mg/L),第3次再骤降(0.51~29.28 mg/L),往后第4~11次趋于平稳(0.25~9.41mg/L);施用镁肥处理淋溶液中镁浓度均高于对照处理,其中一水硫酸镁处理最高(898.81 mg/L),而白云石处理最低(212.50 mg/L)。+K+Al条件下淋溶液中镁浓度显著高于其他条件,镁累积淋失量大致为+K+Al>+Al>+K>–K–Al;不同种类镁肥处理的镁累积淋失量为19.16~142.96 mg,+K+Al条件下镁累积淋失量由高到低顺序为:一水硫酸镁>钙镁磷肥>氢氧化镁>氧化镁>白云石,镁淋失率最低的是白云石处理(8.22%),最高是一水硫酸镁处理(82.54%)。11次淋洗结束,0~20 cm土层中,与对照处理相比,除一水硫酸镁处理外,施用镁肥处理均提高了土壤p H,土壤交换性镁含量大致为+K+Al<+Al<+K<–K–Al;同一钾铝条件下对照处理与一水硫酸镁、白云石处理的土壤交换性镁含量几乎没有显著差异,而且都显著低于氢氧化镁、氧化镁、钙镁磷肥处理。综上所述,施用镁肥后,应注意水分管理防止镁被大量淋洗;+Al处理对镁淋洗的影响大于+K处理,且+K+Al处理对镁淋洗有促进作用。在海南浅海沉积物发育的砖红壤上易淋洗的一水硫酸镁不宜作为基肥施用,尤其在钾铝共存条件下应少量多次施用,可选择镁肥淋失率较低的白云石做基肥。

浅层气浮处理矿井水工程实践

为解决河北某矿矿井水处理工艺存在的运行效果不稳定、出水水质差、药剂费用高等问题,提出拆除纤维转盘、增加二次沉淀池等改进措施。改进后工艺为“调节(一次混凝)预沉池+(二次混凝)气浮池+二次沉淀池”。实验表明:一次混凝PAC投加50mg/L,二次混凝PAC投加10mg/L,PAM投加0.5mg/L时,效果最好,上清液浊度为1.14NTU。改进后系统运行稳定,药剂费减少30%以上,预沉池、气浮池和二次沉淀池出水浊度分别为33.5~58.1NTU、5.8~11.3NTU、1.9~5.1NTU。二次沉淀池起到良好的稳定水质作用,出水达到矿井水回用和排放相关标准。

武汉市东湖底泥污染风险评估及精细化清淤研究

城市浅水湖泊泥-水界面营养物质交换强烈且频繁,底泥污染释放对上覆水体影响显著,是浅水湖泊污染的主要途径之一。以武汉市东湖为例,采用氮磷综合污染指数法和静态释放试验方法,评估底泥污染风险,并综合考虑清淤工艺及水生植物分布等因素,精确确定清淤范围及厚度。结果表明:东湖底泥总氮和有机质含量分布具有较高的协同性,总磷与有机质含量之间呈弱相关;东湖上、中、下层底泥氮磷综合污染指数分别为0.85~11.39,0.52~7.40和0.49~6.33,大部分区域处于轻度污染—重度污染范围;东湖清淤深度以29.04~110 cm为宜。研究成果可为东湖水环境综合治理及类似城市浅水湖泊治理提供理论依据和技术支撑。

市政污水深度处理中的高效沉淀池应用

本文介绍了高效沉淀池和浅层高效滤池相结合的市政污水深度处理工艺,首先介绍高效沉淀池的净化过程和沉淀机理,接着分析工艺的进、出水质设计、工艺流程设计以及相关系统参数设计,希望能对该工艺的应用起到一定的促进作用。

Concentrations and contamination trends of heavy metals in the sediment cores of Taihu Lake,East China,and their relationship with historical eutrophication

To assess the contamination trends and potential bio-availability of sediment-bound heavy metals,concentrations of heavy metals in acid-leaching fraction and in bulk sediments from the two typical bays(the Meiliang Bay and Xuhu Bay) of the Taihu Lake,East China,were studied.Pb and Zn showed elevated concentrations in the sediments from both areas,although sedimentation history and degree of pollution are different between the two bays.In the Meiliang Bay,both Pb and Zn pollutions started in the late 1970's,the same time as the beginning of eutrophication of the lake,while the in the Xuhu Bay the metal contamination started since recent 10 years.The concentrations of acid-leachable Pb in the sediments from the Meiliang Bay are correlated with the historical eutrophication process.Before the eutrophication and heavy metal pollution,the chemical properties of the lake sediments were the same as the source compositions of the Xiashu loess.Both Pb and Zn in the sediments mainly occur in leachable forms by nitric or hydrochloric acid,whilst most of Cu is in residual fraction.The results indicate that both Pb and Zn may have higher mobility and bioavailability in water and biology than Cu.

Soil detachment and transport under the combined action of rainfall and runoff energy on shallow overland flow

Rainfall and runoff energy results in soil erosion. This paper presents new the concepts of rainfall and runoff energy and analyzes the relationship of rainfall energy and runoff energy with sediment transport based on the conversion theory of kinetic and potential energy using artificial rainfall and mechanical calculation. The results show that the ratio of sediment detachment in sloping fallow overland flow increases with the slope gradient,rainfall energy and runoff energy, while the sediment detachment ratio under raindrop impact are significantly higher than those under no raindrop impact. The sediment concentration increases with the slope gradient and rainfall energy; when the slope gradient and rainfall energy are constant, the sediment concentration decreases as the runoff energy increases. Rainfall disturbance coefficients have a logarithmic correlation with the rate of rainfall energy and runoff energy. On the same slope gradient,when the rainfall energy is constant, the disturbance coefficient decreases as the runoff energy increases,while when the runoff energy is constant, the disturbance coefficient increases as the rainfall energyincreases. Rainfall energy results in sediment detachment, and runoff energy is the transportation for erosion sediment. This showed that rainfall energy and runoff energy are important in the sediment detachment and transportation of shallow overland flow.

Comparison of depth-averaged concentration and bed load flux sediment transport models of dam-break flow

This paper presents numerical simulations of dam-break flow over a movable bed. Two different mathematical models were compared: a fully coupled formulation of shallow water equations with erosion and deposition terms(a depth-averaged concentration flux model), and shallow water equations with a fully coupled Exner equation(a bed load flux model). Both models were discretized using the cell-centered finite volume method, and a second-order Godunov-type scheme was used to solve the equations. The numerical flux was calculated using a Harten, Lax, and van Leer approximate Riemann solver with the contact wave restored(HLLC). A novel slope source term treatment that considers the density change was introduced to the depth-averaged concentration flux model to obtain higher-order accuracy. A source term that accounts for the sediment flux was added to the bed load flux model to reflect the influence of sediment movement on the momentum of the water. In a onedimensional test case, a sensitivity study on different model parameters was carried out. For the depth-averaged concentration flux model,Manning's coefficient and sediment porosity values showed an almost linear relationship with the bottom change, and for the bed load flux model, the sediment porosity was identified as the most sensitive parameter. The capabilities and limitations of both model concepts are demonstrated in a benchmark experimental test case dealing with dam-break flow over variable bed topography.

Exhalative Lead-Zinc Deposits in Shallow Sea,Southern Xicheng Belt,Gansu Province

SEDEX-type lead-zinc deposits in the southern belt of the Xicheng Devonian basin, Gansu Province has been already identified. However, the sedimentary environment of the limestone and philite of the Xihanshui Group within which the lead-zinc deposits occur is littoral and shallow sea. This is different from those in the northern belt such as the Changba-Lijiagou lead-zinc deposits, which were formed in deep sea. The reef and bioclastic limestone are widespread in the southern belt. Particularly they are associated with lead-zinc ores and there are no striae and banding but massive or disseminated structures. It is discovered that the black chimney consists of sphalerite, ankerite, pyrite and galena, in which black, coarse and radial sphalerite occurs as irregularly veins or cylindricality with a width of 10-40 cm in the center, and it is surround by fine ankerite and minor celestite with ribbon structure. The immediate wall rock of the chimney, reef limestone, was unaltered and the outside reef and bioclastic limestone were intensively silicified. Those silicified reef and bioclastic limestone host disseminated lead-zinc ores of the Luoba and Bijiashan type. It is concluded that the exhalative system occurred in a shallow sea in the Givetian of the middle Devonian. Brine is boiled due to low pressure, and a great deal of lead and zinc was dispersed in the interface between the limestone and phyllite and formed a source bed. In the Triassic period, meta-hydrothermal fluids leached and extracted metals from the source bed, and then moved and mineralized in open space such as arches and inverse limbs of anticlines, and formed massive and vein ores such as the Jianyagou and Dengjiashan type deposits.

On the Existence of Global Weak Solutions to 1D Sediment Transport Model

This paper is devoted to the study of the existence of weak solution in time with a periodic domain of sediment transport model. We consider a one-dimensional viscous sediment transport model which combines a viscous Shallow-Water system with a transport equation that describes the bottom evolution. The model studied does not take into account all the regularizing terms used by Roamba Brahima, Zongo Yacouba and Jean de Dieu Zabsonré (2017) and we use a better transport equation than that used by Zabsonré (2012).

Hydrogeochemical Characteristics of Fluorine in Shallow Groundwater of Tongshan Area

Tongshan area,a part of the floodplain of the abandoned Huanghe River, is one of the popular endemic fluorosis areas in East China. One of the reasons is high concentration of fluorine in shallow groundwater. Test results of 36 groundwater samples show that fluorine concentration in shallow groundwater is 0.18–6.7 mg/L and 50 % of the samples exceed the Chinese drinking water quality standard. There exists a significant negative correlation in content between Ca2+ and F - . The correlations between fluorine concentration and other cations (for example Na+, K+, Mg2+) are not significant. The content of dissolved fluorine from the flooding sediments of the Huanghe River that varying from 5.6 mg/kg to 15.2 mg/kg plays an important role in forming the high fluorine groundwater. Usually, the dissolved fluorine content in silt is much higher than that in silty clay and clay. According to the geological investigation fluorine content in deep groundwater (over 60 m) is less than 1.0 mg/L and suitable for drinking, so it is an effective measure to prevent endemic fluorosis by extracting deep groundwater in disease areas.

湖北网湖沉积物重金属分布特征、源解析及风险评价

为揭示湖北网湖沉积物重金属污染特征,采用空间插值法、主成分分析法和地累积指数对其污染特征、来源识别及生态风险状况进行分析。结果表明:5种重金属的平均浓度从高到低依次为Zn>Cr>Cu>Pb>Cd,且浓度均超过湖北省土壤背景值;Pearson相关性分析表明,Zn与Cd、Pb浓度呈正相关(P<0.05),Cu与Zn、Cr浓度呈负相关(P<0.05)。主成分分析发现,主成分1由Pb、Cd、Zn构成,主要来源于河流运输和农业活动影响;主成分2由Cr和Cu构成,主要来源于矿物风化等自然背景和工业活动及水产养殖等人类活动污染影响。地累积指数结果显示,网湖沉积物中重金属处于低风险状态,但Cd和Cu达到中度污染,为主要污染物,应予以关注。

莱州湾海洋沉积物粒度特征及其环境响应分析

基于20个柱状样粒度信息,文章对山东莱州湾海域1~3 m厚度的沉积环境展开了研究。莱州湾海域沉积物粒度组分以砂质和粉砂质为主,整体上分选性偏差,在沉积过程中受周边环境改造明显。莱州湾海洋沉积动力环境在粒度方面有较好的响应,柱状样粒度分布图反映不同海域沉积物所处的外力作用阶段各有不同,但总体上随着搬运距离增大,至中部浅海平原,概率累积曲线斜率逐渐变大,阶段分化愈发明显。莱州湾浅部海域共同环境敏感组分为3≤φ≤4,沿岸河流性质和泥沙输运路径对粒度组分影响明显。综合前人关于沉积速率的研究成果,表明莱州湾东部海域粒度组分阶段性变化与1855年黄河改道在时间上存在一定的对应关系。就沉积物形成环境而言,莱州湾中部海域沉积环境水动力较强,物质来源多样。屺坶岛—刁龙嘴海域沉积物的颗粒略粗,需要的临界起动速度较大,发生再悬浮的几率相对较小。黄河水下三角洲沉积环境比较动荡,能量不稳定,处于重力流后期,能量衰减并向牵引流转化。南部的水下岸坡在波浪、潮流作用下有一定量的泥沙淤积。