Stephen Macko
University of Virginia, Environmental Sciences, Faculty Member
... the Ark of Bulrushes used to float the infant Moses down the Nile, and the boat of Gilgamesh in Mesopotamia), waterproofing pottery vessels and reed baskets, the construction of buildings (such as the Tower of Babel), walls and roads,... more
... the Ark of Bulrushes used to float the infant Moses down the Nile, and the boat of Gilgamesh in Mesopotamia), waterproofing pottery vessels and reed baskets, the construction of buildings (such as the Tower of Babel), walls and roads, gluing flint and stone utensils to wooden ...
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Research Interests: Environmental Science, Water Availability, Southern Africa, Nitrogen Cycle, Multidisciplinary, and 14 moreGlobal change, Soil moisture, Nitrogen, Transect, Soil Carbon, Climatic Change, Ecosystem, Nutrient Availability, Plant Community, Large Scale, Soil Water, Nitrogen mineralization, Climatic condition, and nutrient cycle
Research Interests: Oceanography, Chemistry, Food composition, USA, Mediterranean Sea, and 15 morePuget Sound, Marine, Coarse Woody Debris, Nitrogen, Fishery, Washington, Benthos, High Density Concrete, Nitrogen Cycling, Polychaete, Total Organic Matter, Sedimentary organic matter, particle density, High density, and Low density
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Research Interests: Environmental Science, Agronomy, Climate Change, Stable Isotopes, Productivity, and 15 moreBiological Sciences, Environmental Sciences, Stable Isotope, Transect, Nutrient, Nitrogen Fertilizer, Fertilization, Ecosystem, Gramineae, Humidity, Savannah, Arid, Soil management, Fertilisation, and Tropical Zone
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Research Interests: Environmental Science, Geology, Southern Africa, Multidisciplinary, Spatial autocorrelation, and 13 moreSpatial Heterogeneity, Nitrogen, Nutrient Content, Soil organic matter, Spatial Distribution, Spatial Pattern, Total Organic Carbon, Geophysical, Woody Plants, Soil Nutrients, Vegetation Cover, Total Nitrogen, and nutrient cycle
Research Interests: Earth Sciences, Stable Isotopes, Arid environments, Biological Sciences, Phosphorus, and 14 moreEnvironmental Sciences, Stable Isotope, Nitrogen, Soils, Sol, Soil Fertility, Vertical Distribution, Soil Types, Soil Nutrients, Arid Lands, Soil Profile, Seasonal Dynamics, Dry Season, and Climatic condition
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Research Interests: Earth Sciences, Geology, Biogeochemistry, Stable Isotopes, Arid environments, and 14 moreBiological Sciences, Global change, Environmental Sciences, Isotopes, Stable Isotope, ARENA, SAND, Isotope, Soil Hydraulic Properties, Arid, Soil Physical Properties, Soil Texture, nutrient cycle, and Biogeochemical Cycle
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A table listing the C and N stable-isotope composition of the plants at the study sites.
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EL DOCTOR STEPHEN MACKO, PROFESOR DEL DEPARTAMENTO DE CIENCIAS AMBIENTALES DE LA UNIVERSIDAD DE VIRGINIA, OFRECIO DOS CONFERENCIAS, EN LOS INSTITUTOS DE GEOLOGIA Y DE FISIOLOGIA CELULAR, SOBRE LA UTILIZACION DE ISOTOPOS ESTABLES DE... more
EL DOCTOR STEPHEN MACKO, PROFESOR DEL DEPARTAMENTO DE CIENCIAS AMBIENTALES DE LA UNIVERSIDAD DE VIRGINIA, OFRECIO DOS CONFERENCIAS, EN LOS INSTITUTOS DE GEOLOGIA Y DE FISIOLOGIA CELULAR, SOBRE LA UTILIZACION DE ISOTOPOS ESTABLES DE CARBONO Y NITROGENO EN LA INVESTIGACION DE DIVERSOS PROBLEMAS DE LA CIENCIA. DIJO QUE ESTA T‚CNICA ES UNA HERRAMIENTA UTILIZADA POR GEOLOGOS, QUIMICOS, BIOLOGOS Y GEOFISICOS, ENTRE OTROS ESPECIALISTAS, PARA TRATAR DE COMPRENDER ACERCA DEL ORIGEN Y DESTINO DE COMPUESTOS DE CARBONO, NITROGENO Y AZUFRE. EL DOCTOR MACKO LA HA UTILIZADO EN ESTUDIOS DE GEOQUIMICA ORGANICA Y APLICADA A PROBLEMAS DE TIPO QUIMICO, ECOLOGICO Y BIOLOGICO. RECIENTEMENTE ESTA T‚CNICA LE HA PERMITIDO ACLARAR EL ORIGEN DE COMPUESTOS QUIMICOS EXTRATERRESTRES, COMO SON ALGUNOS AMINO CIDOS CONTENIDOS EN METEORITOS Y ROCAS PROVENIENTES DE LA LUNA Y MARTE.
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Increasing nitrate-N in ground water is a problem in many areas with limited ground-water supplies, such as west-central Kansas. However, potential sources of nitrate-N are not known. Nitrate-N concentrations in ground water in the Hays... more
Increasing nitrate-N in ground water is a problem in many areas with limited ground-water supplies, such as west-central Kansas. However, potential sources of nitrate-N are not known. Nitrate-N concentrations in ground water in the Hays study area in Ellis County, west-central Kansas, range from 0.9 to 26 mg/L. The δ15N signatures of the ground waters are more enriched (+16.8 to +28.7‰) than those of the soils (+8.4 to +13.7‰), strongly suggesting that nitrogen sources are not from mineralized and labile nitrogen present in the unsaturated zone. In this study, nitrate-N values greater than the U.S. EPA drinking water limit of 10 mg/L occur with δ15N values of greater than +10‰. This relationship between high nitrate-N concentrations and enriched δ15N values (greater than +10‰) in ground water has been observed in other studies in Kansas and is usually related to a human- and/or animal-waste source. Soil cores collected near municipal wells had mean total nitrogen values of 1.2-15 mg...
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Stable isotopic analyses of carbon, nitrogen, and sulfur were performed on teeth of different ages and sexes of the longbeaked common dolphin, Delphinus capensis, from the Gulf of California. Similarities in diet are suggested between the... more
Stable isotopic analyses of carbon, nitrogen, and sulfur were performed on teeth of different ages and sexes of the longbeaked common dolphin, Delphinus capensis, from the Gulf of California. Similarities in diet are suggested between the sexes, with no significant differences in isotopic compositions being observed. Differences in the δ13C, δ15N, and δ34S signatures were found among the age groups (nursing calf, juvenile, subadult, and adult). These data suggest that this species is generally a coastal feeder, and that it changes its feeding habits with increasing age, drawing more nutrition from higher trophic level organisms later in life.
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... a clear distinction that may prove useful in tracing the fate of fertilizer nitrate in both terrestrial and aquatic environments (Amberger & Schmidt ... Jl, Port Aransas Jetty; CCS, Corpus Christi Ship Channel; MI, Mud... more
... a clear distinction that may prove useful in tracing the fate of fertilizer nitrate in both terrestrial and aquatic environments (Amberger & Schmidt ... Jl, Port Aransas Jetty; CCS, Corpus Christi Ship Channel; MI, Mud Island; CCB, Corpus Christi Bay; LA, Lydia Anne Ship Channel; HIOS ...
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Karst aquifers are susceptible to contamination by microorganisms, but relatively few studies have used bacteria as tracers. We demonstrate the utility of Escherichia coli enriched in the stable isotope nitrogen-15 ((15) N) as a novel... more
Karst aquifers are susceptible to contamination by microorganisms, but relatively few studies have used bacteria as tracers. We demonstrate the utility of Escherichia coli enriched in the stable isotope nitrogen-15 ((15) N) as a novel bacterial tracer. Nonpathogenic E. coli from two springs in central Kentucky were grown on (15) N-enriched media. Survival of E. coli and persistence of the isotopic signal were assessed in two sets of laboratory experiments conducted with sterilized spring water in dark microcosms at 14 °C. First, isotopically labeled bacteria survived for 130 d at concentrations within one log unit of the average initial value, and there was no significant difference in δ(15) N values from Day 1 to Day 130. Second, water samples with E. coli were inoculated with either of two different species of protozoa (Tetrahymena pyriformis or Colpoda steinii). During 7 d, δ(15) N values increased in T. pyriformis while bacterial populations decreased. In a field test, following...
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Nitrate-N concentrations have increased to greater than 10 mg/L in a municipal water supply in western Kansas from 1995 to 2002. A study was done by the Kansas Geological Survey using the nitrogen-15 natural abundance isotope method to... more
Nitrate-N concentrations have increased to greater than 10 mg/L in a municipal water supply in western Kansas from 1995 to 2002. A study was done by the Kansas Geological Survey using the nitrogen-15 natural abundance isotope method to determine potential sources for the increasing nitrate concentrations. Preliminary results of the isotope analyses on water samples suggest that animal waste and/or denitrification enrichment has affected the water supply. Soil samples from areas near the wells that were not treated with manure show a general increase of nitrogen-15 signature (+9 to +15 \permil) to a depth of 5 m. Soils are silt loams with measurable carbonate (0.8 to 2 % by weight) in the profile, which may permit volatilization enrichment to occur in the soil profile. Wells in the area range from 11 to 20 m in alluvial deposits with depth to water at approximately 9 m). Nitrate-N values range from 8 to 26 mg/L. Nitrogen-15 values range from (+17 to +28 \permil) with no obvious source of animal waste near the well sites. There are potential nearby long-term sources of animal waste - an abandoned sewage treatment plant and an agricultural testing farm. One well has a reducing chemistry with a nitrate value of 0.9 mg/L and a nitrogen-15 value of +17 \permil suggesting that alluvial sediment variation also has an impact on the water quality in the study area. The other wells show values of nitrate and nitrogen-15 that are much greater than the associated soils. The use of nitrogen-15 alone permited limited evaluation of sources of nitrate to ground water particularly in areas with carbonate in the soils. Use of oxygen-18 on nitrate will permit the delineation of the processes affecting the nitrogen in the soil profile and determination of the probable sources and the processes that have affected the nitrogen in the ground water. Final results of the nitrogen-15 and oxygen-18 analyses will be presented.