Distribution and Trophic Importance of Anthropogenic Nitrogen in Narragansett Bay: An Assessment Using Stable Isotopes     

Autumn Oczkowski  Scott Nixon  Kelly Henry  Peter DiMilla  Michael Pilson  Stephen Granger  Betty Buckley  Carol Thornber  Richard McKinney  Joaquin Chaves 《Estuaries and Coasts》2008,31(1):53-69

Narragansett Bay has been heavily influenced by human activities for more than 200 years. In recent decades, it has been one of the more intensively fertilized estuaries in the USA, with most of the anthropogenic nutrient load originating from sewage treatment plants (STP). This will soon change as tertiary treatment upgrades reduce nitrogen (N) loads by about one third or more during the summer. Before these reductions take place, we sought to characterize the sewage N signature in primary (macroalgae) and secondary (the hard clam, Mercenaria mercenaria) producers in the bay using stable isotopes of N (δ¹⁵N) and carbon (δ¹³C). The δ¹⁵N signatures of the macroalgae show a clear gradient of approximately 4‰ from north to south, i.e., high to low point source loading. There is also evidence of a west to east gradient of heavy to light values of δ¹⁵N in the bay consistent with circulation patterns and residual flows. The Providence River Estuary, just north of Narragansett Bay proper, receives 85% of STP inputs to Narragansett Bay, and lower δ¹⁵N values in macroalgae there reflected preferential uptake of ¹⁴N in this heavily fertilized area. Differences in pH from N stimulated photosynthesis and related shifts in predominance of dissolved C species may control the observed δ¹³C signatures. Unlike the macroalgae, the clams were remarkably uniform in both δ¹⁵N (13.2 ± 0.54‰ SD) and δ¹³C (−16.76 ± 0.61‰ SD) throughout the bay, and the δ¹⁵N values were 2–5‰ heavier than in clams collected outside the bay. We suggest that this remarkable uniformity reflects a food source of anthropogenically heavy phytoplankton formed in the upper bay and supported by sewage derived N. We estimate that approximately half of the N in the clams throughout Narragansett Bay may be from anthropogenic sources.  相似文献   

Sediment Organic Carbon in Todos Santos Bay, Baja California, Mexico     

Stephen V. Smith  Silvia E. Ibarra-Obando  Victoria Díaz-Castañeda  Francisco Javier Aranda-Manteca  José D. Carriquiry  Brian N. Popp  Oscar Gonzalez-Yajimovich 《Estuaries and Coasts》2008,31(4):719-727

Sediment grain size and organic carbon (OC) data collected over the past 50 years, together with δ¹³C values of OC in recently collected samples, were analyzed to improve understanding of sediment OC distribution and abundance in Todos Santos Bay. Sediments in the submarine canyon at the mouth of the bay and in quiet-water locations along the shore are fine grained, high in OC, and have generally low δ¹³C values; sediments in high-energy environments are low in OC and have high δ¹³C values. A bivariate isotopic mixing model indicates that none of the sediments contain >50% terrigenous OC (average ~30%), and that the terrigenous OC content of the sediments is a small proportion of the OC content of local soils. Sediment OC composition is apparently controlled by energy-related sorting and deposition, oxidation of much of the original terrigenous OC, and replacement of some terrigenous OC by marine OC.  相似文献   

The stellar populations within theρ Oph cloud cores     

Karen M. Strom  Jeremy Kepner  Stephen E. Strom 《Astrophysics and Space Science》1994,217(1-2):223-224

We have obtained infrared colors and limiting magnitudes from 1.25–4.8µm for a sample of 26 of the cm continuum radio sources located in the core of the Oph molecular cloud. Their colors demonstrate that the majority of the sources appear to be heavily reddened objects surrounded by circumstellar accretion disks. In these cases the radio emission most likely diagnoses accretion driven energetic outflow phenomena: either ionized winds or possibly synchrotron emission from shocked gas associated with stellar jets.  相似文献   

Solar and stellar chromospheric contrast     

Robert A. Donahue  Sergio R. Restaino  Stephen L. Keil 《Solar physics》1994,149(2):257-265

Positions of active regions estimated from observations of the whole solar disk in Caii K _iv during the period 1977–1989 at the Coimbra Astronomical Observatory are compared with the time-dependent latitudinal distribution of background solar magnetic fields and with the latitudinal shifts of boundaries of their polarities. We confirm that the sunspot groups are located near the zonal boundaries between the opposite polarities of the solar background magnetic field during different phases of the two recent consecutive cycles of activity. We demonstrate a probable connection between the increased number of groups and the commencement of poleward migration of zonal boundaries in both hemispheres. But the influence of the dominant convective rolls seems to he still unclear. A new problem of interrelation between the zonal and sector boundaries has also appeared.  相似文献   

The history and impact of air pollution at Čertovo Lake,southwestern Czech Republic     

Josef Vesely  Heather Almquist-Jacobson  Lisa M. Miller  Stephen A. Norton  Peter Appleby  Aruna S. Dixit  John P. Smol 《Journal of Paleolimnology》1993,8(3):211-231

This multi-disciplinary investigation documents the longterm effects of atmospheric pollution of metals and acids on a geologically sensitive catchment in the umava Mountains, southwestern Czech Republic, a region with a long history of human disturbance. A 30 cm long sediment core (I) from ertovo Lake was analyzed for natural and artifical radionuclides, metals, diatoms, chrysophytes, and pollen in sediments accumulated during the last 200 years. A second core (II), extending to 95 cm, included sediment judged to be free of atmospheric deposition of pollutants associated with the Industrial Revolution. Chronostratigraphic markers include several changes in the pollen assemblages corresponding to well-documented changes in land-use, and distinct distributions of ¹³⁷Cs, ¹³⁴Cs and ²⁴¹Am from weapons testing and the 1986 nuclear accident at Chernobyl, Russia. These markers corroborate the ²¹⁰Pb dating and, together, produce a reliable chronology extending back nearly to 1800 A.D.Stratigraphic profiles of Cu, Pb, and Zn in Core I are unlike any previously reported in the literature. Concentrations of Cu, Pb, and Zn remain generally above 100, 400, and 200 g g^-1, respectively, for the 200 years represented by Core I. These values are unusually high for sediments from a watershed with no known heavy-metal ore bodies. Accumulation rates for Cu, Pb, and Zn, which include both atmospheric and watershed contributions, are also high (ca 1, > 1 and > 1 g cm^-2 yr^-1, respectively) for the same period, although the anthropogenic contribution of Zn rose from nearly zero at 1800 A.D. The Cu and Pb accumulation rates rose dramatically about 1640 A.D.Accumulation rates of anthropogenically-derived Be, a relatively abundant element in the soft coals of the region, are also elevated by about 0.01 g cm^-2 yr^-1 in sediments of this period. Vanadium accumulation rates increased only since 1980 A.D., presumably along with increased consumption of oil.Diatom assemblages illustrate that the lake was acidic (pH between 4.5 and 5) through at least the past 200 years. The pH declined significantly (from ca 5 to 4) between 1960 and 1985 with a slight increase to 4.5 in the last few years. Recent diatom and chrysophyte assemblages suggest high trace metal concentrations, consistent with the present lake-water chemistry.  相似文献   

Geochemistry of the Grenville Dyke Swarm: role of plume-source mantle in magma genesis     

Karen St. Seymour  P. Stephen Kumarapeli 《Contributions to Mineralogy and Petrology》1995,120(1):29-41

Major and trace element data of samples from the approximately 590 Ma Grenville dyke swarm, in the southeastern parts of the Canadian Shield, were used to evaluate the extent of crustal contamination of the dyke magma and to model its probable mantle source. The dyke rocks are mostly saturated, quartz tholeiites. A few samples represent transitional basalts. Their overall chemistries are similar to those of continental flood basalts. Their compositions resemble those of liquids initially produced in the garnet peridotite mantle zone and then subjected to polybaric fractionation. However, fractionation models fail to mass-balance Ti, Fe, K, and P. Geochemical and isotopic criteria indicate that crustal contamination was minimal. The incompatible elements Zr, Y, K, Rb, Nb, V, Ta, Hf, and Th show hyperbolic elemental ratio-ratio distributions indicative of mixing between two end-members. One end-member has elemental ratios similar to those of a depleted N-MORB source and the second of a P-MORB i.e. ertile or plume MORB source. The more enriched dyke compositions can be successfully reproduced by mixing models in the ratio of 6:1 between the most depleted MORB-like dyke magma and a liquid composition similar to metasomatic glass veinlets coexisting with mica peridotite mantle xenoliths, and subsequent crystal fractionation. The Grenville dykes are probably a synrift swarm that was emplaced along a rift arm related to an Iapetan rrr triple junction that is thought to have formed over a mantle plume. The chemistry of the dyke swarm is consistent with its derivation from a plume head, in that the minor enriched source can be identified with plume-source mantle and the major depleted source with entrained mantle. The magma probably originated in the upper cooler parts of the plume head.  相似文献   

Primodial retention of carbon by the terrestrial planets     

John S. Lewis  Stephen S. Barshay  Barbara Noyes 《Icarus》1979,37(1):190-206

Chemical equilibrium calculations on the stability of pure and dissolved graphite and cohenite (Fe₃C), several other carbides, and several carbonates have been carried out for a system with solar elemental abundances over a very wide range of temperature and pressure. The calculated abundances of condensed carbon compounds are similar to the observed inventories on Earth and Venus, but fully 10 times smaller than the minimum carbon abundance found in ordinary chondrites. The total carbon content of most iron meteorites is compatible with their origin as a cooling FeNiCSP solution which was saturated with dissolved carbon at the solidus, such as would be produced by melting an ordinary chondrite, not by direct condensation from or equilibrium with the primitive solar nebula. It is argued that the carbon content of Mars need not be appreciably greater than that of the Earth. Material with even lower formation temperatures than Mars, such as the primitive material in the asteroid belt, may retain substantially more carbon as disequilibrium polymeric organic matter, possibly by the Fischer-Tropsch mechanism favored by Anders. Carbonates are not found as equilibrium products in a solar-composition system, and are probably secondary alteration products. CaCO₃ might, however, persist in a solar-composition gas at temperatures below 460°K and pressures below 10^?6.6 bar. The most stable condensed carbon compounds are found to be graphite, Fe₃C, and possibly TiC, all in solid solution in the metal phase.  相似文献   

Book reviews     

Tom L. McKnight  J. M. Powell  Stephen Codrington  John Connell  Stewart F. Richards  Ronald J. Horvath 《The Australian geographer》1991,22(1):86-96

REGIONAL GEOGRAPHY: Current Developments and Future Prospects edited by R. J. Johnston, J Hauer and G. A. Hoekveld. 14 × 22 cm, xiii and 216 pages. Routledge: London 1990 (ISBN 0 415 05247 5) $A89.95 (hard).

THE MAKING OF THE AMERICAN LANDSCAPE edited by M. P. Conzen. 19 × 25 cm, xvi and 433 pages. Unwin Hyman: Boston 1990 (ISBN 0 04 917010 4) $A59.95 (soft).

EASTERN EUROPE: An Historical Geography 1815–1945 by D. Turnock. 14 × 22 cm, ix and 357 pages. Routledge: London 1989 (ISBN 0 415 01269 4) $A115.00 (hard), distributed by the Law Book Co.

THE HUMAN GEOGRAPHY OF EASTERN EUROPE by D. Turnock. 14 × 22 cm, xii and 345 pages. Routledge: London 1989 (ISBN 0 415 00469 1) $A105.00 (hard), distributed by the Law Book Co.

A HISTORY OF THE PACIFIC ISLANDS by I. C. Campbell. 14 × 21 cm, 239 pages. University of Queensland Press: St Lucia 1990 (ISBN 0 7022 2291 7) $A34.95 (soft).

THE CORPORATE FIRM IN A CHANGING WORLD ECONOMY: Case Studies in the Geography of Enterprise edited by M. de Smidt and E. Wev‐er. 14 × 23 cm, xiv and 247 pages. Routledge: London 1990 (ISBN 0 415 03497 3) $A105.00 (hard).

THE CAPITALIST CITY: Global Restructuring and Community Politics by M. P. Smith and J. R. Feagin. 15 × 23 cm, 393 pages. Basil Black‐well: Oxford 1988 (ISBN 0 631 15182 6) £35 (hard).

CONFLICT AND CHANGE IN THE COUNTRYSIDE: Rural Society, Economy and Planning in the Developed World by G. M. Robinson. 15 × 23 cm, xxvi and 482 pages. Belhaven Press: London 1990 (ISBN 1 85293 043 8) £40.00 (hard); (ISBN 1 85293 044 6) £14.95 (soft).

ENVIRONMENTAL SCIENCE (Collins Reference Dictionary) by G. Jones, A. Robertson, J. Forbes and G. Hollier. 13 × 20 cm, vi and 473 pages. Collins: London 1990 (ISBN 0 00 434348 4) £5.95 (soft).

THE HUMAN IMPACT ON THE NATURAL ENVIRONMENT (Third Edition) by A. Goudie. 17 × 24 cm, xi and 388 pages. Blackwell: Oxford 1990 (ISBN 0 631 16164 3) $A39.95 (soft).

PATTERNS OF LIFE: Biogeography of a Changing World by H. W. Mielke. 19 × 24 cm, xiv and 370 pages. Unwin Hyman: London 1989 (ISBN 0 04 574032 1).  相似文献   

Structure and oscillations in quiescent filaments from observations in He i λ10830 å     

Yi Zhang  Oddbjørn Engvold  Stephen L. Keil 《Solar physics》1991,132(1):63-80

Observations of two quiescent filaments show oscillatory variations in Doppler shift and central intensity of the He i 10830 Å line.The oscillatory periods range from about 5 to 15 min, with dominant periods of 5, 9, and 16 min. The 5-min period is also detected in the intensity variations, after correction for atmospheric effects. Doppler shifts precede intensity variations by about one period. The possibility that the oscillations are Alfvén waves is discussed.The Doppler signals of the filament form fibril-like structures. The fibrils are all inclined at an angle of about 25° to the long axis of the filament. The magnetic field has a similar orientation relative to the major direction of the filament, and the measured Doppler signals are apparently produced by motions along magnetic flux tubes threading the filament.The measured lifetimes of the small-scale fibrils of quiescent disk filaments are very likely a combined effect of intensity modulations and reshuffling of the structures.  相似文献   

Deep drilling at the Siljan Ring impact structure: oxygen-isotope geochemistry of granite     

Stephen C. Komor  John W. Valley 《Contributions to Mineralogy and Petrology》1990,105(5):516-532

The Siljan Ring is a 362-Ma-old impact structure formed in 1700-Ma-old I-type granites. A 6.8-km-deep borehole provides a vertical profile through granites and isolated horizontal diabase sills. Fluid-inclusion thermometry, and oxygen-isotope compositions of vein quartz, granite, diabase, impact melt, and pseudotachylite, reveal a complex history of fluid activity in the Siljan Ring, much of which can be related to the meteorite impact. In granites from the deep borehole, ¹⁸O values of matrix quartz increase with depth from near 8.0 at the surface to 9.5 at 5760 m depth. In contrast, feldspar ¹⁸O values decrease with depth from near 10 at the surface to 7.1 at 5760 m, forming a pattern opposite to the one defined by quartz isotopic compositions. Values of ¹⁸O for surface granites outside the impact structure are distinct from those in near-surface samples from the deep borehole. In the deep borehole, feldspar coloration varies from brick-red at the surface to white at 5760 m, and the abundances of crack-healing calcite and other secondary minerals decrease over the same interval. Superimposed on the overall decrease in alteration intensity with depth are localized fracture zones at 4662, 5415, and 6044 m depth that contain altered granites, and which provided pathways for deep penetration of surface water. The antithetic variation of quartz and feldspar ¹⁸O values, which can be correlated with mineralogical evidence of alteration, provides evidence for interaction between rocks and impact-heated fluids (100–300° C) in the upper 2 km of the pluton. Penetration of water to depths below 2 km was restricted by a general decrease in impact-fracturing with depth, and by a 60-m-thick diabase sill at 1500 m depth that may have been an aquitard. At depths below 4 km in the pluton, where water/rock ratios were low, oxygen isotopic compositions preserve evidence for limited high-temperature (>500° C) exchange between alkali feldspar and fluids. The high-temperature exchange may have been a post-impact event involving impact-heated fluids, or a post-magmatic event.  相似文献