Scale Dependencies of Vegetation and Topography in a Mountainous Environment of Montana   总被引：2，自引：2，他引：2  

Ling Bian  Stephen J. Walsh 《The Professional geographer》1993,45(1):1-11

This research examines the effects of spatial scale on estimating the relationship between vegetation biomass and topography within a portion of Glacier National Park, Montana. The Reflectance/Absorptance vegetation index, developed from processed Landsat Thematic Mapper digital data, is related to three topographic variables obtained through processed Digital Elevation Models: elevation, slope angle, and slope aspect. R² values between the vegetation index and the topographic variables are obtained from regression analyses at a series of aggregated spatial scales. The effective range of spatial scales within which the two sets of variables are spatially dependent and the degree of the spatial dependencies are characterized through semivariance and fractal analyses.  相似文献   

Sediment oxygen consumption and benthic nutrient fluxes on the Louisiana continental shelf: A methodological comparison     

Tina Miller-Way  Gregory S. Boland  Gilbert T. Rowe  Robert R. Twilley 《Estuaries and Coasts》1994,17(4):809-815

There has been considerable discussion but little experimental evidence regarding the comparability of in-situ and remote (shipboard or laboratory) incubations for the determination of sediment oxygen consumption and benthic nutrient flux rates. This paper presents the results of such a comparison, using in situ chamber and shipboard chemostatic systems, for a shallow station on the Louisiana, continental shelf during April 1992. Results indicated no methodological differences between rates of sediment oxygen consumption and nutrient flux (NH₄ ⁺, NO₅ ^?, NO₂ ^?, PO₄ ^3?, and SiO₂/Si(OH)₂) that could be attributed to the removal of cores from shelf sediments. This conclusion implies that subcoring from box cores is no more destructive of sediment structure and salient environmental characteristics than chamber emplacement. Differences between the methods occurred when ambient oxygen concentrations were low (<2 ml l^?1). These differences were caused by initial reaeration of bottom water in the shipboard system and reflect the sensitivity of heterotrophic metabolism, dissolution kinetics, and diffusive fluxes to low oxygen concentrations. The differences in exchange rates observed in this study reiterate the importance in maintaining ambient conditions in the experimental apparatus. The results of this study corroborate the small body of, data that addresses this issue and extends methodological similarities to include nutrient exchanges. Given the comparability of rates, use of remote chemostatic systems is more advantageous for work in shelf environments than in-situ batch methods due to increased statistical rigor, logistical convenience, and the ability to minimize changes in experimental conditions during incubations.  相似文献   

Ground-Water Tracing with Injected Helium     

S. K. Gupta  L. Stephen Lau  Philip S. Moravcik 《Ground water》1994,32(1):96-102

Helium has several characteristics that make it attractive for use as a tracer in hydrological studies. Two types of experiments were conducted to investigate applicability of helium as a tracer of ground-water movement. The experiments included studies using laboratory sand and soil columns and field ground-water tracing in a basaltic aquifer. A water helium analyzer comprised of a thin quartz glass membrane and diode ion pump (making use of the preferential permeation of helium through the quartz glass into an evacuated space) was developed and used for the experiments. Results of our studies demonstrated that breakthrough curves of specific conductance and helium were similar under saturated conditions. In the unsaturated sand/soil columns, breakthrough curves of helium were retarded relative to specific conductance reducing the usefulness of helium as a tracer.  相似文献   

An annual fossil record of production,planktivory and piscivory during whole-lake manipulations     

Peter R. Leavitt  Patricia R. Sanford  Stephen R. Carpenter  James F. Kitchell 《Journal of Paleolimnology》1994,11(2):133-149

Annual and subannual paleolimnological records of pigments and zooplankton were used to analyze three whole-lake manipulations. The relative abundance of cladoceran remains in recent seasonal laminae was significantly correlated with the relative abundance of species in the plankton (r ²=0.59,P<0.001). Comparison of food-web structure after piscivore introduction showed that there are multiple outcomes of predation and that final food-web structure depended on the strength of interaction between piscivorous and planktivorous fish. Intense predation on cyprinids (Phoxinus eos, P. neogaeus, Umbra limi) by largemouth bass (Micropterus salmoides) allowed large herbivores (Daphnia pulex) and invertebrate predators (Chaoborus punctipennis) to dominate. Analysis of fossil invertebrate morphology suggested that small grazers (Bosmina longirostris, Diaphanosoma birgei) were eliminated by invertebrate predators. Under moderate predation by rainbow trout (Oncorhynchus mykiss), cyprinids remained, only intermediate-size herbivores (D. rosea) increased in abundance, andBosmina persisted. In contrast to food-web manipulations, increased algal abundance resulting from watershed disturbance (road construction) did not alter the species composition or size-structure of fossil Cladocera.  相似文献   

Inversion of Reflection Seismic Amplitude Data For Interface Geometry   总被引：1，自引：0，他引：1  

Yanghua Wang  Gregory A. Houseman 《Geophysical Journal International》1994,117(1):92-110

  相似文献   

Partitioning of platinum-group elements and Au in the Fe−Ni−Cu−S system: experiments on the fractional crystallization of sulfide melt   总被引：6，自引：0，他引：6  

Michael E. Fleet  Stephen L. Chryssoulis  William E. Stone  Christopher G. Weisener 《Contributions to Mineralogy and Petrology》1993,115(1):36-44

Partitioning of platinum-group elements (PGE) between sulfide liquid and monosulfide solid solution (mss) has been investigated by crystallizingmss from Fe–Ni–Cu sulfide liquid at 1,000–1,040° C, using bulk compositions and PGE contents typical of magmatic sulfides associated with mafic and ultramafic systems. Products were analyzedin situ for PGE and Au using SIMS. Sulfide liquid compositions were more Ni- and Cu-rich than coexistingmss. Liquid/mss partition coefficients are: Os-0.23±0.04, Ir-0.28±0.11, Ru-0.24±0.05, Rh-0.33±0.06, Pt-4.8±0.7, Pd-4.8±1.9, Au-11.4. Partitioning of PGE is independent of PGE concentration and Ni content in the composition range investigated. Additionally, Henry's law appears to be obeyed up to minor-element contents in the sulfide liquid andmss. Osmium, Ir, Ru, and Rh are compatible elements in the anhydrous Fe–Ni–Cu–S system, whereas Pt, Pd and Au are incompatible elements. These affinities correspond to the partitions of PGE between massive and Cu-rich magmatic sulfides. However, the detailed precious-metal compositions of the Cu-rich sulfides of mafic rock systems, disseminated ores of komatiites and Cu-rich assemblage of droplet ore from the Noril'sk-Talnakh deposits are not consistent with those expected for pristine fractionated sulfide liquids.  相似文献   

Vesicular-arbuscular mycorrhizae in salt marshes in North Carolina     

Marielle H. Hoefnagels  Stephen W. Broome  Steven R. Shafer 《Estuaries and Coasts》1993,16(4):851-858

The primary objective of this research was to determine if vesicular-arbuscular (VA) mycorrhizal fungi are associated with the roots of common plant species found in North Carolina salt marshes. Root samples of Spartina alterniflora, S. patents, S. cynosuroides, Distichlis spicata, and Juncus roemerianus were collected from eight salt marsh sites. With the exception of S. alterniflora, all plant species were mycorrhizal. A greenhouse experiment was conducted to determine whether unfavorable soil conditions or inherent resistance by the plant inhibited development of mycorrhizal infection in field-collected S. alterniflora. Spartina alterniflora and S. patens were grown from seeds in soil collected from a pure stand of S. alterniflora (soil A) or a mixed stand of S. patens and D. spicata (soil P). Seedlings were harvested weekly for 8 wk, and roots were evaluated for infection by mycorrhizal fungi. Seedlings of S. patens were infected when grown for 2 wk in either soil A or soil P, indicating that soil collected from stands of S. alterniflora did not inhibit mycorrhizal infection in a susceptible host. Percent root length infected in S. patens was always greater in soil P than in soil A. Seedlings of S. alterniflora were not infected by mycorrhizal fungi in either soil A or soil P. Results of the greenhouse study indicate that S. alterniflora may be resistant to infection by vesicular-arbuscular mycorrhizal fungi.  相似文献   

Rb,Sr and strontium isotopic composition,K/Ar age and large ion lithophile trace element abundances in rocks and glasses from the Wanapitei Lake impact structure     

Stephen R. Winzer  R.K.L. Lum  Shuford Schuhmann 《Geochimica et cosmochimica acta》1976,40(1):51-57

Shock metamorphosed rocks and shock-produced melt glasses from the Wanapitei Lake impact structure have been examined petrographically and by electron microprobe. Eleven clasts exhibiting varying degrees of shock metamorphism and eight impact-produced glasses have been analyzed for Rb, Sr and Sr isotopic composition. Five clasts and one glass have also been analyzed for large ion lithophile (LIL) trace element abundances including Li, Rb, Sr, and Ba and the REE's.The impact event forming the Wanapitei Lake structure occurred 37 m.y. ago based on K/Ar dating of glass and glassy whole-rock samples. Rb/Sr isotopic dating failed to provide a meaningful whole-rock or internal isochron. The isotopic composition of the glasses can be explained by impact-produced mixing and melting of metasediments. Large ion lithophile trace element abundance patterns confirm the origin of the glasses by total shock melting of metasediments.  相似文献   

The stable isotopic composition of coral skeletons: control by environmental variables   总被引：1，自引：0，他引：1  

Sandra M. Weil  Robert W. Buddemeier  Stephen V. Smith  Peter M. Kroopnick 《Geochimica et cosmochimica acta》1981,45(7):1147-1153

The reef corals Pocillopora damicornis and Montipora verrucosa were cultured under various controlled temperature and light conditions. The corals were analyzed for growth rate, tissue pigment content and skeletal ¹³C and ¹⁸O. Coral skeletal δ¹³C values varied with light dose and correlated with changes in zooxanthellar pigment. The δ¹³C values of skeletal aragonite seem to be modified by oxidation of photosynthetically produced organic matter.Functionally significant relationships between coral skeletal δ¹⁸O values and temperature have been determined. The temperature coefficients of the δ¹⁸O values [?4.4°C (%.)^?1] are similar to the first order coefficient in the equilibrium paleotemperature equation, but the δ¹⁸O values have taxonomically consistent offsets from equilibrium. The offsets may be attributed to the coral metabolism with slight but statistically significant differences between the two genera. Environmental and metabolic variables other than temperature have little or no effect on skeletal δ¹⁸O.  相似文献   

The compositional classification of chondrites—I. The carbonaceous chondrite groups     

Gregory W. Kallemeyn  John T. Wasson 《Geochimica et cosmochimica acta》1981,45(7):1217-1230

Twenty carbonaceous chondrites were analyzed by instrumental and radiochemical neutron activation analysis for Na, Mg, Al, K, Ca, Sc, V. Cr, Mn. Fe, Co, Ni, Zn, Ga, Ge, As, Se. Br. Ru, Cd, In, Sb, La, Sm, Eu, Yb, Lu, Os, Ir, and Au. Analysis of 2 or more samples of all but 2 chondrites has helped yield a high precision that allowed the resolution of numerous previously unrecognized trends. Refractory lithophile abundances decrease through the sequence CV (1.33 × CI), CM-CO (1.11 × CI) and CI. The abundances of the common siderophiles Fe, Ni and Co follow the order CI >CM >CO >CV, with CV chondrites depleted about 15% relative to CI. Volatile lithophile (Mn to K) and volatile siderophile (As to Ge) abundances decrease in the order CI >CM >CO >CV. The volatile trends in CO and CV chondrites reverse for the more volatile elements (Br to Cd) producing the sequence CI >CM >CV >CO. These three different sequences in the ordering of group elemental abundances can be used to resolve compositionally the four carbonaceous chondrite groups.We define clans to consist of one or more groups formed at a narrow range of heliocentric distances. Quantization of refractory lithophile abundances indicates the existence of three carbonaceous chondrite clans: CI, CM-CO, and CV. Despite similarities in parameters such as volatile abundances and O-isotope compositions differences in chondrule size and refractory abundances suggest that CO and CV chondrites are indeed best placed in separate clans. The relative heliocentric distance at which CI chondrites formed cannot be inferred, thus it seems safer to assign them to a separate clan.  相似文献