Measurement of soluble reactive phosphorus concentration profiles and fluxes in river-bed sediments using DET gel probes   总被引：3，自引：0，他引：3  

Helen P. Jarvie  Robert J.G. Mortimer  Elizabeth J. Palmer-Felgate  Katherine St. Quinton  Sarah A. Harman  Patricia Carbo 《Journal of Hydrology》2008,350(3-4):261-273

DET (diffusive equilibrium in thin films) gel probes were used for sampling river-bed sediment porewaters, to characterise in situ soluble reactive phosphorus (SRP) concentration profiles and fluxes. DET probes were deployed in three contrasting rural streams: (1) a headwater ‘pristine’ stream, with minimal P inputs from low intensity grassland and no point sources, (2) an intensively cultivated arable catchment, and (3) a stream subject to high P loadings from sewage effluent and intensive arable farming. The DET results showed highly enriched porewater SRP concentrations of between ca. 400 and 5000 μg-P l⁻¹ in the sewage-impacted stream. In contrast, the arable and pristine streams had porewater SRP concentrations <70 μg-P l⁻¹ and <20 μg-P l⁻¹, respectively. Porewater SRP concentration profiles in both the sewage-impacted and arable-impacted streams showed well-defined vertical structure, indicating internal sources and sinks of SRP within the sediment. However, there was little variability in porewater SRP concentrations in the pristine stream. The DET porewater profiles indicated net diffusion of SRP (a) from the overlying river water into the surface sediment and (b) from subsurface sediment upwards towards the sediment–water interface. A mass balance for the sewage-impacted site showed that the influx of SRP into the surface sediments from the overlying river water was small (ca. 1% of the daily river SRP load). The DET results indicated that, in the arable and sewage-impacted streams, the surface ‘cap’ of fine sediment may play an important role in inhibiting upward movement of SRP from subsurface porewaters into the overlying river water, under steady-state, low-flow conditions.  相似文献   

A heat perturbation flow meter for application in soft sediments     

Richard B. Greswell  Michael S. Riley  Patricia Fernandes Alves  John H. Tellam 《Journal of Hydrology》2009,370(1-4):73-82

A prototype flow meter has been developed, based upon the heat perturbation principle, to monitor groundwater specific discharge in soft sediments. The device is designed for use in spatially intensive, long-term monitoring campaigns in remote or inconvenient locations, and is cheap, robust and capable of being logged automatically. The results of the laboratory tests indicate that the heat perturbation principle is suitable for determining the magnitude of specific discharge to a degree of accuracy that would be useful in practical applications in dynamic groundwater systems with rapidly changing flows of approximately 1 md⁻¹ or more and that the groundwater flow direction can generally be determined to a high level of precision. The accuracy and reliability of the estimates of specific discharge have been shown to depend strongly upon the geometrical precision of manufacture and the quality of the temperature monitoring system. These factors become most significant in the estimation of lower flows and further investigation is required to determine the detection limit of the device. Specific discharge estimates have been shown to be insensitive to dispersivity values appropriate to the scale of the device. Unlike the majority of heat perturbation devices, calibration is unnecessary.  相似文献   

Source process of very-long-period events accompanying long-period signals at Cotopaxi Volcano,Ecuador     

Indira Molina  Hiroyuki Kumagai  Alexander García-Aristizábal  Masaru Nakano  Patricia Mothes 《Journal of Volcanology and Geothermal Research》2008

Renewed seismic activity of Cotopaxi, Ecuador, began in January 2001 with the increased number of long-period (LP) events, followed by a swarm of volcano-tectonic (VT) earthquakes in November 2001. In late June 2002, the activity of very-long-period (VLP) (2 s) events accompanying LP (0.5–1 s) signals began beneath the volcano. The VLP waveform was characterized by an impulsive signature, which was accompanied by the LP signal showing non-harmonic oscillations. We observed temporal changes of both the VLP and LP signals from the beginning until September 2003: The VLP signal gradually disappeared and the LP signal characterized by decaying harmonic oscillations became dominant. Assuming possible source geometries, we applied a waveform inversion method to the observed waveforms of the largest VLP event. Our inversion and particle motion analyses point to volumetric changes of a sub-vertical crack as the VLP source, which is located at a depth of 2–3 km beneath the northeastern flank. The spectral analysis of the decaying harmonic oscillations of LP events shows frequencies between 2.0 and 3.5 Hz, with quality factors significantly above 100. The increased VT activity and deformation data suggest an intrusion of magma beneath the volcano. A release of gases with small magma particles may have repetitively occurred due to the pressurization, which was caused by sustained bubble growth at the magma ceiling. The released particle-laden gases opened a crack above the magma system and triggered the resonance of the crack. We interpret the VLP and LP events as the gas-release process and the resonance of the crack, respectively.  相似文献   

Seasonal variation in di-nitrogen fluxes and associated processes (denitrification, anammox and nitrogen fixation) in sediment subject to shellfish farming influences     

Laura Minjeaud  Valerie D. Michotey  Nicole Garcia  Patricia C. Bonin 《Aquatic Sciences - Research Across Boundaries》2009,71(4):425-435

Seasonal patterns of di-nitrogen fluxes together with denitrification, anammox, and N-fixation rates were studied in sediment in an area subject to strong human pressure via waste water, tributaries and shellfish farming in the Mediterranean Sea (Carteau Cove, NW area of the Gulf of Lion). Ammonium concentration demonstrated no seasonal variation, however, a large increase in its concentration was observed over a 10 years period due to intense biodeposition of organic matter. In contrast, nitrate concentration demonstrated no seasonal or long-term (10 years) variation. The main processes affecting di-nitrogen flux magnitudes were denitrification and N-fixation. Anammox was only detected occasionally, nevertheless it represented at times up to 39% of the N₂-flux. Nitrate reducing processes were variable and denitrification showed a 20-fold increase over the past 10 years and might actually have reached its potential maximal activity. Rates of N₂ production (denitrification and anammox) were generally higher than those of N-fixation, leading to elimination of nitrogen from the ecosystem.  相似文献   

ESR dating of dental enamel from Middle Palaeolithic levels at Lazaret Cave,France     

Véronique Michel  Guanjun Shen  Patricia Valensi  Henry de Lumley 《Quaternary Geochronology》2009,4(3):233-240

ESR dating was carried out on Cervus elaphus tooth enamel samples from the depositional sequence of Lazaret Cave, Nice, France. The deposits contain Anteneandertal hominid fossils associated with abundant lithic artefacts and faunal remains. Three samples from the Mousterian occupations in complex CIII (Fouille d'entrée) yielded early uptake (EU) ages between 108 and 125 ka and linear uptake (LU) ages between 133 and 160 ka. Seven samples from the Acheulian levels in the upper part of the complex CII (Fouille d'entrée and Fouille centre) gave EU ages between 113 and 165 ka and LU ages between 147 and 210 ka, with weighted means at 131 ± 7 and 165 ± 9 ka, respectively. The results of six enamel samples from the lower Acheulian levels at Locus VIII, another place in the cave, were discarded because of their decreasing tendency with depth. The US–ESR combination method was also applied and the CSUS–ESR dates were calculated using the ESR-DATA program. Altogether, the data suggest that the Lazaret Acheulian and Mousterian occupations were rapidly formed during OIS 6.  相似文献   

Mira kinematics from Hipparcos data: a Galactic bar to beyond the Solar circle     

Michael W. Feast  Patricia A. Whitelock 《Monthly notices of the Royal Astronomical Society》2000,317(2):460-487

The space motions of Mira variables are derived from radial velocities, Hipparcos proper motions and a period–luminosity relation. The previously known dependence of Mira kinematics on the period of pulsation is confirmed and refined. In addition, it is found that Miras with periods in the range 145–200 d in the general Solar neighbourhood have a net radial outward motion from the Galactic Centre of 75±18 km s⁻¹. This, together with a lag behind the circular velocity of Galactic rotation of 98±19 km s⁻¹, is interpreted as evidence for an elongation of their orbits, with their major axes aligned at an angle of ∼17° with the Sun–Galactic Centre line, towards positive Galactic longitudes. This concentration seems to be a continuation to the Solar circle and beyond of the bar-like structure of the Galactic bulge, with the orbits of some local Miras probably penetrating into the bulge. These conclusions are not sensitive to the distance scale adopted. A further analysis is given of the short-period (SP) red group of Miras discussed in companion papers in this series. In Appendix A the mean radial velocities and other data for 842 oxygen-rich Mira-like variables are tabulated. These velocities were derived from published optical and radio observations.  相似文献   

Determination of the optimal conditions for inclination maneuvers using a Swing-by     

O. MouraJr.  C. C. Celestino  A. F. B. A. Prado 《Astrophysics and Space Science》2018,363(5):91

The search for methods to reduce the fuel consumption in orbital transfers is something relevant and always current in astrodynamics. Therefore, the maneuvers assisted by the gravity, also called Swing-by maneuvers, can be an advantageous option to save fuel. The proposal of the present research is to explore the influence of some parameters in a Swing-by of an artificial satellite orbiting a planet with one of the moons of this mother planet, with the goal of changing the inclination of the artificial satellite around the main body of the system. The fuel consumption of this maneuver is compared with the required consumption to perform the same change of inclination using the classical approach of impulsive maneuvers.  相似文献   

Analytical study of the swing-by maneuver in an elliptical system     

Alessandra F. S. Ferreira  Antônio F. B. A. Prado  Othon C. Winter  Denilson P. S. Santos 《Astrophysics and Space Science》2018,363(2):24

The objective of the present paper is to derive a set of analytical equations that describe a swing-by maneuver realized in a system of primaries that are in elliptical orbits. The goal is to calculate the variations of energy, velocity and angular momentum as a function of the usual basic parameters that describe the swing-by maneuver, as done before for the case of circular orbits. In elliptical orbits the velocity of the secondary body is no longer constant, as in the circular case, but it varies with the position of the secondary body in its orbit. As a consequence, the variations of energy, velocity and angular momentum become functions of the magnitude and the angle between the velocity vector of the secondary body and the line connecting the primaries. The “patched-conics” approach is used to obtain these equations. The configurations that result in maximum gains and losses of energy for the spacecraft are shown next, and a comparison between the results obtained using the analytical equations and numerical simulations are made to validate the method developed here.  相似文献   

Managing land-use effects on Northland dune lakes: lessons from the past     

Tom Stephens  Paul Augustinus  Brett Rip  Patricia Gadd  Atun Zawadski 《新西兰海洋与淡水研究杂志》2018,52(3):409-429

The Northland region of New Zealand includes numerous high-value, macrophyte-dominated dune lakes. Recent water policy reforms offer limited guidance on managing for aquatic macrophytes. In addition, dune lake histories are poorly known as regular monitoring dates to 2005 AD. Here, ca. 4000 years of lake functional behaviour is reconstructed from sedimentary archives in two Northland dune lakes (Humuhumu and Rotokawau). Results demonstrated that macrophyte dominance is sensitive to catchment erosion and hydrological drawdown. Degradation of macrophyte communities occurred in the nineteenth and twentieth centuries, earlier at Lake Humuhumu than Lake Rotokawau (post-1880 AD and post-1930 AD, respectively). In both lakes, increased erosional influx reduced macrophyte productivity, before later increases to wider trophic state (post-1970 AD). Lake-level decline is linked to increased nutrient loading at Lake Rotokawau but less so, Lake Humuhumu which is more strongly groundwater-fed. In Northland dune lakes, water-level reduction and erosional influx from land use have driven macrophyte degradation.  相似文献   

Zooplankton research off Peru: A review   总被引：2，自引：1，他引：1  

Patricia Ayn  Maria I. Criales-Hernandez  Ralf Schwamborn  Hans-Jürgen Hirche 《Progress in Oceanography》2008,79(2-4):238

A review of zooplankton studies conducted in Peruvian marine waters is given. After a short history of the development of zooplankton research off Peru, we review zooplankton methodology, taxonomy, biodiversity, spatial distribution, seasonal and interannual variability, trophodynamics, secondary production, and modelling. We review studies on several micro-, meso-, macro-, and meroplankton groups, and give a species list from both published and unpublished reports. Three regional zooplankton groups have been identified: (1) a continental shelf group dominated by Acartia tonsa and Centropages brachiatus; (2) a continental slope group characterized by siphonophores, bivalves, foraminifera and radiolaria; (3) and a species-rich oceanic group. The highest zooplankton abundances and biomasses were often found between 4–6°S and 14–16°S, where continental shelves are narrow. Species composition changes with distance from the shore. Species composition and biomass also vary strongly on short time scales due to advection, peaks of larval production, trophic interactions, and community succession. The relation of zooplankton to climatic variability (ENSO and multi-decadal) and fish stocks is discussed in the context of ecological regime shifts. An intermediate upwelling hypothesis is proposed, based on the negative effects of low upwelling intensity in summer or extremely strong and enduring winter upwelling on zooplankton abundance off Peru. According to this hypothesis, intermediate upwelling creates an optimal environmental window for zooplankton communities. Finally, we highlight important knowledge gaps that warrant attention in future.  相似文献