Spatiotemporal Patterns of Subtidal Benthic Microalgal Biomass and Community Composition in Galveston Bay,Texas, USA     

James L. Pinckney  Alyce R. Lee 《Estuaries and Coasts》2008,31(2):444-454

Many Gulf of Mexico estuaries have low ratios of water volume to bottom surface area, and benthic processes in these systems likely have a major influence on system structure and function. The purpose of this study was to determine the spatiotemporal distribution of biomass and community composition of subtidal benthic microalgal (BMA) communities in Galveston Bay, TX, USA, compare BMA community composition and biomass to phytoplankton in overlying waters, and estimate the potential contribution of BMA to the trophodynamics in this shallow, turbid, subtropical estuary. The estimates of BMA biomass (mean = 4.21 mg Chl a m⁻²) for Galveston Bay were within the range of the reported values for similar Gulf of Mexico estuaries. BMA biomass in the central part of the bay was essentially homogeneous, whereas biomass at the seaward and upper bay ends of the transect were significantly lower. Peridinin, fucoxanthin, and alloxanthin were the three carotenoids with the highest concentrations, with fucoxanthin having the highest mean concentration (1.82 mg m⁻²). The seaward and landward ends of the transect differed from the central region of the bay with respect to the relative abundances of chlorophytes, cyanobacteria, and photosynthetic bacteria. Benthic microalgal community composition also showed a gradual shift over time due to changes in the relative abundances of photosynthetic bacteria, cryptophytes, dinoflagellates, and cyanobacteria. Major changes in community composition occurred in the spring months (March to April). On an areal basis, BMA biomass in Galveston Bay occurred at minor concentrations (16.5%) relative to phytoplankton. Furthermore, the concentrations of carotenoid pigments for phytoplankton and BMA (fucoxanthin, alloxanthin, and zeaxanthin) were correlated (r = 0.48 to 0.61), suggesting a close linkage between microalgae in the water column and sediments. The contribution of BMA to the primary productivity of the deeper waters (>2 m) of Galveston Bay is probably very small in comparison to shallower waters along the bay margins. The significant similarities in the community composition of phytoplankton and BMA illustrate the potential importance of deposition and resuspension processes in this turbid, shallow estuary.  相似文献   

Estimating hydraulic conductivity using grain-size analyses, aquifer tests, and numerical modeling in a riverside alluvial system in South Korea   总被引：2，自引：0，他引：2  

Jae-Yeol Cheong  Se-Yeong Hamm  Hyoung-Soo Kim  Eun-Joung Ko  Kyounghee Yang  Jeong-Hwan Lee 《Hydrogeology Journal》2008,16(6):1129-1143

Hydraulic conductivity (K) for an alluvial system in a riverbank filtration area in Changwon City, South Korea, has been studied using grain-size distribution, pumping and slug tests, and numerical modeling. The alluvial system is composed of layers: upper fine sand, medium sand, lower fine sand, and a highly conductive sand/gravel layer at the base. The geometric mean of K for the sand/gravel layer (9.89?×?10^?4 m s^?1), as determined by grain-size analyses, was 3.33 times greater than the geometric mean obtained from pumping tests (2.97?×?10^?4 m s^?1). The geometric mean of K estimates obtained from slug tests (3.08?×?10^?6 m s^?1) was one to two orders of magnitude lower than that from pumping tests and grain-size analyses. K estimates derived from a numerical model were compared to those derived from the grain-size methods, slug tests and pumping tests in order to determine the degree of deviation from the numerical model. It is considered that the K estimates determined by the slug tests resemble the uppermost part of the alluvial deposit, whereas the K estimates obtained by grain-size analyses and pumping tests are similar to those from the numerical model for the sand/gravel layer of the riverside alluvial system.  相似文献   

On the sampling of airborne measurements of radiative properties of cloud fields: Results from International Cirrus Experiment (ICE), 1987     

F. Y. P. Lee  E. Raschke 《Theoretical and Applied Climatology》1993,48(2-3):115-125

Summary During the first pilot phase of the International Cirrus Experiment (ICE) in September/October 1987 radiation measurements were carried out above and below broken cloud fields over the German Bight. Analyses of the measurements of 25.9.1987 (broken cumulus cloud field) showed an unexpected high absorption of solar radiation but not those of 28.9.1987 (stratocumulus/stratus cloud field). This might be explained by a partial negligence of cloud side factor under the viewing geometry of the pyranometer and other reasons. The light guide effect (leakage) within holes can account for the depletion of cloud reflectance and the enhancement of cloud transmittance at large cloud cover, as observed during the measurements on 28.9.1987. The fluctuation of the irradiances, which can be characterized by the intermittency parameter, has been related to the corresponding cloud cover by a regression equation. On the condition of similarity, this scaling parameter derived from sample measurements could be extrapolated to that of the whole cloud field. Thus, the estimation of the irradiance spectrum for the whole cloud field may be possible, from samples taken with aircraft and imaging data.With 5 Figures  相似文献   

Origin of the hydrocarbon component of carbonaceous chondrites: the star-meteorite connection     

Lee W  Wdowiak TJ 《The Astrophysical journal》1993,417(1):L49-L51

We report the results of an experiment that produced a residue which closely matches the hydrocarbon component of the Murchison carbonaceous chondrite. This experiment suggests that the parent material of the meteoritic component originated as polycyclic aromatic hydrocarbon species in carbon stars during their later stages of evolution. The experiments also indicate that the pathway from those formation sites to eventual incorporation into the meteorite parent body involved hydrogenation in a plasma in the solar nebula or in H II regions prior to the solar nebula. This model is consistent with what is known about the meteoritic hydrocarbon component including deuterium abundance, the observation of cosmic infrared emission bands best attributed to polycyclic aromatic hydrocarbon molecules, and the inherent stability of these molecules that allows their formation in stars and subsequent survival in the interstellar medium.  相似文献   

Microwave emission from a sunspot     

Jeongwoo W. Lee  G. J. Hurford  Dale E. Gary 《Solar physics》1993,144(1):45-57

From the gyroresonance brightness temperature spectrum of a sunspot, one can determine the magnetic field strength by using the property that microwave brightness is limited above a frequency given by an integer-multiple of the gyrofrequency. In this paper, we use this idea to find the radial distribution of magnetic field at the coronal base of a sunspot in the active region, NOAA 4741. The gyroresonance brightness temperature spectra of this sunspot are obtained from multi-frequency interferometric observations made at the Owens Valley Radio Observatory at 24 frequencies in the range of 4.0–12.4 GHz with spatial resolution 2.2″–6.8″. The main results of present study are summarized as follows: first, by comparison of the coronal magnetic flux deduced from our microwave observation with the photospheric magnetic flux measured by KPNO magnetograms, we show that theo-mode emission must arise predominantly from the second harmonic of the gyrofrequency, while thex-mode arises from the third harmonic. Second, the radial distribution of magnetic fieldsB(r) at the coronal base of this spot (say, 2000–4000 km above the photosphere) can be adequately fitted by $$B(r) = 1420(1 \pm 0.080)\exp \left[ { - \left( {\frac{r}{{11.05''(1 \pm 0.014)}}} \right)^2 } \right]G,$$ wherer is the radial distance from the spot center at coronal base. Third, it is found that coronal magnetic fields originate mostly from the photospheric umbral region. Fourth, although the derived vertical variation of magnetic fields can be approximated roughly by a dipole model with dipole moment 1.6 × 10³⁰ erg G^?1 buried at 11000 km below the photosphere, the radial field distribution at coronal heights is found to be more confined than predicted by the dipole model.  相似文献   

Geochronology and geochemistry of eclogites from the Mariánské Lázně Complex,Czech Republic: Implications for Variscan orogenesis     

Brian L. Beard  L. Gordon Medaris Jr  Clark M. Johnson  Emil Jelínek  J. Tonika  Lee R. Riciputi 《International Journal of Earth Sciences》1995,84(3):552-567

The Mariánské Lázn complex (MLC) is located in the Bohemian Massif along the north-western margin of the Teplá-Barrandian microplate and consists of metagabbro, amphibolite and eclogite, with subordinate amounts of serpentinite, felsic gneiss and calcsilicate rocks. The MLC is interpreted as a metaophiolite complex that marks the suture zone between the Saxothuringian rocks to the north-west and the Teplá-Barrandian microplate to the south-east. Sm-Nd geochronology of garnet-omphacite pairs from two eclogite samples yields ages of 377±7, and 367±4 Ma. Samples of eclogite and amphibolite do not define a whole rock Sm-Nd isochron, even though there is a large range in Sm/Nd ratio, implying that the suite of samples may not be cogenetic. Eclogites do not have correlated _Nd values and initial ⁸⁷Sr/⁸⁶Sr ratios. Five of the eight eclogite samples have high _Nd values (+10.2 to +7.1) consistent with derivation from a MORB-like source, but variable ⁸⁷Sr/⁸⁶Sr ratios (0.7033 to 0.7059) which probably reflect hydrothermal seawater alteration. Three other eclogite samples have lower _Nd values (+ 5.4 to –0.8) and widely variable ⁸⁷Sr/⁸⁶Sr ratios (0.7033 to 0.7096). Such low _Nd values are inconsistent with derivation from a MORB, source and may reflect a subduction or oceanic island basalt component in their source. The MLC is an important petrotectonic element in the Bohemian Massif, providing evidence for Cambro-Ordovician formation of oceanic crust and interaction with seawater, Late Devonian (Frasnian-Famennian) high- and medium-pressure metamorphism related to closure of a Saxothuringian ocean basin, Early Carboniferous (Viséan) thrusting of the Teplá terrane over Saxothuringian rocks and Late Viséan extension.  相似文献   

Plasma processing of interstellar PAHs into solar system kerogen     

Wdowiak TJ  Lee W  Cronin J  Beegle LW  Robinson MS 《Planetary and Space Science》1995,43(10-11):1175-1182

Processes resulting in the formation of hydrocarbons of carbonaceous chondrites and the identity of the interstellar molecular precursors involved are an objective of investigations into the origin of the solar system and perhaps even life on earth. We have combined the resources and experience of an astronomer and physicists doing laboratory simulations with those of a chemical expert in the analysis of meteoritic hydrocarbons, in a project that investigated the conversion of polycyclic aromatic hydrocarbons (PAHs) formed in stellar atmospheres into alkanes found in meteorites. Plasma hydrogenation has been found in the University of Alabama at Birmingham Astrophysics Laboratory to produce from the precursor PAH naphthalene, a new material having an IR absorption spectrum (Lee, W. and Wdowiak, T.J., Astrophys. J. 417, L49-L51, 1993) remarkably similar to that obtained at Arizona State University of the benzene-methanol extract of the Murchison meteorite (Cronin, J.R. and Pizzarello, S., Geochim. Cosmochim. Acta 54, 2859-2868, 1990). There are astrophysical and meteoritic arguments for PAH species from extra-solar sources being incorporated into the solar nebula, where plasma hydrogenation is highly plausible. Conversion of PAHs into alkanes could also have occurred in the interstellar medium. The synthesis of laboratory analogs of meteoritic hydrocarbons through plasma hydrogenation of PAH species is underway, as is chemical analysis of those analogs. The objective is to clarify this heretofore uninvestigated process and to understand its role during the origin of the solar system as a mechanism of production of hydrocarbon species now found in meteorites. Results have been obtained in the form of time-of-flight spectroscopy and chemical analysis of the lab analog prepared from naphthalene.  相似文献   

On the astrometric detection of neighboring planetary systems,II     

George Gatewood  Lee Breakiron  Ronald Goebel  Steven Kipp  Jane Russell  John Stein 《Icarus》1980,41(2):205-231

Extensive testing suggests that astrometric techniques can be employed to detect and study virtually any planetary system that may exist within 40 light years (12.5 parsec) of the Sun. Following the conclusion of Paper I [G. Gatewood, Icarus27 (1976), 1–12], the astrometric group at the Allegheny Observatory began an intensive survey of 20 nearby stars to detect the nonlinear variations in their motion that planetary systems would induce. Several tests conducted to further our understanding of the limitations of this survey indicated that the photographic detector itself is responsible for the majority of the random error. A new photoelectric detector has been designed and a simplified prototype of it successfully tested. The new detector is expected to be able to utilize virtually all of the astrometric information transmitted through the Earth's atmosphere. This is sufficient to determine relative positions to within an accuracy of approximately 1 milliarcsec/hr. Such precisions exceed the design capabilities of the best existing astrometric telescopes, thus a feasibility study has been conducted for the design of an improved instrument. The study concludes that a new ground-based telescope and the new detector combined should be able to study stars as faint as the 17th magnitude with an annual accuracy of a few tenths of a milliarcsecond. However, to obtain the ultimate accuracy possible from current technology, we must place an astrometric system above the Earth's atmosphere. A space-borne instrument utilizing the new detector would in theory have sufficient accuracy to detect any Earth-like planet orbiting any of the several hundred stars nearest the Sun.  相似文献   

Coherent amplification and pulsar phenomena     

Lee W. Casperson 《Astrophysics and Space Science》1977,48(2):389-399

A modification of the rotating-star model has been developed to interpret the periodic energy bursts from pulsars. This new configuration involves -directed oscilltion modes in the stellar atmosphere or magnetosphere, and most aspects of the typical pulse characteristics are well accounted for. Gain is provided by resonant interactions with particles trapped in the stellar magnetic field. The most significant feature is the fact that highly directional beaming of the output energy results as a natural consequence of coherence between the radiation fields emerging from various locations about the pulsar; and a localized radiation origin is not required.  相似文献   

M computed from strong motion accelerograms recorded in Yugoslavia     

V. Lee  M. Trifunac  M. Herak  M. iv i   D. Herak 《地震工程与结构动力学》1990,19(8):1167-1179

It is shown that the new definition¹ of strong motion local magnitude M leads to stable estimates of magnitudes for earthquakes in Yugoslavia, with epicentral distances R <100 km and for 2.5 < M < 6.5. Tables with magnitudes computed using this new procedure are presented for all earthquakes contributing to the strong motion accelerogram files in EQINFOS for Yugoslavia.² The similarity of our findings with the analogous analyses for California suggests new possibilities for relative calibration between various local magnitude scales, which are used in southeastern Europe, and M_L in California.  相似文献