An urban street canyon radiation obstruction model has been developed. The model can describe community structure in terms of the type and dimensions of every building, block, road, park, etc. The need for massive data acquisition in regard to obstruction modeling calls for computerized algorithms, relieving the researcher of the needless tedium of hand calculations and the accompanying high degree of error and labor costs. The model program OBSTRUCT was written in FORTRAN IV for use on the IBM 3033. To facilitate changes or modifications, OBSTRUCT was written in modular form. 相似文献
Macroscopic marine algae were collected at a variety of intertidal sites and on cruises throughout the Maryland Chesapeake Bay in 1972–73, and numerous specimens from the University of Maryland herbarium were examined. The revised species list contains 62 taxa as follows: 26 Rhodophyceae, 1 Xanthophyceae, 6 Phaeophyceae, 29 Chlorophyceae. Grinnellia americana, Neoagardhiella baileyi, Porphyra sp.,Vaucheria sp.,Desmotrichum undulatum, Ectocarpus confervoides, Enteromorpha compressa var.lingulata, E. linza, Entocladia viridis andUrospora sp. are new records for the flora of the upper Bay. Records ofAscophyllum are believed to represent discarded bait-packing material rather than an endemic population in the upper Bay. Ceramium, Polysiphonia, Cladophora, Enteromorpha andUlva are the genera most likely to be encountered in the upper Bay. In winter, brown algae, mainlyEctocarpus species, become a more conspicuous component of the flora. Comments on distribution, seasonality, taxonomic problems, and invalid or questionable records are included. Literature pertinent to the Delmarva region is reviewed briefly. 相似文献
The vertical distribution of dissolved Al in interstitial waters of recent marine sediments has been determined using a fluorimetric analytical method adapted for interstitial water analysis. The results suggest that diagenetic reactions occur in the sediment soon after deposition. A narrow depth zone acting as a source of dissolved Al is found in each core. Outside this zone Al appears to be removed from solution and its concentration decreases to values of 1.5 μgAl/l or less, comparable to those of open ocean waters. Dissolved Al and SiO2 concentrations in interstitial waters close to the sediment-seawater interface are linearly correlated in most cases, suggesting that the geochemistry of Al may be related to the behaviour of biogenic silica in marine sediments. 相似文献
Solubilities of methane in multisalt solutions at 550 psia and 25°C can be predicted from single-salt salting coefficients. The ionic strength contribution of the ith salt, Ii, is multiplied by its molal salting coefficient, kmi, in the following summation over all salts: where mo and ms are molal methane solubilities in distilled water and the salt solution, respectively, at the T, P and methane fugacity of interest.This equation predicts methane solubility in multisalt brines containing Na+, K+, Mg+2, Ca+2, Cl?, SO4?2 and CO3?2 ions. kmi values reported by Stoessell and Byrne (1982b) can be used in solubility predictions in brines at earth surface conditions. Prediction in reservoir brines would require determination of kmi, for the different salts at reservoir temperatures and pressures. 相似文献
The impact ofMnemiopsis leidyi as a predator was studied quantitatively to determine their feeding rates on mixed natural zooplankton. These studies showed that feeding rate was independent of food concentration, but a function of both temperature and size of ctenophore. The feeding rate (liters cleared per mg dry weight per day) ranged from about 0.01 for larger ctenophores at lower temperatures (10–15°C) to about 0.1 for smaller ctenophores at higher temperatures (20–25°C). Combining these results with ctenophore biomass estimates from three years of sampling, numerical estimates were made of zooplankton mortality due to ctenophore predation. The maximum summer cropping byM. leidyi was calculated to be an average of 5–10% per day for the bay as a whole. Although substantial, this predation pressure alone does not account for the observed summer decline of zooplankton. 相似文献
Collections of winter flounder (Pseudopleuronectes americanus) larvae were made biweekly from March to May in 1999 and 2000 in the Navesink River-Sandy Hook Bay estuarine system, New
Jersey, to determine stage-specific spatial and temporal variability in diets. Relatively high percentages of larvae with
empty guts were found at low water temperatures. Percentages of empty guts did not differ by larval stage (preflexion and
postflexion) or region of collection (river and bay). There was high intraregional variability in percentages of larvae with
empty guts. Nauplii, invertebrate eggs, and polychaete larvae were dominant prey items followed by tintinnids, bivalve and
gastropod veligers, and diatoms. Ontogenetic dietary shifts were evident in both years. Preflexion winter flounder largely
consumed nauplii, invertebrate eggs, and tintinnids; postflexion winter flounder consumed the largest prey (polychaete larvae)
but also retained small prey items in their diets. Water temperature significantly affected the percentages of larvae feeding
on nauplii (p<0.05) and tintinnids (p<0.08) in 2000. Region of collection was not significantly related to diets because of
high intraregional variability. Fine scale spatial (within regions, stations were approximately 3 km apart) and temporal (weeks)
dietary variation of larval winter flounder could result in accompanying variation in development, growth stage duration,
and survival. 相似文献
After accretion of the Pampean continental fragment to the western Rio de la Plata craton margin (530 Ma), subsequent deformation, crustal anatexis and plutonism may have been intraplate responses to Brasiliano-PanAfrican collisional tectonism on the eastern margin during the amalgamation of Gondwana. Investigations of intraplate orogens such as the Tien Shan and the Ancestral Rocky Mountains, as well as of analogue and numerical models, permit discrimination of two early Paleozoic tectonomagmatic phases in the Sierras Pampeanas. The first involved marginal trough subduction and calc-alkaline magmatism, culminating in accretion of the Pampean terrane to the western craton edge; the second was characterized by crustal anatexis and peraluminous plutonism, penetrative deformation and high-angle reverse faulting resulting from continental collision on the eastern craton margin.Field observations from modern (Tien Shan) and ancient (Ancestral Rocky Mountains) intraplate chains, deep seismic and borehole data, radiometric and fission-track data constitute control for analogue and numerical models of intraplate deformation resulting from continental collision. Near-simultaneous continent-wide deformation, regularly spaced ranges/buckles, reverse-fault initiation at fold hinges of buckles, and doubling of crustal thickness are replicated in structural arrays formed in four-layer analogue models of lithospheric buckling. These data have significant implications for the ductile deformation, crustral thickening and post-subduction plutonism that spanned central South America in Late Cambrian time. 相似文献
Geographers at the AAG's centennial are challenged with exceptional opportunities to create a more central place for geography in society and in the university. Realizing these opportunities requires identifying and leveraging key emerging trends in the formation and uses of geographic knowledge. Better integration of geography's profound technological innovations with its core traditions also is necessary to strengthen the discipline's research capacity, and to more effectively engage with and contribute to the needs of society. Trends toward multidisciplinary research and integrative science, and the heightened need for geographic understanding in today's world, hold further promise for advancing the discipline while sustaining its historic strengths and diversity. 相似文献
We examined the chemical reactions influencing dissolved concentrations, speciation, and transport of naturally occurring arsenic (As) in a shallow, sand and gravel aquifer with distinct geochemical zones resulting from land disposal of dilute sewage effluent. The principal geochemical zones were: (1) the uncontaminated zone above the sewage plume [350 μM dissolved oxygen (DO), pH 5.9]; (2) the suboxic zone (5 μM DO, pH 6.2, elevated concentrations of sewage-derived phosphate and nitrate); and (3) the anoxic zone [dissolved iron(II) 100–300 μM, pH 6.5–6.9, elevated concentrations of sewage-derived phosphate]. Sediments are comprised of greater than 90% quartz but the surfaces of quartz and other mineral grains are coated with nanometer-size iron (Fe) and aluminum (Al) oxides and/or silicates, which control the adsorption properties of the sediments. Uncontaminated groundwater with added phosphate (620 μM) was pumped into the uncontaminated zone while samples were collected 0.3 m above the injection point. Concentrations of As(V) increased from below detection (0.005 μM) to a maximum of 0.07 μM during breakthrough of phosphate at the sampling port; As(III) concentrations remained below detection. These results are consistent with the hypothesis that naturally occurring As(V) adsorbed to constituents of the coatings on grain surfaces was desorbed by phosphate in the injected groundwater. Also consistent with this hypothesis, vertical profiles of groundwater chemistry measured prior to the tracer test showed that dissolved As(V) concentrations increased along with dissolved phosphate from below detection in the uncontaminated zone to approximately 0.07 and 70 μM, respectively, in the suboxic zone. Concentrations of As(III) were below detection in both zones. The anoxic zone had approximately 0.07 μM As(V) but also had As(III) concentrations of 0.07–0.14 μM, suggesting that release of As bound to sediment grains occurred by desorption by phosphate, reductive dissolution of Fe oxides, and reduction of As(V) to As(III), which adsorbs only weakly to the Fe-oxide-depleted material in the coatings. Results of reductive extractions of the sediments suggest that As associated with the coatings was relatively uniformly distributed at approximately 1 nmol/g of sediment (equivalent to 0.075 ppm As) and comprised 20%-50% of the total As in the sediments, determined from oxidative extractions. Quartz sand aquifers provide high-quality drinking water but can become contaminated when naturally occurring arsenic bound to Fe and Al oxides or silicates on sediment surfaces is released by desorption and dissolution of Fe oxides in response to changing chemical conditions.
