A nutrient loading budget for Biscayne Bay, Florida     

Caccia VG  Boyer JN 《Marine pollution bulletin》2007,54(7):994-1008

The water quality in Biscayne Bay has been significantly affected by past and continuing coastal and watershed development. The nutrient concentrations in the Bay have been dramatically changed by the conversion of natural creeks and sheet flow freshwater inputs to rapid and episodic canal inputs from the large and rapidly expanding Miami metropolitan area. This study is an evaluation of nutrient loadings to Biscayne Bay for 1994-2002 from canal, atmospheric, and groundwater sources. Dissolved inorganic nitrogen (DIN, as nitrate, nitrite, and ammonium) and total phosphorus (TP) loadings by the canals were influenced by their geographic locations relative to discharge amount, watershed land use, stormwater runoff, and proximity to landfills. Annual budgets showed that canals contributed the bulk of N loading to the bay as 1687.2 metric ton N yr(-1) (88% total load). Direct atmospheric DIN load for Biscayne Bay was only 231.7 ton N yr(-1), based on surface area. Of the canal DIN load, nitrate+nitrite (NO(x)(-)) loading (1294.5 ton N yr(-1)) made up a much greater proportion than that of ammonium (NH(4)(+), 392.6 ton N yr(-1)). In the urbanized north and central Bay, canal DIN load was evenly split between NO(x)(-) and NH(4)(+). However, in the south, 95% of the DIN load was in the form of NO(x)(-), reflecting the more agricultural land use. Contrary to N, canals contributed the only 66% of P load to the bay (27.5 ton P yr(-1)). Atmospheric TP load was 14 ton Pyr(-1). In the north, canal P load dominated the budget while in the south, atmospheric load was almost double canal load. Groundwater inputs, estimated only for the south Bay, represented an important source of N and P in this zone. Groundwater input of N (141 ton N yr(-1)) was about equal to atmospheric load, while P load (5.9 ton P yr(-1)) was about equal to canal load.  相似文献   

Effects of ulvoid (Ulva spp.) accumulation on the structure and function of eelgrass (Zostera marina L.) bed     

Sugimoto K  Hiraoka K  Ohta S  Niimura Y  Terawaki T  Okada M 《Marine pollution bulletin》2007,54(10):1582-1585

The objective of this study is to clarify the effect of ulvoid (Ulva spp.) accumulation on the structure and function of an eelgrass bed by the coast of Iwakuni, Seto Inland Sea, Japan. We monitored eelgrass shoot density and volume of ulvoid accumulation in the study site and evaluated effects of the accumulated ulvoid canopy on the percent survival, seedling density, growth rates, photosynthetic photon flux density (PPFD) and carbon contents of eelgrass. Eelgrass shoot density decreased by the accumulation of ulvoid. Also, seedling density decreased by the increase in the ulvoid volumes. Shoot density, seedling density and leaf elongation were negatively correlated with ulvoid volume. Carbon contents in eelgrass decreased by the accumulation of ulvoid (canopy height: 25cm). These results suggest that accumulation of ulvoid bloom has significant negative impacts on the structure and function of eelgrass bed, i.e. decreases in vegetative shoot density, seedling density, shoot height and growth rate.  相似文献   

Influence of pyroclastic soil on epikarst formation: a test study in southern Italy   总被引：1，自引：0，他引：1  

Fulvio Celico  Gino Naclerio  Antonio Bucci  Valentina Nerone  Paolo Capuano  Massimiliano Carcione  Vincenzo Allocca  Pietro Celico 《地学学报》2010,22(2):110-115

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Experimental studies of Ta2O5 and columbite–tantalite solubility in fluoride solutions from 300 to 550°C and 50 to 100 MPa     

George Pavlovich Zaraisky  Valentina Korzhinskaya  Nataliya Kotova 《Mineralogy and Petrology》2010,99(3-4):287-300

It is well established that the fractionation of Li–F granitic magmas at depth leads to the accumulation of flux elements such as F and Li, and metal cations such as Ta and Nb in residual melts. However, it remains to be determined whether magmatic fractionation is sufficient to concentrate Nb and Ta into economically significant quantities, and what role hydrothermal–metasomatic processes play in the formation of such ore deposits. In the literature, reliable data about the solubility of Ta and Nb in hydrothermal solutions is missing or incomplete. This study provides a quantitative experimental estimation of the possible contribution from hydrothermal processes in Ta enrichment in cupolas of albitized and greisenized Li–F granite. Experimental studies of Ta₂O₅ and columbite–tantalite (Mn,Fe)(Nb,Ta)₂O₆ solubility were carried out in fluoride solutions consisting of HF, NaF, KF, and LiF. At low fluoride concentrations (0.01 and 0.1 m), Ta₂O₅ solubility at 550°C and 100 MPa under Co–CoO oxidizing conditions is low (near 10^?5–10^?4 m) in all fluoride solutions (HF, NaF, KF, LiF). At high fluoride concentrations (1 and 2 m) the highest Ta₂O₅ concentrations (10^?1 m) were detected in HF solutions. In KF, NaF, and LiF solutions, the Ta₂O₅ solubility is also high (10^?3–10^?2 m). The dependence of columbite–tantalite (Nb₂O₅-59 wt. %, Ta₂O₅-18 wt. %) solubility as a function of solution composition, T, and P has also been investigated. Tantalum and Nb concentrations have the highest values in HF solutions at reduced conditions (up to 10^?3 to 10^?2 m Ta in 1 m HF). In 1 m NaF solutions, the concentrations of Nb and Ta are, respectively, 2.5 and 3 orders of magnitude less than those in the 1 m HF solutions. Solubility of Ta and Nb in KF solutions has intermediate values. It is established that in NaF and KF solutions the dependence of solubility on pressure is distinctly negative. The Nb and Ta contents increase with increasing concentrations of HF and KF in solution, however, they do not change with increasing NaF concentration. In NaHCO₃, Na₂CO₃, and HCl solutions columbite–tantalite solubility is low. Even in 1 m chloride solutions the content is within the limits of 10^?5 m for Nb and 10^?6 to 10^?8 m for Ta. We conclude that hydrothermal transport of Ta and Nb is possible only in concentrated fluoride solutions.  相似文献   

The effects of frequency-dependent quasar variability on the celestial reference frame     

Stanislav S. Shabala  Jonathan G. Rogers  Jamie N. McCallum  Oleg A. Titov  Jay Blanchard  James E. J. Lovell  Christopher S. Watson 《Journal of Geodesy》2014,88(6):575-586

We examine the relationship between source position stability and astrophysical properties of radio-loud quasars making up the International Celestial Reference Frame (ICRF2). Understanding this relationship is important for improving quasar selection and analysis strategies, and therefore reference frame stability. We construct flux density time series, known as light curves, for 95 of the most frequently observed ICRF2 quasars at both the 2.3 and 8.4 GHz geodetic very long baseline interferometry (VLBI) observing bands. Because the appearance of new quasar components corresponds to an increase in quasar flux density, these light curves alert us about potential changes in source structure before they appear in VLBI images. We test how source position stability depends on three astrophysical parameters: (1) flux density variability at X band; (2) time lag between flares in S and X bands; (3) spectral index root-mean-square (rms), defined as the variability in the ratio between S and X band flux densities. We find that the time lag between S and X band light curves provides a good indicator of position stability: sources with time lags $<$ 0.06 years are significantly more stable ( $>$ 20 % improvement in weighted rms) than sources with larger time lags. A similar improvement is obtained by observing sources with low $(<$ 0.12) spectral index variability. On the other hand, there is no strong dependence of source position stability on flux density variability in a single frequency band. These findings can be understood by interpreting the time lag between S and X band light curves as a measure of the size of the source structure. Monitoring of source flux density at multiple frequencies therefore appears to provide a useful probe of quasar structure on scales important to geodesy. The observed astrometric position of the brightest quasar component (the core) is known to depend on observing frequency. We show how multi-frequency flux density monitoring may allow the dependence on frequency of the relative core positions along the jet to be elucidated. Knowledge of the position–frequency relation has important implications for current and future geodetic VLBI programs, as well as the alignment between the radio and optical celestial reference frames.  相似文献   

Geoarchaeological and Bioarchaeological Studies at Mira,an Early Upper Paleolithic Site in the Lower Dnepr Valley,Ukraine     

John F. Hoffecker  Vance T. Holliday  Vadim N. Stepanchuk  Alexis Brugre  Steven L. Forman  Paul Goldberg  Oleg Tubolzev  Igor Pisarev 《Geoarchaeology》2014,29(1):61-77

New geoarchaeological and bioarcheological research was undertaken at the open‐air site of Mira, which is buried in deposits of the Second Terrace of the Dnepr River, roughly 15 km downstream from the city of Zaporozhye in Ukraine. Previous excavation of the site revealed two occupation layers dating to ∼32,000 cal BP. The lower layer (II/2) yielded bladelets similar to those of the early Gravettian, while the upper layer (I) contained traces of an artificial shelter and hundreds of bones and teeth of horse (Equus latipes). Mira represents the only firmly dated early Upper Paleolithic (EUP) site in the Dnepr Basin, and occupies a unique topographic setting for the EUP near the center of the broad floodplain of the Dnepr River. The site was visited during a period of floodplain stability, characterized by overbank deposition and weak soil formation under cool climate conditions. Mira was used as a long‐term camp, but also was the locus of large‐mammal carcass processing associated with a nearby kill of a group of horses (Layer I).  相似文献   

日本大沼湖沉积物碳氮比值、有机碳同位素特征及其近400年的古气候环境意义   总被引：1，自引：0，他引：1  

孙伟伟  沈吉  张恩楼  陈嵘  Kenji Kashiwaya  Noriko Hasebe 《第四纪研究》2014,34(6)

通过对日本大沼湖沉积物样品总有机碳含量(TOC)及其稳定同位素、总氮含量(TN)和C/N值的测定,结合沉积岩芯火山灰和1℃年代,分析了大沼湖沉积物中有机质的来源,探讨了沉积物有机碳同位素的主要影响因素.结果表明:大沼湖沉积物中有机质主要来源于自生藻类,受陆源输入的影响较小;沉积物δ13C值指示了夏季温度的变化.过去400年来,大沼湖地区存在1660～ 1730年和1780～ 1860年两个明显的冷期,与邻近地区冰芯、树轮和湖泊沉积物记录的冷期基本一致,分别对应于Maunder和Dalton太阳黑子极小期.  相似文献   

Numerical simulations on the relative importance of starbursts and AGN in ultraluminous infrared galaxies     

Kenji Bekki  Yasuhiro Shioya  Matthew Whiting 《Monthly notices of the Royal Astronomical Society》2006,371(2):805-820

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The XMM-Newton Bright Serendipitous Survey: First Extragalactic Results     

Tommaso Maccacaro  Roberto Della Ceca  Valentina Braito  Alessandro Caccianiga  Paola Severgnini  Anna Wolter 《Astrophysics and Space Science》2004,294(1-2):89-94

We present here some initial results from the ongoing XMM-Newton bright serendipitous survey. The survey is aimed at selecting and spectroscopically identifying a large and statistically representative sample of bright (f _x ≳ 7× 10⁻¹⁴ c.g.s) serendipitous X-ray sources in the 0.5–4.5 keV energy band (BSS) and a complementary (smaller) sample in the 4.5–7.5 keV energy band (HBSS). The work is partly based on observations obtained with XMM-Newton, an ESA science mission with instruments and contributors directly founded by ESA member states and the USA(NASA) and on observations collected at TNG. The TNG telescope is operated on the island of La Palma by the Centro Galileo Galilei of the INAF in the Spanish Observatorio del Roque de Los Muchachos of the Instituto de Astrofísica de Canarias. On behalf of the XMM-Newton Survey Science Center.  相似文献   

A potentiometric study of the stability of aqueous yttrium-acetate complexes from 25 to 175 °C and 1-1000 bar     

Boris Tagirov  Alexander Zotov  Oleg Suleimenov 《Geochimica et cosmochimica acta》2007,71(7):1689-1708

The stability of yttrium-acetate (Y-Ac) complexes in aqueous solution was determined potentiometrically at temperatures 25-175 °C (at P_s) and pressures 1-1000 bar (at 25 and 75 °C). Measurements were performed using glass H⁺-selective electrodes in potentiometric cells with a liquid junction. The species YAc²⁺ and were found to dominate yttrium aqueous speciation in experimental solutions at 25-100 °C (log [Ac⁻] < −1.5, pH < 5.2), whereas at 125, 150 and 175 °C introduction of into the Y-Ac speciation model was necessary. The overall stability constants β_n were determined for the reaction