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Articles 1 - 27 of 27
Full-Text Articles in Physical Sciences and Mathematics
Intensification Of The Northeast Pacific Oxygen Minimum Zone During The Bolling-Allerod Warm Period, Yan Zheng, Alexander Van Green, Robert F. Anderson, James V. Gardner, Walter E. Dean
Intensification Of The Northeast Pacific Oxygen Minimum Zone During The Bolling-Allerod Warm Period, Yan Zheng, Alexander Van Green, Robert F. Anderson, James V. Gardner, Walter E. Dean
United States Geological Survey: Staff Publications
Although climate records from several locations around the world show nearly synchronous and abrupt changes, the nature of the inferred teleconnection is still poorly understood. On the basis of preserved laminations and molybdenum enrichments in open margin sediments we demonstrate that the oxygen content of northeast Pacific waters at 800 m depth during the Bolling-Allerod warm period (15-13 kyr) was greatly reduced. Existing oxygen isotopic records of benthic and planktonic foraminifera suggest that this was probably due to suppressed ventilation at higher latitudes of the North Pacific. Comparison with ventilation records for the North Atlantic indicates an antiphased pattern of …
Parent Brine Of The Castile Evaporites (Upper Permian), Texas And New Mexico, Walter E. Dean, Douglas W. Kirkland, Rodger E. Denison
Parent Brine Of The Castile Evaporites (Upper Permian), Texas And New Mexico, Walter E. Dean, Douglas W. Kirkland, Rodger E. Denison
United States Geological Survey: Staff Publications
The Upper Permian (lower Ochoan) Castile Formation is a major evaporite sequence (~10,000 km3) of calcite, anhydrite, and halite in west Texas and southeastern New Mexico. Traditionally the Castile brine has been considered to have been derived from seawater. This tradition has recently been challenged by two versions of the closed-basin drawdown model. They call for deposition from a mixed brine, in part marine and in large part nonmarine. They propose drawdown of as much as 500 m to form a major sink for ground water issuing from the surrounding Capitan reef complex. A large fraction of the …
Post-Mazama (7 Ka) Faulting Beneath Upper Klamath Lake, Oregon, Steven M. Colman, Joseph G. Rosenbaum, Richard L. Reynolds, Andrei M. Sarna-Wojcicki
Post-Mazama (7 Ka) Faulting Beneath Upper Klamath Lake, Oregon, Steven M. Colman, Joseph G. Rosenbaum, Richard L. Reynolds, Andrei M. Sarna-Wojcicki
United States Geological Survey: Staff Publications
High-resolution seismic-reflection profiles (3.5 kHz) show that a distinctive, widespread reflection occurs in the sediments beneath Upper Klamath Lake, Oregon. Coring reveals that this reflection is formed by Mazama tephra (MT), about 7 ka in age. The MT horizon is faulted in many places and locally displaced by as much as 3.1 m. Differential displacement of multiple horizons indicates recurrent fault movement, perhaps three episodes since deposition of the Mazama. The pattern of faulting indicates northeast–southwest extension beneath the lake basin.
Geochemical And Mineralogical Evidence From Eolian Sediments For Northwesterly Mid-Holocene Paleowinds, Central Kansas, Usa, Alan F. Arbogast, Daniel R. Muhs
Geochemical And Mineralogical Evidence From Eolian Sediments For Northwesterly Mid-Holocene Paleowinds, Central Kansas, Usa, Alan F. Arbogast, Daniel R. Muhs
United States Geological Survey: Staff Publications
A prominent (4500 km2) dune field in the Great Plains is the Great Bend Sand Prairie of south-central Kansas. Dunes here overlie late Quaternary alluvium and were reactivated extensively in the late Holocene. Geomorphic and soil evidence suggests that the most likely eolian sand source is the Arkansas River valley to the northwest. Nevertheless, orientations of stabilized dunes indicate that the most recent dune-forming winds came from the south or southwest, in agreement with modern wind data.
Mineralogy and trace element concentrations in eolian sands of the Great Bend Sand Prairie are similar to those of the Arkansas …
Geochemical Variations In Peoria Loess Of Western Iowa Indicate Paleowinds Of Midcontinental North America During Last Glaciation, Daniel R. Muhs, E. Arthur Bettis Iii
Geochemical Variations In Peoria Loess Of Western Iowa Indicate Paleowinds Of Midcontinental North America During Last Glaciation, Daniel R. Muhs, E. Arthur Bettis Iii
United States Geological Survey: Staff Publications
Peoria Loess deposited in western Iowa during the last glacial maximum (LGM) shows distinct geochemical and particle-size variations as a function of both depth and distance east of the Missouri River. Geochemical and particle-size data indicate that Peoria Loess in western Iowa probably had two sources: the Missouri River valley, and a source that lay to the west of the Missouri River. Both sources indicate that LGM paleowinds in western Iowa had a strong westerly component, similar to interpretations of previous workers. A compilation of loess studies in Iowa and elsewhere indicates that westerlv winds were dominant during loess transport …
Paleoclimate Reconstruction Along The Pole-Equator-Pole Transect Of The Americas (Pep 1), Vera Markgraf, T.R Baumgartner, J. P. Bradbury, H. F. Diaz, R. B. Dunbar, B. H. Luckman, G. O. Seltzer, T. W. Swetnam, R. Villalba
Paleoclimate Reconstruction Along The Pole-Equator-Pole Transect Of The Americas (Pep 1), Vera Markgraf, T.R Baumgartner, J. P. Bradbury, H. F. Diaz, R. B. Dunbar, B. H. Luckman, G. O. Seltzer, T. W. Swetnam, R. Villalba
United States Geological Survey: Staff Publications
Examples are presented of inter-hemispheric comparison of instrumental climate and paleoclimate proxy records from the Americas for different temporal scales. Despite a certain symmetry of seasonal precipitation patterns along the PEP 1 transect, decadal variability of winter precipitation shows different characteristics in terms of amplitude and frequency in both the last 100 and last 1000 years. Such differences in variability are also seen in a comparison of time series of different El Nino/Southern Oscillation proxy records from North and South America, however, these differences do not appear to affect the spatial correlation with Pacific sea surface temperature patterns. Local and …
Modeling Regional Salinization Of The Ogallala Aquifer, Southern High Plains, Tx, Usa, S. Mehta, A. E. Fryar, R. M. Brady, Roger H. Morin
Modeling Regional Salinization Of The Ogallala Aquifer, Southern High Plains, Tx, Usa, S. Mehta, A. E. Fryar, R. M. Brady, Roger H. Morin
United States Geological Survey: Staff Publications
Two extensive plumes (combined area >1000 km2) have been delineated within the Ogallala aquifer in the Southern High Plains, TX, USA. Salinity varies within the plumes spatially and increases with depth; Cl ranges from 50 to >500 mg l21. Variable-density flow modeling using SUTRA has identified three broad regions of upward cross-formational flow from the underlying evaporite units. The upward discharge within the modeled plume area is in the range of 10-4–10-5 m3 day-1, and the TDS concentrations are typically >3000 mg l-1. Regions of increased salinity, identified within the …
Occurrence Of Pesticides In Rain And Air In Urban And Agricultural Areas Of Mississippi, April-September 1995, R. H. Coupe, M. A. Manning, W. T. Foreman, D. A. Goolsby, M. S. Majewski
Occurrence Of Pesticides In Rain And Air In Urban And Agricultural Areas Of Mississippi, April-September 1995, R. H. Coupe, M. A. Manning, W. T. Foreman, D. A. Goolsby, M. S. Majewski
United States Geological Survey: Staff Publications
In April 1995, the US Geological Survey began a study to determine the occurrence and temporal distribution of 49 pesticides and pesticide metabolites in air and rain samples from an urban and an agricultural sampling site in Mississippi. The study was a joint effort between the National Water-Quality Assessment and the Toxic Substances Programs and was part of a larger study examining the occurrence and temporal distribution of pesticides in air and rain in the Mississippi River basin. Concurrent high-volume air and wet-only deposition samples were collected weekly. The air samplers consisted of a glass-fiber filter to collect particles and …
Metal Exposure In A Benthic Macroinvertebrate, Hydropsyche Californica, Related To Mine Drainage In The Sacramento River, Daniel J. Cain, James L. Carter, Steven V. Fend, Samuel N. Luoma, Charles N. Alpers, Howard E. Taylor
Metal Exposure In A Benthic Macroinvertebrate, Hydropsyche Californica, Related To Mine Drainage In The Sacramento River, Daniel J. Cain, James L. Carter, Steven V. Fend, Samuel N. Luoma, Charles N. Alpers, Howard E. Taylor
United States Geological Survey: Staff Publications
A biomonitoring technique was employed to complement studies of metal transport in the upper Sacramento River affected by acid mine drainage. Metals (Al, Cd, Cu, Fe, Hg, Pb, and Zn) were determined in a resident invertebrate, Hydropsyche californica (Insecta: Trichoptera), and streambed sediments (<62 >μm) to assess metal contamination within a 111-km section of the river downstream of the mining area. Metals in H. californica also were interpreted to be broadly indicative of metal exposure in fish. Total Hg was determined in the whole body of the insect, whereas Al, Cd, Cu, Fe, Pb, and Zn were additionally separated into …
Distribution, Speciation, And Transport Of Mercury In Stream-Sediment, Stream-Water, And Fish Collected Near Abandoned Mercury Mines In Southwestern Alaska, Usa, John E. Gray, Peter M. Theodorakos, Elizabeth A. Bailey, Ralph R. Turner
Distribution, Speciation, And Transport Of Mercury In Stream-Sediment, Stream-Water, And Fish Collected Near Abandoned Mercury Mines In Southwestern Alaska, Usa, John E. Gray, Peter M. Theodorakos, Elizabeth A. Bailey, Ralph R. Turner
United States Geological Survey: Staff Publications
Concentrations of total Hg, Hg(II), and methylmercury were measured in stream-sediment, stream-water, and fish collected downstream from abandoned mercury mines in southwestern Alaska to evaluate environmental effects to surrounding ecosystems. These mines are found in a broad belt covering several tens of thousands of square kilometers, primarily in the Kuskokwim River basin. Mercury ore is dominantly cinnabar (HgS), but elemental mercury (Hg °) is present in ore at one mine and near retorts and in streams at several mine sites. Approximately 1400 t of mercury have been produced from the region, which is approximately 99% of all mercury produced from …
Multivariate Correlation Between Concentrations Of Selected Herbicides And Derivatives In Outflows From Selected U.S. Midwestern Reservoirs, R. Tauler, D. Barcelo, E. Michael Thurman
Multivariate Correlation Between Concentrations Of Selected Herbicides And Derivatives In Outflows From Selected U.S. Midwestern Reservoirs, R. Tauler, D. Barcelo, E. Michael Thurman
United States Geological Survey: Staff Publications
Multivariate correlations between the concentrations of selected herbicides and herbicide derivatives in outflows from selected reservoirs in the Midwestern United States for April 1992 through September 1993 were investigated using principal component analysis (PCA) and multivariate curve resolution (MCR). Two independent sources for alachlor ethanesulfonic acid, one major source related to spring flush and seasonal runoff and another minor source related to groundwater, were identified using PCA. Results of MCR provided a semiquantitative interpretation of the environmental sources of the observed herbicide concentrations in reservoir outflows and allowed the examination of their temporal and geographical distributions. Samples with higher herbicide …
Chronology And Geochemistry Of Late Holocene Eolian Deposits In The Brandon Sand Hills, Manitoba, Canada, Stephen A. Wolfe, Daniel R. Muhs, Peter P. David, John P. Mcgeehin
Chronology And Geochemistry Of Late Holocene Eolian Deposits In The Brandon Sand Hills, Manitoba, Canada, Stephen A. Wolfe, Daniel R. Muhs, Peter P. David, John P. Mcgeehin
United States Geological Survey: Staff Publications
Accelerator mass spectrometry and conventional radiocarbon age determinations of organic matter from paleosols indicate that the Brandon Sand Hills area of southern Manitoba has been subjected to recurrent intervals of eolian activity in the past 5000 years. Although precise regional correlations are precluded by dating uncertainties, periods of most notable paleosol development occurred around 2300 to 2000, 1400 to 1000, and 600 to 500 cal yr BP with eolian activity occurring before and after each of these periods. Episodes of eolian activity may correspond to periods of regional drought, whereas paleosols mark periods of increased moisture availability and stabilization by …
Nest Predation On Black-Tailed Prairie Dog Colonies, Bruce Baker, Thomas R. Stanley, Glenn Plumb
Nest Predation On Black-Tailed Prairie Dog Colonies, Bruce Baker, Thomas R. Stanley, Glenn Plumb
United States Geological Survey: Staff Publications
Nest predation is the principal cause of mortality for many grassland birds. Predation rates may be higher on prairie dog colonies because they may have less available nesting cover and may increase predator abundance. We compared 14-day nest predation rates for 1,764 artificial nests on 102 black-tailed prairie dog (Cynovnys ludovicianus) colonies and their paired off-colony sites (similar habitat lacking prairie dogs) from 14 May to 26 June 1998 in South Dakota and Wyoming. Predation rates on colonies (66.2 ± 2.2%; x ± SE) were 29.5% higher than at off-colony sites (51.1 ± 2.7%). Nesting cover on colonies …
Fractured-Aquifer Hydrogeology From Geophysical Logs: Brunswick Group And Lockatong Formation, Pennsylvania, Roger H. Morin, Lisa A. Senior, Edward R. Decker
Fractured-Aquifer Hydrogeology From Geophysical Logs: Brunswick Group And Lockatong Formation, Pennsylvania, Roger H. Morin, Lisa A. Senior, Edward R. Decker
United States Geological Survey: Staff Publications
The Brunswick Group and the underlying Lockatong Formation are composed of lithified Mesozoic sediments that constitute part of the Newark Basin in southeastern Pennsylvania. These fractured rocks form an important regional aquifer that consists of gradational sequences of shale, siltstone, and sandstone, with fluid transport occurring primarily in fractures. An extensive suite of geophysical logs was obtained in seven wells located at the borough of Lansdale, Pennsylvania, in order to better characterize the areal hydrogeologic system and provide guidelines for the refinement of numerical ground water models. Six of the seven wells are approximately 120 m deep and the seventh …
Negative Ph And Extremely Acidic Mine Waters From Iron Mountain, California, Darrell Kirk Nordstrom, Charles N. Alpers, Carol J. Ptacek, David W. Blowes
Negative Ph And Extremely Acidic Mine Waters From Iron Mountain, California, Darrell Kirk Nordstrom, Charles N. Alpers, Carol J. Ptacek, David W. Blowes
United States Geological Survey: Staff Publications
Extremely acidic mine waters with pH values as low as -3.6, total dissolved metal concentrations as high as 200 g/L, and sulfate concentrations as high as 760 g/L, have been encountered underground in the Richmond Mine at Iron Mountain, CA. These are the most acidic waters known. The pH measurements were obtained by using the Pitzer method to define pH for calibration of glass membrane electrodes. The calibration of pH below 0.5 with glass membrane electrodes becomes strongly nonlinear but is reproducible to a pH as low as -4. Numerous efflorescent minerals were found forming from these acid waters. These …
Ecogeochemistry Of The Subsurface Food Web At Ph 0–2.5 In Iron Mountain, California, U.S.A., Eleanora I. Robbins, Teresa M. Rodgers, Charles N. Alpers, D. Kirk Nordstrom
Ecogeochemistry Of The Subsurface Food Web At Ph 0–2.5 In Iron Mountain, California, U.S.A., Eleanora I. Robbins, Teresa M. Rodgers, Charles N. Alpers, D. Kirk Nordstrom
United States Geological Survey: Staff Publications
Pyrite oxidation in the underground mining environment of Iron Mountain, California, has created the most acidic pH values ever reported in aquatic systems. Sulfate values as high as 120 000 mg 1-1 and iron as high as 27600mg 1-1 have been measured in the mine water, which also carries abundant other dissolved metals including Al, Zn, Cu, Cd, Mn, Sb and Pb. Extreme acidity and high metal concentrations apparently do not preclude the presence of an underground acidophilic food web, which has developed with bacterial biomass at the base and heliozoans as top predators. Slimes, oil-like films, flexible …
Natural And Anthropogenic Influences On The Distribution Of The Threatened Neosho Madtom In A Midwestern Warmwater Stream, Mark L. Wildhaber, Vernon M. Tabor, Daniel W. Mulhern, Kenneth L. Powell, Scott P. Sowa
Natural And Anthropogenic Influences On The Distribution Of The Threatened Neosho Madtom In A Midwestern Warmwater Stream, Mark L. Wildhaber, Vernon M. Tabor, Daniel W. Mulhern, Kenneth L. Powell, Scott P. Sowa
United States Geological Survey: Staff Publications
We attempted to discern the contributions of physical habitat, water chemistry, nutrients, and contaminants from historic lead-zinc mining activities on the riffle-dwelling benthic fish community of the Spring River, a mid western warm water stream that originates in Missouri and flows into Kansas and Oklahoma. The Spring River has a fish community that includes the Neosho madtom Noturus placidus, a species federally listed as threatened. Although anthropogenic factors such as contaminants limited populations and densities of fishes, an integrated assessment of natural and anthropogenic factors was necessary to effectively estimate the influence of the latter. Fish populations in the …
Restoring Ecological Integrity Of Great Rivers: Historical Hydrographs Aid In Defining Reference Conditions For The Missouri River, David L. Galat, Robin Lipkin
Restoring Ecological Integrity Of Great Rivers: Historical Hydrographs Aid In Defining Reference Conditions For The Missouri River, David L. Galat, Robin Lipkin
United States Geological Survey: Staff Publications
Restoring the ecological integrity of regulated large rivers necessitates characterizing the natural flow regime. We applied ‘Indicators of Hydrologic Alteration’ to assess the natural range of variation of the Missouri River’s flow regime at 11 locations before (1929–1948) and after (1967–1996) mainstem impoundment. The 3768 km long Missouri River was divided into three sections: upper basin least-altered from flow regulation, including the lower Yellowstone River; middle basin inter-reservoir, and lower basin channelized. Flow regulation was associated with a reduction in magnitude and duration of the annual flood pulse, an increase in magnitude and duration of annual discharge minima, a reduction …
Nutrients In Groundwaters Of The Conterminous United States, 1992-1995, Bernard Nolan, Jeffrey Stoner
Nutrients In Groundwaters Of The Conterminous United States, 1992-1995, Bernard Nolan, Jeffrey Stoner
United States Geological Survey: Staff Publications
Results of a national water quality assessment indicate that nitrate is detected in 71% of groundwater samples, more than 13 times as often as ammonia, nitrite, organic nitrogen, and orthophosphate, based on a common detection threshold of 0.2 mg/L. Shallow groundwater (typically 5 m deep or less) beneath agricultural land has the highest median nitrate concentration (3.4 mg/L), followed by shallow groundwater beneath urban land (1.6 mg/L) and deeper groundwater in major aquifers (0.48 mg/L). Nitrate exceeds the maximum contaminant level, 10 mg/L as nitrogen, in more than 15% of groundwater samples from 4 of 33 major aquifers commonly used …
Geomorphometry – Diversity In Quantitative Surface Analysis, Richard J. Pike
Geomorphometry – Diversity In Quantitative Surface Analysis, Richard J. Pike
United States Geological Survey: Staff Publications
A widening variety of applications is diversifying geomorphometry (digital terrain modelling), the quantitative study of topography. An amalgam of earth science, mathematics, engineering and computer science, the discipline has been revolutionized by the computer manipulation of gridded terrain heights, or digital elevation models (DEMs). Its rapid expansion continues. This article reviews the remarkable diversity of recent morphometric work in 15 selected topics and discusses their significance and prospects. The quantitative analysis of industrial microsurface topography is introduced to the earth science community. The 14 other topics are Internet access to geomorphometry; global DEMs; DEM modelling of channel networks; …
Single-Dilution Enzyme-Linked Immunosorbent Assay For Quantification Of Antigen-Specific Salmonid Antibody, Stewart W. Alcorn, Ronald J. Pascho
Single-Dilution Enzyme-Linked Immunosorbent Assay For Quantification Of Antigen-Specific Salmonid Antibody, Stewart W. Alcorn, Ronald J. Pascho
United States Geological Survey: Staff Publications
An enzyme-linked immunosorbent assay (ELISA) was developed on the basis of testing a single dilution of serum to quantify the level of antibody to the p57 protein of Renibacterium salmoninarum in sockeye salmon (Oncorhynchus nerka). The levels of antibody were interpolated from a standard curve constructed by relating the optical densities (OD) produced by several dilutions of a high-titer rainbow trout (O. mykiss) antiserum to the p57 protein. The ELISA OD values produced by as many as 36 test sera on each microplate were compared with the standard curve to calculate the antigen-specific antibody activity. Repeated …
Holocene Environmental And Climatic Change In The Northern Great Plains As Recorded In The Geochemistry Of Sediments In Pickerel Lake, South Dakota, Walter E. Dean, Antje Schwalb
Holocene Environmental And Climatic Change In The Northern Great Plains As Recorded In The Geochemistry Of Sediments In Pickerel Lake, South Dakota, Walter E. Dean, Antje Schwalb
United States Geological Survey: Staff Publications
The sediments in Pickerel Lake, northeastern South Dakota, provide a continuous record of climatic and environmental change for the last 12000 yr. Sediments deposited between 12 and 6 ka (radiocarbon) show extreme variations in composition, oxygen and carbon isotopic composition of bulk carbonate, carbon isotopic composition of organic matter, and magnetic susceptibility. These variations reflect changes in sources of moisture, regional vegetation types, precipitation-evaporation balance, ground- and surface-water influx, water residence time, erosion, lake productivity, water level, and water temperature. The total carbonate content of late Pleistocene sediments steadily increased from <20% at the base of the core to as much as 80% in sediments deposited between 11 and 9 ka. By about 8 ka, the total carbonate content of the sediments had declined to about 40% where it remained with little variation for the past 8 kyr, suggesting relatively stable conditions. There are marked increases in values of δ13C and δ18O in bulk carbonate, …
Pore Fluid Pressure, Apparent Friction, And Coulomb Failure, N. M. Beeler, R. W. Simpson, S. H. Hickman, D. A. Lockner
Pore Fluid Pressure, Apparent Friction, And Coulomb Failure, N. M. Beeler, R. W. Simpson, S. H. Hickman, D. A. Lockner
United States Geological Survey: Staff Publications
Many recent studies of stress-triggered seismicity rely on a fault failure
model with a single free parameter, the apparent coefficient of friction, presumed to be a material constant with possible values 0 ≤ μ ' ≤ 1. These studies may present a misleading view of fault strength and the role of pore fluid pressure in earthquake failure. The parameter μ ' is intended to incorporate the effects of both friction and pore pressure, but is a material constant only if changes in pore fluid pressure induced by changes in stress are proportional to the normal stress change across the potential …
Analysis Of Selected Herbicide Metabolites In Surface And Ground Water Of The United States, Elisabeth A. Scribner, E. M. Thurman, Lisa R. Zimmerman
Analysis Of Selected Herbicide Metabolites In Surface And Ground Water Of The United States, Elisabeth A. Scribner, E. M. Thurman, Lisa R. Zimmerman
United States Geological Survey: Staff Publications
One of the primary goals of the US Geological Survey (USGS) Laboratory in Lawrence, Kansas, is to develop analytical methods for the analysis of herbicide metabolites in surface and ground water that are vital to the study of herbicide fate and degradation pathways in the environment. Methods to measure metabolite concentrations from three major classes of herbicides ─ triazine, chloroacetanilide and phenyl-urea ─ have been developed. Methods for triazine metabolite detection cover nine compounds: six compounds are detected by gas chromatography/mass spectrometry; one is detected by high-performance liquid chromatography with diode-array detection; and eight are detected by liquid chromatography/mass spectrometry. …
Dating Marine Terraces With Relative-Age And Correlated-Age Methods, Daniel R. Muhs
Dating Marine Terraces With Relative-Age And Correlated-Age Methods, Daniel R. Muhs
United States Geological Survey: Staff Publications
Coastal landforms, and particularly emergent marine terraces, a re amongt he most importantg eomorphicfe aturesi n studieso f Quaternarys eal evel fluctuationsa nd neotectonics. A general model, first articulated by Alexander (1953) and borne out by detailedr ecent studieso n many coastlinesi,s that emergent flights of erosional terraces and coral reefs (Fig. 1) are the resulto f glacioeustaticallyc ontrolledf luctuations of global sea level superimposed on steady uplift. Similiarity of U-series ages of coral from both constructional reefsi n the tropicsa nd erosionalt erracesi n midlatitudesh as provided a rigorous test of this model (Mesolella and others, 1969; Bloom and …
Relation Of Pathways And Transit Times Of Recharge Water To Nitrate Concentrations Using Stable Isotopes, Matthew K. Landon, Geoffrey N. Delin, Stephen C. Komor, Charles P. Regan
Relation Of Pathways And Transit Times Of Recharge Water To Nitrate Concentrations Using Stable Isotopes, Matthew K. Landon, Geoffrey N. Delin, Stephen C. Komor, Charles P. Regan
United States Geological Survey: Staff Publications
Oxygen and hydrogen stable isotope values of precipitation, irrigation water, soil water, and ground water were used with soil-moisture contents and water levels to estimate transit times and pathways of recharge water in the unsaturated zone of a sand and gravel aquifer.
Effects Of Topography And Soil Properties On Recharge At Two Sites In An Agricultural Field, Geoffrey N. Delin, Richard W. Healy, Matthew K. Landon, John Karl Böhlke
Effects Of Topography And Soil Properties On Recharge At Two Sites In An Agricultural Field, Geoffrey N. Delin, Richard W. Healy, Matthew K. Landon, John Karl Böhlke
United States Geological Survey: Staff Publications
Field experiments were conducted from 1992 to 1995 to estimate ground water recharge rates at two sites located within a 2.7-hectare agricultural field. The field lies in a sand plain setting in central Minnesota and is cropped continuously in field corn. The sites are located at a topographically high (upland) site and a topographically low (lowland) site in an effort to quantify the effects of depression focusing of recharge. Three site-specific methods were used to estimate recharge rates: well hydrograph analysis, chlorofluorocarbon age dating, and an unsaturated zone water balance. All three recharge methods indicated that recharge rates at the …