Elevated mercury concentrations in failed eggs of Snowy Plovers at Point Reyes National Seashore     

Schwarzbach SE  Stephenson M  Ruhlen T  Abbott S  Page GW  Adams D 《Marine pollution bulletin》2005,50(11):1444-1447

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Nitrogen, phosphorus, silica, and carbon in Moreton Bay, Queensland, Australia: Differential limitation of phytoplankton biomass and production     

Patricia M. Glibert  Cynthia A. Heil  Judith M. O'Neil  William C. Dennison  Mark J. H. O'Donohue 《Estuaries and Coasts》2006,29(2):209-221

Subtropical estuaries have received comparatively little attention in the study of nutrient loading and subsequent nutrient processing relative to temperate estuaries. Australian estuaries are particularly susceptible to increased nutrient loading and eutrophication, as 75% of the population resides within 200 km of the coastline. We assessed the factors potentially limiting both biomass and production in one Australian estuary, Moreton Bay, through stoichiometric comparisons of nitrogen (N), phosphorus (P), silicon (Si), and carbon (C) concentrations, particulate compositions, and rates of uptake. Samples were collected over 3 seasons in 1997–1998 at stations located throughout the bay system, including one riverine endmember site. Concentrations of all dissolved nutrients, as well as particulate nutrients and chlorophyll, declined 10-fold to 100-fold from the impacted western embayments to the eastern, more oceanic-influenced regions of the bay during all seasons. For all seasons and all regions, both the dissolved nutrients and particulate biomass yielded N:P ratios <6 and N:Si ratios <1. Both relationships suggest strong limitation of biomass by N throughout the bay. Limitation of rates of nutrient uptake and productivity were more complex. Low C:N and C:P uptake ratios at the riverine site suggested light limitation at all seasons, low N:P ratios suggested some degree of N limitation and high N:Si uptake ratios in austral winter suggested Si limitation of uptake during that season only. No evidence of P limitation of biomass or productivity was evident.  相似文献   

Historical trace element distribution in sediments from the Mississippi River delta     

Peter W. Swarzenski  Mark Baskaran  Robert J. Rosenbauer  William H. Orem 《Estuaries and Coasts》2006,29(6):1094-1107

Five sediment cores were collected on the shelf of the inner Mississippi Bight in June 2003 for a suite of radionuclides to establish geochronologies and trace elements to examine patterns of contaminant deposition and accumulation. Core sites were chosen to reflect a matrix of variable water depths, proximity to the Mississippi River mouth as the primary source for terrigenous particles, and extent and duration of summertime water column hypoxia. The vertical distribution of^239,240Pu and²¹⁰Pb_xs(=²¹⁰Pb_total−²²⁶Ra) provided reliable geochronological age constraints to develop models for mass accumulation rates and historic trace element inputs and variations. Mass accumulation rates ranged from 0.27 to 0.87 g cm⁻²yr⁻¹ and were internally consistent using either²¹⁰Pb_xs or^239,240Pu. Measured inventories of¹³⁷Cs,^239,240Pu, and²¹⁰Pb_xs were compared to atmospheric deposition rates to quantify potential sediment focusing or winnowing. Observed variability in calculated mass accumulation rates may be attributed foremost to site-specific proximity to the river mouth (i.e., sediment source), variability in water depth, and enhanced sediment focusing at the Mississippi River canyon site. Trace element concentrations were first normalized to Al, and then Al-normalized enrichment factors (ANEF) were calculated based on preanthropogenic and crustal trace element abundances. These ANEFs were typically >1 for V and Ba, while for most other elements studied, either no enrichment or depletion was observed. The enrichment of Ba may be related, in part, to the seasonal occurrence of oxygen-depleted subsurface waters off the Mississippi River delta, as well as being an ubiquitous byproduct of the petroleum industry.  相似文献   

Horseshoe crabs (Limulus polyphemus) in an urban estuary (Jamaica Bay, New York) and the potential for ecological restoration     

Mark L. Botton  Robert E. Loveland  John T. Tanacredi  Tomio Itow 《Estuaries and Coasts》2006,29(5):820-830

We assessed the suitability of intertidal habitats for spawning by horseshoe crabs (Limulus polyphemus) at 12 proposed restoration sites identified by the United States Army Corps of Engineers along the shore of Jamaica Bay, a highly developed estuary in New York City. Based on beach geomorphology, we chose to quantify horseshoe crab activity at five of the sites during the May–July 2000 breeding season. Horseshoe crabs spawned intensively on small patches of suitable sand within larger areas of eroding shoreline with bulkheads and rubble fill. Small areas of sand behind grounded barges at Brant Point and Dubos Point had densities of over 100,000 eggs m⁻², which was equal to or greater than the egg densities on longer, more natural appearing beaches at Spring Creek and Dead Horse Bay, or at a sand spit at Bayswater State Park. There were no significant differences in the percentage of Jamaica Bay horseshoe crab eggs that completed development when cultured using water from Jamaica Bay or lower Delaware Bay, a less polluted location. Only 1% of the embryos from Jamaica Bay exhibited developmental anomalies, a frequency comparable to a previously studied population from Delaware Bay. We suggest that the distribution and abundance of horseshoe crabs at our study areas in Jamaica Bay is presently limited by the availability of suitable shoreline for breeding, rather than by water quality. Restoration efforts that increase the amount of sandy beach in this urban estuary have a good likelihood of benefiting horseshoe crabs and providing additional value to migrating shorebirds that use horseshoe crab eggs as food.  相似文献   

Erratum to “Regional atmospheric circulation change in the North Pacific during the Holocene inferred from lacustrine carbonate oxygen isotopes, Yukon Territory, Canada” [Quaternary Research 64 (2005) 21-35]     

Lesleigh Anderson  Mark B. Abbott  Stephen J. Burns 《Quaternary Research》2006,65(2):350-351

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Deglaciation and Holocene climate change in the western Peruvian Andes     

Chengyu Weng  Mark B. Bush  Tom D. Dillehay  Michael W. Binford 《Quaternary Research》2006,66(1):87-96

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An analytical treatment of resonance effects on satellite orbits     

Mark T. Lane 《Celestial Mechanics and Dynamical Astronomy》1987,42(1-4):3-38

A first order analytical approximation of the tesseral harmonic resonance perturbations of the Keplerian elements is presented, and the mean elements (the Keplerian elements with the long period portions averaged out) will also be given in closed form. Finally the results of a numerical test, which compares the analytical solution against a numerical integration of the Lagrange equations of motion, will be summarized.This work was sponsored with the support of the Department of the Air Force under contract F19628-85-C-0002.The views expressed are those of the author and do not reflect the official policy or position of the U.S. Government.  相似文献   

COMPUTERIZED NAVIGATION ASSISTANCE FOR DRIVERS     

David M. Mark  Michael D. Gould  Matthew McGranaghan 《The Professional geographer》1987,39(2):215-220

Computer-assisted navigation systems provide navigation information to automobile drivers and are now available. They are capable of storing, processing and displaying information about street networks. The display typically mimics a printed street map. The underlying capabilities of these systems present unique opportunities for geographers to study spatial cognition, wayfinding, spatial search, the impact of spatial information on trip behavior, and market responses to potentially different travel patterns. Such systems are reviewed and key areas for future research are identified.  相似文献   

Fluorescence spectra of Titan tholins: in-situ detection of astrobiologically interesting areas on Titan's surface     

Robert Hodyss  Gene McDonald  Mark A. Smith  J.L. Beauchamp 《Icarus》2004,171(2):525-530

We report the three-dimensional fluorescence spectra of Titan tholins in water and acetonitrile, and separate some of the fluorescent components of tholins using two-dimensional thin layer chromatography. In acetonitrile, tholins exhibit a broad fluorescence with a maximum at 471 nm, and an excitation maximum at 410 nm. The fluorescence spectrum of a water extraction displays a more complicated spectrum with multiple peaks. TLC results indicate the presence of at least three distinct fluorescent species. In addition, we obtained the two-dimensional fluorescence spectrum of tholins in water ice at 77 K, close to the surface temperature of Titan. The fluorescence of tholins in a 77 K ice matrix is red-shifted in comparison to a water solution, and undergoes a further red-shift when the water solution is heated prior to freezing. These results suggest that a simple fluorescence probe could be used on the surface of Titan to identify sites where tholins have been mixed with water, and possibly reveal information about the extent of heating the tholin-water mixture has undergone. This would be useful for a future mission with the goal of examining the organic chemistry of Titan.  相似文献   

Twisted accretion curtains in the intermediate polar FO Aquarii     

P. A. Evans  Coel Hellier  Gavin Ramsay  Mark Cropper 《Monthly notices of the Royal Astronomical Society》2004,349(2):715-721

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