Epibenthic megacrustaceans from the continental margin, slope and abyssal plain of the Southwestern Gulf of Mexico: Factors responsible for variability in species composition and diversity     

Elva G. Escobar-Briones  Adriana Gaytn-Caballero  Pierre Legendre 《Deep Sea Research Part II: Topical Studies in Oceanography》2008,55(24-26):2667

The community structure of megacrustaceans (orders Lophogastrida, Isopoda, and Decapoda) collected in trawls on the continental margin, upper slope and abyssal plain of the southern Gulf of Mexico was studied to determine to what extent broad-scale variation in community composition and diversity was influenced by geographic regions environmental variability and depth. Trawls were collected in the Mexican Ridges, the Campeche Bank, and the Sigsbee abyssal plain. There was variability in species composition, density and diversity among geographic regions and along the depth gradient. A total of 106 species were identified and grouped in three orders; five infraorders, 40 families, and 70 genera. This study extends the known geographic ranges of the species Homolodromia monstrosa and Ephyrina benedicti. The largest number of species was recorded in the Mexican Ridges and on the upper continental shelf; lower values were found on the continental margin and in the abyssal plain. The largest densities were recorded on the continental margin in the Mexican Ridges. Megacrustaceans show in general low frequencies and low abundances in trawls, characterizing them as rare components of benthic assemblages. Contrary to an accepted paradigm about deep-sea biodiversity, the highest H′ diversity values were recorded in the Sigsbee abyssal plain, followed by values from the upper continental slope; diversity values were correlated with evenness. Canonical Redundancy analysis results showed a significant affinity to regions for 18 crustacean species; 33 species showed a significant affinity to both regions and depth zones within regions.  相似文献   

Discharge and suspended sediment transport in the Ayeyarwady River,Myanmar: centennial and decadal changes     

T. Furuichi  Z. Win  R. J. Wasson 《水文研究》2009,23(11):1631-1641

Among the large rivers rising on the Tibetan Plateau and adjacent high mountains, the discharge and suspended sediment load of the Ayeyarwady (Irrawaddy) River are the least well known. Data collected between 1969 and 1996 at Pyay (Prome) are analysed to provide the best available modern estimate of discharge (379 ± 47 × 10⁹ m³/year) and suspended sediment load (325 ± 57 × 10⁶ t/year) for the river upstream of the delta head. A statistical comparison with data collected in the nineteenth century (1871 to 1879) shows discharge has significantly decreased in the last ～100 years. Regression and correlation analyses between discharge in the modern period and indices of El Niño–Southern Oscillation (ENSO) show a relationship. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

The linkage between velocity patterns and sediment entrainment in a forced‐pool and riffle unit     

D. M. Thompson  E. E. Wohl 《地球表面变化过程与地形》2009,34(2):177-192

A field‐based project was initiated in order to characterize velocities and sediment entrainment in a forced‐pool and riffle sequence. Three‐dimensional velocities and turbulence intensities were measured with an acoustic Doppler velocimeter at 222 different points at three similar flows that averaged approximately 4·35 m³ s⁻¹ within a large pool–riffle unit on North Saint Vrain Creek, Colorado. Sediment‐sorting patterns were observed with the introduction of 500 tracer particles painted according to initial seeding location. Tracer particles moved sporadically during a 113 day period in response to the annual snowmelt peak flow, which reached a maximum level of 14·8 m³ s⁻¹. Velocity data indicate high instantaneous velocities and turbulence levels in the centre of pools. Patterns of sediment deposition support the notion that stream competence is higher in the pool than the downstream riffle. Flow convergence around a large channel constriction appears to play a major role in multiple processes that include helical flow development and sediment routing, and backwater development with low velocities and turbulence levels above the constriction that may locally limit sediment supply. Jet flow, flow separation, vortex scour and turbulence generation enhance scour in the centre of pools. Ultimately, multiple processes appear to play some role in maintenance of this forced pool and the associated riffle. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

ESTIMATE OF METHANE EMISSIONS FROM RICE FIELDS IN CHINA BY CLIMATE-BASED NET PRIMARY PRODUCTIVITY     

KANG Guo-ding    CAI Zu-cong  ZHANG Zi-heng    XIAO Peng-feng 《中国地理科学(英文版)》2004,14(4):326-331

1INTRODUCTIONIrrigated ricefieldsarecharacterizedbylargespatialandtemporalvariationsin CH4 emissiontotheatmo-sphere.Accordingly,thereisagreatuncertaintyintheestimate ofCH4 emissionsfromricefields.GreateffortshavebeenmadetoestimatetheCH4 emissionsfromricefieldsandseveralapproacheshavebeendeveloped.TherepresentativemethodsincludetheIPCC(Inter-governmentPanelofClimateChange)region-specificemissionfactormethodandthemodelcalculationmethod.Toimprovethecalculationaccuracy,theIPCCmethodreq…  相似文献   

新疆天山北坡一次区域性暴雪形成机制及水汽输送特征分析     

万瑜 《沙漠与绿洲气象(新疆气象)》2024,18(4):9-16

利用高空、地面常规观测资料、NCEP/NCAR再分析资料，诊断分析了2017年2月新疆天山北坡一次区域性暴雪过程的特征及成因，结合GDAS再分析资料并采用HYSPLIT模式，模拟追踪水汽源地、主要水汽输送通道及其对水汽输送的贡献。结果表明：此次天山北坡暴雪是在典型后倾结构的高低空系统配置下产生的，中、高纬地区短波槽在东移过程中同位相叠加，为暴雪长时间维持提供了稳定的天气尺度背景；暴雪发生时位势不稳定性加强，中低层持续冷垫抬升是主要的动力机制，较强垂直风切变是降雪强度较大的重要原因，高低空急流耦合激发中尺度垂直上升支和次级环流圈，地形作用对暴雪有增幅作用；暴雪主要水汽源地位于阿拉伯半岛西侧的红海和伊朗高原西南侧的波斯湾至阿拉伯海北部一带，水汽通道主要集中在500～850 hPa，水汽辐合区位于700～850 hPa，中高层有偏西气流、中层有西南气流、低层有西北急流将水汽接力输送至暴雪区；利用HYSPLIT模式模拟发现，暴雪期间，西、东、南边界水汽输入均起重要作用，主要水汽输送通道分别为偏西路径、偏西南路径、局地水汽路径，1500 m高度的追踪，三者贡献率大致相当，3000 m高度，局地水汽和偏西路径水汽贡献率更大。  相似文献   

基于同轴差距测量法的南海深水海底沉积物声衰减特性研究   总被引：4，自引：3，他引：1  

邹大鹏  卢博  吴百海  梁润华  陈飞燕 《热带海洋学报》2009,28(3):35-39

通过分析沉积物声波测量过程能量损失的实质，阐述平行轴差距衰减测量法和垂直轴差距衰减测量法的研究基础——差动式衰减测量方法原理，并推导了其衰减系数公式。根据南海沉积物的柱状样品分装的特点，结合以上两种方法，提出了同轴差距衰减测量法，这种方法具有原理上的合理性并且其可操作性强；运用此方法测量了沉积物在常温和温度控制变化条件下的声波信号，计算了衰减系数，研究了温度对沉积物声波传播能量的影响，得出南海深水海底沉积物具有以下声衰减特性：沉积物含砂量高，声衰减系数大；随着温度的升高，沉积物的声衰减系数变化具有不均匀性，整体呈非线性减小趋势。以上研究将为声学遥测和反演海底沉积物的物理力学特性提供数据和方法支持。  相似文献   

The trade of live crustaceans in Portugal: space for technological improvements     

Barrento  Sara; Marques  Antonio; Pedro  Sonia; Vaz-Pires  Paulo; Nunes  Maria Leonor 《ICES Journal of Marine Science》2008,65(4):551-559

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Detecting environmental change in estuaries: Nutrient and heavy metal distributions in sediment cores in estuaries from the Gulf of Finland,Baltic Sea     

S. Vaalgamaa  D.J. Conley 《Estuarine, Coastal and Shelf Science》2008

Historical sediment nutrient concentrations and heavy metal distributions were studied in four estuaries in the Gulf of Finland, Baltic Sea to examine the response of these estuaries to temporal changes in human activities. Cores were collected using a 1-m Mackereth corer and dated using ²¹⁰Pb and ¹³⁷Cs. The cores were analyzed for total carbon (TC), total nitrogen (TN), total phosphorus (TP), organic phosphorus (OP), inorganic phosphorus (IP), biogenic silica (BSi), loss-on-ignition (LOI), Cu, Zn, Al, Fe, Mn, K, Ca, Mg and Na. Principal component analysis (PCA) was used to summarize the trends in the chemical variables and to compare the trends at the different sites. Applying the 1986 ¹³⁷Cs date as a reference point, ²¹⁰Pb chronologies were constructed for the sites using either the CRS model or a composite model (using both CIC and CRS). Significant increases were observed in sedimentation rates, TP and TN concentrations in all of the cores. Copper showed clear increases from 1850 towards present at all sites. Furthermore, redundancy analysis (RDA) was used to correlate environmental variables (catchment land use, catchment size, estuary surface area, depth and lake percentage) to sediment geochemistry. Based on redundancy analysis (RDA), the percentage of agriculture in the catchment was the most important factor affecting the sediment accumulation rate. Urban land-use types and industry correlate well with sediment Cu and Ca concentrations. Forest areas were related to high sediment BSi concentrations. Catchment land use was the most significant factor affecting sediment geochemical composition and sediment accumulation rates in these coastal embayments. Our results demonstrate that the coastal estuaries of the Gulf of Finland respond to the increased nutrient loading with the increased sedimentation and nutrient accumulation rates.  相似文献   

Streambank dewatering for increased stability     

F. Douglas Shields Jr  Andrew Simon  Seth M. Dabney 《水文研究》2009,23(11):1537-1547

Streambank erosion is often the dominant source of sediment leaving modified watersheds. Mass failure of high, steep banks is one of the most serious forms of streambank erosion. The risk of a given bank experiencing mass failure is a function of bank height, angle, and soil strength, which is governed by soil moisture. Two methods for bank dewatering were tested in adjacent sections of streambank bordering a deeply incised channel in northern Mississippi: a low‐cost pump system and subsurface horizontal drains. Pore water pressures (both positive and negative pressures, or matric suction) were continuously monitored for 2 years at the pumped site, at an adjacent untreated control section, and for 1 year at the site stabilized with horizontal drains. Resulting data were used to calculate a time series of the factor of safety using a computer model. Over the course of two wet seasons, average bank retreats for the control and pumped plots were 0·43 and 0·21 m, respectively. More limited monitoring revealed that the site with passive drains retreated about 0·23 m. At the pumped site pore water pressure was 3–4 kPa lower than at the control site during the most critical periods. Accordingly, computed factors of safety were above the failure threshold at the pumped site, but fell below unity at the control site on 11 occasions over the period of observation. Similarly, the drained site displayed generally lower pore water pressure and higher safety factors except for two events when drains were evidently overwhelmed with the volume of local surface and subsurface flows. These results suggest, but do not prove, that bank dewatering promoted lower rates of bank retreat and higher levels of stability since the three sites had slight differences in soils, geometry and boundary conditions. Initial cost of the dewatering treatments were significantly less than orthodox bank stabilization measures, but operation and maintenance requirements may be greater. Published in 2009 by John Wiley & Sons, Ltd.  相似文献   

BZ19—4海底混输管网优化算法探讨     

余智  王彦瑞  高秀敏  严雪莲 《海洋地质译丛》2009,(3):96-102

以海洋油气开发工程为实例，利用HYSYS和PIPEFLOW软件，分析了影响海底混输管网计算的若干因素，指出了HYSYS和PIPEFLOW的适用条件，最终确立了海底混输管网优化算法，提高计算效率。  相似文献