A review of water column processes influencing hypoxia in the northern Gulf of Mexico   总被引：1，自引：0，他引：1  

Michael J. Dagg  James W. Ammerman  Rainer M. W. Amon  Wayne S. Gardner  Rebecca E. Green  Steven E. Lohrenz 《Estuaries and Coasts》2007,30(5):735-752

In this review, we use data from field measurements of biogeochemical processes and cycles in the Mississippi River plume and in other shelf regions of the northern Gulf of Mexico to determine plume contributions to coastal hypoxia. We briefly review pertinent findings from these process studies, review recent mechanistic models that synthesize these processes to address hypoxia-related issues, and reinterpret current understanding in the context of these mechanistic models. Some of our conclusions are that both nitrogen and phosphorus are sometimes limiting to phytoplankton growth; respiration is the main fate of fixed carbon in the plume, implying that recycling is the main fate of nitrogen; decreasing the river nitrate loading results in less than a 1:1 decrease in organic matter sinking from the plume; and sedimenting organic matter from the Mississippi River plume can only fuel about 23% of observed coastal hypoxia, suggesting significant contributions from the Atchafalaya River and, possibly, coastal wetlands. We also identify gaps in our knowledge about controls on hypoxia, and indicate that some reinterpretation of our basic assumptions about this system is required. There are clear needs for improved information on the sources, rates, and locations of organic matter sedimentation; for further investigation of internal biogeochemical processes and cycling; for improved understanding of the rates of oxygen diffusion across the pycnocline; for identification and quantification of other sources of organic matter fueling hypoxia or other mechanisms by which Mississippi River derived organic matter fuels hypoxia; and for the development of a fully coupled physical-biogeochemical model.  相似文献   

Higher Seismic Activity During Local Night on the Raw Worldwide Earthquake Catalogue   总被引：1，自引：0，他引：1  

L. Knopoff  J. K. Gardner 《Geophysical Journal International》1972,28(3):311-313

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Export of Acidity in Drainage Water from Acid Sulphate Soils     

F.J Cook  W Hicks  E.A Gardner  G.D Carlin  D.W Froggatt 《Marine pollution bulletin》2000,41(7-12):319-326

Disturbed acid sulphate soils are potent sources of acidity in coastal waterways. Monitoring studies of the drainage water for sites at East Trinity, Cairns and Pimpama, south-east Queensland indicate that considerable acidity is found in the drainage water from these sites. Hydrogen (H⁺), ferrous (Fe²⁺) and aluminium (Al) ions are the dominant acid cations involved. When drainage water is mixed with fresh or marine waters the effect of H⁺ on acidity generation is immediate. Aluminium can release acidity on hydrolysis, while the oxidation of Fe²⁺ to Fe³⁺ both acidifies and removes dissolved oxygen from the water. Strongly acidic waters with low levels of dissolved oxygen concentration are undesirable for most forms of aquatic life. Export of acidity from acid sulphate soil is likely to have a major effect on inshore fisheries and breeding grounds especially in periods of flood following drought or periods of low rainfall, where large volumes of acidity can be flushed/leached into sensitive aquatic/marine habitats. Impacts may include low dissolved oxygen, fish kills, epizootic ulceration syndrome and damage to oysters. During the processes of oxidation and hydrolysis, iron and aluminium flocs form, that can smother benthic communities. Heavy metals are found in the drainage water at elevated levels and may also be of concern for aquatic organisms. Chronic effects such as habitat degradation, mortality of marine worms, bivalves, invasion of acid tolerant species (both plant and animal) and avoidance of habitat have been documented elsewhere. These areas require further research.  相似文献   

The caldera-forming eruption of Volcán Ceboruco, Mexico   总被引：1，自引：1，他引：0  

James E. Gardner  Steve Tait 《Bulletin of Volcanology》2000,62(1):20-33

3 of magma erupted, ∼95% of which was deposited as fall layers. During most of the deposition of P1, eruptive intensity (mass flux) was almost constant at 4–8×10⁷ kg s⁻¹, producing a Plinian column 25–30 km in height. Size grading at the top of P1 indicates, however, that mass flux waned dramatically, and possibly that there was a brief pause in the eruption. During the post-P1 phase of the eruption, a much smaller volume of magma erupted, although mass flux varied by more than an order of magnitude. We suggest that caldera collapse began at the end of the P1 phase of the eruption, because along with the large differences in mass flux behavior between P1 and post-P1 layers, there were also dramatic changes in lithic content (P1 contains ∼8% lithics; post-P1 layers contain 30–60%) and magma composition (P1 is 98% rhyodacite; post-P1 layers are 60–90% rhyodacite). However, the total volume of magma erupted during the Jala pumice event is close to that estimated for the caldera. These observations appear to conflict with models which envision that, after an eruption is initiated by overpressure in the magma chamber, caldera collapse begins when the reservoir becomes underpressurized as a result of the removal of magma. The conflict arises because firstly, the P1 layer makes up too large a proportion (∼75%) of the total volume erupted to correspond to an overpressurized phase, and secondly, the caldera volume exceeds the post-P1 volume of magma by at least a factor of three. The mismatches between model and observations could be reconciled if collapse began near the beginning of the eruption, but no record of such early collapse is evident in the tephra sequence. The apparent inability to place the Jala pumice eruptive sequence into existing models of caldera collapse, which were constructed to explain the formation of calderas much greater in volume than that at Ceboruco, may indicate that differences in caldera mechanics exist that depend on size or that a more general model for caldera formation is needed. Received: 18 November 1998 / Accepted: 23 October 1999  相似文献   

The atmospheric lead record preserved in lagoon sediments at a remote equatorial Pacific location: Palmyra Atoll, northern Line Islands     

Collen JD  Baker JA  Dunbar RB  Rieser U  Gardner JP  Garton DW  Christiansen KJ 《Marine pollution bulletin》2011,62(2):251-257

Anthropogenic lead (Pb) inputs to the atmosphere increased greatly over the past century and now dominate Pb supply to the oceans. However, the Pb content of sediments across the equatorial Pacific region is relatively unknown, and data exist only for deep sea sites where Pb deposition lags surface water inputs by up to a century. Here we present ICP-MS analyses of Pb of a core from a lagoon at Palmyra Atoll, northern Line Islands, that spans approximately the past 160 years. The non-bioturbated sediments of the euxinic lagoon, coupled with rapid rates of deposition, provide a unique fine-scale record of atmospheric Pb supply at a remote Pacific location. These first observations of historic Pb sedimentation in an atoll lagoon reveal a 63-fold increase in Pb flux to sediments during the past century and correlate directly with the North American consumption of leaded gasoline that began in 1926.  相似文献   

Commentary on Palmyra atoll     

Gardner J  Collen J  Dunbar R  Garton D 《Marine pollution bulletin》2011,62(12):2876-2877

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Computations and estimates of rate coefficients for hydrocarbon reactions of interest to the atmospheres of the outer solar system     

A.H. Laufer  E.P. Gardner  T.L. Kwok  Y.L. Yung 《Icarus》1983,56(3):560-567

The rate coefficients, including Arrhenius parameters, have been computed for a number of chemical reactions involving hydrocarbon species for which experimental data are not available and which are important in planetary atmospheric models. The techniques used to calculate the kinetic parameters include the Troe and semiempirical bond energy-bond order (BEBO) or bond strength-bond length (BSBL) methods.  相似文献   

The photoabsorption coefficients of CO and CO2 in the region 350 to 650Å     

W.S. Watson  D.T. Stewart  A.B. Gardner  M.J. Lynch 《Planetary and Space Science》1975,23(2):384-386

The photoabsorption coefficients of CO and CO₂ have been measured to ± 3% accuracy in the 350–650 Å spectral region.  相似文献   

Multi-frequency synthetic-aperture imaging with a lightweight ground penetrating radar system     

Steven K. Koppenjan  Curt M. Allen  Duane Gardner  Howard R. Wong  Hua Lee  Stephanie J. Lockwood 《Journal of Applied Geophysics》2000,43(2-4)

The detection of buried objects, particularly hazardous waste containers and unexploded ordnance (UXO), has gained significant interest in the Unites States in the late 1990s. The desire to remediate the thousands of sites worldwide has become an increasing concern and the application of radar to this problem has received renewed attention. The US Department of Energy's Special Technologies Laboratory (STL), operated by Bechtel Nevada, has developed several frequency-modulated, continuous-wave (FM-CW) ground penetrating radar (GPR) units. To meet technical requirements for higher-resolution data, STL and the University of California, Santa Barbara (UCSB) is investigating advanced GPR hardware, signal processing, and synthetic-aperture imaging with the development of an innovative system. The goal is to design and fabricate a lightweight, battery-operated unit that does not require surface contact, can be operated by a novice user, and can achieve improved resolution. The latter is accomplished by using synthetic-aperture imaging, which forms the subsurface images by fully utilizing the data sequences collectively along a scan path. We also present the backward propagation algorithm as the basic structure of the multiple-frequency tomographic imaging technique, and the conventional fast Fourier transform (FFT) method which can be described as a degenerated case of the model where the computation procedure is approximated under the narrow-beam assumption.  相似文献   

VASCULAR PLANTS OF MOUNTAIN TALUS SLOPES,MT. RAE AREA,ALBERTA, CANADA     

Linda J. Kershaw  James S. Gardner 《自然地理学》2013,34(3):218-230

The vascular flora of talus slopes in the Mt. Rae area, Canadian Rocky Mountain Front Ranges, is discussed in the context of edaphic and geomorphic conditions. Thirteen talus slopes were sampled systematically for the presence of vegetation, and vascular plants were identified to the species level. Such talus slopes are generally considered relatively sterile and too unstable for the development of distinctive flora. The presence of vegetation is usually taken as an indicator of slope stability. A total of 77 species with boreal and arctic affinities was identified. Most plants display growth forms suitable to the unstable and xeric talus substrate with Schroeter's Schuttstrecker and Schuttdecker forms being most common. Although areal coverage by plants is sparse, a large number of species with morphological characteristics suitable for the talus environment suggests that the presence of plants should not be regarded as an absolute indicator of slope stability. Rather, these plants may represent a long-term equilibrium assemblage characteristic of active talus slopes in a mountain environment.  相似文献