Robert J. Ryan
Temple University
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Publication
Featured researches published by Robert J. Ryan.
Ground Water | 2012
Laura Toran; Brian Hughes; Jonathan E. Nyquist; Robert J. Ryan
A freeze core sampler was used to characterize hyporheic zone storage during a stream tracer test. The pore water from the frozen core showed tracer lingered in the hyporheic zone after the tracer had returned to background concentration in collocated well samples. These results confirmed evidence of lingering subsurface tracer seen in time-lapse electrical resistivity tomographs. The pore water exhibited brine exclusion (ion concentrations in ice lower than source water) in a sediment matrix, despite the fast freezing time. Although freeze core sampling provided qualitative evidence of lingering tracer, it proved difficult to quantify tracer concentration because the amount of brine exclusion during freezing could not be accurately determined. Nonetheless, the additional evidence for lingering tracer supports using time-lapse resistivity to detect regions of low fluid mobility within the hyporheic zone that can act as chemically reactive zones of importance in stream health.
23rd Symposium on the Application of Geophysics to Engineering and Environmental Problems (SAGEEP) | 2010
Jonathan E. Nyquist; Laura Toran; Allison C. Fang; Robert J. Ryan; Donald O. Rosenberry
Characterization of the hyporheic zone is of critical importance for understanding stream ecology, contaminant transport, and groundwater-surface water interaction. A salt water tracer test was used to probe the hyporheic zone of a recently re-engineered portion of Crabby Creek, a stream located near Philadelphia, PA. The tracer solution was tracked through a 13.5 meter segment of the stream using both a network of 25 wells sampled every 5-15 minutes and time-lapse electrical resistivity tomographs collected every 11 minutes for six hours, with additional tomographs collected every 100 minutes for an additional 16 hours. The comparison of tracer monitoring methods is of keen interest because tracer tests are one of the few techniques available for characterizing this dynamic zone, and logistically it is far easier to collect resistivity tomographs than to install and monitor a dense network of wells. Our results show that resistivity monitoring captured the essential shape of the breakthrough curve and may indicate portions of the stream where the tracer lingered in the hyporheic zone. Timelapse resistivity measurements, however, represent time averages over the period required to collect a tomographic data set, and spatial averages over a volume larger than captured by a well sample. Smoothing by the resistivity data inversion algorithm further blurs the resulting tomograph; consequently resistivity monitoring underestimates the degree of fine-scale heterogeneity in the hyporheic zone.
Environmental Earth Sciences | 2006
Robert J. Ryan; Michel C. Boufadel
Stochastic Environmental Research and Risk Assessment | 2007
Robert J. Ryan; Michel C. Boufadel
Journal of Hydrology | 2010
Robert J. Ryan; Claire Welty; Philip C. Larson
Hydrological Processes | 2013
Laura Toran; Jonathan E. Nyquist; Allison C. Fang; Robert J. Ryan; Donald O. Rosenberry
Environmental & Engineering Geoscience | 2012
Laura Toran; Brian Hughes; Jonathan E. Nyquist; Robert J. Ryan
Environmental Science & Technology | 2007
Robert J. Ryan; Michel C. Boufadel
Urban Ecosystems | 2011
Robert J. Ryan; Philip C. Larson; Claire Welty
Journal of Environmental Management | 2006
Robert J. Ryan; Michel C. Boufadel