Diel and seasonal variability in the fish community structure of a mud‐bottom estuarine habitat in the Gulf of Mexico     

Manuel Castillo‐Rivera  Rocío Zárate‐Hernández  Selene Ortiz‐Burgos  José Zavala‐Hurtado 《Marine Ecology》2010,31(4):633-642

We hypothesized that temporal variation in fish species composition and community structure in a low complexity habitat in the Pueblo Viejo Lagoon, Mexico, is influenced by diel light/dark cycles and tidal stage, and by seasonal changes in salinity and temperature. We collected a total of 17,661 individuals during 2‐h interval sampling over six bi‐monthly 24‐h sampling cycles representing 53 species, of which 11 (～20%) were previously unknown in the system. Diel variation indicated that significantly higher numbers of individuals and species were caught at night, whereas diversity and evenness were higher during the day. Species richness was significantly higher in July and January, whereas diversity and evenness peaked around May; both were correlated with temperature. Diel variation in species composition was influenced primarily by the light/dark cycle. Cluster analyses of each diel cycle separated fish assemblages from midday samples from those of nocturnal samples, separated by an extended wide transition period as fish moved at dawn and during the late afternoon/dusk. Significant shifts (as determined by MANOVA) in assemblage structure occurred between months. Canonical correspondence analysis showed that temperature and day/night effects were the most important environmental variables structuring the fish community. This constrained ordination also defined species with specific habitat preferences as follows: (i) diurnal, warm temperature species (mainly planktivores) (Brevoortia gunteri, Cetengraulis edentulus, Diapterus auratus, and Membras martinica); (ii) nocturnal, warm temperature species (mainly predators) (Citharichthys spilopterus, Cathorops melanopus, and Bairdiella spp.); and (iii) low temperature, diurnal species (Brevoortia patronus and Mugil curema) or those with twilight and nocturnal distributions (Anchoa mitchilli, the most numerically abundant species). Our results indicate that diel and seasonal changes in fish community structure were mainly related to day/night cycles and temperature regimes.  相似文献   

基于我国全球连续监测与评估系统的ERP测定的精度分析     

何战科  李志刚  杨旭海  程宗颐 《全球定位系统》2010,35(5):21-24

利用GPS观测资料解算地球自转参数，用全球均匀分布的22个IGS跟踪站（IGS05）的连续观测资料估计地球自转参数（ERP），并与IERSC04（UTC0时）的结果相比较，二者相差很小，均在IERS的ERP估计精度范围之内。基于即将建成的COMPASS全球连续监测与评估系统跟踪站，选择其网的8个IGS跟踪站的资料进行了解算并进行了分析和比对。  相似文献   

砂土颗粒三维形态的定量表征方法     

付茹  胡新丽  周博  汪华斌  王剑峰 《岩土力学》2018,39(2):483-490

颗粒形态是影响砂土力学特性的重要因素,特别是影响砂土在低应力状态下的抗剪强度、剪胀效应和临界状态行为,以及高应力状态下的颗粒破碎行为。因此,准确地重构砂粒的三维形态,并量化计算其形态表征参数是研究砂粒形态效应的前提工作。借助于高精度的CT扫描技术和图像处理技术,获得近海石英砂和风化花岗岩残积砂这两类砂土颗粒的三维形态信息。采用球谐函数序列实现两种砂颗粒三维形态的准确重构,并通过球谐函数分析计算砂土颗粒的体积来验证该方法的有效性。基于球谐重构的三维砂粒表面,提出了实用性的方法来计算砂粒的表面积、表面曲率和三维尺寸等,进而计算砂粒的三维球度、圆度和伸长率等形态表征参数。结果表明,当球谐函数阶达到15时,其重构的砂粒基本形状和表面纹理均与真实砂粒非常接近;近海石英砂在水流搬运和磨蚀的作用下颗粒形态较为规则和圆滑,球度和圆度较大,而风化花岗岩残积砂则在物理风化和剥蚀作用下颗粒形态较为复杂和粗糙,球度和圆度较小;而这两种地质作用对砂土颗粒的伸长率则没有明显的影响。  相似文献   

基于GSI值量化和修正方法的岩体力学参数确定     

姜光成  胡乃联  洪根意  李国清  方京珍 《岩土力学》2018,39(6):2211-2218

为了准确确定岩体力学参数,通过综合分析多种地质强度指标(GSI)量化方法,提出了一种改进的GSI值量化和修正方法。首先,利用测线法估算结构面平均间距(d)和岩体块度指数(RBI)的改进型岩体块度率(RBR),根据岩体三维结构面网络,获得岩体体积节理数(Jv)和岩体结构等级(SR),然后采用上述参数和结构表面条件(SCR)及结构表面特性参数(Jc)进行了GSI值的定量化处理。为了克服GSI体系的缺点,考虑结构面产状和地下水对岩体力学性质的影响,提出了GSI值的修正方法和公式。以某铅锌矿体的矿岩体为例,根据改进的GSI值量化和修正方法及Hoek-Brown强度准则来确定矿岩体力学参数,通过与原位变形试验的对比分析,验证了该方法的精确性和可行性。该方法为从室内岩石力学试验合理地获取节理岩体力学参数提供了理论及实现的依据。  相似文献   

徐家围子断陷深层火石岭组致密火山岩储层地应力分布规律研究   总被引：4，自引：4，他引：0  

毛哲  曾联波  秦龙卜  祖克威  刘国平  田鹤 《地质力学学报》2018,24(3):321-331

徐家围子断陷位于松辽盆地北部,其深层中生代火石岭组为致密火山岩气藏,天然裂缝发育,地应力分布非均质性强。结合诱导裂缝法与井径崩落法进行单井现今地应力方向分析,利用声波测井法计算现今地应力大小的纵向分布。依据火石岭组构造顶底面图、火山岩相组及断层分布特征建立非均质三维地质模型;在动、静态岩石物理参数拟合校正的基础上,结合实验测试及已有研究成果,确定不同岩相组和断层岩石物理参数,建立三维力学模型;利用Ansys有限元数值模拟软件建立火石岭组三维数学模型并进行相关运算获得三维现今地应力分布模型。计算结果表明在火石岭组地层中,水平最大主应力方向主要为东西向,应力值范围在86~110 MPa;水平最小主应力方向主要为南北向,应力值范围在67~84 MPa。分析模拟结果可知火山岩相、断层和构造起伏三者对火石岭组现今地应力分布影响较大。其中水平主应力的方向主要受断层和近火山口相分布的影响,而水平主应力的大小则是受三者综合作用。在构造低部位,近火山口相组发育处,断层上盘及断层端部皆为主应力的集中区域。依据现今地应力研究成果可为徐家围子断陷下一步开发井网部署、压裂改造方案和水平井的设计以及注水管理提供重要指导。   相似文献   

同位素131Ⅰ测西台吉乃尔湖矿区含水层地质参数   总被引：1，自引：0，他引：1       下载免费PDF全文

杨海镇  马海州  高东林 《盐湖研究》2008,16(1)

盐湖区的水文地质参数特性与淡水区迥然不同。同位素示踪法可以利用西台盐湖区已有的长观井,机动灵活的随时监测含水层水文地质参数;由于介质的特殊性以及卤水性质的垂直差异性,造成水文地质参数的时空可变性;测试结果表明,对于完整井以及深的非完整井,该方法切实有效,但对于很浅的非完整井,测试结果具有很大的随机性。最后,根据测试结果以及有关的水文地质资料,把研究区分成7个渗透系数分区。  相似文献   

Extended consecutive modal pushover procedure for estimating seismic responses of one-way asymmetric plan tall buildings considering soil-structure interaction     

Mohammad Hadikhan Tehrani  Faramarz Khoshnoudian 《地震工程与工程振动(英文版)》2014,13(3):487-507

Performance based design becomes an effective method for estimating seismic demands of buildings. In asymmetric plan tall building the effects of higher modes and torsion are crucial. The consecutive modal pushover (CMP) procedure is one of the procedures that consider these effects. Also in previous studies the influence of soil-structure interaction (SSI) in pushover analysis is ignored. In this paper the CMP procedure is modified for one-way asymmetric plan mid and high-rise buildings considering SSI. The extended CMP (ECMP) procedure is proposed in order to overcome some limitations of the CMP procedure. In this regard, 10, 15 and 20 story buildings with asymmetric plan are studied considering SSI assuming three different soil conditions. Using nonlinear response history analysis under a set of bidirectional ground motion; the exact responses of these buildings are calculated. Then the ECMP procedure is evaluated by comparing the results of this procedure with nonlinear time history results as an exact solution as well as the modal pushover analysis procedure and FEMA 356 load patterns. The results demonstrate the accuracy of the ECMP procedure.  相似文献   

The four dimensional variational data assimilation with multiple regularization parameters as a weak constraint (Tikh-4D-Var) and its preliminary application on typhoon initialization     

Jian Zhong  JianFang Fei  XiaoPing Cheng  XiaoGang Huang 《中国科学:地球科学(英文版)》2014,57(11):2690-2701

Traditional variational data assimilation (VDA) with only one regularization parameter constraint cannot produce optimal error tuning for all observations. In this paper, a new data assimilation method of “four dimensional variational data assimilation (4D-Var) with multiple regularization parameters as a weak constraint (Tikh-4D-Var)” is proposed by imposing different regularization parameters for different observations. Meanwhile, a new multiple regularization parameters selection method, which is suitable for actual high-dimensional data assimilation system, is proposed based on the posterior information of 4D-Var system. Compared with the traditional single regularization parameter selection method, computation of the proposed multiple regularization parameters selection method is smaller. Based on WRF3.3.1 4D-Var data assimilation system, initialization and simulation of typhoon Chaba (2010) with the new Tikh-4D-Var method are compared with its counterpart 4D-Var to demonstrate the effectiveness of the new method. Results show that the new Tikh-4D-Var method can accelerate the convergence with less iterations. Moreover, compared with 4D-Var method, the typhoon track, intensity (including center surface pressure and maximum wind speed) and structure prediction are obviously improved with Tikh-4D-Var method for 72-h prediction. In addition, the accuracy of the observation error variances can be reflected by the multiple regularization parameters.  相似文献   

吉林台网测震台站监测效能评估   总被引：1，自引：0，他引：1  

康建红  张宇  郑国栋  张晨侠 《防灾减灾学报》2014,(4):74-77

由于种种原因,台站地震计的固有周期、阻尼、灵敏度、观测动态范围等参数和台基噪声在运行的过程中会发生变化。本文用阶跃标定和计算观测动态范围、台基噪声功率谱的方法,得到吉林测震台网各台站地震计参数和台基噪声的变化情况,掌握吉林测震台网各台站的监测能力,为以后吉林测震台网的建设和发展提出建议。  相似文献   

Runoff change of Naoli River in Northeast China in 1955–2009 and its influencing factors     

Xiaolin Song  Xianguo Lu  Zhengmao Liu  Yonghe Sun 《中国地理科学(英文版)》2012,22(2):144-153

Runoff change and trend of the Naoli River Basin were studied through the time series analysis using the data from the hydrological and meteorological stations. Time series of hydrological data were from 1957 to 2009 for Bao′an station, from 1955 to 2009 for Baoqing station, from 1956 to 2009 for Caizuizi station and from 1978 to 2009 for Hongqiling station. The influences of climate change and human activities on runoff change were investigated, and the causes of hydrological regime change were revealed. The seasonal runoff distribution of the Naoli River was extremely uneven, and the annual change was great. Overall, the annual runoff showed a significant decreasing trend. The annual runoff of Bao′an, Baoqing, and Caizuizi stations in 2009 decreased by 64.1%, 76.3%, and 84.3%, respectively, compared with their beginning data recorded. The wet and dry years of the Naoli River have changed in the study period. The frequency of wet year occurrence decreased and lasted longer, whereas that of dry year occurrence increased. The frequency of dry year occurrence increased from 25.0%-27.8% to 83.9%-87.5%. The years before the 1970s were mostly wet, whereas those after the 1970s were mostly dry. Precipitation reduction and land use changes contributed to the decrease in annual runoff. Rising temperature and water project construction have also contributed important effects on the runoff change of the Naoli River.  相似文献