Identifying sources of groundwater in the lower Colorado River valley, USA, with δ18O, δD, and 3H: implications for river water accounting

Isotope measurements (48v56mcn62386/xxlarge948.gif" alt="delta" align="BASELINE" BORDER="0">¹⁸O, 48v56mcn62386/xxlarge948.gif" alt="delta" align="BASELINE" BORDER="0">D, ³H) indicate groundwater origin in the Lower Colorado River Valley (LCRV) and provide an alternative, or supplement, to the US Bureau of Reclamation48v56mcn62386/xxlarge8217.gif" alt="rsquo" align="BASELINE" BORDER="0">s proposed 48v56mcn62386/xxlarge8220.gif" alt="ldquo" align="MIDDLE" BORDER="0">accounting surface48v56mcn62386/xxlarge8221.gif" alt="rdquo" align="MIDDLE" BORDER="0"> method. The accounting surface method uses a hydraulic criterion to identify certain wells away from the flood plain that will eventually yield mainstream Colorado River water. New isotope data for 5 surface-water and 18 groundwater sites around Topock Marsh, Arizona, are compared with river-water data (1974–2002) from 11 sites between Utah and Mexico and with groundwater data from previous LCRV studies. Three groundwater sources are repeatedly identified in the LCRV: (1) local recharge derived from precipitation, usually winter rain, plots slightly below the global meteoric water line (GMWL) and has 48v56mcn62386/xxlarge948.gif" alt="delta" align="BASELINE" BORDER="0">D values that are 2048v56mcn62386/xxlarge8240.gif" alt="permil" align="MIDDLE" BORDER="0"> greater than those of recent river water; (2) 48v56mcn62386/xxlarge8220.gif" alt="ldquo" align="MIDDLE" BORDER="0">older48v56mcn62386/xxlarge8221.gif" alt="rdquo" align="MIDDLE" BORDER="0"> (pre-1950) upper basin river-water plots on or near the GMWL, distinct from local rainfall and recent river water; and (3) recent (post-1950) Colorado River water, including Topock Marsh samples, plots below the GMWL along an evaporation trend. Large floods, as in 1983, complicate interpretation by routing less evaporated upper basin water into the LCRV; however, tritium content can indicate the age of a water. River-water tritium has declined steadily from its peak of 716 TU in 1967 to about 11 TU in 2002. Mixtures of all three groundwater sources are common.

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Resumen Mediciones isotópicas (48v56mcn62386/xxlarge948.gif" alt="delta" align="BASELINE" BORDER="0">¹⁸O, 48v56mcn62386/xxlarge948.gif" alt="delta" align="BASELINE" BORDER="0">D, ³H) indican cual es el origen del agua subterránea en el Valle Bajo del Río Colorado (LCRV) y aportan una alternativa, o complemento, para el método 48v56mcn62386/xxlarge8220.gif" alt="ldquo" align="MIDDLE" BORDER="0">superficie de conteo48v56mcn62386/xxlarge8221.gif" alt="rdquo" align="MIDDLE" BORDER="0"> propuesto por el Buró de Reclamación de Estados Unidos. El método superficie de conteo utiliza un criterio hidráulico para identificar ciertos pozos alejados de la planicie de inundación que eventualmente producirán agua a partir de la corriente principal del Río Colorado. Los nuevos datos isotópicos para 18 sitios de agua subterránea y 5 sitios de agua superficial cerca de los Pantanos Topock, Arizona, se comparan con datos de agua de río (1974–2002) provenientes de 11 sitios localizados entre Utah y México, y con datos de aguas subterráneas de estudios previos realizados en el LCRV. Se identifican reiteradamente tres fuentes de aguas subterráneas en el LCRV: (1) recarga local derivada de precipitación, generalmente lluvia de invierno, cuya composición cae ligeramente por debajo de la línea de agua meteórica global (GMWL) y tiene valores 48v56mcn62386/xxlarge948.gif" alt="delta" align="BASELINE" BORDER="0">D que son 2048v56mcn62386/xxlarge8240.gif" alt="permil" align="MIDDLE" BORDER="0"> mayores que los reportados para agua de río reciente; (2) el agua de río 48v56mcn62386/xxlarge8220.gif" alt="ldquo" align="MIDDLE" BORDER="0">más vieja48v56mcn62386/xxlarge8221.gif" alt="rdquo" align="MIDDLE" BORDER="0"> (pre-1950) de la cuenca alta cuya composición cae sobre o cerca de la GMWL, diferente de la lluvia local y del agua de río reciente; (3) agua reciente (post-1950) del Río Colorado, incluyendo muestras de los Pantanos Topock, con composición por debajo de la GMWL a lo largo de una tendencia a la evaporación. Inundaciones grandes, como en 1983, complican la interpretación al transmitir menos agua evaporada de la cuenca alta hacia el LCRV; sin embargo, el contenido de tritio puede indicar la edad del agua. El contenido de tritio en agua de río ha disminuido constantemente desde la concentración pico de 716 TU en 1967 a cerca de 11 TU en 2002. Es común que exista mezclas de las tres fuentes de agua subterránea.

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Résumé Les mesures isotopiques (d18O, dD, 3H) indiquent les origine de l48v56mcn62386/xxlarge8217.gif" alt="rsquo" align="BASELINE" BORDER="0">eaux souterraines dans la Vallée de la Rivière du Bas Colorado (LCRV) et sont une alternative, ou un supplément, à la méthode des bilans hydrologiques proposée par du «US Bureau of Reclamation». Cette méthode de bilan hydrologique utilise un critère hydraulique permettant d48v56mcn62386/xxlarge8217.gif" alt="rsquo" align="BASELINE" BORDER="0">identifier certains puits hors de la plaine d48v56mcn62386/xxlarge8217.gif" alt="rsquo" align="BASELINE" BORDER="0">inondation qui pomperaient une part non négligeable de leur eau dans la rivière Colorado. De nouvelles données isotopiques provenant de 5 sites d48v56mcn62386/xxlarge8217.gif" alt="rsquo" align="BASELINE" BORDER="0">eau de surface et 18 d48v56mcn62386/xxlarge8217.gif" alt="rsquo" align="BASELINE" BORDER="0">eaux souterraines autour de Topock Marsh en Arizona, sont comparées avec les données (1974–2000) de 11 sites localisés entre Utah et Mexico, ainsi que des données d48v56mcn62386/xxlarge8217.gif" alt="rsquo" align="BASELINE" BORDER="0">autres études sur la LCRV. Ces sources d48v56mcn62386/xxlarge8217.gif" alt="rsquo" align="BASELINE" BORDER="0">eaux souterraines sont identifiées à plusieurs reprises dans la LCRV: (1) la recharge locale dérivant des précipitations, généralement les pluies hivernales, se retrouvent légèrement sous la ligne d48v56mcn62386/xxlarge8217.gif" alt="rsquo" align="BASELINE" BORDER="0">eau météoritique globale (GMWL) et possède des valeurs de dD 20% supérieures aux valeurs des eaux récentes de la rivière; (2) les eaux vieilles (pre-1950) du bassin supérieur de la rivière possèdent une valeurs très proches de la GMWL, distinctes des valeurs de la pluie locale et des eaux récentes de la rivière; et (3) les eaux récentes (post-1950) de la Rivière Colorado, incluant les échantillons de Topock Marsh, se positionnent à côté de la GMWL sur une droite d48v56mcn62386/xxlarge8217.gif" alt="rsquo" align="BASELINE" BORDER="0">évaporation. Les grandes inondations, par exemple celle de 1983, compliquent l48v56mcn62386/xxlarge8217.gif" alt="rsquo" align="BASELINE" BORDER="0">interprétation en reprenant dans la LCRV moins d48v56mcn62386/xxlarge8217.gif" alt="rsquo" align="BASELINE" BORDER="0">eaux marquées comme évaporées et provenant du bassin supérieur; par ailleurs le pic de tritium est descendu de 716 TU en 1967 à 11 TU en 2002. Les mélanges de ces trois sources sont assez fréquentes.

     

Active hot star shells

Interferometry in the visible provides milliarcsecond spatial resolution and thus has been used for studying the circumstellar environment of active hot stars. In this paper I will illustrate how the visibility modulus and phase can be used to better constrain the physics of Be disks through results from the VLA, the MkII and the GI2T interferometers. I will insist on the importance and the potential of coupling high angular resolution with high spectral resolution to the study of Be shells. Finally I will present a possible study of the circumstellar disk of Be stars using the VLTI. This revised version was published online in July 2006 with corrections to the Cover Date.     

A study of the Galactic plane towards l= 305°

We present optical  ( UBVI _C )  observations of a rich and complex field in the Galactic plane towards   l ∼ 305°  and   b ∼ 0°  . Our analysis reveals a significantly high interstellar absorption  ( A _V ∼ 10)  and an abnormal extinction law in this line of sight. Availing a considerable number of colour combinations, the photometric diagrams allow us to derive new estimates of the fundamental parameters of the two open clusters Danks 1 and Danks 2. Due to the derived abnormal reddening law in this line of sight, both clusters appear much closer (to the Sun) than previously thought. Additionally, we present the optical colours and magnitudes of the WR 48a star, and its main parameters were estimated. The properties of the two embedded clusters, DBS2003 130 and 131, are also addressed. We identify a number of young stellar objects which are probable members of these clusters. This new material is then used to revisit the spiral structure in this sector of the Galaxy showing evidence of populations associated with the inner Galaxy Scutum-Crux arm.     

On the sensitivity of tidal residuals off the west coast of Britain to mesh resolution

An irregular mesh model of the west coast of Britain is used to examine the sensitivity of tidal residuals to mesh resolution in the region. Computed residuals are compared with earlier published results determined with a high resolution (1 km grid) finite difference model of the eastern Irish Sea. Initial calculations show that tidal residuals are largest in nearshore regions particularly in the vicinity of headlands. Local refinement of the mesh in these regions leads to a more detailed picture of the flow field, particularly adjacent to the coast. Although large scale offshore features of the flow can be resolved using the high resolution finite difference model, such an approach leads to a “stair case” representation of the coastal boundary with an adjacent near coastal region of spurious tidal residuals. By using an irregular mesh that follows the coast, this effect is removed. In the Mersey river region the tidal residual is resolved with a mesh resolution of 120 m, although calculations show that its distribution is particularly sensitive to small scale features of the topography. A variable mesh that can accurately represent the lateral variations in river width and details of topography in both the nearshore and estuarine environment appears essential in modelling the coastal spread of freshwater plumes from rivers and pollutants discharged into the near coastal environment.     

苏里格西部致密砂岩气藏储层成岩作用特征及孔隙度定量演化

为了探究鄂尔多斯盆地苏里格西部地区储层致密成因及孔隙演化规律,本文基于铸体薄片、电镜分析和高压压汞等室内测试,通过建立理论计算模型,对其苏48区储层的孔隙演化进行定性分析与量化表征。分析结果表明,区内盒8段储层岩性主要为石英砂岩和岩屑石英砂岩,储层成岩阶段处于早成岩和中成岩阶段,部分达到晚成岩期,成岩作用顺序依次为:压实-硅质胶结-绿泥石胶结-黏土矿物胶结-溶蚀溶解-碳酸盐胶结;量化结果显示:压实作用和胶结作用是造成储层孔隙度下降的主要因素,其中压实作用使得原始孔隙度下降22%,胶结作用使其下降9.81%,溶蚀作用对储集空间有所改善,增加了3.88%的孔隙,最终形成了当今平均孔隙度为7.47%的致密砂岩储层。据理论计算与实测物性数据进行对比,计算结果与实测结果基本吻合,相对误差小于3%。根据成岩作用的作用强度,结合岩石特征分析,可将研究区盒8段储层成岩相划分出4种,即弱-中胶结强溶蚀相、中胶结中溶蚀相、中溶蚀强胶结相和强压实致密相。综合试气成果可知,弱-中胶结强溶蚀相区域气产量较为可观,可将弱-中胶结强溶蚀相区域作为天然气持续上产的主要研究区域。     

The embedded cluster DBSB 48 in the nebula Hoffleit 18: Comparison with Trumpler 14

We derive fundamental parameters of the embedded cluster DBSB 48 in the southern nebula Hoffleit 18 and the very young open cluster Trumpler 14, by means of deep JHK_s infrared photometry. We build colour–magnitude and colour–colour diagrams to derive reddening and age, based on main sequence and pre-main sequence distributions. Radial stellar density profiles are used to study cluster structure and guide photometric diagram extractions. Field-star decontamination is applied to uncover the intrinsic cluster sequences in the diagrams. Ages are inferred from K-excess fractions. A prominent pre-main sequence population is present in DBSB 48, and the K-excess fraction f_K = 55 ± 6% gives an age of 1.1 ± 0.5 Myr. A mean reddening of A_Ks=0.9±0.03 was found, corresponding to A_V = 8.2 ± 0.3. The cluster CMD is consistent with the far kinematic distance of 5 kpc for Hoffleit 18. For Trumpler 14 we derived similar parameters as in previous studies in the optical, in particular an age of 1.7 ± 0.7 Myr. The fraction of stars with infrared excess in Trumpler 14 is f_K = 28 ± 4%. Despite the young ages, both clusters are described by a King profile with core radii R_core = 0.46 ± 0.05 pc and R_core = 0.35 ± 0.04 pc, respectively, for DBSB 48 and Trumpler 14. Such cores are smaller than those of typical open clusters. Small cores are probably related to the cluster formation and/or parent molecular cloud fragmentation. In DBSB 48, the magnitude extent of the upper main sequence is ΔK_s "48; 2 mag, while in Trumpler 14 it is ΔK_s "48; 5 mag, consistent with the estimated ages.     

The EC 14026 stars — XI. Feige 48: a link in its class

Rapid oscillations in the sdB star Feige 48 have been discovered. The frequency spectrum reveals at least four periods in a narrow interval from 340 to 380 s. The oscillation amplitude is typically a few per cent, but this star shows perhaps the most dramatic amplitude variability from night to night of any of the known sdB pulsators (EC 14026 stars). Analysis of multicolour absolute photometry, as well as low- and intermediate-dispersion spectroscopy, yields an effective temperature of 28 900 ± 300 K and log g  = 5.45 ± 0.05. Feige 48 is thus the coolest EC 14026 star. Its intermediate gravity and intermediate period suggest the existence of a period–gravity correlation, and unite the majority of the EC 14026 stars with the extreme object, PG 1605+072. The narrow frequency intervals in which the pulsations of Feige 48 and other EC 14026 stars fall suggest a narrow bandpass for the excitation mechanism.