Indirect Hurricane Effects on Resource Availability and Microbial Communities in a Subtropical Wetland-Estuary Transition Zone     

Clayton J. Williams  Joseph N. Boyer  Frank J. Jochem 《Estuaries and Coasts》2008,31(1):204-214

Three sequential hurricanes made landfall over the South Florida peninsula in August and September 2004. The storm systems passed north of the Everglades wetlands and northeastern Florida Bay, but indirect storm effects associated with changes in freshwater discharge during an otherwise drought year occurred across the wetland–estuary transition area. To assess the impacts of the 2004 hurricane series on hydrology, nutrients, and microbial communities in the Everglades wetlands to Florida Bay transition area, results are presented in the context of a seasonal cycle without hurricane activity (2003). Tropical activity in 2004 increased rainfall over South Florida and the study area, thereby temporarily relieving drought conditions. Not so much actual rainfall levels at the study site but more so water management practices in preparation of the hurricane threats, which include draining of an extensive freshwater canal system into the coastal ocean to mitigate inland flooding, rapidly reversed hypersalinity in the wetlands-estuary study area. Although annual discharge was comparable in both years, freshwater discharge in 2004 occurred predominantly during the late wet season, whereas discharge was distributed evenly over the 2003 wet season. Total organic carbon (TOC), ammonium ( \operatornameNH ⁺ ₄ \operatorname{NH} ^{ + }_{4} ), and soluble reactive phosphorus (SRP) concentrations increased during the hurricane series to concentrations two to five times higher than long-term median concentrations in eastern Florida Bay. Spatiotemporal patterns in these resource enrichments suggest that TOC and SRP originated from the Everglades mangrove ecotone, while \operatornameNH ⁺ ₄ \operatorname{NH} ^{ + }_{4} originated from the bay. Phytoplankton biomass in the bay increased significantly during storm-related freshwater discharge, but declined at the same time in the wetland mangrove ecotone from bloom conditions during the preceding drought. In the bay, these changes were associated with increased nanophytoplankton and decreased picophytoplankton biomass. Heterotrophic bacterial production increased in response to freshwater discharge, whereas bacterial abundance decreased. Hydrochemical and microbial changes were short-lived, and the wetland–bay transition area reverted to more typical oligotrophic conditions within 3 months after the hurricanes. These results suggest that changes in freshwater discharge after drought conditions and during the hurricane series forced the productivity and P-enriched characteristics of the wetland’s mangrove ecotone, although only briefly, to the south into Florida Bay.  相似文献   

Uranium and thorium diffusion in diopside   总被引：2，自引：0，他引：2  

James A. Van Orman  Timothy L. Grove  Nobumichi Shimizu 《Earth and Planetary Science Letters》1998,160(3-4):505-519

This paper presents new experimental data on the tracer diffusion rates of U and Th in diopside at 1 atm and 1150–1300°C. Diffusion couples were prepared by depositing a thin layer of U–Th oxide onto the polished surface of a natural diopside single crystal, and diffusion profiles were measured by ion microprobe depth profiling. For diffusion parallel to [001] the following Arrhenius relations were obtained: log₁₀D_U=(−5.75±0.98)−(418±28 kJ/mol)/2.303RT log₁₀D_Th=(−7.77±0.92)−(356±26 kJ/mol)/2.303RT. The diffusion data are used to assess the extent to which equilibrium is obtained during near fractional melting of a high-Ca pyroxene bearing mantle peridotite. We find that the diffusion rates for both elements are slow and that disequilibrium between solid and melt will occur under certain melting conditions. For near-fractional adiabatic decompression melting at ascent rates >3 cm/yr, high-Ca pyroxene will exhibit disequilibrium effects. High-Ca pyroxene will become zoned in U and Th and the melts extracted will be depleted in these incompatible elements relative to melts produced by equilibrium fractional melting. U and Th diffusivities in high-Ca pyroxene are similar, and diffusive fractionation of these elements will be limited. Numerical solutions to a dynamic melting model with diffusion-controlled chemical equilibration indicate that the activity ratio [²³⁰Th/²³⁸U] in a partial melt of spinel peridotite will be slightly less than 1 for a broad range of melting parameters. This result reinforces the already widely accepted conclusion that melting of spinel peridotite cannot account for ²³⁰Th excesses in mid-ocean ridge and ocean island basalts, and that garnet must therefore be present over part of the melting column.  相似文献   

Estimating Stable Measured Values and Detecting Anomalies in Groundwater Geochemistry Time Series Data Across the Athabasca Oil Sands Area,Canada     

Manchuk  John G.  Birks  Jean S.  McClain  Cynthia N.  Bayegnak  Guy  Gibson  John J.  Deutsch  Clayton V. 《Natural Resources Research》2021,30(2):1755-1779

Regional groundwater monitoring in the Athabasca region of Alberta, Canada, provides information on groundwater quality and geochemical changes over time, including data useful for evaluating potential impacts of industrial activity such as oil sands mining and in situ operations. Data collected from over 5000 wells from the 1950s to 2014, including 161 wells from government’s monitoring network, were used to develop and apply bootstrap techniques for the detection of changes in groundwater geochemistry over time and at specific points in time. Increasing temporal anomalies were identified in Cl, TDS, B, and naphthenic acids in the McMurray formation across 2003 and 2008, while decreasing anomalies were found for SO₄. Temporal variance for 15 indicators was quantified for a smooth bootstrap approach to arrive at stable values representative of the most recent samples taken from wells in the study area. Stable values revealed sampling bias in the Devonian, Grand Rapids, Empress, Channel Beverly, and Muriel Lake formations suggesting expansion of sampling may be necessary. Although temporal anomalies were found in the McMurray formation, sampling bias was not identified. The entropy and relative magnitude of time series were evaluated to identify candidate wells for continued observations, which consist of wells with low measurements and low entropy that are near active industry lease boundaries. Temporal anomalies, stable values, and entropy were combined into type-well information to provide plots for visual inspection and interpretation. Stable values are useful for regional mapping, for detecting future changes and trends, and for identifying areas of interest warranting further investigation.

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Efficient Multivariate Property Modeling with Seismic Data     

Erten  Oktay  Deutsch  Clayton V. 《Natural Resources Research》2021,30(6):4107-4121

Natural Resources Research - The joint modeling of the petrophysical properties (i.e., porosity, permeability) from wells in the presence of one or more seismic attributes (i.e., impedance) may be...  相似文献   

Distribution gradients of ichthyoplankton in an East African mangrove creek     

M. C. Little  P. J. Reay  S. J. Grove 《Estuarine, Coastal and Shelf Science》1988,26(6)

As part of an investigation into the role of East African mangrove creeks as fish spawning and nursery areas, nocturnal ichthyoplankton sampling was carried out at five stations in Tudor Creek, Mombasa, Kenya, from September to November 1985. Throughout the creek, the salinity was close to that of seawater at about 35‰, but from the mouth to the upper creek there were gradients of increasing temperature and turbidity, and decreasing depth and dissolved oxygen concentration. Pelagic eggs and larvae of fish considered to be creek residents and creek non-residents were distinguished. Gradients of decreasing egg and larval abundance (particularly of non-residents), and of decreasing diversity of recognized types, were apparent from the mouth towards the upper creek. Such a distribution suggests that the mangrove system is not an important spawning or development area for the earliest life-history stages of non-resident species. The existence of the gradients also has implications both for sampling at fixed stations in tidal waters, and for investigating the existence of circatidal and semilunar spawning cycles in fish.  相似文献   

Detrital thermochronologic record of burial heating and sediment recycling in the Magallanes foreland basin,Patagonian Andes          下载免费PDF全文

Julie C. Fosdick  Marty Grove  Stephan A. Graham  Jeremy K. Hourigan  Oscar Lovera  Brian W. Romans 《Basin Research》2015,27(4):546-572

The Patagonian Magallanes retroarc foreland basin affords an excellent case study of sediment burial recycling within a thrust belt setting. We report combined detrital zircon U–Pb geochronology and (U–Th)/He thermochronology data and thermal modelling results that confirm delivery of both rapidly cooled, first‐cycle volcanogenic sediments from the Patagonian magmatic arc and recycled sediment from deeply buried and exhumed Cretaceous foredeep strata to the Cenozoic depocentre of the Patagonian Magallanes basin. We have quantified the magnitude of Eocene heating with thermal models that simultaneously forward model detrital zircon (U–Th)/He dates for best‐fit thermal histories. Our results indicate that 54–45 Ma burial of the Maastrichtian Dorotea Formation produced 164–180 °C conditions and heating to within the zircon He partial retention zone. Such deep burial is unusual for Andean foreland basins and may have resulted from combined effects of high basal heat flow and high sediment accumulation within a rapidly subsiding foredeep that was floored by basement weakened by previous Late Jurassic rifting. In this interpretation, Cenozoic thrust‐related deformation deeply eroded the Dorotea Formation from ca. 5 km burial depths and may be responsible for the development of a basin‐wide Palaeogene unconformity. Results from the Cenozoic Río Turbio and Santa Cruz formations confirm that they contain both Cenozoic first‐cycle zircon from the Patagonian magmatic arc and highly outgassed zircon recycled from older basin strata that experienced burial histories similar to those of the Dorotea Formation.  相似文献   

Multivariate Categorical Modeling with Hierarchical Truncated Pluri-Gaussian Simulation     

Silva  Diogo  Deutsch  Clayton 《Mathematical Geosciences》2019,51(5):527-552

Multiple categorical variables such as mineralization zones, alteration zones, and lithology are often available for geostatistical modeling. Each categorical variable has a number of possible categorical outcomes. The current approach for numerical modeling of categorical variables is to either combine the categorical variables or to model them independently. The collapse of multiple categorical variables into a single variable with all combinations is impractical due to the large number of combinations. In some cases, lumping categorical variables is justified in terms of stationary domains; however, this decision is often due to the limitations of existing techniques. The independent modeling of each categorical variable will fail to reproduce the collocated joint categorical relationships. A methodology for the multivariate modeling of categorical variables utilizing the hierarchical truncated pluri-Gaussian approach is developed and illustrated with the Swiss Jura data set. The multivariate approach allows for improved reproduction of multivariate relationships between categorical variables.

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Roosevelt County 075: A petrologic,chemical and isotopic study of the most unequilibrated known H chondrite     

T. J. McCoy  K. Keil  R. D. Ash  A. D. Morse  C. T. Pillinger  R. Wieler  T. K. Mayeda  R. N. Clayton  P. H. Benoit  D. W. G. Sears  I. Casanova  D. W. Muenow  C. B. Moore  C. F. Lewis  I. E. Wilson 《Meteoritics & planetary science》1993,28(5):681-691

Abstract— Roosevelt County (RC) 075 was recovered in 1990 as a single 258-gram stone. Classification of this meteorite is complicated by its highly unequilibrated nature and its severe terrestrial weathering, but we favor H classification. This is supported by O isotopes and estimates of the original Fe, Ni metal content. The O isotopic composition is similar to that of a number of reduced ordinary chondrites (e.g., Cerro los Calvos, Willaroy), although RC 075 exhibits no evidence of reduced mineral compositions. Chondrule diameters are consistent with classification as an L chondrite, but large uncertainties in chondrule diameters of RC 075 and poorly constrained means of H, L and LL chondrites prevent use of this parameter for reliable classification. Other parameters are compromised by severe weathering (e.g., siderophile element abundances) or unsuitable for discrimination between unequilibrated H, L and LL chondrites (e.g., Co in kamacite, δ¹³C). Petrologic subtype 3.2± 0.1 is suggested by the degree of olivine heterogeneity, the compositions of chondrule olivines, the thermoluminescence sensitivity, the abundances and types of chondrules mapped on cathodoluminescence mosaics, and the amount of presolar SiC. The meteorite is very weakly shocked (S2), with some chondrules essentially unshocked and, thus, is classified as an H3.2(S2) chondrite. Weathering is evident by a LREE enrichment due to clay contamination, reduced levels of many siderophile elements, the almost total loss of Fe, Ni metal and troilite, and the reduced concentrations of noble gases. Some components of the meteorite (e.g., type IA chondrules, SiC) appear to preserve their nebular states, with little modification from thermal metamorphism. We conclude that RC 075 is the most unequilibrated H chondrite yet recovered and may provide additional insights into the origin of primitive materials in the solar nebula.  相似文献   

Remediation Decision‐Making and Behavioral Economics: Results of an Industry Survey          下载免费PDF全文

Wilson S. Clayton 《Ground Water Monitoring & Remediation》2017,37(4):23-33

Decision methods applied in the remediation industry were evaluated using a survey of industry practitioners, in order to assess the relative roles of quantitative decision analysis and gut intuition. Principals from the disciplines of behavioral economics and decision theory were used as a framework to evaluate remediation decision behaviors revealed by the survey. The survey was completed by 118 respondents representing academia, consultants, clients, and others. Survey questions focused on perceptions and experiences related to inputs to decisions and decision processes, as well as remediation goal setting and outcomes. The most common remediation objective cited was short‐term interim measures and the least common was no further action (NFA) with clean closure. NFA was also sparingly achieved: 33% of respondents reported zero NFA closures in their career, and an overall 15% to 20% NFA closure rate was reported among more experienced respondents. Data inputs were ranked most important to decisions, while the decision process itself was ranked lowest. Intuition‐based decision methods such as asking for a trusted opinion, rules of thumb, and meetings were all used at last twice as often as decision analysis such as discounted cash flow or probabilistic analysis. Analysis of survey responses showed that cognitive biases, including overconfidence effect and intuition bias, are present to some extent in remediation decision‐making. Practitioners are advised to be mindful of the decision‐making processes they apply, and to incorporate elements of both intuition and decision analysis, as appropriate to the decisions being made.  相似文献   

Incremental melting in the ureilite parent body: Initial composition,melting temperatures,and melt compositions     

Max Collinet  Timothy L. Grove 《Meteoritics & planetary science》2020,55(4):832-856

Ureilites are carbon‐rich ultramafic achondrites that have been heated above the silicate solidus, do not contain plagioclase, and represent the melting residues of an unknown planetesimal (i.e., the ureilite parent body, UPB). Melting residues identical to pigeonite‐olivine ureilites (representing 80% of ureilites) have been produced in batch melting experiments of chondritic materials not depleted in alkali elements relative to the Sun’s photosphere (e.g., CI, H, LL chondrites), but only in a relatively narrow range of temperature (1120 ºC–1180 ºC). However, many ureilites are thought to have formed at higher temperature (1200 ºC–1280 ºC). New experiments, described in this study, show that pigeonite can persist at higher temperature (up to 1280 ºC) when CI and LL chondrites are melted incrementally and while partial melts are progressively extracted. The melt productivity decreases dramatically after the exhaustion of plagioclase with only 5–9 wt% melt being generated between 1120 ºC and 1280 ºC. The relative proportion of pyroxene and olivine in experiments is compared to 12 ureilites, analyzed for this study, together with ureilites described in the literature to constrain the initial Mg/Si ratio of the UPB (0.98–1.05). Experiments are also used to develop a new thermometer based on the partitioning of Cr between olivine and low‐Ca pyroxene that is applicable to all ureilites. The equilibration temperature of ureilites increases with decreasing Al₂O₃ and Wo contents of pyroxene and decreasing bulk REE concentrations. The UPB melted incrementally, at different fO₂, and did not cool significantly (0 ºC–30 ºC) prior to its disruption. It remained isotopically heterogenous, but the initial concentration of major elements (SiO₂, MgO, CaO, Al₂O₃, alkali elements) was similar in the different mantle reservoirs.  相似文献