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1.
G. C. Poole J. A. Stanford S. W. Running C. A. Frissell W. W. Woessner B. K. Ellis 《地球表面变化过程与地形》2004,29(10):1259-1274
Geomorphology interacts with surface‐ and ground‐water hydrology across multiple spatial scales. Nonetheless, hydrologic and hydrogeologic models are most commonly implemented at a single spatial scale. Using an existing hydrogeologic computer model, we implemented a simple hierarchical approach to modeling surface‐ and ground‐water hydrology in a complex geomorphic setting. We parameterized the model to simulate ground‐ and surface‐water ?ow patterns through a hierarchical, three‐dimensional, quantitative representation of an anabranched montane alluvial ?ood plain (the Nyack Flood Plain, Middle Fork Flathead River, Montana, USA). Comparison of model results to ?eld data showed that the model provided reasonable representations of spatial patterns of aquifer recharge and discharge, temporal patterns of ?ood‐water storage on the ?ood plain, and rates of ground‐water movement from the main river channel into a large lateral spring channel on the ?ood plain, and water table elevation in the alluvial aquifer. These results suggest that a hierarchical approach to modeling ground‐ and surface‐water hydrology can reproduce realistic patterns of surface‐ and ground‐water ?ux on alluvial ?ood plains, and therefore should provide an excellent ‘quantitative laboratory’ for studying complex interactions between geomorphology and hydrology at and across multiple spatial scales. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
2.
Michael R. Morris Brook O. Brouwer Jeremy K. Caves Mary J. Harner Jack A. Stanford 《Aquatic Sciences - Research Across Boundaries》2010,72(4):519-532
In floodplain primary succession, vegetation colonizes nitrogen-poor alluvial deposits and fertility improves as soil nitrogen
accumulates over time. It is generally assumed that vegetation assimilates the vast majority of its nitrogen from the soil;
however, recent studies have suggested that the hyporheic zone also may be an important nitrogen source. We investigated the
potential relative importance of hyporheic nitrogen by comparing fertility indices, specifically total (TN), dissolved inorganic
(DIN), potentially mineralizable (PMN) and ion exchange resin nitrogen (IERN) in both soils and the hyporheic zone at early,
mid and late succession stands on an expansive river flood plain. We also constructed mesocosms to assess growth of cottonwood
cuttings with access to soil and/or hyporheic water. We found TN and PMN increased from early to mid succession in both the
soil (to 10 cm) and hyporheic zone (in a 10 cm layer). While TN, DIN and PMN were an order of magnitude higher in the soil
than in the hyporheic zone, IERN was higher in the hyporheic zone, indicating that subsurface flow through the flood plain
may be important in delivering nitrogen to the root zone. However, even when flux was added to the hyporheic PMN pool, nitrogen
availability in the hyporheic zone (in a 10 cm layer) was vastly lower than soil PMN (to 10 cm). Further, the instantaneous
standing stock of DIN in the surface soil alone was about equal to the sum of the DIN pool, the mean subsurface flux and the
PMN pool in a 10 cm layer of hyporheic zone. In the mesocosm experiment, cottonwood cuttings with access to both soil and
hyporheic water grew fastest; however, they also had the lowest foliar nitrogen concentrations, indicating that this was not
due to greater nitrogen availability. In the field, nitrogen content of cottonwood foliage increased along with soil (but
potentially hyporheic as well) nitrogen accumulation during succession, suggesting the vegetation responded to increasing
nitrogen fertility. We conclude that at least on a per unit-volume basis, the hyporheic zone probably provides little nitrogen
relative to the surface soil, except on new alluvial bars that characteristically are nitrogen poor. Therefore, the hyporheic
zone is probably a much smaller nitrogen source for mature forests relative to the surface soil unless the vegetation exploits
a much larger volume of the hyporheic zone than surface soil. 相似文献
3.
河北承德黑山铁矿床热液成矿特征及流体包裹体研究 总被引：3，自引：2，他引：1
黑山大型钒钛磁铁矿矿床产于大庙斜长岩杂岩体中,是承德地区最重要的"大庙式"岩浆型铁矿床。笔者在矿区野外地质观察过程中发现,穿插于斜长岩中的铁磷矿脉、磁铁矿硫化物矿脉有热液成矿作用的显示,表明黑山铁矿床成因除传统认为的岩浆期结晶、熔离、矿浆贯入成矿作用外,还有热液期的成矿作用发生。本文对热液成矿期铁磷矿石中磷灰石和矿化蚀变石英中的流体包裹体进行了显微测温和激光拉曼光谱分析。结果表明,磷灰石中原生包裹体可以分为气液两相包裹体、含子矿物包裹体、含液态CO2三相包裹体、单液相、单气相包裹体5类,均一温度主要集中于180～420℃,盐度主要集中于6.2%～38.9%NaCleq,流体包裹体气相成分主要为CO2、N2和CH4,液相成分主要为H2O,固相成分主要为方解石、石盐、白云石及铁氧化物子矿物。石英中流体包裹体类型和成分与磷灰石中的类似,但固相成分未发现石盐和不透明金属子矿物,均一温度变化于149～422℃,盐度变化于5.7%～22.9%NaCleq。成矿流体为CaCl2-NaCl-H2O-CO2体系,均一温度和盐度呈现正相关连续渐变的特征。铁磷矿石的磷灰石中原生包裹体为流体包裹体,盐度高,子矿物种类复杂,组成中富含CO2和CH4等,这些特征显示成矿流体以岩浆热液为主;成矿机理可能与大气降水对岩浆热液的稀释有关。 相似文献
4.
北祁连东部两类Ⅰ型花岗岩定年及其地质意义 总被引：21，自引：7，他引：21
北祁连东部早古生代地层中产出两种特征不同的I型花岗岩类,其一以井子川岩体为代表,暗色矿物以角闪石为主,稀土总量为90×10~(-6)～106×10~(-6),轻重稀土比值小于8,锆石的SHRIMP年龄为464±15Ma,岩体形成的构造环境类似于岛弧;其二是以黄羊河岩体为代表,暗色矿物以黑云母为主,稀土总量为214×10~(-6)～250×10~(-6),轻重稀土比值大于8,锆石的LA-ICP-MS年龄为383±6 Ma,岩体形成于碰撞后环境。 相似文献
5.
A potentiostat was used to study the electrolytic corrosion of iron meteorites in a neutral solution. Low current densities were chosen so that the observed potentials would more closely approximate the theoretical Nernst values. Iron, nickel, and cobalt ions, the products of corrosion, were soluble in the electrolyte solution, and were determined after each electrolysis by atomic absorption spectrophotometry. Kamacite and taenite dissolved as individual phases, with kamacite dissolving preferentially. Cobalt dissolved along with iron and nickel from each phase. There is a direct relationship between nickel content and the potential at which a meteorite first starts to dissolve; the higher the nickel content, the more resistant the meteorite is to corrosion. None of the six meteorites observed started to dissolve at a lower potential than pure iron, nor at a higher potential than pure nickel 相似文献
6.
The slug test is the most widely used technique for the in situ estimation of hydraulic conductivityin confined and unconfined formations. Currently, there are no generally accepted methods in thegroundwater literature for the analysis of response data from slug tests performed in wells screenedacross the watertable. A field study was undertaken in an attempt to develop a set of practicalguidelines for tests conducted in such wells. Three wells, screened within unconsolidated materialexhibiting a range of hydraulic conductivities (.05–30.0 m/day), were installed to depths of up to9 m (30 ft) in Kansas River alluvium that ranges in thickness from 15 m to 21 m (50 ft to 70 ft)near Lawrence, Kansas. Intensive well-development efforts removed any drilling debris that couldinterfere with well-formation hydraulics. Once the wells were developed properly, a series of slugtests was performed at each well. The tests were designed to assess the role of the unsaturatedzone and the appropriateness of assuming a fixed hydraulic head upper boundary. The results ofthis investigation can be summarized as follows: (1) the sufficiency of well development shouldbe based on repeat slug tests and not the clarity of pumped water; (2) the effective screen radiusfor best model analysis should be based on a mass balance and not nominal screen dimensions;(3) the watertable can be represented as a constant head boundary and flow in the unsaturatedzone can be ignored in most situations; (4) conventional techniques for the analysis of slug-testdata seem to be reasonable for slug tests conducted in wells screened across the watertable, whenused with the appropriate effective screen radius and normalized head range; and (5) fluctuationsin the watertable elevation through time can be exploited to obtain some insight into the natureof vertical variation in hydraulic conductivity at a well. The results of this investigation indicatethat multiple slug tests should be performed at wells screened across the watertable in order toreliably assess the sufficiency of well development and the appropriateness of conventional theory. 相似文献
7.
R. De Propris S.A. Stanford P. Eisenhardt Mark Dickinson 《Astrophysics and Space Science》2003,285(1):43-47
We derive the blue fraction for a sample of K-selected galaxies in 25 clusters at 0.15 <z<0.92. We find a much smaller blue fraction and weaker trend with redshift than measured in optically selected samples. We
suggest that the Butcher-Oemler effect is primarily due to star forming low luminosity galaxies.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
8.
Abstract The clean development mechanism (CDM) requires developing countries to set up designated national authorities (DNAs). The DNA should be designed to both attract investment and to establish an effective regulatory framework for project approval—including assessment to ensure that CDM projects contribute to national sustainable development objectives. Since CDM investment flows to Africa are uncertain, however, countries cannot risk large investments in institutional infrastructure and need to build on existing institutions. This article examines the critical functions that a DNA has to fulfil, and outlines several institutional models. It concludes that models that minimize institutional cost by drawing on existing institutions for environmental impact assessment and promotion of foreign direct investment are likely to be the best starting-point for DNAs in many African countries. 相似文献
9.
Mary J. Harner Jeff S. Piotrowski Ylva Lekberg Jack A. Stanford Matthias C. Rillig 《Aquatic Sciences - Research Across Boundaries》2009,71(3):331-337
Riparian areas are diverse systems where flooding creates new sites for establishment of vegetation. Symbioses with soil microorganisms,
such as mycorrhizal fungi, affect vascular plant growth and community composition. It is unknown, however, how mycorrhizal
fungi are dispersed along rivers and what potential they have to inoculate roots of plants establishing on recently deposited
sedimentary surfaces of flood plains. We measured AMF inocula in sediment deposited by an average spring flood along an expansive
riverine flood plain in Montana, USA, to determine whether AMF inocula were present in sediments and what types of propagules
(spores, hyphae, or colonized root fragments) contribute to AMF infectivity. Flood-deposited sediments contained sufficient
inocula for AMF to colonize host plants (Sorghum sudanense) grown in a greenhouse, and both AMF hyphal lengths and spore densities were correlated with infectivity. Availability of
mycorrhizal inocula, which is patchily distributed in this system, may lead to microsites that differ in ability to support
establishment and growth of early-successional plants. 相似文献
10.
Seagrass beds serve as nursery grounds for many fish species and often play an important role in the juvenile stages of economically and recreationally important fishes. The eelgrass Zostera capensis is the dominant submerged macrophyte in permanently open South African estuaries and occupies large intertidal and subtidal areas within the Knysna system. The primary objective of this study was to compare the occurrence of sparids and mugilids in eelgrass and nearby bare sediment areas using sampling with seine nets. The hypothesis that was tested is that mugilids are dominant in unvegetated areas of the Knysna Estuary littoral whereas sparids predominate within eelgrass beds located in the same zone. The results indicate that the family Mugilidae is better represented at unvegetated sites when compared to members of the family Sparidae, with the exception of Lithognathus lithognathus, but that the dominant three sparids and dominant two mugilids were most abundant in sparse eelgrass beds that included both bare and vegetated areas within this habitat type. The main fish species responsible for the separation of fish assemblages associated with unvegetated sites versus those associated with vegetated areas were Rhabdosargus holubi, Liza dumerili, Liza richardsonii, Lithognathus lithognathus, Sarpa salpa and Diplodus capensis, with R. holubi, S. salpa and D. capensis being mainly attracted to eelgrass habitats and L. dumerili, L. richardsonii and L. lithognathus having a stronger affinity for bare areas. This finding confirms a previous estuarine study in the nearby Swartvlei lake littoral, which found that sparids dominated areas where aquatic macrophytes were extensive and that mugilids became more prevalent at those same sites when the macrophytes underwent complete senescence. The length-frequency distributions of some sparid and mugilid species differed considerably between eelgrass and bare sediment areas, whereas those of other species showed little or no difference between these two habitat types. 相似文献