Geology topics

J.L. Robinson

Publications and source records attributed to J.L. Robinson.

4 recordsLinked to original sources

USGS2016

A fractured rock geophysical toolbox method selection tool

Geophysical technologies have the potential to improve site characterization and monitoring in fractured rock, but the appropriate and effective application of geophysics at a particular site strongly depends on project goals (e.g., identifying discrete fractures) and site characteristics (e.g., lithology). No method works at every site or for every goal. New approaches are needed to identify a set of geophysical methods appropriate to specific project goals and site conditions while considering budget constraints. To this end, we present the Excel-based Fractured-Rock Geophysical Toolbox Method Selection Tool (FRGT-MST). We envision the FRGT-MST (1) equipping remediation professionals with a tool to understand what is likely to be realistic and cost-effective when contracting geophysical services, and (2) reducing applications of geophysics with unrealistic objectives or where methods are likely to fail.

Groundwater↗

USGS2011

Accelerated construction of a regional DNA-barcode reference library: Caddisflies (Trichoptera) in the Great Smoky Mountains National Park

Deoxyribonucleic acid (DNA) barcoding is an effective tool for species identification and lifestage association in a wide range of animal taxa. We developed a strategy for rapid construction of a regional DNA-barcode reference library and used the caddisflies (Trichoptera) of the Great Smoky Mountains National Park (GSMNP) as a model. Nearly 1000 cytochrome c oxidase subunit I (COI) sequences, representing 209 caddisfly species previously recorded from GSMNP, were obtained from the global Trichoptera Barcode of Life campaign. Most of these sequences were collected from outside the GSMNP area. Another 645 COI sequences, representing 80 species, were obtained from specimens collected in a 3-d bioblitz (short-term, intense sampling program) in GSMNP. The joint collections provided barcode coverage for 212 species, 91% of the GSMNP fauna. Inclusion of samples from other localities greatly expedited construction of the regional DNA-barcode reference library. This strategy increased intraspecific divergence and decreased average distances to nearest neighboring species, but the DNA-barcode library was able to differentiate 93% of the GSMNP Trichoptera species examined. Global barcoding projects will aid construction of regional DNA-barcode libraries, but local surveys make crucial contributions to progress by contributing rare or endemic species and full-length barcodes generated from high-quality DNA. DNA taxonomy is not a goal of our present work, but the investigation of COI divergence patterns in caddisflies is providing new insights into broader biodiversity patterns in this group and has directed attention to various issues, ranging from the need to re-evaluate species taxonomy with integrated morphological and molecular evidence to the necessity of an appropriate interpretation of barcode analyses and its implications in understanding species diversity (in contrast to a simple claim for barcoding failure).

Journal of the North American Benthological Societ↗

USGS2007

Geochemical characterization of shallow ground water in the Eutaw aquifer, Montgomery, Alabama

Ground water samples were collected from 30 wells located in, or directly down gradient from, recharge areas of the Eutaw aquifer in Montgomery, Alabama. The major ion content of the water evolves from calcium-sodium-chloride- dominated type in the recharge area to calcium-bicarbonate-dominated type in the confined portion of the aquifer. Ground water in the recharge area was undersaturated with respect to aluminosilicate and carbonate minerals. Ground water in the confined portion of the aquifer was at equilibrium levels for calcite and potassium feldspar. Dissolved oxygen and nitrite-plus-nitrate concentrations decreased as ground water age increased; pH, iron, and sulfate concentrations increased as ground water age increased. Aluminum, copper, and zinc concentrations decreased as ground water age and pH increased. These relations indicate that nitrate, aluminum, copper, and zinc are removed from solution as water moves from recharge areas to the confined areas of the Eutaw aquifer. The natural evolution of ground water quality, which typically increases the pH and decreases the dissolved oxygen content, may be an important limiting factor to the migration of nitrogen based compounds and metals.

Alabama↗

USGS1995

Hydrogeology and results of tracer tests at the old Tampa well field in Hillsborough County, with implications for wellhead-protection strategies in west-central Florida

Wellhead-protection strategies were evaluated for the Upper Floridan aquifer of west-central Florida using the old Tampa well field in northeastern Hillsborough County, Florida, as a test site. The upper 400 feet of the Upper Floridan aquifer responded to pumping as an equivalent, porous medium for a range of discharge rates from 450 to 1,000 gallons per minute. Transmissivity and storage coefficient values determined for the Upper Floridan aquifer were 23,000 feet squared per day and 0.0001, respectively. Rock cores from the Upper Floridan aquifer have effective porosity values from 21 to 46 percent. Tracer tests were conducted using a fluorescent dye. A bimodal distribution of tracer arrival times indicates ground-water flow through a dual porosity system. Analysis of tracer test results an effective porosity of 25 percent and a longitudinal dispersivity of 1.3 feet for the aquifer matrix. A numerical aquifer-simulation equivalent porous media model of the Upper Floridan aquifer was calibrated using results of aquifer tests. A particle-tracking program was used to simulate the matrix flow groundwater travel time measured with the fluorescent dye tracer test. An evaluation of wellhead-protection strategies was conducted using the particle-tracking program to simulate areas of contribution from the aquifer matrix. The results of this study demonstrate the heterogeneity of the Upper Floridan aquifer. Because of this heterogeneity, the use of uniform porosity models to delineate time-related areas of wellhead protection in the karst Upper Floridan aquifer is inappropriate; however, ground-water movement in the aquifer matrix can be simulated with uniform porosity models.

Water-Resources Investigations Report↗