Temporal and spatial differences in salinity and water chemistry in SW Florida estuaries: Effects of human-impacted watersheds   总被引：1，自引：0，他引：1  

Donna M. Surge  Kyger C. Lohmann 《Estuaries and Coasts》2002,25(3):393-408

Three estuaries near Naples, Florida with variably modified watersheds have been investigated to understand the chemical consequences of altering drainage patterns. Blackwater River (near natural drainage, control site), Henderson Creek (moderately modified watershed), and Faka-Union Canal (severe channelization) were sampled for temperature, salinity, δ¹⁸O, δ¹³C of dissolved inorganic carbon (DIC), molality of CO₂ (ΣCO₂), and Mg:Ca and Sr:Ca ratios between freshwater and marine water end members over a 17-mo period. Carbon isotope composition followed similar seasonal patterns as salinity. Freshwater and seawater end members are more negative than the global average, likely reflecting equilibration with local carbon sources derived from mangrove leaf litter and groundwater. δ¹³C responds to differences in primary productivity between estuaries. Henderson Creek has higher primary productivity than Blackwater River (probable due to higher sewage input and agricultural runoff) and has more positive δ¹³C and lower ΣCO₂. δ¹⁸O is affected by seasonal input of freshwater from atmospheric precipitation, evaporation, and groundwater. Late summer and fall rains lower the δ¹⁸O of estuarine water, whereas evaporative conditions in the dry season elevate δ¹⁸O to values that can be more positive upstream than those from the Gulf of Mexico (estuarine inversion). Evaporation produces water in the Gulf of Mexico that is >1‰ more positive than the global sea surface average most of the year. The very negative δ¹⁸O values in Blackwater River and Henderson Creek likely reflect atmospheric and groundwater contribution. Mg:Ca and Sr:Ca ratios of Gulf water from all three estuaries are similar to global averages at low latitudes. Freshwater end members among estuaries are different in that Blackwater River has higher ratios, suggesting a groundwater contribution. Dolomitic rocks in the subsurface likely provide a source of Mg ions.  相似文献   

Interpretation of single-well tracer tests using fractional-flow dimensions. Part 2: A case study     

Kornelius Riemann  Gerrit van Tonder  Panganai Dzanga 《Hydrogeology Journal》2002,10(3):357-367

Generalized equations using fractional-flow dimensions were derived to estimate the Darcy and groundwater-flow velocities obtained from the point-dilution and the single-well injection-withdrawal field tests. Flow velocities can only be estimated from single-well tests if the kinematic porosity or the hydraulic conductivity and hydraulic gradient are known a priori. A pumping test performed on the boreholes will yield an estimate of the fractional-flow dimension and the extent of the flow region by applying the generalized radial flow (GRF) model of Barker [Barker JA (1988) A generalized radial flow model for hydraulic tests in fractured rock. Water Resour Res 24(10):1796–1804]. These parameters are used in the generalised equations for the single-well tracer tests to estimate the flow-through area and, therewith, the Darcy or flow velocity. The generalized procedure, described in detail in Part 1 of this paper, is applied to two boreholes on the Campus Test Site located at the University of the Free State, Bloemfontein, South Africa, and it is shown that the two independent tests (i.e. the point-dilution and the single-well injection-withdrawal tests) yield similar estimates of the natural-seepage velocity in the aquifer. The estimated natural-flow velocity obtained by using fractional dimensions is about two times higher than the velocity estimated by using the standard method (i.e. flow dimension n=2, flow thickness equal to length of the sealed-off section of the borehole). Electronic Publication  相似文献   

Spectral mixture analysis for mapping land degradation in semi-arid areas     

Tromp  Maarten  Epema  Gerrit F. 《Geologie en Mijnbouw》1998,77(2):153-160

Spectral mixture analysis (SMA) is an image-processing technique used for the analysis of airborne hyperspectral remote-sensing data which consist of a large number of spectral bands, typically over 100. In this paper the possibilities are examined of using SMA for the analysis of Landsat Thematic Mapper satellite data with only six bands in the visible to shortwave-infrared wavelength. We use data from a semi-arid area in the Sanmatenga province of Burkina Faso, an area known to experience land-degradation problems. In SMA, we assume that pixels in an image consist of one or more homogeneous (uniform in character) or pure surfaces, the so called end-members. The end-members were derived from the image data on the basis of specific image characteristics. Field data was collected to describe the characteristics of these end-members in terms of land cover, soil and degradation phenomena. The end-members derived from the image analysis, although statistically pure in terms of image spectral characteristics, prove to be mixtures at a field scale. This lack of purity is explained by the nature of semi-arid areas which is more heterogeneous than that of most other areas. The SMA yielded cover percentages for the end-members from which an unsupervised classification was made. Comparison of the classification with the results of SMA shows that the latter provides information on the amount and spatial distribution of land characteristics such as land degradation.  相似文献   

Beryllium in four NIMROC reference samples     

E. Vilcsek  G. Lohmann 《Earth and Planetary Science Letters》1982,57(2):448-450

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Der offene sternhaufen NGC 2362     

Werner Lohmann 《Astrophysics and Space Science》1977,51(1):173-176

The very young open star cluster NGC 2362 was investigated by the strip method on charts of two photographs taken with the 1-m Schmidt telescope of the European Southern Observatory. Up to the limiting magnitudeM _v ^* =5 _. ^m 8 the cluster contains 100 stars and can be described by the Gaussian density law (6). Further results are: Mass = 246 , central mass density ₀ = 43.1 = 246 pc^-3 , radiusR2.6 pc, mean velocity of the stars = 0.64 km s^–1.

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Mitteilungen Serie A.  相似文献   

Der offene sternhaufen NGC 6067     

Werner Lohmann 《Astrophysics and Space Science》1977,47(2):447-455

The open star cluster NGC 6067 was investigated by the strip method on charts of photographs with different exposure times taken with the 1-m Schmidt telescope of the European Southern Observatory. Because of the large distance (1820 pc) of the cluster its luminosity function is known up to date only betweenM _v =–4.5 andM _v =+1.5. In this paper it is continued toM _v =4.4 and further extrapolated by means of 2 variants. The cluster contains 419 respectively 476 stars with total masses of 1453 resp. 1483. On account of its radius of 5.9 pc the cluster is a rather extended object, which can be described by the generalized density law of Schuster withn=4.42 and the central star density 8.9 stars pc^–3. The mean velocity of the stars amounts to 1.03 km s^–1, the massbrightness relation is 0.031 in solar units.

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Mitteilungen Serie A.  相似文献   

Unusual carbon and oxygen isotopic ratios of ostracodal calcite from last interglacial (Sangamon episode) lacustrine sediment in Raymond Basin, Illinois, USA     

B. Brandon Curry  Thomas F. Anderson  Kyger C. Lohmann 《Journal of Paleolimnology》1997,17(4):421-435

The stable isotopic records of ostracode valves deposited during the last interglaciation in Raymond Basin, Illinois, have ¹³C and ¹⁸O values as high as +16.5 and +9.2 respectively, the highest values yet reported from continental ostracodal calcite. Located in south-central Illinois, Raymond, Pittsburg, Bald Knob, and Hopwood Farm basins collectively have yielded important long pollen and ostracode records that date from about 130000 years ago to the present. Although fossils from the present-day interglaciation are not well preserved, these records constitute the only described, conformable, fossiliferous successions of this age from the interior of glaciated North America.The high ¹³C values from Raymond Basin are attributed to the residual effects of methane loss either by ebullition or by emission through the stems of senescent emergent aquatic vegetation. A mass balance model suggests that an increase in ¹³C of dissolved inorganic carbon on the order of +15 is possible within a few hours given modest rates of methanogenesis of about 0.02 mol m^-2 d^-1. The ¹³C records from other studies of ostracode valves have values approaching, but not exceeding about +14 suggesting a limiting value to ¹³C enrichment due to simultaneous inputs and outputs of dissolved inorganic carbon.Values of ¹⁸O in ostracodal calcite are quite variable (–4 to +9) in sediment from the late Sangamon subepisode. A model of isotopic enrichment in a desiccating water body implies that a reduction in reservoir volume of 20% could produce this range of isotopic values. High humidity and evaporation probably account for most of the ¹⁸O variability.  相似文献   

A simple gibbsite analyzer for rapid field determination of the available alumina content in bauxites     

Marius J. van Essen  Johannes A. C. Heynen  Adriaan H. van der Veen  Gerrit H. Vonkeman 《Mineralium Deposita》1971,6(1):41-48

A portable gibbsite analyzer suited for field operation and intended for rapid determination of available alumina is described. The available alumina content is calculated from the relative weight loss caused by the dehydration of gibbsite. More than 100 samples of gibbsite-containing bauxites of different origin, were analyzed with this apparatus. The results always appeared to be correct within 10% of the actual content. In the laboratory, an accuracy of ±2.60% gibbsite, and a reproducibility of ±1.87% gibbsite, both at the 95% confidence interval, could be achieved. The apparatus can be used under tropical conditions. Its weight is 13 kg. It can be fed from a motor-driven generator weighing 18 kg. The duration of a single analysis in the field is 30–40 minutes. In the laboratory about 25 analyses can be performed within 8 hours. The apparatus can be handled by an untrained operator. One operator can run at least two analyzers at a time. The complete set-up, including the generator, costs less than US $ 1500.

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Zusammenfassung Ein tragbarer Apparat für die Gibbsit Bestimmung im Freien wird beschrieben. Der Gibbsitgehalt wird berechnet aus dem Gewichtsverlust während der Entwässerung. Für Gibbsit-haltige Bauxite, die mit diesem Apparat analysiert sind, wurden Resultate gefunden, die immer weniger als 10% vom richtigen Gehalt abwichen. Im Labor konnte eine Genauigkeit von ±2.60% Gibbsit und eine Reproduzierbarkeit von ±1.87% Gibbsit, beide mit einer Wahrscheinlichkeit von 95%, erreicht werden. Der Apparat ist ausgerüstet für den Gebrauch in den Tropen. Er wiegt 13 kg und kann von einem durch einen Benzinmotor angetriebenen Generator gespeist werden. Der Generator hat ein Gewicht von 18 kg. Eine einzige Bestimmung im Freien dauert 30–40 Minuten. Im Labor können etwa 25 Bestimmungen innerhalb von 8 Stunden gemacht werden. Ein Mann kann mindestens zwei Apparate zugleich beobachten. Apparat und Generator kosteten weniger als US $ 1500.

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3‐D shallow‐water seismic survey evaluation and design using the focal‐beam method: a case study offshore Abu Dhabi          下载免费PDF全文

Tomohide Ishiyama  Gerrit Blacquière 《Geophysical Prospecting》2016,64(5):1215-1234

For 3‐D shallow‐water seismic surveys offshore Abu Dhabi, imaging the target reflectors requires high resolution. Characterization and monitoring of hydrocarbon reservoirs by seismic amplitude‐versus‐offset techniques demands high pre‐stack amplitude fidelity. In this region, however, it still was not clear how the survey parameters should be chosen to satisfy the required data quality. To answer this question, we applied the focal‐beam method to survey evaluation and design. This subsurface‐ and target‐oriented approach enables quantitative analysis of attributes such as the best achievable resolution and pre‐stack amplitude fidelity at a fixed grid point in the subsurface for a given acquisition geometry at the surface. This method offers an efficient way to optimize the acquisition geometry for maximum resolution and minimum amplitude‐versus‐offset imprint. We applied it to several acquisition geometries in order to understand the effects of survey parameters such as the four spatial sampling intervals and apertures of the template geometry. The results led to a good understanding of the relationship between the survey parameters and the resulting data quality and identification of the survey parameters for reflection imaging and amplitude‐versus‐offset applications.  相似文献   

A multi-model comparison of Atlantic multidecadal variability     

Jin Ba  Noel S. Keenlyside  Mojib Latif  Wonsun Park  Hui Ding  Katja Lohmann  Juliette Mignot  Matthew Menary  Odd Helge Otterå  Bert Wouters  David Salas y Melia  Akira Oka  Alessio Bellucci  Evgeny Volodin 《Climate Dynamics》2014,43(9-10):2333-2348

A multi-model analysis of Atlantic multidecadal variability is performed with the following aims: to investigate the similarities to observations; to assess the strength and relative importance of the different elements of the mechanism proposed by Delworth et al. (J Clim 6:1993–2011, 1993) (hereafter D93) among coupled general circulation models (CGCMs); and to relate model differences to mean systematic error. The analysis is performed with long control simulations from ten CGCMs, with lengths ranging between 500 and 3600 years. In most models the variations of sea surface temperature (SST) averaged over North Atlantic show considerable power on multidecadal time scales, but with different periodicity. The SST variations are largest in the mid-latitude region, consistent with the short instrumental record. Despite large differences in model configurations, we find quite some consistency among the models in terms of processes. In eight of the ten models the mid-latitude SST variations are significantly correlated with fluctuations in the Atlantic meridional overturning circulation (AMOC), suggesting a link to northward heat transport changes. Consistent with this link, the three models with the weakest AMOC have the largest cold SST bias in the North Atlantic. There is no linear relationship on decadal timescales between AMOC and North Atlantic Oscillation in the models. Analysis of the key elements of the D93 mechanisms revealed the following: Most models present strong evidence that high-latitude winter mixing precede AMOC changes. However, the regions of wintertime convection differ among models. In most models salinity-induced density anomalies in the convective region tend to lead AMOC, while temperature-induced density anomalies lead AMOC only in one model. However, analysis shows that salinity may play an overly important role in most models, because of cold temperature biases in their relevant convective regions. In most models subpolar gyre variations tend to lead AMOC changes, and this relation is strong in more than half of the models.  相似文献