The history and fate of the Nubian Sandstone Aquifer springs in the oasis depressions of the Western Desert,Egypt     

Owen Powell  Rod Fensham 《Hydrogeology Journal》2016,24(2):395-406

Extraction of groundwater for agriculture has resulted in the loss of springs across arid regions of the globe. The history and fate are recorded of the artesian springs of Egypt’s Western Desert, from ancient times to the present, spanning the rise and fall of the great civilisations from the Pharoanic dynasties to Persian, Greek and Roman conquests. The study area includes oases Kharga, Dakhla, Bahriya, Farafra and Siwa, and several outer and small oases around Siwa and the edge of the Qattara Depression. The region is hyper-arid, receiving 10 mm or less average annual precipitation and evaporation rates are in the vicinity of 3,000 mm/a. Groundwater in the oases is largely derived from bores discharging from the Nubian Sandstone Aquifer. Based on an extensive survey, conducted for the first time, attention is drawn to the rapid demise of springs as a result of modern irrigation schemes which continue to deplete groundwater supplies.  相似文献   

Differences in trophodynamics of commercially important fish between artificial waterways and natural coastal wetlands     

Rod M. Connolly 《Estuarine, Coastal and Shelf Science》2003,58(4):929-936

Extensive artificial waterways have replaced natural wetlands and created new estuarine habitats on the southern Queensland coast, Australia. Economically important fish species found in adjacent natural wetlands of mangrove, saltmarsh and seagrass also occur in the artificial waterways. Stable isotope analyses (δ¹³C, δ¹⁵N) were used to test whether the relative importance of basal sources of energy varied for foodwebs found in artificial (canals and tidal lakes) and natural waterways. None of the fish species differed in their isotope values between artificial waterways. In contrast, isotopic signatures of snub-nosed garfish (Arrhamphus sclerolepis; Hemiramphidae) varied greatly between natural and artificial waterways, having highly enriched δ¹³C values (−10.5‰) in natural wetlands, demonstrating reliance on seagrass (−11.4‰), and significantly less enriched values (−19.0‰) in artificial waterways, consistent with either local algal sources (−19.8 to −20.4‰) or a mixture of seagrass and other less enriched autotrophs from adjacent natural wetlands. Isotopic signatures of sand whiting (Sillago ciliata; Sillaginidae) were also significantly more enriched in natural (−18.2‰) than artificial (−21.0‰) habitats, but means were not far enough apart to distinguish between different sources of nutrition. δ¹³C values of yellowfin bream (Acanthopagrus australis; Sparidae) did not differ between artificial and natural habitats (about −20‰ in both). δ¹⁵N values of fish varied among habitats only for A. sclerolepis, which in artificial waterways had values enriched by 2‰ over those in natural waterways. This was consistent with a shift from seagrass (relatively depleted δ¹⁵N) as a source in natural habitat to algal sources (relatively enriched δ¹⁵N) in artificial habitats. This study provides some of the first evidence that at least some fish species rely on different autotrophs in artificial waterways than in adjacent natural wetlands.  相似文献   

F.W. Bessel (1825): The calculation of longitude and latitude from geodesic measurements     

C.F.F. Karney  R.E. Deakin 《Astronomische Nachrichten》2010,331(8):852-861

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Future changes in Central Europe heat waves expected to mostly follow summer mean warming     

Joan Ballester  Xavier Rodó  Filippo Giorgi 《Climate Dynamics》2010,35(7-8):1191-1205

Daily output from the PRUDENCE ensemble of regional climate simulations for the end of the twentieth and twenty-first centuries over Europe is used to show that the increasing intensity of the most damaging summer heat waves over Central Europe is mostly due to higher base summer temperatures. In this context, base temperature is defined as the mean of the seasonal cycle component for those calendar days when regional heat waves occur and is close, albeit not identical, to the mean temperature for July–August. Although 36–47% of future Central Europe July and August days at the end of the twenty-first century are projected to be extreme according to the present day climatology, specific changes in deseasonalized heat wave anomalies are projected to be relatively small. Instead, changes in summer base temperatures appear much larger, clearly identifiable and of the same order of magnitude as changes in the whole magnitude of heat waves. Our results bear important consequences for the predictability of central European heat wave intensity under global warming conditions.  相似文献   

Diatom-based Holocene paleoenvironmental records from continental sites on northeastern Ellesmere Island, high Arctic, Canada   总被引：2，自引：0，他引：2  

I. Rod Smith 《Journal of Paleolimnology》2002,27(1):9-28

Stratigraphic changes in diatom assemblages from four small lakes on northeastern Ellesmere Island, high Arctic, Canada, provide a proxy lake-ice cover and paleoenvironmental record. Low absolute diatom abundances and a benthic Fragilaria (sensu lata) dominated assemblage during the postglacial (< 7.6 ka B.P.) to mid-Holocene record the moderating effects of locally retreating glaciers. Around 5.5 ka B.P. diatom concentrations begin to rise, reaching their highest levels (10⁹ valves per g dry sediment) between 4.2 and 3 ka B.P., interpreted to be the warmest period in this region. Topoclimatic differences between lakes on Hazen Plateau and those lower in Lake Hazen Basin account for the initial decline in diatom abundances in the upper lakes after 3 ka B.P. This change is thought to reflect a lowering of the regional snowline, accordant with widely recognized Neoglacial advances on Ellesmere Island and Greenland. Lakes in lower Lake Hazen Basin maintained extensive summer ice free conditions until ~ 1.9 ka B.P., after which diatom abundances declined, suggesting prolonged summer lake-ice cover through the remainder of the recovered Holocene record. Differences between the records presented here and those from coastal areas of the Canadian high Arctic highlight the unique topoclimatic characteristics and continentality of the Lake Hazen region, and possible effects that local marine environments may have had on coastal records. Such differences serve to demonstrate the inherent geographic variability of paleoenvironmental records from the high Arctic.  相似文献   

Concepts,Conceptualization, and Conceptions in Geography     

Rod Lane  Jennifer Carter  Theresa Bourke 《The Journal of geography》2019,118(1):11-20

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A High-Performance,High-Accuracy RTK GPS Machine Guiadance System     

Hugh Baertlein  Bruce Carlson  Rod Eckels  Stacey Lyle  Steve Wilson 《GPS Solutions》2000,3(3):4-11

As technology matures, Real Time Kinematic (RTK) global positioning system (GPS) receivers are providing increased performance in accuracy, on-the-fly (OTF) initialization times, measurement speed, and latency. Leica's Dozer 2000 machine guidance system combines an MC1000 GPS sensor, graphic intensive guidance software, a digital terrain model, and a digital site plan. Figure 1 shows the operator's view of the system. The end results is a highly accurate, extremely responsive local navigation system. Engineers can easily upload design information onto a touch-screen machine guidance personal computer (PC) and greatly reduce earthmoving costs while simultaneously recording “as-built” inspection data. The Leica MC1000 machine control sensor is a true 10-Hz, centimeter-level-accuracy, open-architecture GPS sensor specifically designed for machine guidance and control. At the heart of the MC1000's performance are a very stable oven-controlled oscillator (3 × 10⁻¹¹/s short-term stability), a low-power Intel 486-DX4-80 processor, and four user-configurable input/output (I7O) ports. Special algorithms mitigate the effects of multipath and Selective Availability (SA) while providing centimeter accuracy up to 10 times per second with only 30 milliseconds' latency. The high update rate and low latency are essential for machine guidance and control. The MC1000 GPS reference station is capable of outputting RTK and Differential GPS (DGPS) data simultaneously, providing and entire site with GPS information for machine guidance and control, tracking and dispatching of vehicles, and support of survey crews. This article describes how recent advances in technology have combined to produce the Leica Dozer 2000 – a machine guidance system that is ideal for a wide range of earthmoving and inspection applications. ? 2000 John Wiley & Sons, Inc.  相似文献   

Going West: Nutrient Limitation of Primary Production in the Northern Gulf of Mexico and the Importance of the Atchafalaya River     

Antonietta Quigg  Jason B. Sylvan  Anne B. Gustafson  Thomas R. Fisher  Rod L. Oliver  Sasha Tozzi  James W. Ammerman 《Aquatic Geochemistry》2011,17(4-5):519-544

To investigate controls on phytoplankton production along the Louisiana coastal shelf, we mapped salinity, nutrient concentrations (dissolved inorganic nitrogen (DIN) and phosphorus (P_i), silicate (Si)), nutrient ratios (DIN/P_i), alkaline phosphatase activity, chlorophyll and ¹⁴C primary productivity on fine spatial scales during cruises in March, May, and July 2004. Additionally, resource limitation assays were undertaken in a range of salinity and nutrient regimes reflecting gradients typical of this region. Of these, seven showed P_i limitation, five revealed nitrogen (N) limitation, three exhibited light (L) limitation, and one bioassay had no growth. We found the phytoplankton community to shift from being predominately N limited in the early spring (March) to P limited in late spring and summer (May and July). Light limitation of phytoplankton production was recorded in several bioassays in July in water samples collected after peak annual flows from both the Mississippi and Atchafalaya Rivers. We also found that organic phosphorus, as glucose-6-phosphate, alleviated P limitation while phosphono-acetic acid had no effect. Whereas DIN/P_i and DIN/Si ratios in the initial water samples were good predictors of the outcome of phytoplankton production in response to inorganic nutrients, alkaline phosphatase activity was the best predictor when examining organic forms of phosphorus. We measured the rates of integrated primary production (0.33?C7.01 g C m^?2 d^?1), finding the highest rates within the Mississippi River delta and across Atchafalaya Bay at intermediate salinities. The lowest rates were measured along the outer shelf at the highest salinities and lowest nutrient concentrations (<0.1 ??M DIN and Pi). The results of this study indicate that P_i limitation of phytoplankton delays the assimilation of riverine DIN in the summer as the plume spreads across the shelf, pushing primary production over a larger region. Findings from water samples, taken adjacent the Atchafalaya River discharge, highlighted the importance of this riverine system to the overall production along the Louisiana coast.  相似文献   

Discussion: Evolution of central eastern Australia during the Palaeozoic and early Mesozoic     

Emile Rod 《Australian Journal of Earth Sciences》2013,60(1-2):95-96

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Dynamical linkage of tropical and subtropical weather systems to the intraseasonal oscillations of the Indian summer monsoon rainfall. Part II: Simulations in the ENSEMBLES project     

Shujie Ma  Xavier Rodó  Yongjia Song  Benjamin A. Cash 《Climate Dynamics》2012,39(6):1219-1239

We assess the ability of individual models (single-model ensembles) and the multi-model ensemble (MME) in the European Union-funded ENSEMBLES project to simulate the intraseasonal oscillations (ISOs; specifically in 10–20-day and 30–50-day frequency bands) of the Indian summer monsoon rainfall (ISMR) over the Western Ghats (WG) and the Bay of Bengal (BoB), respectively. This assessment is made on the basis of the dynamical linkages identified from the analysis of observations in a companion study to this work. In general, all models show reasonable skill in simulating the active and break cycles of the 30–50-day ISOs over the Indian summer monsoon region. This skill is closely associated with the proper reproduction of both the northward propagation of the intertropical convergence zone (ITCZ) and the variations of monsoon circulation in this band. However, the models do not manage to correctly simulate the eastward propagation of the 30–50-day ISOs in the western/central tropical Pacific and the eastward extension of the ITCZ in a northwest to southeast tilt. This limitation is closely associated with a limited capacity of models to accurately reproduce the magnitudes of intraseasonal anomalies of both the ITCZ in the Asian tropical summer monsoon regions and trade winds in the tropical Pacific. Poor reproduction of the activity of the western Pacific subtropical high on intraseasonal time scales also amplify this limitation. Conversely, the models make good reproduction of the WG 10–20-day ISOs. This success is closely related to good performance of the models in the representation of the northward propagation of the ITCZ, which is partially promoted by local air–sea interactions in the Indian Ocean in this higher-frequency band. Although the feature of westward propagation is generally represented in the simulated BoB 10–20-day ISOs, the air–sea interactions in the Indian Ocean are spuriously active in the models. This leads to active WG rainfall, which is not present in the observed BoB 10–20-day ISOs. Further analysis indicates that the intraseasonal variability of the ISMR is generally underrepresented in the simulations. Skill of the MME in seasonal ISMR forecasting is strongly dependent on individual model performance. Therefore, in order to improve the model skill with respect to seasonal ISMR forecasting, we suggest it is necessary to better represent the robust dynamical links between the ISOs and the relevant circulation variations, as well as the proportion of intraseasonal variability in the individual models.  相似文献