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71.
Katherine C. Filippino Peter W. Bernhardt Margaret R. Mulholland 《Estuaries and Coasts》2009,32(3):410-424
To determine the effects of the Chesapeake Bay outflow plume on the coastal ocean, nutrient concentrations and climatology
were evaluated in conjunction with nitrogen (N) and carbon (C) uptake rates during a 3-year field study. Sixteen cruises included
all seasons and captured high- and low-flow freshwater input scenarios. Event-scale disturbances in freshwater flow and wind
speed and direction strongly influenced the location and type of plume present and thus the biological uptake of N and C.
As expected, volumetric primary productivity rates did not always correlate with chlorophyll a concentrations, suggesting that high freshwater flow does not translate into high productivity in the coastal zone; rather,
high productivity was observed during periods where recycling processes may have dominated. Results suggest that timing of
meteorological events, with respect to upwelling or downwelling favorable conditions, plays a crucial role in determining
the impact of the estuarine plume on the coastal ocean. 相似文献
72.
73.
Margaret A. McManus Jeff C. Sevadjian Kelly J. Benoit-Bird Olivia M. Cheriton Amanda H. V. Timmerman Chad M. Waluk 《Estuaries and Coasts》2012,35(4):1119-1127
Thin layers of plankton have been documented in a wide variety of environments. The growing body of observations indicates that these features are a critical component of marine ecosystem dynamics and functioning. In the past two decades, much of the research on thin layers was undertaken in temperate coastal waters. Here, we report the first known observations of thin layers of phytoplankton in tropical Hawaiian waters. We conducted an overnight shipboard study during which time we made high-resolution observations of physical and optical structure in the water column. During the overnight cruise, we observed the greatest number of thin layers in the early evening hours when thermal stratification was strongest and most persistent due to a combination of warm air and surface water, as well as light winds. A comparison of these observations with those from temperate regions leads us to hypothesize that the nature and persistence of the physical structure is very important in determining the persistence of thin layered structures. Because plankton biomass is generally lower in tropical regions, the heterogeneous aggregation of food in thin subsurface layers may be more critical to the marine ecosystem than it is in temperate regions where plankton are generally more abundant. 相似文献
74.
Adrian Spence David J. Mcnally Margaret V. McCaul Brett Paull 《Geochimica et cosmochimica acta》2011,75(10):2571-2581
Soil microbial biomass is a primary source of soil organic carbon (SOC) and therefore plays a fundamental role in carbon and nitrogen cycling. However, little is known about the fate and transformations of microbial biomass in soil. Here we employ HR-MAS NMR spectroscopy to monitor 13C and 15N labeled soil microbial biomass and leachate degradation over time. As expected, there is a rapid loss of carbohydrate structures. However, diffusion edited HR-MAS NMR data reveals that macromolecular carbohydrates are more resistant to degradation and are found in the leachate. Aromatic components survive as dissolved species in the leachate while aliphatic components persist in both the biomass and leachate. Dissolved protein and peptidoglycan accumulate in the leachate and recalcitrant amide nitrogen and lipoprotein persists in both the degraded biomass and leachate. Cross-peaks that appear in 1H-15N HR-MAS NMR spectra after degradation suggest that specific peptides are either selectively preserved or used for the synthesis of unknown structures. The overall degradation pathways reported here are similar to that of decomposing plant material degraded under similar conditions suggesting that the difference between recalcitrant carbon from different sources is negligible after decomposition. 相似文献
75.
A method to estimate stream conveyance losses, including stream bank seepage and evapotranspiration from riparian areas, was developed for the Truckee River in California and Nevada (USA). Aquifer diffusivity is the primary variable required to compute aquifer head and seepage. Head and seepage conceptual models developed in previous studies were calibrated using stream stage and aquifer head at five sites along the Truckee River. The equations for head require numerical convolution to solve. It was found that head is insensitive to diffusivity and a single value for diffusivity provides good results at all study sites. Also, because releases from storage are usually prescribed as a step increase in flow for a given period of time followed by a step decrease in flow, an analytic solution for volume of seepage can be used in place of numerical convolution. Under typical operating conditions, seepage volume represents a small fraction of the total reservoir releases. Uncertainty in seepage estimates can be reduced with increased accuracy in hydraulic conductivity. This work demonstrates a valuable technique to estimate conveyance losses under natural and managed stream flow. 相似文献
76.
Katherine C. Filippino Margaret R. MulhollandPeter W. Bernhardt 《Estuarine, Coastal and Shelf Science》2011
Nutrient concentrations, primary productivity, and nitrogen uptake rates were measured in coastal waters of the Mid-Atlantic Bight over a two-year period that included measurements from all four seasons. In order to assess carbon productivity and nitrogen demand within the context of the physical environment, the region was divided into three distinct hydrographic regimes: the Chesapeake and Delaware Bay outflow plumes (PL), the southern Mid-Atlantic shelf influenced by the Gulf Stream (SS), and the mid-shelf area to the north of the Chesapeake Bay mouth (MS). Annual areal rates of total nitrogen (N) uptake were similar across all regions (10.9 ± 2.1 mol N m−2 y−1). However, annual areal rates of net primary productivity were higher in the outflow plume region (43 mol C m−2 y−1), than along the Mid-Atlantic shelf and in areas influenced by the Gulf Stream (41 and 34 mol C m−2 y−1, respectively). Rates of net primary productivity were not well correlated with Chl a concentrations and were uncoupled with net N uptake rates. Seasonally averaged annual areal rates of net primary productivity for the Mid-Atlantic Bight measured in this study were higher than those calculated in previous decades and provide important validation information for biogeochemical models and satellite remote sensing algorithms developed for the region. 相似文献
77.
Margaret Armstrong Aziz Ndiaye Rija Razanatsimba Alain Galli 《Mathematical Geosciences》2013,45(2):165-182
Having a large number of geostatistical simulations of a mineral or petroleum deposit provides a better idea of its upside potential and downside risk; however, large numbers of simulated realizations of a deposit may pose computational difficulties in subsequent decision-making phases. Hence, depending on the specific case, there can be a need to select a representative subset of conditionally simulated deposit realizations. This paper examines and extends an approach developed by the stochastic optimization community based on stochastic mathematical programming with recourse and is discussed here in the context of mineral deposits while it is possibly suitable for other earth science applications. The approach is based on measuring the “distance” between simulations and the introduced distance measure between simulated realizations of a mineral deposit is based on the metal above a given set of cutoff grades while a pre-existing mine design is available. The approach is tested on 100 simulations of the Walker Lake data with promising results. 相似文献
78.
Jay Parker Gregory Lyzenga Charles Norton Cinzia Zuffada Margaret Glasscoe John Lou Andrea Donnellan 《Pure and Applied Geophysics》2008,165(3-4):497-521
GeoFEST (Geophysical Finite Element Simulation Tool) is a two- and three-dimensional finite element software package for the modeling of solid stress and strain in geophysical and other continuum domain applications. It is one of the featured high-performance applications of the NASA QuakeSim project. The program is targeted to be compiled and run on UNIX systems, and is running on diverse systems including sequential and message-passing parallel systems. Solution to the elliptical partial differential equations is obtained by finite element basis sampling, resulting in a sparse linear system primarily solved by conjugate gradient iteration to a tolerance level; on sequential systems a Crout factorization for the direct inversion of the linear system is also supported. The physics models supported include isotropic linear elasticity and both Newtonian and power-law viscoelasticity, via implicit quasi-static time stepping. In addition to triangular, quadrilateral, tetrahedral and hexahedral continuum elements, GeoFEST supports split-node faulting, body forces, and surface tractions. This software and related mesh refinement strategies have been validated on a variety of test cases with rigorous comparison to analytical solutions. These include a box-shaped domain with imposed motion on one surface, a pair of strike slip faults in stepover arrangement, and two community-agreed benchmark cases: a strike slip fault in an enclosing box, and a quarter-domain circular fault problem. Scientific applications of the code include the modeling of static and transient co- and post-seismic earth deformation, Earth response to glacial, atmospheric and hydrological loading, and other scenarios involving the bulk deformation of geologic media. 相似文献
79.
临界转换的早期预警信号 总被引:1,自引:0,他引:1
Marten Scheffer George Sugihara Jordi Bascompte Victor Brovkin Vasilis Dakos Hermann Held Max Rietkerk 李迎春 闫伟 蒋长胜 《国际地震动态》2009,(9):1-14
从生态系统到金融市场和气候在内的很多复杂动力系统,都会有临界点,在这样的点上系统可能会发生突变,从而演变到一个对立的动力模式上。在这样的临界点到达之前对其进行预测极为困难,但是现在,不同科学领域的研究工作表明,普遍性的早期预警信号有迹可循。对一系列不同类型的系统来说,这些信号会指示是否正在趋近一个临界阈值。 相似文献
80.
Margaret M. Dekshenieks Eileen E. Hofmann John M. Klinck Eric N. Powell 《Estuaries and Coasts》2000,23(5):593-610
Three models are combined to investigate the effects of changes in environmental conditions on the population structure of the Eastern oyster,Crassostrea virginica. The first model, a time-dependent model of the oyster population as described in Powell et al. (1992, 1994, 1995a,b, 1996, 1997) and Hofmann et al. (1992, 1994, 1995), tracks the distribution, development, spawning, and mortality of sessile oyster populations. The second model, a time-dependent larval growth model as described in Dekshenieks et al. (1993), simulates larval growth and mortality. The final model, a finite element hydrodynamic model, simulates the circulation in Galveston Bay, Texas. The coupled post-settlement-larval model (the oyster model) runs within the finite element grid at locations that include known oyster reef habitats. The oyster model was first forced with 5 yr of mean environmental conditions to provide a reference simulation for Galveston Bay. Additional simulations considered the effects of long-term increases and decreases in freshwater inflow and temperature, as well as decreases in food concentration and total seston on Galveston Bay oyster populations. In general, the simulations show that salinity is the primary environmental factor controling the spatial extent of oyster distribution within the estuary. Results also indicate a need to consider all environmental factors when attempting to predict the response of oyster populations; it is the superposition of a combination of these factors that determines the state of the population. The results from this study allow predictions to be made concerning the effects of environmental change on the status of oyster populations, both within Galveston Bay and within other estuarine systems supporting oyster populations. 相似文献