Surface complexation modeling of Co(II) adsorption on mixtures of hydrous ferric oxide, quartz and kaolinite   总被引：1，自引：0，他引：1  

Christopher J. Landry  Tracy J. Lund  Soumya Das 《Geochimica et cosmochimica acta》2009,73(13):3723-7017

Co sorption was measured as a function of pH, ionic strength (0.001-0.1 M NaNO₃) and sorbate/sorbent ratio on pure quartz, HFO and kaolinite and on binary and ternary mixtures of the three solids. Sorption data measured for the pure solids were used to derive internally-consistent diffuse layer surface complexation model (DLM) stability constants for Co sorption. Co sorption on HFO could be adequately modeled over a broad range of ionic strengths and sorbate/sorbent ratios with a two variable-charge site model. Fits based on a single variable-charge site model were reasonable, but were improved by using ionic-strength dependent stability constants. A single variable-charge site model with an additional permanent ion exchange site produced the best fit to Co edges measured on kaolinite over a range of ionic strength and sorbate/sorbent ratios. These DLM fits were also improved by using ionic-strength dependent stability constants. The DLM approach could not adequately describe the slope of Co sorption edges on quartz. This study demonstrates that for accurate prediction of Co sorption over wide ranges of ionic strength and sorbate/sorbent ratio, the DLM may require ionic-strength dependent stability constants. DLM stability constants for Co sorption derived for the pure solids were used to predict sorption as a function of pH and solid concentration on binary and ternary mixtures of the three solids. Discrepancies between predictions and measurements were quantitatively similar to those observed for the pure mineral systems. Thus, a simple component additivity approach provides useful predictions of metal sorption in the mixed solid systems.  相似文献   

Stratigraphic controls on seawater intrusion and implications for groundwater management, Dominguez Gap area of Los Angeles, California, USA   总被引：1，自引：0，他引：1  

Tracy Nishikawa  A. J. Siade  E. G. Reichard  D. J. Ponti  A. G. Canales  T. A. Johnson 《Hydrogeology Journal》2009,17(7):1699-1725

Groundwater pumping has led to extensive water-level declines and seawater intrusion in coastal Los Angeles, California (USA). A SUTRA-based solute-transport model was developed to test the hydraulic implications of a sequence-stratigraphic model of the Dominguez Gap area and to assess the effects of water-management scenarios. The model is two-dimensional, vertical and follows an approximate flow line extending from the Pacific Ocean through the Dominguez Gap area. Results indicate that a newly identified fault system can provide a pathway for transport of seawater and that a stratigraphic boundary located between the Bent Spring and Upper Wilmington sequences may control the vertical movement of seawater. Three 50-year water-management scenarios were considered: (1) no change in water-management practices; (2) installation of a slurry wall; and (3) raising inland water levels to 7.6 m above sea level. Scenario 3 was the most effective by reversing seawater intrusion. The effects of an instantaneous 1-m sea-level rise were also tested using water-management scenarios 1 and 3. Results from two 100-year simulations indicate that a 1-m sea-level rise may accelerate seawater intrusion for scenario 1; however, scenario 3 remains effective for controlling seawater intrusion.  相似文献   

Lava lakes on Io: New perspectives from modeling     

Tracy K.P. Gregg  Rosaly M. Lopes 《Icarus》2008,194(1):166-172

Loki Patera (310° W, 12° N) is Io's largest patera at ∼180 km in diameter. Its morphology and distinct thermal behavior have led researchers to hypothesize that Loki Patera may either be an active lava lake that experiences periodic overturn, or a shallow depression whose floor is episodically resurfaced with thin flows. Using results from mathematical models, we suggest that a better model for Loki's behavior is the terrestrial superfast spreading East Pacific Rise (EPR), near 17°^30′ south. We propose that, like at the southern EPR, Loki Patera is underlain by a thin, persistent magma “lens” that feeds thin, temporary lava lakes within the patera. Also like the southern EPR, overspilling of the volcanic depression is rare, with most of the lava volume being emplaced via a subsurface network of lava tubes.  相似文献   

Results of Two Pumping Tests in Wisconsin Age Weathered Till in Iowa   总被引：2，自引：0，他引：2  

LaDon Jones  Tracy Lemar  Chin-Ta Tsai 《Ground water》1992,30(4):529-538

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Letter from the editors     

Alan GillespiePat Anderson  Tracy FurutaniEric Steig 《Quaternary Research》2003,59(1):1

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1-D, 2-D, and 3-D analytical solutions of unsaturated flow in groundwater     

Fred T. Tracy 《Journal of Hydrology》1995,170(1-4):199-214

An excellent tool for checking numerical models of unsaturated flow in groundwater is analytical solutions. However, because of the highly nonlinear nature of the governing partial differential equation, only a limited number of analytical solutions are available. This paper first gives some simple 1-D solutions. Next, by use of a transformation, the nonlinear partial differential equation is converted to a linear one for a specific form of the moisture content vs. pressure head and relative hydraulic conductivity vs. pressure head curves. This allows both 2-D and 3-D solutions to be derived, which is done in this paper. Finally, computations from a finite element computer program are compared with results from one of the analytical solutions to illustrate the use of the derived equations.  相似文献   

Maps as mediated seeing: Fundamentals of cartography     

Tracy Connolly 《New Zealand geographer》2007,63(3):232-233

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Natural recharge estimation and uncertainty analysis of an adjudicated groundwater basin using a regional-scale flow and subsidence model (Antelope Valley,California, USA)     

Adam Siade  Tracy Nishikawa  Peter Martin 《Hydrogeology Journal》2015,23(6):1267-1291

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Quantitative analysis of small-plastic debris on beaches in the Hawaiian Archipelago   总被引：1，自引：0，他引：1  

McDermid KJ  McMullen TL 《Marine pollution bulletin》2004,48(7-8):790-794

Small-plastic beach debris from nine coastal locations throughout the Hawaiian Archipelago was analyzed. At each beach, replicate 20 l samples of sediment were collected, sieved for debris between 1 and 15 mm in size, sorted by type, counted and weighed. Small-plastic debris occurred on all of the beaches, but the greatest quantity was found at three of the most remote beaches on Midway Atoll and Moloka'i. Of the debris analyzed, 72% by weight was plastic. A total of 19100 pieces of plastic were collected from the nine beaches, 11% of which was pre-production plastic pellets. This study documents for the first time the presence of small-plastic debris on Hawaiian beaches and corroborates estimates of the abundance of plastics in the marine environment in the North Pacific.  相似文献   

Using cytochrome P450 to monitor the aquatic environment: Initial results from regional and national surveys     

Tracy K. Collier  S.Denise Connor  Bich-Thuy L. Eberhart  Bernadita F. Anulacion  Anders Goksoyr  Usha Varanasi 《Marine environmental research》1992,34(1-4)

We are currently analyzing hepatic cytochrome P4501A and associated monooxygenase activities in fish sampled in several regional and national monitoring programs, including the National Benthic Surveillance Project of NOAA's Status and Trends Program, damage assessment studies of the Exxon Valdez oil spill, and intensive surveys of specific embayments, such as Puget Sound, Washington. Thus far, apparent contaminant-related increases in the activities of cytochrome P4501A-dependent monooxygenases have been readily measured in most test species. The results presented in this paper show that, for II species of fish, there is excellent concordance between hepatic activities of aryl hydrocarbon hydroxylase (AHH) and ethoxyresorufin-O-deethylase (EROD); moreover, levels of cytochrome P4501A determined by an enzyme-linked immunosorbent assay (ELISA) are also generally concordant with results from catalytic assays. The use of both a catalytic assay and immunoquantitation is recommended, because of the additional quality assurance provided by concurrent use of an immunoquantitation technique, which is desirable in large monitoring programs.  相似文献