EY60回声探测仪在青海湖鱼类资源量评估中的应用

2006年8月16-18日通过使用回声探测仪(Simrad公司EY60型,200kHz换能器)对青海湖的鱼类资源进行了探测评估.结果表明:青海湖裸鲤(Gymnocypris przewalski)水平分布具不均匀性,有小型鱼群聚集现象;在不同的设定分区,鱼类密度在0.168-12.8ind./1000m~3之间,均值为1.16 ind./1000m~3;布哈河口鱼类较为密集,密度最大值为12.8ind./1000m~3.初步估算青海湖裸鲤达可捕规格(体长大于20cm)个体数量为6.5×10~7ind.,95%置信度区间为35.6×10~7-118.4×10~7ind.,应用资源密度体积法估算青海湖裸鲤的可捕资源量约为1 5275t.探测实验还证实,EY60回声探测仪在青海湖中进行鱼类资源评估时探测效果良好,分析软件Sonar5可以对鱼类个体自动识别、计数,便于进行鱼类资源量评估.     

青海湖裸鲤(湟鱼)鱼骨产出层位及其耳石微化学对明朝青海湖水位的指示

鱼耳石是硬骨鱼类内耳中的生物碳酸盐矿物,其组成可以记录鱼体生活水体的物理和化学状况.以青海湖鸟岛附近发现的青海湖裸鲤鱼骨及耳石为研究对象,通过古代和现代耳石微化学组成的对比分析,结合裸鲤鱼骨及耳石AMS-14C定年、产出层位和周边地形,认为这些裸鲤是小冰期时青海湖高湖面退却形成的残余湖内生长的.通过保存的青海湖裸鲤鱼骨和耳石的AMS-14C定年,确定这些裸鲤生活的时代距今300~680年左右,即我国历史上的明朝时期.X射线衍射图谱表明,青海湖裸鲤古代微耳石的矿物是纯文石,这与现代微耳石一致,说明埋藏后微耳石的矿物类型没有发生变化,可用于对比分析.微化学分析结果表明,古代微耳石的Mg/Ca比值((70.12±18.50)×10-5)和δ18O值(1.76‰±1.03‰)均明显高于现代微耳石(Mg/Ca平均值为(3.11±0.41)×10-5,δ18O平均值为-4.82‰±0.96‰).这反映了明朝时青海湖裸鲤生活的水体具有比现代青海湖高得多的Mg/Ca和δ18O值,这是与大湖隔离后强烈蒸发浓缩的结果,类似于现代的尕海等.根据裸鲤鱼骨产出的层位和海拔高度,推断明朝时期青海湖的湖面海拔至少达到3202 m,经计算当时的湖面面积至少为4480 km2,比现在大5%左右.     

西江广东鲂(Megalobrama terminalis)繁殖生物学及繁殖策略

探究鱼类繁殖策略是了解鱼类种群动态的关键.通过对珠江西江流域重要的经济鱼类广东鲂(Megalobrama terminalis)生殖周期、产卵时间、成熟期长度、生殖力类型和生殖力等方面进行研究,阐明在人类活动日益加强下,西江广东鲂的繁殖策略适应性变化情况.研究表明,广东鲂个体平均体长245 mm,优势体长集中在260~280 mm,平均体重347 g,优势体重集中在320~480 g.用L 50逻辑斯谛回归方法推算广东鲂雌鱼和雄鱼初次性成熟体长分别为244.5和232.2 mm.雌雄性比例为1.105∶1,且随着体长增加,雌雄性比呈现出先下降后上升的变化趋势.广东鲂繁殖群体在产卵季节为48月,产卵高峰为6月初持续到7月上旬,产卵季节内广东鲂鱼苗的密度与径流量显著相关.广东鲂绝对繁殖力平均为73069粒,相对繁殖力平均为118.7粒/g,绝对繁殖力与体长和体重均呈正相关.广东鲂繁殖群体性腺成熟系数与性腺重、肥满度以及体重密切相关.广东鲂种群繁殖策略在人类活动加剧影响下呈现出适应性变化:初次性成熟体长变小,绝对繁殖力下降.     

海洋水色遥感产品在青海湖鱼产潜力估算中的应用

鱼产潜力可为渔业资源保护和管理提供科技支撑,传统的鱼产潜力估算方法在大型湖泊中往往成本高、采样率低、时效差.本研究基于2018—2020年非冰封期(5—10月)在青海湖的实测数据,通过提取和校对海洋水色遥感MODIS卫星数据反演产品(1 km分辨率)并结合垂向归纳模型(VGPM)构建了青海湖浮游植物初级生产力及鱼产潜力估算模型,估算的浮游植物初级生产力与实测值对比的平均相对误差小于25%.利用该模型估算2018—2020年非冰封期青海湖基于浮游植物初级生产力的鱼产潜力并分析其时空分布规律,结果显示青海湖鱼产潜力在5—10月呈现先增加后减少的季节波动规律,最大值出现在夏季(7—8月);空间分布上呈现湖心小,岸边及靠近入湖支流河口区域大的分布状态,全湖总鱼产潜力月均变化范围为2.5万~17.6万t.鱼产潜力的时空分布规律主要受气温、外源营养物质、裸鲤摄食等影响.研究表明青海湖非冰封期的鱼类资源承载力年累计值可达45.8万t,明显高于现有裸鲤资源的现存量和历史产量高峰值,表明青海湖仍然具备很大的鱼类资源承载力与增殖空间.本研究为同类型的大型高原湖泊基于卫星遥感的高效长期鱼产潜力监测估算提供了范例,为青海湖“封湖育鱼”政策制定和增殖放流保护决策提供参考.     

汾河太原河段水华藻类分类及分子系统研究

2012-2016年,每年的春、夏、秋季对汾河太原河段进行浮游植物样品采集.通过对样品的形态观察和描述,共鉴定出5种水华优势种,5月发生的裸藻水华优势种为裸藻属的膝曲裸藻(Euglena geniculata)和血红裸藻(E.sanguinea).而7-9月发生的微囊藻水华优势种为微囊藻属的铜绿微囊藻(Microcystis aeruginosa)、挪氏微囊藻(M.novacekii)和惠氏微囊藻(M.wesenbergii).分离纯化共得到11株单克隆水华藻,其中铜绿微囊藻8株,挪氏微囊藻2株,血红裸藻1株.运用cpcBA-IGS、gyrB和cpSSU基因序列构建分子系统发育树,进一步确定水华藻的系统分类地位,结果表明cpcBA-IGS是研究汾河太原河段铜绿微囊藻分类很好的分子标记,而cpSSU基因可很好地区分血红裸藻和其他裸藻种.     

湖北牛山湖高体鳑鮍的年龄、生长与繁殖

研究了牛山湖高体鳑鲏的年龄、生长和繁殖特征. 鳞片上年轮清晰,主要呈现疏密特征.种群年龄结构简单,仅由一个世代组成;雄与雌的比例为1.59∶1(n= 332),显著不同于1∶1(Xc2 ＝16.94, p<0.005)而符合2∶1的类型(Xc2 ＝3.82, p> 0.05). 两性最大寿命不超过2a.雄、雌体全长与体重、全长与体长的回归方程差异显著. 在繁殖期间,雌雄鱼均出现第二性征.雄鱼最小成熟个体的全长和体重分别为26mm、0.216g,雌鱼则分别为32mm、0.393g. 性成熟年龄为1a,属分批产卵类型.成熟卵粒呈葫芦状,长度平均3.31mm. 每尾雌鱼平均繁殖力为61粒,繁殖力与全长及体重均呈显著相关(p＜0.001).     

滇池沉积物金属污染及环境质量评价

对滇池126个采样点沉积物0-5cm、5-10cm和10-20~m中Cu、Zn、Fb、Cr、CA、Hg和As等7种金属的含量进行了分析测定.用基于多方的基准中阈值效应含量TEC和可能效应含量PEC划分出5个沉积物环境质量等级.并借助灰色聚类分析方法对滇池沉积物环境质量进行了评价.结果表明,滇池沉积物环境质量整体上为Ⅲ类,存在中度的金属污染.其中0-5m和5-10cm为Ⅲ类沉积物,10-20Cm为Ⅱ类沉积物.沉积物环境质量下层优于上层,表明滇池沉积物金属污染仍存在不断加剧的趋势.     

2007-2008年云南高原湖泊鱼类多样性与资源现状

为了解云南高原湖泊鱼类资源及多样性现状,于2007-2008年对云南高原11个大型湖泊进行了2次调查.共鉴定鱼类39种,隶属于7目13科33属,鲤形目鱼类最多,占65.0%.其中共调查到土著鱼类14种,外来鱼类25种.在种数上,外来鱼类已经成为各湖泊的主体.在鱼类区系上,由高原鱼类区系向长江中下游鱼类区系演变.主要经济鱼类年龄结构以0+和1+鱼为主.分析表明,土著鱼类多样性与海拔和湖泊面积密切相关.土著鱼类物种数在中等海拔(1700-1800m)处最高,并与湖泊面积呈显著正相关.最后根据调查结果,提出了一些保护建议.     

青藏高原及邻近区域的S波三维速度结构

本文收集了WWSSN台网和我国台网中13个地震台站的长周期地震记录,用140条10-90s瑞利波频散曲线和作者提出的Tarantola-Backus面波频散层析成象方法,作了青藏高原及邻区的速度反演,得出该地区岩石层速度结构的三维图象.结果表明,1.在10-110km深度范围内,速度结构出现与大地构造特征相关的分区性,显示出四个构造单元:青藏块体、柴达木-巴颜喀拉-三江块体、塔里木块体和印度块体.2.高原内部,深度为10-70km内速度较低,莫霍界面呈不对称盆形分布,藏北那曲附近地壳厚度超过70km,高原边缘壳厚为45-50km,90-110km为高速异常,表明高原内部存在上地幔盖层.3.高原北部的班公湖断裂和东部的三江断裂系是该区重要的分界线,是岩石层结构存在明显差异的重要接触部位,可能是冈瓦纳古陆与欧亚古陆的缝合带.4.柴达木-巴颜喀拉-三江块体内部速度分布不均匀,地壳厚度由北向南从45km加深到60km;在深度90-110km存在一低速层.5.塔里木地块内速度随深度均匀增加,从地壳到上地幔110km内没有发现低速层.地壳厚度约50km.     

青藏高原古近纪-新近纪地层分区与序列及其对隆升的响应

在系统查阅1996～2008年中国地质调查局在青藏高原完成的177幅1:25万地质填图和前人已发表的新生代地层资料的基础上,划分出青藏高原及邻区古近纪-新近纪残留盆地共98个,归属为南疆-西昆仑、柴达木-祁连-西秦岭、羌塘-川西、扬子西缘、冈底斯-喜马拉雅-恒河共5个地层区,进一步细分为13个地层分区.通过对各个地层分区的残留盆地类型、形成构造背景、各分区内的岩石地层序列及其沉积特征、地层接触关系、时代确定依据与沉积演化过程的描述,将青藏高原新生代的隆升及其沉积响应划分为3大阶段、8个亚阶段:一是俯冲碰撞隆升阶段(65～34Ma),含3个亚阶段:(1)65～56Ma:印度与欧亚板块初始碰撞,恒河前陆盆地和成都、塔里木压陷盆地形成.(2)56～45Ma:印度与欧亚板块碰撞高峰期,高原北部柴达木-可可西里-羌塘压陷盆地和东北缘的兰州-西宁压陷盆地形成.(3)45～34Ma:约40Ma左右藏南新特提斯残留海消亡,印度与欧亚板块全面完成碰撞;高原东缘走滑拉分盆地初始发育.约40Ma以来喜马拉雅沉积缺失,标志喜马拉雅初始隆升;约36Ma以来冈底斯带区域不整合面发育,标志冈底斯初始隆升.二是陆内汇聚挤压隆升阶段(34～13Ma),含3个亚阶段:(1)34～25Ma:沿冈底斯分布日贡拉砾岩,是冈底斯持续隆升的产物.高原东北缘出现临夏-循化新的压陷盆地.(2)25～20Ma:沿冈底斯带南缘广布大竹卡组砾岩.可可西里-沱沱河地区角度不整合面发育和盆地内的古近纪地层抬升变形,指示可可西里-沱沱河发生较大幅度隆升.约23Ma时塔里木海相沉积结束,高原及周边不整合面广布,标志高原整体隆升.(3)20～13Ma:高原内及周边大型盆地全面发展,盆内发育持续湖侵充填序列,高原及周边出现最大湖泊扩张期;高原东缘走滑拉分盆地发育进入鼎盛期.三是陆内均衡调整隆升阶段(13Ma以来),含2个亚阶段:(1)13～5Ma:喜马拉雅-冈底斯隆升到相当高度,使该带因东西向伸展而导致南-北向断陷盆地形成;约8Ma左右出现强的构造抬升剥露,8Ma之后高原及邻区大型湖泊进入湖退期.(2)5Ma以来:高原整体隆升;高原内和周缘盆地沉积萎缩.约3.5Ma高原周缘堆积巨砾岩.     

A Monte Carlo study of rainfall forecasting with a stochastic model

A procedure for short-term rainfall forecasting in real-time is developed and a study of the role of sampling on forecast ability is conducted. Ground level rainfall fields are forecasted using a stochastic space-time rainfall model in state-space form. Updating of the rainfall field in real-time is accomplished using a distributed parameter Kalman filter to optimally combine measurement information and forecast model estimates. The influence of sampling density on forecast accuracy is evaluated using a series of a simulated rainfall events generated with the same stochastic rainfall model. Sampling was conducted at five different network spatial densities. The results quantify the influence of sampling network density on real-time rainfall field forecasting. Statistical analyses of the rainfall field residuals illustrate improvement in one hour lead time forecasts at higher measurement densities.     

Earthquake Engineering and Engineering Vibration Aims And Scope

正This journal is established by the Institute of Engineering Mechanics(IEM),China Earthquake Administration,to promote scientific exchange between Chinese and foreign scientists and engineers so as to improve the theory and practice of earthquake hazards mitigation,preparedness,and recovery.To accomplish this purpose,the journal aims to attract a balanced number of papers between Chinese and     

Solute concentrations in the lower niger river and the source rock contribution

Water quality analyses for the Niger River for the 1980/81 hydrological year are presented. The samples were collected from the main river at Lokoja, and from two main tributaries, the Kaduna and the Benue Rivers. Different water types were distinguished by the concentrations of major ions. The type Ca > Na > Mg > K - HCO₃ > SO₄ > Cl was represented at all stations during at least part of the year. Chloride was found to dominate the sulphate ion in the Kaduna and Niger, while the Benue maintained a higher concentration of sulphate relative to chloride all year round. Distinct patterns of seasonal variation in the ion concentrations were observed, particularly for the samples collected at Lokoja. Low ion concentrations were prominent during periods of high discharge, while low flow periods coincided with high dissolved ion concentrations. The contribution of rainwater to the total dissolved solids in the river waters was assessed indirectly using rainwater chemistry data from the Gulf of Guinea. The estimated rainwater contribution to the Lower Niger amounts to 5.15 mg 1^?1. Geochemical weathering calculations involving reactions of the four major minerals of granitic rocks - anorthite, biotite, albite, and K-feldspar - with carbon dioxide and water, can account for the average water composition of the Lower Niger. The proportion of the ionic components was also related to the occurrence of the respective element in the minerals.     

Scenario predictions for potential near-field and far-field earthquakes affecting Hong Kong

Historical earthquakes noted in the written records of the South China region, including Hong Kong, are not well delineated along identified prominent fault sources. Despite the lack of any definitive, localised trend in the spatial distribution of seismic activity in the region, there does appear to be some major disparity in the seismic activity rates (especially for large magnitude earthquakes) between the near-field and the far-field regions of Hong Kong. Despite this observation, previous studies of the regional seismic activity and seismic ground motion hazard (the latter using a probabilistic seismic hazard assessment, PSHA) have considered very broad source zone regions, in which uniform levels of seismic activity have been assumed. The present paper further scrutinises this broad source zone (BSZ) approach by adopting a novel expanding circular disc (ECD) method to determine the rates of earthquake recurrence. Such a method is intended to counter-check previously developed models by determining earthquake scenario events in terms of magnitude–distance (M–R) pairs or combinations, having defined values of average return period. Unlike the BSZ approach, the ECD method specifically accounts for the supposed variations in the seismic activity rates between events in the near-field and the far-field of Hong Kong.The form of the developed method is particularly suited to the determination of design-level earthquake ground motions for bedrock sites, since it assumes a directionally-independent attenuation model as described in the companion paper. It is found that, whilst the BSZ approach may indicate the overall average levels of hazard that are representative of the South China region as a whole, it does not capture the large disparity in seismic activity rates between near-field and far-field events. This important feature is expected to have a significant impact upon engineering assessments of the seismic safety of structures in Hong Kong and elsewhere in the South China region. For example, it is found that for events with M≥6, the seismic activity rate (normalised by time and area) in the very far-field is around 3.5 times larger than in the near-field and medium-field of Hong Kong. The resulting design M-R combinations, covering a range of return periods from 70 to 2500 years, are limited, for very long return periods and for distant events, by the maximum credible earthquake (MCE) magnitude. Intensive research to determine this seismic hazard parameter is recommended, in order to refine further the results of the ECD analysis, which presently conservatively assumes the MCE to range between M=6 in the near-field of Hong Kong to M=8 in the very far-field, at distances greater than 280 km from Hong Kong.     

Depositional ages and characteristics of Middle–Upper Jurassic and Lower Cretaceous lacustrine deposits in southeastern Mongolia

Lower Cretaceous lacustrine oil shales are widely distributed in southeastern Mongolia. Due to the high organic carbon content of oil shale, many geochemical studies and petroleum exploration have been conducted. Although most of the oil shales are considered to be Early Cretaceous in age, a recent study reveals that some were deposited in the Middle Jurassic. The present study aims at establishing depositional ages and characteristics of the Jurassic and Cretaceous lacustrine deposits in Mongolia. The Lower Cretaceous Shinekhudag Formation is about 250 m thick and composed of alternating beds of shale and dolomite. The Middle Jurassic Eedemt Formation is about 150 m thick and composed of alternating beds of shale, dolomitic marl, and siltstone. The alternations of shale and dolomite in both formations were formed by lake level changes, reflecting precipitation changes. Shales were deposited in the center of a deep lake during highstand, while dolomites were formed by primary precipitation during lowstand. Based on the radiometric age dating, the Shinekhudag Formation was deposited between 123.8 ±2.0 Ma and 118.5 ±0.9 Ma of the early Aptian. The Eedemt Formation was deposited at around 165–158 Ma of Callovian–Oxfordian. The calculated sedimentation rate of the Shinekhudag Formation is between 4.7 ±2.6 cm/ky and 10.0 ±7.6 cm/ky. Shales in the Shinekhudag Formation show micrometer‐scale lamination, consisting of algal organic matter and detrital clay mineral couplets. Given the average thickness of micro‐laminae and calculated sedimentation rate, the micro‐lamination is most likely of varve origin. Both Middle–Upper Jurassic and Lower Cretaceous lacustrine oil shales were deposited in intracontinental basins in the paleo‐Asian continent. Tectonic processes and basin evolution basically controlled the deposition of these oil shales. In addition, enhanced precipitation under humid climate during the early Aptian and the Callovian–Oxfordian was another key factor inducing the widespread oil shale deposition in Mongolia.     

THEORETICAL APPROACH TO THE SOLUTION OF THE INFILTRATION PROBLEM

ABSTRACT

The one-dimensional transient downward entry of water in unsaturated soils is investigated theoretically. The mathematical equation describing the infiltration process is derived by combining Darcy's dynamic equation of motion with the continuity and thermodynamic state equations adjusted for the unsaturated flow conditions. The resulting equation together with the corresponding initial and boundary conditions constitues a mathematical initial boundary value problem requiring the solution of a nonlinear partial differential equation of the parabolic type. The volumetric water content is taken as the dependent variable and the time and the position along the vertical direction are taken as the independent variables. The governing equation is of such nature that a solution exists for t > 0 and is uniquely determined if two relationships are defined, together with the specified state of the system, at the initial time t = 0 and at the two boundaries. The two required relations are those of pressure versus permeability and pressure versus volumetric water content.

Since the partial differential equation has strong non-linear terms, a discrete solution is obtained by approximating the derivatives with finite-differences at discrete mesh points in the solution domain and integrated for the corresponding initial and boundary conditions. The use of an implicit difference scheme is employed in order to generate a system of simultaneous non-linear equations that has to be solved for each time increment. For n mesh points the two boundary conditions provide two equations and the repetition of the recurrence formula provides n—2 equations, the total being n equations for each time increment. The solution of the system is obtained by matrix inversion and particularly with a back-substitution technique. The FORTRAN statements used for obtaining the solution with an electronic digital computer (IBM 704) are presented together with the input data.

Analysis of the errors involved in the numerical solution is made and the stability and convergence of the solution of the approximate difference equation to that of the differential equation is investigated. The method applied is that of making a Fourier series expansion of a whole line of errors and then following the progress of the general term of the series expansion and also the behavior of each constituent harmonic. The errors (forming a continuous function of points in an abstract Banach space) are represented by vectors with the Fourier coefficients constituting a second Banach space. The amplification factor of the difference equation is shown to be always less than unity which guarantees the stability of the employed implicit recurrence scheme.

Experiments conducted on a vertical column packed uniformly with very fine sand, show a satisfactory agreement between the theoretically and experimentally obtained values. Many experimental results are shown in an attempt to explain the infiltration phenomenon with emphasis on the shape and movement of the wet front, and the effects of the degree of compaction, initial water content and deaired water on the infiltration rate.     

Late Permian post‐ophiolitic trondhjemites from Central Iran: a mark of subduction role in growth of Paleozoic continental crust

Late Permian trondhjemites in the Anarak area occur as stocks and dykes, which cross cut the Anarak ophiolite and its overlying metasedimentary rocks, and are exposed along the northern Anarak east–west main faults. These leucocratic intrusive bodies have enclaves of all ophiolitic units and metamorphic rocks. They are composed of amphibole, plagioclase (oligoclase), quartz, zircon and muscovite. Secondary minerals are chlorite (pycnochlorite), epidote, albite, magnetite and calcite. Whole‐rock major‐ and trace‐element analyses reveal that they are characterized by high SiO ₂ (67.8–71.0 wt%), Al ₂ O ₃ (14.9–17.1 wt%) and Na ₂ O (5.3–8.6 wt%), low K ₂ O (0.1–1.5 wt%; average: 0.8 wt%), low Rb/Sr ratio (0.01–0.40; average: 0.09), low Y (3–6 ppm), negative Ti, Nb and Ta anomalies, slightly negative or positive Eu anomaly, LREE enrichment and fractionated HREE. These rocks present 2 to 40 times enrichment in inclined chondrite‐normalized REE patterns. Geochemical characteristics of the Anarak trondhjemites all reflect melting of a mafic protolith at more than 10 kbar. The field evidence and whole‐rock chemistry reveal that these rocks have been crystallized from magmas derived from melting of subducted Anarak oceanic crust. This study reveals that melting of garnet amphibolite was an important element of continent formation in the study area.