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At least 379 records · Page 21Linked to original sources
USGS2006

Association of polychlorinated biphenyls (PCBs) with live algae and total lipids in rivers - A field-based approach

The association of PCBs and live algal cells in rivers was studied at four locations during four seasons in two Wisconsin rivers. Positive relations between particle-associated PCBs and both chlorophyll-a and algal carbon concentrations indicated that live algal cells were a significant sorption phase for dissolved PCBs. Large Pennate diatoms (Navicula, Synedra, Pinnularia, Diatoma, and Cocconeis), or more rarely, Euglenoids (Trachelomonas sp.), dominated most sample assemblages on an algal carbon basis. These assemblages made up the highest percentage of total SOC during spring (average=50%) and lowest during summer (average=15%). At the three impounded sites, most individual PCB congeners were relatively enriched in samples characterized by: (1) high concentrations of algal carbon (as a percent of SOC), (2) algal assemblages dominated (or co-dominated) by Euglenoids, and (3) high concentrations of total lipids. Despite relatively higher masses of sorbed PCBs in the most lipid-rich samples, there was no robust correlation between total lipid content and particle-associated PCBs when aggregating all samples from the study. A possible explanation is that PCBs are associated with other structural components in live algae and (or) departure from chemical equilibrium in the river due to algal growth kinetics. A kinetic uptake model was used to calculate the mass of PCBs associated with the total organic carbon content of live algae. Based on this model, PCBs were enriched in algal cells during bloom seasons (spring and fall) compared to non-bloom seasons (summer and winter). Further, although individual PCB congener partition coefficients (log) to live algal cells (range=5.3-6.4) overlapped to those for detritus (range=3.6-7.4), PCBs tended to be enriched in detrital carbon pools during non-bloom conditions. The larger range of estimated PCB partition coefficients for detritus likely reflects the more heterogeneous nature of this material compared to live algal cells.

Science of the Total Environment↗
USGS2006

Prolactin and growth hormone in fish osmoregulation

Prolactin is an important regulator of multiple biological functions in vertebrates, and has been viewed as essential to ion uptake as well as reduction in ion and water permeability of osmoregulatory surfaces in freshwater and euryhaline fish. Prolactin-releasing peptide seems to stimulate prolactin expression in the pituitary and peripheral organs during freshwater adaptation. Growth hormone, a member of the same family of hormones as prolactin, promotes acclimation to seawater in several teleost fish, at least in part through the action of insulin-like growth factor I. In branchial epithelia, development and differentiation of the seawater-type chloride cell (and their underlying biochemistry) is regulated by GH, IGF-I, and cortisol, whereas the freshwater-type chloride cell is regulated by prolactin and cortisol. In the epithelia of gastrointestinal tract, prolactin induces cell proliferation during freshwater adaptation, whereas cortisol stimulates both cell proliferation and apoptosis. We propose that control of salinity acclimation in teleosts by prolactin and growth hormone primarily involves regulation of cell proliferation, apoptosis, and differentiation (the latter including upregulation of specific ion transporters), and that there is an important interaction of these hormones with corticosteroids. ?? 2005 Elsevier Inc. All rights reserved.

General and Comparative Endocrinology↗
USGS2003

Applicability of tetrazolium salts for the measurement of respiratory activity and viability of groundwater bacteria

A study was undertaken to measure aerobic respiration by indigenous bacteria in a sand and gravel aquifer on western Cape Cod, MA using tetrazolium salts and by direct oxygen consumption using gas chromatography (GC). In groundwater and aquifer slurries, the rate of aerobic respiration calculated from the direct GC assay was more than 600 times greater than that using the tetrazolium salt 2-(4-iodophenyl)-3-(4-nitrophenyl)-5-phenyl tetrazolium chloride (INT). To explain this discrepancy, the toxicity of INT and two additional tetrazolium salts, sodium 3′-[1-(phenylamino)-carbonyl]-3,4-tetrazolium]-bis(4-methoxy-6-nitro) benzenesulfonic acid hydrate (XTT) and 5-cyano-2,3-ditolyl tetrazolium chloride (CTC), to bacterial isolates from the aquifer was investigated. Each of the three tetrazolium salts was observed to be toxic to some of the groundwater isolates at concentrations normally used in electron transport system (ETS) and viability assays. For example, incubation of cells with XTT (3 mM) caused the density of four of the five groundwater strains tested to decline by more than four orders of magnitude. A reasonable percentage (>57%) of cells killed by CTC and INT contained visible formazan crystals (the insoluble, reduced form of the salts) after 4 h of incubation. Thus, many of the cells reduced enough CTC or INT prior to dying to be considered viable by microscopic evaluation. However, one bacterium ( Pseudomonas fluorescens ) that remained viable and culturable in the presence of INT and CTC, did not incorporate formazan crystals into more than a few percent of cells, even after 24 h of incubation. This strain would be considered nonviable based on traditional tetrazolium salt reduction assays. The data show that tetrazolium salt assays are likely to dramatically underestimate total ETS activity in groundwater and, although they may provide a reasonable overall estimate of viable cell numbers in a community of groundwater bacteria, some specific strains may be falsely considered nonviable by this assay due to poor uptake or reduction of the salts.

Massachusetts↗
USGS2002

Possible importance of algal toxins in the Salton Sea, California

In response to wildlife mortality including unexplained eared grebe ( Podiceps nigricollis ) die-off events in 1992 and 1994 and other mortality events including large fish kills, a survey was conducted for the presence of algal toxins in the Salton Sea. Goals of this survey were to determine if and when algal toxins are present in the Salton Sea and to describe the phytoplankton composition during those times. A total of 29 samples was collected for toxicity analysis from both nearshore and midlake sites visited biweekly from January to December 1999. Dinoflagellates and diatoms dominated most samples, but some were dominated by a prymnesiophyte ( Pleurochrysis pseudoroscoffensis ) or a raphidophyte ( Chattonella marina ). Several types of blooms were observed and sampled. The dinoflagellate Gyrodinium uncatenum formed an extensive, dense (up to 310 000 cells ml −1 ) and long-lasting bloom during the winter in 1999. A coccolithophorid, Pleurochrysis pseudoroscoffensis , occurred at high densities in surface films and nearshore areas during the spring and summer of 1999. These surface films also contained high densities of one or two other species (an unidentified scrippsielloid, Heterocapsa niei , Chattonella marina ). Localized blooms were also observed in the Salton Sea. An unknown small dinoflagellate reached high densities (110 000 cells ml −1 ) inside Varner Harbor, and an unidentified species of Gymnodinium formed a dense (270 000 cells ml −1 ) band along part of the southern shoreline during the summer. Three species known to produce toxins in other systems were found. Protoceratium reticulatum (= Gonyaulax grindleyi ) and Chattonella marina were found in several samples taken during summer months, and Prorocentrum minimum was found in low densities in several samples. Extracts of most samples, including those containing known toxic species, showed a low level (<10% mortality across all concentrations) of activity in the brine shrimp lethality assay and were not considered toxic. All sample extracts tested in the mouse bioassay showed no activity. One sample extract taken from the bloom of the small dinoflagellate was highly active (100% mortality across all concentrations) in the brine shrimp lethality assay, but the active material could not be isolated. While dense algal blooms are common at the Salton Sea, no evidence gathered in this study suggests that algal toxins are present within phytoplankton cells; however, toxins actively excreted by cells may have been missed. Blooms of phytoplankton likely contribute to wildlife mortality at the Salton Sea. Possible mechanisms including intoxication due to ingestion of feathers in grebes and waterlogging caused by changes in surface tension are discussed.

California↗
USGS2010

Estimation of aquifer scale proportion using equal area grids: assessment of regional scale groundwater quality

The proportion of an aquifer with constituent concentrations above a specified threshold (high concentrations) is taken as a nondimensional measure of regional scale water quality. If computed on the basis of area, it can be referred to as the aquifer scale proportion. A spatially unbiased estimate of aquifer scale proportion and a confidence interval for that estimate are obtained through the use of equal area grids and the binomial distribution. Traditionally, the confidence interval for a binomial proportion is computed using either the standard interval or the exact interval. Research from the statistics literature has shown that the standard interval should not be used and that the exact interval is overly conservative. On the basis of coverage probability and interval width, the Jeffreys interval is preferred. If more than one sample per cell is available, cell declustering is used to estimate the aquifer scale proportion, and Kish's design effect may be useful for estimating an effective number of samples. The binomial distribution is also used to quantify the adequacy of a grid with a given number of cells for identifying a small target, defined as a constituent that is present at high concentrations in a small proportion of the aquifer. Case studies illustrate a consistency between approaches that use one well per grid cell and many wells per cell. The methods presented in this paper provide a quantitative basis for designing a sampling program and for utilizing existing data.

Water Resources Research↗
USGS2020

A rasterized building footprint dataset for the United States

Microsoft released a U.S.-wide vector building dataset in 2018. Although the vector building layers provide relatively accurate geometries, their use in large-extent geospatial analysis comes at a high computational cost. We used High-Performance Computing (HPC) to develop an algorithm that calculates six summary values for each cell in a raster representation of each U.S. state, excluding Alaska and Hawaii: (1) total footprint coverage, (2) number of unique buildings intersecting each cell, (3) number of building centroids falling inside each cell, and area of the (4) average, (5) smallest, and (6) largest area of buildings that intersect each cell. These values are represented as raster layers with 30 m cell size covering the 48 conterminous states. We also identify errors in the original building dataset. We evaluate precision and recall in the data for three large U.S. urban areas. Precision is high and comparable to results reported by Microsoft while recall is high for buildings with footprints larger than 200 m2 but lower for progressively smaller buildings.

Scientific Data↗
USGS2001

N2-dependent growth and nitrogenase activity in the metal-metabolizing bacteria, Geobacter and Magnetospirillum species

Cells of Geobacter metallireducens, Magnetospirillum strain AMB-1, Magnetospirillum magnetotacticum and Magnetospirillum gryphiswaldense showed N2-dependent growth, the first anaerobically with Fe(lll) as the electron acceptor, and the latter three species micro-aerobically in semi-solid oxygen gradient cultures. Cells of the Magnetospirillum species grown with N2 under microaerobic conditions were magnetotactic and therefore produced magnetosomes. Cells of Geobacter metallireducens reduced acetylene to ethylene (11.5 ?? 5.9nmol C2H4 produced min-1 mg-1 cell protein) while growing with Fe(lll) as the electron acceptor in anaerobic growth medium lacking a fixed nitrogen source. Cells of the Magnetospirillum species, grown in a semi-solid oxygen gradient medium, also reduced acetylene at comparable rates. Uncut chromosomal and fragments from endonuclease-digested chromosomal DNA from these species, as well as Geobacter sulphurreducens organisms, hybridized with a nifHDK probe from Rhodospirillum rubrum, indicating the presence of these nitrogenase structural genes in these organisms. The evidence presented here shows that members of the metal-metabolizing genera, Geobacter and Magnetospirillum, fix atmospheric dinitrogen.

Environmental Microbiology↗
USGS2000

Controlled field study on the use of nitrate and oxygen for bioremediation of a gasoline source zone

Controlled releases of unleaded gasoline were utilized to evaluate the biotransformation of the soluble aromatic hydrocarbons (benzene, toluene, ethylbenzene, xylene isomers, trimethylbenzene isomers, and naphthalene) within a source zone using nitrate and oxygen as electron acceptors. Experiments were conducted within two 2 m ?? 2 m ?? 3.5 m deep sheet-piling cells. In each treatment cell, a gasoline-contaminated zone was created below the water table. Groundwater amended with electron acceptors was then flushed continuously through the cells for 174 day. Electron-acceptor utilization and hydrocarbon-metabolite formation were noted in both cells, indicating that some microbial activity had been induced in response to flushing. Relative to the cell residence time, nitrate utilization was slow and aromatic-hydrocarbon mass losses in response to microaerophilic dissolved oxygen addition were not obvious under these in situ conditions. There was relatively little biotransformation of the aromatic hydrocarbons over the 2-m flow path monitored in this experiment. A large denitrifying population capable of aromatic hydrocarbon biotransformation failed to develop within the gasoline source zone over a 14-mo period of nitrate exposure.

Bioremediation Journal↗
USGS2009

A grid-doubling finite-element technique for calculating dynamic three-dimensional spontaneous rupture on an earthquake fault

We present a new finite-element technique for calculating dynamic 3-D spontaneous rupture on an earthquake fault, which can reduce the required computational resources by a factor of six or more, without loss of accuracy. The grid-doubling technique employs small cells in a thin layer surrounding the fault. The remainder of the modelling volume is filled with larger cells, typically two or four times as large as the small cells. In the resulting non-conforming mesh, an interpolation method is used to join the thin layer of smaller cells to the volume of larger cells. Grid-doubling is effective because spontaneous rupture calculations typically require higher spatial resolution on and near the fault than elsewhere in the model volume. The technique can be applied to non-planar faults by morphing, or smoothly distorting, the entire mesh to produce the desired 3-D fault geometry. Using our FaultMod finite-element software, we have tested grid-doubling with both slip-weakening and rate-and-state friction laws, by running the SCEC/USGS 3-D dynamic rupture benchmark problems. We have also applied it to a model of the Hayward fault, Northern California, which uses realistic fault geometry and rock properties. FaultMod implements fault slip using common nodes, which represent motion common to both sides of the fault, and differential nodes, which represent motion of one side of the fault relative to the other side. We describe how to modify the traction-at-split-nodes method to work with common and differential nodes, using an implicit time stepping algorithm.

Geophysical Journal International↗
USGS2006

Comparison of local grid refinement methods for MODFLOW

Many ground water modeling efforts use a finite-difference method to solve the ground water flow equation, and many of these models require a relatively fine-grid discretization to accurately represent the selected process in limited areas of interest. Use of a fine grid over the entire domain can be computationally prohibitive; using a variably spaced grid can lead to cells with a large aspect ratio and refinement in areas where detail is not needed. One solution is to use local-grid refinement (LGR) whereby the grid is only refined in the area of interest. This work reviews some LGR methods and identifies advantages and drawbacks in test cases using MODFLOW-2000. The first test case is two dimensional and heterogeneous; the second is three dimensional and includes interaction with a meandering river. Results include simulations using a uniform fine grid, a variably spaced grid, a traditional method of LGR without feedback, and a new shared node method with feedback. Discrepancies from the solution obtained with the uniform fine grid are investigated. For the models tested, the traditional one-way coupled approaches produced discrepancies in head up to 6.8% and discrepancies in cell-to-cell fluxes up to 7.1%, while the new method has head and cell-to-cell flux discrepancies of 0.089% and 0.14%, respectively. Additional results highlight the accuracy, flexibility, and CPU time trade-off of these methods and demonstrate how the new method can be successfully implemented to model surface water-ground water interactions. Copyright ?? 2006 The Author(s).

Conference Paper↗
USGS2004

Comparison of fluorescence microscopy and solid-phase cytometry methods for counting bacteria in water

Total direct counts of bacterial abundance are central in assessing the biomass and bacteriological quality of water in ecological and industrial applications. Several factors have been identified that contribute to the variability in bacterial abundance counts when using fluorescent microscopy, the most significant of which is retaining an adequate number of cells per filter to ensure an acceptable level of statistical confidence in the resulting data. Previous studies that have assessed the components of total-direct-count methods that contribute to this variance have attempted to maintain a bacterial cell abundance value per filter of approximately 10 6 cells filter -1 . In this study we have established the lower limit for the number of bacterial cells per filter at which the statistical reliability of the abundance estimate is no longer acceptable. Our results indicate that when the numbers of bacterial cells per filter were progressively reduced below 10 5 , the microscopic methods increasingly overestimated the true bacterial abundance (range, 15.0 to 99.3%). The solid-phase cytometer only slightly overestimated the true bacterial abundances and was more consistent over the same range of bacterial abundances per filter (range, 8.9 to 12.5%). The solid-phase cytometer method for conducting total direct counts of bacteria was less biased and performed significantly better than any of the microscope methods. It was also found that microscopic count data from counting 5 fields on three separate filters were statistically equivalent to data from counting 20 fields on a single filter.

Applied and Environmental Microbiology↗
USGS2017

In-vitro replication of Chelonid herpesvirus 5 in organotypic skin cultures from Hawaiian green turtles (Chelonia mydas)

Fibropapillomatosis (FP) is a tumor disease of marine turtles associated with Chelonid herpesvirus 5 (ChHV5) that has historically been refractory to growth in tissue culture. Here, we show for the first time de novo formation of ChHV5-positive intranuclear inclusions in cultured green turtle cells, which is indicative for active lytic replication of the virus. The minimal requirements to achieve lytic replication in cultured cells included 1) either in-vitro culturing of ChHV5-positive tumor biopsies (plugs) or organotypic cultures (rafts) consisting of ChHV5-positive turtle fibroblasts in collagen rafts seeded with turtle keratinocytes and 2) keratinocyte maturation induced by raising raft or biopsy cultures to the air-liquid interface. Virus growth was confirmed by detailed electron microscopic studies revealing intranuclear sun-shaped capsid factories, tubules, various stages of capsid formation, nuclear export by budding into the perinuclear space, tegumentation, and envelopment to complete de novo virus production. Membrane synthesis was also observed as a sign for active viral replication. Interestingly, cytoplasmic particles became associated with keratin filaments, a feature not seen in conventional monolayer cell cultures where most studies of herpesvirus replication have been performed. Our findings draw a rich and realistic picture of ChHV5 replication in cells derived from its natural host and may be crucial not only to better understand ChHV5 circulation but also to eventually complete Koch's postulates for FP. Moreover, the principles described here may serve as model to culture other viruses that are resistant to replication in conventional cell culture.

Hawai'i↗
USGS1991

Nature and time course of acclimation to aluminum in juvenile brook trout ( Salvelinus fontinalis ): II. Gill histology

Gill samples from juvenile brook trout ( Salvelinus fontinalis ) acclimated to low-level aluminum at pH 5.2 showed severe damage by day 4, with necrosis and fusion of secondary lamellae and hyperplasia and hypertrophy of mucous cells. Over the following 20&ensp;d, there was a continual process of repair with proliferation and hypertrophy of mucous cells. Qualitative analysis of gill samples plus physiology and mortality data collected in a companion study indicated progressive development (by day 10 onward) of increasing acclimation to Al. Quantitative analysis of gill samples on day 13 showed that mucous cell volume density had tripled and mucous cell area had doubled in Al-exposed fish compared with control fish. A lamellar fusion index showed evidence of fusion in Al-exposed fish by day 4 with recovery to nearly control levels by day 13. Physiological disturbances appear to be directly related to the histological changes observed in the gill epithelium. At the cellular level, changes in either mucous cell production and secretion or changes in mucus chemistry contribute, in part, to acclimation to Al.

Canadian Journal of Fisheries and Aquatic Sciences↗
USGS2005

Characteristics of seasonal vegetation cover in the conterminous USA

A data set of the fractional green vegetation cover (FGREEN) for the Conterminous USA was evaluated for regional and seasonal variation. The value of FGREEN was derived monthly for the three most dominant land cover classes per 20 km by 20 km grid cell within the study area. At this grid cell resolution (comprised of 400 1-km pixels), 97 percent of the grid cells included three or fewer land cover classes. FGREEN was found to vary regionally due to local land cover and climate variations. FGREEN was found significantly different between one or more of the land cover classes, for one or more months, in 58 percent of the grid cells included in the study. Monthly FGREEN values for the land cover classes vary sufficiently between the land cover classes to warrant monthly FGREEN data for each of the one to three most dominant land cover classes per grid cell .

Photogrammetric Engineering and Remote Sensing↗
USGS1997

Bactericidal activity of juvenile chinook salmon macrophages against Aeromonas salmonicida after exposure to live or heat-killed Renibacterium salmoninarum or to soluble proteins produced by R. salmoninarum

Macrophages isolated from the anterior kidney of juvenile chinook salmon Oncorhynchus tshawytscha in 96-well microtiter plates were exposed for 72 h to 0, 10 5 , or 10 6 live or heat-killed Renibacterium salmoninarum cells per well or to 0, 0.1, 1.0, or 10 μg/mL of R. salmoninarum soluble proteins. After treatment, the bactericidal activity of the macrophages against Aeromonas salmonicida was determined by a colorimetric assay based on the reduction of the tetrazolium dye MTT to formazan by viable bacteria. The MTT assay was modified to allow estimation of the percentage of bacteria killed by reference to a standard curve relating the number of bacteria added to microtiter wells to absorbance by formazan at 600 nm. The live and heatkilled R. salmoninarum treatments significantly ( P < 0.001) increased killing of A. salmonicida by chinook salmon macrophages. In each of the five trials, significantly ( P < 0.05) greater increases in killing occurred after exposure to 10 5 R. salmoninarum cells than to 10 6 R. salmoninarum cells per well. In contrast, treatment of macrophages with 10 ug/mL R. salmoninarum soluble proteins significantly ( P < 0.001) decreased killing of A. salmonicida , but treatment with lower doses did not. These results show that the bactericidal activity of chinook salmon macrophages is stimulated by exposure to R. salmoninarum cells at lower dose levels but inhibited by exposure to R. salmoninarum cells or soluble proteins at higher dose levels.

Journal of Aquatic Animal Health↗
USGS1997

A monoclonal antibody to inclusion body disease of cranes virus enabling specific immunohistochemistry and competitive ELISA

Inclusion body disease of cranes (IBDC) herpesvirus kills some infected cranes and persists in convalescent animals. To enable further study and rapid identification of carrier animals, we developed a monoclonal antibody (MAb) to IBDC virus and used it in immunohistochemistry and a competitive enzyme-linked immunosorbent assay (ELISA). We used conventional techniques to make murine MAbs directed against IBDC virus purified from infected duck embryo cells. Hybridomas reacting in an ELISA with IBDC virus but not uninfected duck embryo cells were characterized by radioimmunoprecipitation, in situ immunohistochemistry, and competitive ELISA with neutralizing and nonneutralizing crane sera. MAb 2C11 immunoprecipitated 59-, 61-, and 110-kD proteins from IBDC virus-infected but not uninfected cells and stained glutaraldehyde-fixed IBDC virus plaques but not surrounding uninfected duck embryo cells in vitro. Antibody 2C11 did not react with duck embryo cells infected with falcon herpesvirus, psittacine herpesvirus, infectious laryngotracheitis, pigeon herpesvirus, or duck plague virus. A competitive ELISA using antibody 2C11 identified most sera that were positive in the neutralization test. This antibody will be useful in further characterizing IBDC virus, its pathogenesis, and its natural history.

Avian Diseases↗
USGS2002

Documentation and analysis of a geographic information system application for combining data layers, using nonpoint-source pollution as an example

A geographical information system application has been developed that allows scientists to combine multiple data layers into a single data layer. This application provides an effective tool for identifying areas where the potential effect of the combination of data layers may be greater than any single data layer. Such a tool is useful in studying an activity that cannot be measured directly. Scientists wanting to identify areas where an activity may have the greatest effect can identify factors that directly or indirectly reflect the effect of the activity being studied. When combined, these factors would identify areas where the potential for the activity to have an effect are greatest. The data layers used to develop the single data layer determine the activity addressed by the application?the application was developed to identify areas where the potential for nonpoint-source pollution to affect areas of Indiana is greater relative to other areas in Indiana. To evaluate the potential in other states or areas, data layers for those states or areas would be used. To address a different activity, even activities not related to water resources, data layers that directly or indirectly reflect the effects of the activity being studied would be used in the application. The application was developed using Environmental System Research Institute's ArcView geographical information system and the ArcView extension, Spatial Analyst. To use the application, the user selects data layers related to the activity being studied, describes the variability of a data element between geographic areas on each data layer, assigns a relative importance factor to each data layer, and focuses the output by identifying a watershed of interest. The application then assigns a rank value to the features within each data layer on the basis of the spatial variation of the data layer. The data layers are converted to grids. The values of the grid cells are the product of the rank values and the importance factors. The cells for each data layer are combined to form a single grid. The combination is summarized to describe the spatial variation for the watershed of interest. The combined data layer does not show the actual potential effect of the selected factors but rather the relative difference in the potential effect among areas when all data layers are considered. An analysis of the application indicates that the selected data layers to be combined should be at the greatest spatial resolution possible; however, all data layers do not have to be at the same spatial resolution. The spatial variation of the data layers should be adequately defined. The size of each grid cell should be small enough to maintain the spatial definition of smaller features within the data layers. The most accurate results are shown to occur when the values for the grid cells representing the individual data layers are summed and the mean of the summed grid-cell values is used to describe the watershed of interest.

Indiana↗
USGS2002

MODFLOW-2000, the U.S. Geological Survey modular ground-water model -- Documentation of the Model-Layer Variable-Direction Horizontal Anisotropy (LVDA) capability of the Hydrogeologic-Unit Flow (HUF) package

This report documents the model-layer variable-direction horizontal anisotropy (LVDA) capability of the Hydrogeologic-Unit Flow (HUF) Package of MODFLOW-2000. The LVDA capability allows the principal directions of horizontal anisotropy to be different than the model-grid row and column directions, and for the directions to vary on a cell-by-cell basis within model layers. The HUF Package calculates effective hydraulic properties for model grid cells based on hydraulic properties of hydrogeologic units with thicknesses defined independently of the model layers. These hydraulic properties include, among other characteristics, hydraulic conductivity and a horizontal anisotropy ratio. Using the LVDA capability, horizontal anisotropy direction is defined for model grid cells within which one or more hydrogeologic units may occur. For each grid cell, the HUF Package calculates the effective horizontal hydraulic conductivity along the primary direction of anisotropy using the hydrogeologic-unit hydraulic conductivities, and calculates the effective horizontal hydraulic conductivity along the orthogonal anisotropy direction using the effective primary direction hydraulic conductivities and horizontal anisotropy ratios. The direction assigned to the model layer effective primary hydraulic conductivity is specified using a new data set defined by the LVDA capability, when active, to calculate coefficients needed to solve the ground-water flow equation. Use of the LVDA capability is illustrated in four simulation examples, which also serve to verify hydraulic heads, advective-travel paths, and sensitivities calculated using the LVDA capability. This version of the LVDA capability defines variable-direction horizontal anisotropy using model layers, not the hydrogeologic units defined by the HUF Package. This difference needs to be taken into account when designing model layers and hydrogeologic units to produce simulations that accurately represent a given field problem. This might be a reason, for example, to make model layer boundaries coincide with hydrogeologic-unit boundaries in all or part of a model grid.

Open-File Report↗