Geology

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    WARM SEASON HYDROLOGIC PROCESSES IN A BOREAL FOREST HILLSLOPE AND CATCHMENT, NEWFOUNDLAND
    (2020) Talbot-Wendlandt, Haley; Prestegaard, Karen; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Prior investigations into boreal forest ecosystems have examined hydrological processes on plot scales, examining factors such as precipitation, soil characteristics, tree rooting depths, evapotranspiration, infiltration, and groundwater, or on the catchment scale, investigating factors such as stream discharge and water chemistry. In this study, I examine hydrological processes at both plot and catchment scales, with the goal of understanding how rooting depths influence evapotranspiration (ET) and the effects of ET on catchment discharge and water chemistry. Evapotranspiration was found to influence seasonal and diurnal fluctuations in groundwater table, stream discharge, and stream electrical conductivity. Tree rooting depths were shallow, primarily within O and Ae soil horizons, suggesting that these trees intercept infiltrating water, reducing summer groundwater recharge. Stream electrical conductivity increased with cumulative ET. Summer streamflow minima coincided with hillslope groundwater minima. Stream depth and conductivity exhibited similar diurnal patterns, suggesting variations in groundwater contributions and opportunities for future research.
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    Groundwater Variations from Autocorrelation and Receiver Functions
    (2019) Kim, Doyeon; Ved, Lekic
    This dataset supports the following research: Using a 20-year continuous broadband record and two independent single-station techniques – ambient noise autocorrelation and receiver functions – we document a relationship between subsurface seismic response and groundwater levels (GWL) in the Gulf Coast Aquifer System of southern Texas. We find that a surge of GWL following three consecutive hurricanes and documented at an adjacent monitoring well is accompanied with changes in receiver function power spectra and ambient noise autocorrelations. Using a simple physical model, we show that GWL changes should affect P- (VP) more strongly than S-wave (VS) velocities, consistent with our observations and previous ones based on inter-station correlations. Agreement between receiver function and ambient noise analyses shows that both can be used to reliably estimate temporal changes in subsurface properties on long timescales. Due to their sensitivity to VP, single-station techniques respond more strongly to GWL changes, making them useful for characterizing and monitoring aquifer systems.
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    Characterization of the spatial differences in hydrological functioning in a tidal marsh, Patuxent River, MD: A framework for understanding nutrient dynamics
    (2004-12-08) Phemister, Karen; Prestegaard, Karen L.; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    This study investigates spatial variations in sediment hydraulic conductivity (K), network channel shape and horizontal groundwater flux magnitude toward tidal network channels in a freshwater tidal marsh. Results showed the average value of K at zero meters from the creekbank was significantly higher than the K at both 5 and 15 meters from the network channel creekbank. Creekbank gradient did increase with increasing distance from the main channel and some data indicated that channel width-to-depth ratio (F), which is inversely related to creekbank gradient, correlates well with K. In addition, horizontal groundwater flux magnitude at a depth of 11 cm was significantly greater than flux magnitude at 22 cm below the ground surface at the first-order network channel location. Horizontal flux magnitude was also significantly higher from 5 to 0 meters than from 15 to 5 meters from the network channel creekbank at both the first- and second-order channel locations.