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  • 1
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    Bacteriophage and microsphere transport in saturated porous media: Forced‐gradient experiment at Borden, Ontario
    American Geophysical Union (AGU) ; 1997
    In:  Water Resources Research Vol. 33, No. 4 ( 1997-04), p. 639-648
    Details
    In: Water Resources Research, American Geophysical Union (AGU), Vol. 33, No. 4 ( 1997-04), p. 639-648
    Abstract: A two‐well forced‐gradient experiment involving virus and microsphere transport was carried out in a sandy aquifer in Borden, Ontario, Canada. Virus traveled at least a few meters in the experiment, but virus concentrations at observation points 1 and 2.54 m away from the injection well were a small fraction of those injected. A simplified planar radial advection‐dispersion equation with constant dispersivity, coupled with equilibrium and reversible first‐order mass transfer, was found to be adequate to simulate the attachment and transport process. During the experiment a short‐duration injection of high‐ p H water was also made, which caused detachment of previously attached viruses. For simulating this detachment and associated transport, the same transport and mass‐ transfer equations were used; but all rate parameters were varied as groundwater p H changed from 7.4 to 8.4 and then back to 7.4. The physicochemical parameters obtained from fitting breakthrough curves at one sampling well were used to predict those at another well downstream. However, laboratory‐determined parameters overpredicted colloid removal. The predicted pattern and timing of biocolloid breakthrough was in agreement with observations, though the data showed a more‐disperse breakthrough than expected from modeling. Though clearly not an equilibrium process, retardation involving a dynamic steady state between attachment and detachment was nevertheless a major determinant of transport versus retention of virus in this field experiment.
    Type of Medium: Online Resource
    ISSN: 0043-1397 , 1944-7973
    URL: Article
    DOI: 10.1029/97WR00025
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 1997
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  • 2
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    Section concerns addressed at Fall Meeting
    American Geophysical Union (AGU) ; 1996
    In:  Eos, Transactions American Geophysical Union Vol. 77, No. 9 ( 1996-02-27), p. 84-84
    Details
    In: Eos, Transactions American Geophysical Union, American Geophysical Union (AGU), Vol. 77, No. 9 ( 1996-02-27), p. 84-84
    Abstract: To keep abreast of current issues and to plan future activities, Hydrology Section President Steve Burges brought a full agenda to the Executive Committee meeting held in San Francisco December 13, 1995. The following highlights of the meeting are offered to keep you informed about what's new in the Hydrology Section. At the 1995 AGU Fall meeting there were 741 hydrology presentations in 62 sessions. Fifty‐five percent of these were in poster form. Over the past 3 years posters have gained acceptance by the hydrology community, and because they can reach a larger audience and can be viewed all day, they are the preferred medium for many presenters. In San Francisco our section continued the Outstanding Student Paper Awards Program that we initiated at the 1995 AGU Spring meeting. Up to 5% of papers given by student colleagues can be recognized as outstanding. Members who can help evaluate student papers in one or more sessions at the Spring Meeting are encouraged to volunteer. To do so, contact section Secretary Roger Bales (roger@hwr.arizona.edu).
    Type of Medium: Online Resource
    ISSN: 0096-3941 , 2324-9250
    URL: Article
    DOI: 10.1029/96EO00056
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 1996
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  • 3
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    Section activities advanced at Spring Meeting
    American Geophysical Union (AGU) ; 1996
    In:  Eos, Transactions American Geophysical Union Vol. 77, No. 38 ( 1996-09-17), p. 368-368
    Details
    In: Eos, Transactions American Geophysical Union, American Geophysical Union (AGU), Vol. 77, No. 38 ( 1996-09-17), p. 368-368
    Abstract: Hydrology Section President Steve Burges brought several new initiatives to the Executive Committee meeting held in Baltimore on May 22, 1996. The following highlights of that meeting are offered to bring you up to date on the latest happenings in the Hydrology Section.
    Type of Medium: Online Resource
    ISSN: 0096-3941 , 2324-9250
    URL: Article
    DOI: 10.1029/96EO00255
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 1996
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  • 4
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    A framework for the study of seasonal snow hydrology and its interannual variability in the alpine regions of the Southwest
    American Geophysical Union (AGU) ; 1999
    In:  Journal of Geophysical Research: Atmospheres Vol. 104, No. D18 ( 1999-09-27), p. 22117-22135
    Details
    In: Journal of Geophysical Research: Atmospheres, American Geophysical Union (AGU), Vol. 104, No. D18 ( 1999-09-27), p. 22117-22135
    Type of Medium: Online Resource
    ISSN: 0148-0227
    URL: Article
    DOI: 10.1029/1999JD900402
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 1999
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  • 5
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    Physically based modeling of atmosphere‐to‐snow‐to‐firn transfer of H 2 O 2 at South Pole
    American Geophysical Union (AGU) ; 1998
    In:  Journal of Geophysical Research: Atmospheres Vol. 103, No. D9 ( 1998-05-20), p. 10561-10570
    Details
    In: Journal of Geophysical Research: Atmospheres, American Geophysical Union (AGU), Vol. 103, No. D9 ( 1998-05-20), p. 10561-10570
    Abstract: Quantitative interpretation of ice core chemical records requires a detailed understanding of the transfer processes that relate atmospheric concentrations to those in the snow, firn, and ice. A unique, 2 year set of year‐round surface snow samples at South Pole and snow pits, with associated accumulation histories, were used to test a physically based model for atmosphere‐to‐firn transfer of H 2 O 2 . The model, which extends our previous transfer modeling at South Pole into the snowpack, is based on the advection‐dispersion equation and spherical diffusion within representative snow grains. Required physical characteristics of the snowpack, such as snow temperature and ventilation, were estimated independently using established physical models. The surface snow samples and related model simulations show that there is a repeatable annual cycle in H 2 O 2 in the surface snow at South Pole. It peaks in early spring, and surface snow concentration is primarily determined by atmospheric concentration and temperature, with some dependence on grain size. The snow pits and associated model simulations point out the importance of accumulation timing and annual accumulation rate in understanding the deposition and preservation of H 2 O 2 and δ 18 O at South Pole. Long‐term snowpack simulations suggest that the firn continues to lose H 2 O 2 to the atmosphere for at least 10–12 years (∼3 m) after burial at current South Pole temperatures and accumulation rates.
    Type of Medium: Online Resource
    ISSN: 0148-0227
    URL: Article
    DOI: 10.1029/98JD00460
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 1998
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  • 6
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    H 2 O 2 in snow, air and open pore space in firn at Summit, Greenland
    American Geophysical Union (AGU) ; 1995
    In:  Geophysical Research Letters Vol. 22, No. 10 ( 1995-05-15), p. 1261-1264
    Details
    In: Geophysical Research Letters, American Geophysical Union (AGU), Vol. 22, No. 10 ( 1995-05-15), p. 1261-1264
    Abstract: Measurements of H 2 O 2 in firn gas down to a 1.7‐m depth showed a consistent trend, with higher firn‐gas concentrations generally associated with higher concentrations in the firn at the same depth. However, firn to firn‐gas concentration ratios still exhibited a seasonal dependence, suggesting that for summer layers equilibrium has not yet been reached. The time to reach equilibrium between firn and firn gas is at least weeks. Snowfall and fog deposit several times more H 2 O 2 than the surface snow will retain at equilibrium, supporting the idea that surface snow is a temporary reservoir for H 2 O 2 . Thus from an equilibrium standpoint, the snow‐pack should be a source of atmospheric H 2 O 2 in the summer as well as fall, resulting in higher daytime concentrations than would occur based on just atmospheric photochemical reactions. But firn‐gas measurements reported here were generally near or lower than those in the atmosphere, suggesting that degassing is too slow to significantly influence atmospheric H 2 O 2 levels.
    Type of Medium: Online Resource
    ISSN: 0094-8276 , 1944-8007
    URL: Article
    DOI: 10.1029/95GL01110
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 1995
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  • 7
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    Effect of Temperature‐Controlled Motility on Transport of Bacteria and Microspheres Through Saturated Sediment
    American Geophysical Union (AGU) ; 1995
    In:  Water Resources Research Vol. 31, No. 2 ( 1995-02), p. 271-280
    Details
    In: Water Resources Research, American Geophysical Union (AGU), Vol. 31, No. 2 ( 1995-02), p. 271-280
    Abstract: Continuous flow column experiments were used at different temperatures to study the importance of motility on advective transport of bacteria through repacked, but otherwise unaltered, natural aquifer sediment. The bacterium used was A0500, a flagellated, spore‐forming rod isolated from the deep subsurface (180 m). At 4°C, A0500 was nonmotile because here was no flagellar metabolism. Bacteria removal was greater at 4°C than at 18°C. Similar experiments with microspheres showed an opposite effect, ith greater removal at 18° than 4°C, which was consistent with colloid filtration theory. The sticking efficiency (α) for nonmotile A0500 (4°C), estimated using a steady state colloid filtration model, was over 3 times that of the motile A0500 (18°C), 0.073 versus 0.022. Analysis of complete breakthrough curves using a nonsteady, kinetically limited, transport model suggested that motile A0500 bacteria traveled twice as far as nonmotile A0500 bacteria before becoming attached to the sediment grains. Once attached, nonmotile bacteria detached on a timescale of 9–17 days versus 4–5 days for the motile bacteria. Bacterial motility facilitates advective transport through sediments by changing the attachment‐detachment kinetics to effectively reduce retardation and increase the fraction of time bacteria spend in a detached versus an attached state. Consequently, travel times to deep aquifers from recharge waters could be significantly affected by bacterial motility.
    Type of Medium: Online Resource
    ISSN: 0043-1397 , 1944-7973
    URL: Article
    DOI: 10.1029/94WR02569
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 1995
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  • 8
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    Estimating the spatial distribution of snow in mountain basins using remote sensing and energy balance modeling
    American Geophysical Union (AGU) ; 1998
    In:  Water Resources Research Vol. 34, No. 5 ( 1998-05), p. 1275-1285
    Details
    In: Water Resources Research, American Geophysical Union (AGU), Vol. 34, No. 5 ( 1998-05), p. 1275-1285
    Abstract: We present a modeling approach that couples information about snow cover duration from remote sensing with a distributed energy balance model to calculate the spatial distribution of snow water equivalence (SWE) in a 1.2 km 2 mountain basin at the peak of the accumulation season. In situ measurements of incident solar radiation, incident longwave radiation, air temperature, relative humidity, and wind speed were distributed around the basin on the basis of topography. Snow surface albedo was assumed to be spatially constant and to decrease with time. Distributed snow surface temperature was estimated as a function of modeled air temperature. We computed the energy balance for each pixel at hourly intervals using the estimated radiative fluxes and bulk‐aerodynamic turbulent‐energy flux algorithms from a snowpack energy and mass balance model. Fractional snow cover within each pixel was estimated from three multispectral images (Landsat thematic mapper), one at peak accumulation and two during snowmelt, using decision trees and a spectral mixture model; from these we computed snow cover duration at subpixel resolution. The total cumulative energy for snowmelt at each remote sensing date was weighted by the fraction of each pixel's area that lost its snow cover by that date to determine an initial SWE for each pixel. We tested the modeling approach in the well‐studied Emerald Lake basin in the southern Sierra Nevada. With no parameter fitting the modeled spatial pattern of SWE and the mean basin SWE agreed with intensive field survey data. As the modeling approach requires only a remote sensing time series and an ability to estimate the energy balance over the model domain, it should prove useful for computing SWE distributions at peak accumulation over larger areas, where extensive field measurements of SWE are not practical.
    Type of Medium: Online Resource
    ISSN: 0043-1397 , 1944-7973
    URL: Article
    DOI: 10.1029/97WR03755
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 1998
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  • 9
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    Development of a Hydrochemical Model for Seasonally Snow‐Covered Alpine Watersheds: Application to Emerald Lake Watershed, Sierra Nevada, California
    American Geophysical Union (AGU) ; 1996
    In:  Water Resources Research Vol. 32, No. 4 ( 1996-04), p. 1061-1074
    Details
    In: Water Resources Research, American Geophysical Union (AGU), Vol. 32, No. 4 ( 1996-04), p. 1061-1074
    Abstract: We have developed and tested a model to assess the hydrologic and biogeochemical responses of seasonally snow covered alpine areas to changes in inputs of water, chemicals, and energy. This alpine hydrochemical model (AHM) is capable of incorporating a detailed understanding of watershed processes in order to simulate events critical to biota such as the ionic pulse associated with spring snowmelt, which is only a few days long and may involve only a portion of the catchment. The model computes integrated water and chemical balances for multiple terrestrial, stream, and lake subunits within a watershed, each of which can have a unique and variable snow‐covered area. Two years of data from the Emerald Lake watershed in the southern Sierra Nevada were used for fitting and testing by comparing observations with modeled daily output. To the extent possible, model parameters were set on the basis of independent physical or chemical measurements, leaving only a few fitted parameters. In its current application, model capabilities include (1) tracking of chemical inputs from precipitation, dry deposition, snowmelt, mineral weathering, flows external to the watershed, and user‐defined sources and sinks; (2) tracking surface and subsurface water and chemical movements through vegetation canopy, snowpack, soil litter, multiple soil layers, streamflow, and lakes; (3) calculating chemical speciation, including precipitates, exchange complexes, and acid‐neutralizing capacity; (4) simulating nitrogen reactions; (5) using a snowmelt optimization procedure to aid in matching observed watershed outflows; and (6) modeling riparian areas. Using one year of stream data for parameter estimation and a second for evaluation, the agreement between model and data was judged to be quite good. AHM is a flexible, precise algorithm for simulating watershed hydrochemistry and can readily be adapted to other alpine catchments using the Emerald results as a guide. Application of AHM to forested catchments should also be feasible.
    Type of Medium: Online Resource
    ISSN: 0043-1397 , 1944-7973
    URL: Article
    DOI: 10.1029/95WR03726
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 1996
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  • 10
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    Recent increase in H 2 O 2 concentration at Summit, Greenland
    American Geophysical Union (AGU) ; 1997
    In:  Journal of Geophysical Research: Atmospheres Vol. 102, No. D15 ( 1997-08-20), p. 19099-19104
    Details
    In: Journal of Geophysical Research: Atmospheres, American Geophysical Union (AGU), Vol. 102, No. D15 ( 1997-08-20), p. 19099-19104
    Abstract: Prior measurements of hydrogen peroxide (H 2 O 2 ) in Greenland ice suggested a 50% increase of the H 2 O 2 concentration during the last 200 years, where most of the increase occurred between 1960 and 1988 [ Sigg and Neftel , 1991]. In this work we present data from two shallow cores drilled at Summit, Greenland in 1995 that confirm the H 2 O 2 increase found earlier and that show a further increase of the H 2 O 2 concentration since 1988, leading to an overall increase of 60±12% during the last 150 years. The new shallow cores were drilled 6 years after the Eurocore, which allowed us to identify the influence of the firnification process on the mean annual H 2 O 2 concentration recorded in the firn. We found that the H 2 O 2 concentration in the upper snow/firn decreased until the layer was buried with at least 1 m of snow and that the mean annual H 2 O 2 concentrations in deeper layers stayed essentially unchanged. Besides the increase in the mean annual concentration, the annual amplitude between winter minima and summer maxima has tripled since 1970. Since there has been no significant change in temperature during either the last 150 years or last 25 years, it is unlikely that the increasing H 2 O 2 concentrations are temperature related. We cannot rule out the possibility that seasonal accumulation patterns at Summit have changed, which could make a small contribution toward the increase. A small part of the increase of both the mean annual concentration and the annual amplitude of H 2 O 2 in recent years could be due to increasing UV‐B radiation caused by the depletion of stratospheric ozone, but a combination of changes in tropospheric chemistry apparently is involved.
    Type of Medium: Online Resource
    ISSN: 0148-0227
    URL: Article
    DOI: 10.1029/97JD01485
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 1997
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