Linking watershed disturbance with nearshore sedimentation and the shell beds of Lake Tanganyika (Mahale Mountains,Tanzania)     

James Busch  Michael Soreghan  Kirsten de Beurs  Michael McGlue  Ismael Kimirei  Andrew Cohen  Emily Ryan 《Environmental Earth Sciences》2018,77(13):514

Extensive deposits of shell-rich sediments in the nearshore environment of Lake Tanganyika, Africa, form a unique habitat for a diverse group of endemic gastropods, crustaceans, fish and sponges, among other organisms. Anthropogenic alteration of the lake’s hinterland from deforestation, fires, and agriculture threaten this crucial habitat through sediment pollution of the littoral environment. This study examines the sedimentology of these nearshore shell beds along a study area north of the Mahale Mountains (Tanzania) to test whether varying levels of watershed disturbance, determined by analysis of satellite imagery, within three moderately sized watersheds (>?100 km²) results in sedimentological differences offshore. The results show that shell beds adjacent to disturbed watersheds (Lagosa and Rukoma) contain more fine-grained sediment compared to shell beds offshore of the undisturbed watershed (Katumbi). Widespread burning, clearance, and land cultivation, and rains of the wet season are causal factors that result in significant differences in fine-grained sedimentation, larger sediment plumes offshore, and increased shoreline progradation. In areas most affected by sedimentation, sponges are largely absent, and shell coverage, which is a measure of fish-nesting capabilities, is lower. The discovery of a small population of live Neothauma tanganyicense offshore of the Katumbi river suggests that the presence of shell-bed forming gastropods in front of a relatively low disturbance watershed, and their conspicuous absence offshore of the other two watersheds, could be related to recent watershed disturbance and increased sedimentation. The increased fine-grained sedimentation and limited shell production by the reduced modern gastropod populations may signal that the shell-bed ecosystem of Lake Tanganyika is at risk.  相似文献   

Predicting the chemical and mechanical properties of gypseous soils using different simulation technics     

Mohammed  Ahmed  Hummadi  Rizgar Ali  Mawlood  Yousif Ismael 《Acta Geotechnica》2022,17(4):1111-1127

Acta Geotechnica - Gypseous soils are soils that contain sufficient quantities of gypsum that are considered collapsible soil. The present study's objective is to predict the shear strength...  相似文献   

Variations in turbulent kinetic energy at a point source submarine groundwater discharge in a reef lagoon     

Sabrina M. Parra  Ismael Mariño-Tapia  Cecilia Enriquez  Arnoldo Valle-Levinson 《Ocean Dynamics》2014,64(11):1601-1614

The influence of sea level variations due to tides and wave setup on turbulent kinetic energy (TKE) was observed at a point source submarine groundwater discharge in a fringing coral reef lagoon. Tidal and wave setup variations modulated speed, TKE, TKE dissipation, and water temperature and salinity at the buoyant jet. The primary driver of jet TKE and speed variations was tides, while wave setup was a minor contributor. An inverse relationship between surface elevation and TKE was explained with an exponential equation based on sea level variations. During low tides, peak jet speeds (up to 0.3 m s^?1) and TKE per unit mass (up to 0.4 m² s^?2) were observed. As high tide approached, the jet produced minimum TKE of ~0.003 m² s^?2 and TKE dissipation ranged from 2 to 8×10^?4 m² s^?3. This demonstrated the sensitivity of the jet discharge to tides despite the small tidal range (<20 cm). Jet temperatures and salinities displayed semidiurnal oscillations with minimum salinity and temperature values during maximum discharge. Jet salinities increased throughout low tides while temperatures decreased. This pattern suggested the jet conduit was connected to a stratified cavity within the aquifer containing cool fresh water over cool salty water. As low tides progressed, jet outflow increased in salinity because of the mixing within the conduit, while lower jet temperatures suggested water coming from further or deeper in the aquifer. The presence of such a cavity has been recently confirmed by divers.  相似文献   

Does Poisson’s downward continuation give physically meaningful results?   总被引：1，自引：0，他引：1  

Petr Vaníček  Pavel Novák  Michael Sheng  Robert Kingdon  Juraj Janák  Ismael Foroughi  Zdeněk Martinec  Marcelo Santos 《Studia Geophysica et Geodaetica》2017,61(3):412-428

The downward continuation (DWC) of the gravity anomalies from the Earth’s surface to the geoid is still probably the most problematic step in the precise geoid determination. It is this step that motivates the quasi-geoid users to opt for Molodenskij’s rather than Stokes’s theory. The reason for this is that the DWC is perceived as suffering from two major flaws: first, a physically meaningful DWC technique requires the knowledge of the irregular topographical density; second, the Poisson DWC, which is the only physically meaningful technique we know, presents itself mathematically in the form of Fredholm integral equation of the 1st kind. As Fredholm integral equations are often numerically ill-conditioned, this makes some people believe that the DWC problem is physically ill-posed. According to a revered French mathematician Hadamard, the DWC problem is physically well-posed and as such gives always a finite and unique solution. The necessity of knowing the topographical density is, of course, a real problem but one that is being solved with an ever increasing accuracy; so sooner or later it will allow us to determine the geoid with the centimetre accuracy.  相似文献   

非正式聚落快速增长下的城市蔓延     

张家旗  陈爽  高群  IsmaelA. Kimirei 《世界地理研究》2019,28(3):32-42

姆万扎是坦桑尼亚第二大城市,也是非洲发展最快的城市之一,近年来城市蔓延问题日益凸显。本文以遥感解译的姆万扎2000、2010、2015年3期土地利用数据为基础,运用GIS空间分析、用地增长弹性系数、景观指数等方法和指标,并结合实地调研和关键知情人访谈,分析了姆万扎2000年以来城市蔓延的空间特征及影响因素。分析结果表明：1）2000年~2015年间姆万扎城市以非正式聚落形式快速蔓延,建成区扩展速度和扩展强度迅速增加;蔓延主要占用裸地,其次是植被,侵占植被的速度迅速加快;2）城市蔓延主要沿3条主干道进行,属于“廊道式为主,填充式为辅”的扩展模式,形成指状的城市空间形态;建成区紧凑度逐渐下降,形状变得更加不规则;3）城市蔓延的主要区域和整体范围都在扩大,距离衰减特征明显,沿东南方向扩展强度最高;4）城市蔓延主要受到人口与经济增长、交通条件改善、土地制度问题及有效规划缺失等因素的影响。加强次干路和地方道路的规划和建设,制定及时、有效、符合地方背景的城市规划,是未来姆万扎控制城市蔓延的可能途径。  相似文献   

Mesoscale eddy variability in the Caribbean Sea     

López-Álzate  Margarita E.  Sayol  Juan-Manuel  Hernández-Carrasco  Ismael  Osorio  Andrés F.  Mason  Evan  Orfila  Alejandro 《Ocean Dynamics》2022,72(9-10):679-693

Ocean Dynamics - The spatial distribution, and the monthly and seasonal variability of mesoscale eddy observations derived from the AVISO eddy atlas are assessed in the Caribbean Sea during...  相似文献   

Flat-spectrum symmetric objects with ∼1 kpc sizes – I. The candidates     

Pedro Augusto  J. Ignacio Gonzalez-Serrano  Ismael Perez-Fournon  Peter N. Wilkinson 《Monthly notices of the Royal Astronomical Society》2006,368(3):1411-1428

  相似文献   

The European Large Area ISO Survey – IX. The 90-μm luminosity function from the Final Analysis sample     

Stephen Serjeant †  Alberto Carramiñana †  Eduardo Gonzáles-Solares  Phillipe Héraudeau  Raúl Mújica †  Ismael Perez-Fournon  Nicola Sedgwick †  Michael Rowan-Robinson  Alberto Franceschini  Thomas Babbedge  Carlos del Burgo  Paolo Ciliegi  reas Efstathiou  Fabio La Franca  Carlotta Gruppioni  David Hughes  Carlo Lari  Seb Oliver  Francesca Pozzi  Manfred Stickel  Mattia Vaccari 《Monthly notices of the Royal Astronomical Society》2004,355(3):813-818

  相似文献   

Structure of interacting elliptical radio galaxies     

Lourdes De Juan  Luis Colina  Ismael Pérez-Fournon 《Astrophysics and Space Science》1993,205(1):209-216

We have used a numerical method based on elliptical fitting of isophotes to analyse the structural parameters of three pairs of elliptical galaxies containing radio jets. The relationship between tidal interactions and radio activity is also investigated.  相似文献   

Grain-scale characterization of water retention behaviour of sand using X-ray CT     

Ghonwa Khaddour  Ismael Riedel  Edward Andò  Pascal Charrier  Pierre Bésuelle  Jacques Desrues  Gioacchino Viggiani  Simon Salager 《Acta Geotechnica》2018,13(3):497-512

  相似文献