Pervasive wetland flooding in the glacial drift prairie of North Dakota (USA)     

Paul E. Todhunter  Bradley C. Rundquist 《Natural Hazards》2008,46(1):73-88

This article describes a unique flood hazard, produced by the dramatic expansion of wetlands in Nelson County, located within the North American Prairie Pothole Region of North Dakota, USA. There has been an unprecedented increase in the number, average size, and permanence of prairie wetlands, and a significant increase in the size of a closed lake (Stump Lake) due to a decade-long wet spell that began in 1993 following a prolonged drying trend. Base-line land cover information from the 1992 USGS National Land Cover Characterization dataset, and a Landsat TM scene acquired 9 July 2001 are used to assess the growth of the closed lake and wetland pond surface areas, and to analyze the type and area of various land cover classes inundated between 1992 and 2001. The open water profile in Nelson County changed from one marked by relatively comparable coverage of closed lake and wetland pond areas in 1992, to one in which wetland open water accounted for the vast majority of total open water in 2001. The bulk of the wetland pond area expansion occurred by displacing existing wetland vegetation and agricultural cropland. Producers responded to the flood hazard by filing Federal Crop Insurance Corporation (FCIC) claims and enrolling cropland in the Conservation Reserve Program (CRP), a federal land retirement program. Land taken out of agricultural production has had an enormous impact upon the agricultural sector that forms the economic base of the rural economy. In 2001 the land taken out of production due to CRP enrollment and preventive planting claims represented nearly 42% of Nelson County’s 205.2 K ha base agricultural land. The patterns obtained from this detailed study of Nelson County are likely to be the representative of the more publicized flood disaster occurring within the Devils Lake Basin of North Dakota.  相似文献   

Zinc concentration effect at the organismal,cellular and subcellular levels in the eastern oyster     

Meiller JC  Bradley BP 《Marine environmental research》2002,54(3-5):401-404

The purpose of this research was to demonstrate a concentration effect of zinc exposure at organismal, cellular and sub-cellular levels in the eastern oyster and to find associated protein expression signatures (PES) for each concentration of zinc. Oysters were exposed to six concentrations of zinc for 48 h in a controlled environment. At the organismal level, fecal material was observed as a measure of physiological health during metal exposures. At the cellular level, lysosomal destabilization was measured using hemolymph. This cellular response was significant only at the highest concentration, when the fecal index was lowest. Protein responses were monitored in the oyster following exposure to zinc. Gill tissue was excised and homogenized, and then analyzed using two-dimensional polyacrylamide gel electrophoresis (2D-PAGE) and digital image analysis. Protein expression signatures were found to be specific to each concentration. The protein responses were linked to the other biological parameters measured, each of which followed a concentration gradient of zinc.  相似文献   

Accurate local upscaling with variable compact multipoint transmissibility calculations     

James V. Lambers  Margot G. Gerritsen  Bradley T. Mallison 《Computational Geosciences》2008,12(3):399-416

We propose a new single-phase local upscaling method that uses spatially varying multipoint transmissibility calculations. The method is demonstrated on two-dimensional Cartesian and adaptive Cartesian grids. For each cell face in the coarse upscaled grid, we create a local fine grid region surrounding the face on which we solve two generic local flow problems. The multipoint stencils used to calculate the fluxes across coarse grid cell faces involve the six neighboring pressure values. They are required to honor the two generic flow problems. The remaining degrees of freedom are used to maximize compactness and to ensure that the flux approximation is as close as possible to being two-point. The resulting multipoint flux approximations are spatially varying (a subset of the six neighbors is adaptively chosen) and reduce to two-point expressions in cases without full-tensor anisotropy. Numerical tests show that the method significantly improves upscaling accuracy as compared to commonly used local methods and also compares favorably with a local–global upscaling method.  相似文献   

The Taconite Inlet Lakes Project: a systems approach to paleoclimatic reconstruction     

R. S. Bradley  M. J. Retelle  S. D. Ludlam  D. R. Hardy  B. Zolitschka  S. F. Lamoureux  M. S. V. Douglas 《Journal of Paleolimnology》1996,16(2):97-110

A comprehensive study of meteorological, hydrological, limnological and sedimentological conditions in the watersheds of density-stratified (meromictic) lakes around Taconite Inlet, Northern Ellesmere Island, N.W.T., Canada was carried out from 1990–1992. Lakes C1 and C2 contain seawater trapped by isostatic uplift as the former embayments became isolated from the sea. These lakes, and Lake C3, contain varved sediments which provide an annually resolvable paleoclimatic record. By studing the major systems influencing sedimentation in one of these lakes (Lake C2) a better understanding of the climatic controls on varve formation, and hence on the paleoclimatic signal in the varved sediment record, was obtained. The varves of Lake C2 provide a proxy record of summer temperature for the region.This is the first in a series of papers published in this issue on the Taconite Inlet Lakes Project. These papers were collected by Dr R. S. Bradley.  相似文献   

Location of type I radio continuum and bursts on Yohkoh soft X-ray maps     

S. Krucker  A. O. Benz  M. J. Aschwanden  T. S. Bastian 《Solar physics》1995,160(1):151-169

A solar type I noise storm was observed on 30 July, 1992 with the radio spectrometer Phoenix of ETH Zürich, the Very Large Array (VLA) and the soft X-ray (SXR) telescope on board theYohkoh satellite. The spectrogram was used to identify the type I noise storm. In the VLA images at 333 MHz a fully left circular polarized (100% LCP) continuum source and several highly polarized (70% to 100% LCP) burst sources have been located. The continuum and the bursts are spatially separated by about 100 and apparently lie on different loops as outlined by the SXR. Continuum and bursts are separated in the perpendicular direction to the magnetic field configuration. Between the periods of strong burst activities, burst-like emissions are also superimposed on the continuum source. There is no obvious correlation between the flux density of the continuum and the bursts. The burst sources have no systematic motion, whereas the the continuum source shows a small drift of 0.2 min^–1 along the X-ray loop in the long-time evolution. The VLA maps at higher frequency (1446 MHz) show no source corresponding to the type I event. The soft X-ray emission measure and temperature were calculated. The type I continuum source is located (in projection) in a region with enhanced SXR emission, a loop having a mean density of n _e = (1.5 ± 0.4) × 10⁹ cm^–3 and a temperature ofT = (2.1 ± 0.1) × 10⁶ K. The centroid positions of the left and right circularly polarized components of the burst sources are separated by 15–50 and seem to be on different loops. These observations contradict the predictions of existing type I theories.Presented at the CESRA-Workshop on Coronal Magnetic Energy Release at Caputh near Potsdam in May 1994.  相似文献   

Decimetric type III radio bursts and associated hard X-ray spikes     

B. R. Dennis  A. O. Benz  M. Ranieri  G. M. Simnett 《Solar physics》1984,90(2):383-399

A detailed comparison is made between hard X-ray spikes and decimetric type III radio bursts for a relatively weak solar flare on 1981 August 6 at 10: 32 UT. The hard X-ray observations were made at energies above 30 keV with the Hard X-Ray Burst Spectrometer on the Solar Maximum Mission and with a balloon-born coarse-imaging spectrometer from Frascati, Italy. The radio data were obtained in the frequency range from 100 to 1000 MHz with the analog and digital instruments from Zürich, Switzerland. All the data sets have a time resolution of 0.1 s or better. The dynamic radio spectrum shows many fast drift type III radio bursts with both normal and reverse slope, while the X-ray time profile contains many well resolved short spikes with durations of 1 s. Some of the X-ray spikes appear to be associated in time with reverse-slop bursts suggesting either that the electron beams producing the radio bursts contain two or three orders of magnitude more fast electrons than has previously been assumed or that the electron beams can trigger or occur in coincidence with the acceleration of additional electrons. One case is presented in which a normal slope radio burst at 600 MHz occurs in coincidence with the peak of an X-ray spike to within 0.1 s. If the coincidence is not merely accidental and if it is meaningful to compare peak times, then the short delay would indicate that the radio signal was at the harmonic and that the electrons producing the radio burst were accelerated at an altitude of 4 × 10⁹ cm. Such a short delay is inconsistent with models invoking cross-field drifts to produce the electron beams that generate type III bursts but it supports the model incorporating a MASER proposed by Sprangle and Vlahos (1983).  相似文献   

Type IV dm bursts: Onset and sudden reductions     

Arnold O. Benz  Jan Kuijpers 《Solar physics》1976,46(2):275-290

The effect of collisions of suprathermal electrons with a thermal background plasma is investigated and is shown to cause flattening of a monotonically descending velocity distribution of fast particles. As a result flare-produced energetic electrons that are trapped in a coronal magnetic arch and that are initially distributed in energy according to a power-law, can give rise to an instability of Langmuir waves in the background plasma and the subsequent emission of continuum radiation as observed in type IV dm bursts.To explain the appearance of sudden reductions observed in type IV dm outbursts the effects both of magnetic compressions of the source region and of renewed injections of fast particles on the continuum source are investigated. It is found that the latter process can explain the observed reductions.  相似文献   

Hurricanes Frances and Jeanne remove blooms of the invasive green algaCaulerpa brachypus formaparvifolia (Harvey) cribb from coral reefs off Northern Palm Beach County, Florida     

Brian E. Lapointe  Bradley J. Bedford  Rex Baumberger 《Estuaries and Coasts》2006,29(6):966-971

Coral reefs worldwide are under stress from a variety of anthropogenic activities that can alter or inhibit recovery from catastrophic physical disturbances such as hurricanes. On coral reefs off southeast Florida, land-based nutrient pollution contributed to a successful invasion ofCaulerpa brachypus fornaparvifolia that dominated (up to 90% cover) reefs between January 2003 and August 2004. In September 2004, physical effects from Hurricanes Frances and Jeanne removed virtually all of theC. brachypus from the affected reefs. In July 2005, small patches ofC. brachypus began to re-emerge and the area was affected again by Hurricane Wilma in October 2005. Although these hurricanes provided temporary relief from theC. brachypus invasion, the future of these reefs is uncertain because of competition with other opportunistic macroalgae and biota that may respond to the combination of newly created space and continued nutrient stress.  相似文献   

The geochemistry and provenance of Apollo 16 mafic glasses     

Ryan A. Zeigler  Randy L. Korotev  Bradley L. Jolliff  Larry A. Haskin  Christine Floss 《Geochimica et cosmochimica acta》2006,70(24):6050-6067

The regolith of the Apollo 16 lunar landing site is composed mainly of feldspathic lithologies but mafic lithologies are also present. A large proportion of the mafic material occurs as glass. We determined the major element composition of 280 mafic glasses (>10 wt% FeO) from six different Apollo 16 soil samples. A small proportion (5%) of the glasses are of volcanic origin with picritic compositions. Most, however, are of impact origin. Approximately half of the mafic impact glasses are of basaltic composition and half are of noritic composition with high concentrations of incompatible elements. A small fraction have compositions consistent with impact mixtures of mare material and material of the feldspathic highlands. On the basis of major-element chemistry, we identified six mafic glass groups: VLT picritic glass, low-Ti basaltic glass, high-Ti basaltic glass, high-Al basaltic glass, KREEPy glass, and basaltic-andesite glass. These glass groups encompass 60% of the total mafic glasses studied. Trace-element analyses by secondary ion mass spectroscopy for representative examples of each glass group (31 total analyses) support the major-element classifications and groupings. The lack of basaltic glass in Apollo 16 ancient regolith breccias, which provide snapshots of the Apollo 16 soil just after the infall of Imbrium ejecta, leads us to infer that most (if not all) of the basaltic glass was emplaced as ejecta from small- or moderate-sized impacts into the maria surrounding the Apollo 16 site after the Imbrium impact. The high-Ti basaltic glasses likely represent a new type of basalt from Mare Tranquillitatis, whereas the low-Ti and high-Al basaltic glasses possibly represent the composition of the basalts in Mare Nectaris. Both the low-Ti and high-Al basaltic glasses are enriched in light-REEs, which hints at the presence of a KREEP-bearing source region beneath Mare Nectaris. The basaltic andesite glasses have compositions that are siliceous, ferroan, alkali-rich, and moderately titaniferous; they are unlike any previously recognized lunar lithology or glass group. Their likely provenance is within the Procellarum KREEP Terrane, but they are not found within the Apollo 16 ancient regolith breccias and therefore were likely deposited at the Apollo 16 site post-Imbrium. The basaltic-andesite glasses are the most ferroan variety of KREEP yet discovered.  相似文献   

Comparison of isotope pairing and N2:Ar methods for measuring sediment denitrification—Assumption, modifications, and implications     

Bradley D. Eyre  Søren Rysgaard  Tage Dalsgaard  Peter Bondo Christensen 《Estuaries and Coasts》2002,25(6):1077-1087

Denitrification has been measured during the last few years using two different methods in particular: isotope pairing measured on a triple-collector isotopic ratio mass spectrometer and N₂:Ar ratios measured on a membrane inlet mass spectrometer (MIMS). This study compares these two techniques in short-term batch experiments. Rates obtained using the original N₂∶Ar method were up to 3 to 4 times higher than rates obtained using the isotope pairing technique due to O₂ reacting with the N₂ during MIMS analysis. Oxygen combines with N₂ within the mass spectrometer ion source forming NO⁺ which reduces the N₂ concentration. The decrease in N₂ is least at lower O₂ concentrations and since oxygen is typically consumed during incubations of sediment cores, the result is often a pseudo-increase in N₂ concentration being interpreted as denitrification activity. The magnitude of this ocygen effect may be instrument specific. The reaction of O₂ with N₂ and the subsequent decrease in N₂ was only partly correctly using an O₂ correction curve for the relationship between N₂ and O₂ concentrations. The O₂ corrected N₂∶Ar denitrification rates were lower, but still did not match the isotope pairing rates and the variability between replicates was much higher. Using a copper reduction column heated to 600°C to remove all of the O₂ from the sample before MIMS analysis resulted in comparable rates (slightly lower), and comparable variability between replicates, to the isotope pairing technique. The N₂:Ar technique determines the net N₂ production as the difference between N₂ production by denitrification and N₂ consumption by N-fixation, while N-fixation has little effect on the isotope pairing technique which determines a rate very close to the gross N₂ production. When the two different techniques were applied on the same sediment, the small difference in rates obtained by the two methods seemed to reflect N-fixation as also supported from measurements of ethylene production in acetylene enriched sediment cores. The N₂:Ar and isotope pairing techniques may be combined to provide simultaneous measurements of denitrification and N-fixation. Both techniques have several assumptions that must be met to achieve accurate rates; a number of tests are outlined that can be applied to demonstrate that these assumptions are being meet.  相似文献