Paleohydrology & The Role of Groundwater in Geologic Processes
On geologic time scales (105 to 106 years), groundwater flow systems have responded dramatically to changes in the Earth’s climatic regimes. During periods of Pleistocene glaciations, sea level was up to 120 m lower than today. Most of the past 2.5 million years have been dominated by these “ice house” conditions. During sea level low standsvast quantities of freshwater were sequestered in permeable sand layers in continental shelf environments. NM Tech hydrologists were among the first to quantify the volume of fresh groundwater (~ 105 km3) sequestered on continental shelf environments around the world (Cohen et al. 2009; Post et al. 2013). To put this number in perspective, the total amount of water pumped from the Ogallala aquifer in the western USA is less than 300 km3. In 2017, New Mexico Tech hydrologists (Denis Cohen and Mark Person) began collaborating with Dr. Aaron Metcalf, a marine geologists from the University of Malta, on a European Union funded project to understand the distribution of freshwater and erosional processes on the Mediterranean continental shelf and offshore New Zealand (www.marcan.eu).
On longer time scales (107 to 108 years), groundwater flow systems have had a profound effect on the formation of energy and mineral deposits (Person and Garven, 1992; Person et al. 2012). In 2017, Professor Mark Person, in collaboration with hydrologists, economic geologists, structural geologists, geochemists from the University of Arizona received a $1M grant from the Keck Foundation to study the role of paleofluid flow in the formation of Copper and Uranium deposits within the Paradox Basin, Utah. Our team plans to test the hypothesis that Geofluids (reduced groundwater, petroleum & supercritical CO2) migrated up along faults adjacent to Paradox formation salt domes before flowing laterally through younger sandstone units, bleaching the redbeds white and depositing world class Uranium and copper deposits.
Karst aquifers are important water resources, providing water for a quarter of the world population. The presence of dissolution channels or karst conduits create highly heterogeneous and anisotropic flow systems, where most of the flow and transport through the aquifer occur via a typically poorly constrained conduit network. To facilitate conduit delineation, to document flow and transport processes, and to constrain the structure of the aquifer system, Assistant Professor Andrew Luhmann in collaboration with Sue Bilek and Ronni Grapenthin (NM Tech) and Jonathan Martin (University of Florida) are using geophysical remote sensing (seismometers, tiltmeters, and GPS instruments) of recharge events in karst aquifers. The group is planning an upcoming field deployment at the Santa Fe River Sink-Rise system in Florida to monitor responses over a two-year period. Two graduate students are needed for the project, and more information can be found here.
Emeritus Professor John Wilson and his students have been studying hyporheic exchange in karst conduits. In many ways, karst conduits are similar to surface streams. Just as hyporheic exchange occurs in surface streams where flow moves into and out of riverbed sediments, Professor Wilson and his group have run models that demonstrate that hyporheic exchange occurs between karst conduits and the surrounding sediments and rock matrix. This exchange has implications for the processing of nutrients and organic carbon, contaminant transformation and sequestration, and speleogenesis. The Wilson research group is also conducting field studies in Florida to observe conduit hyporheic exchange.
In previous work Professor Wilson and his students examined cave micrometeorology in vadose caves (those above the water table), observing with various instruments at Carlsbad Caverns in southern New Mexico and simulating convection with mathematical models. Air currents in caves depend on buoyancy effects driven by the earth’s thermal gradients and on connections to the earth surface with fluctuation of surface temperature and wind.
New Mexico Tech benefits from being the academic partner of the National Cave and Karst Research Institute (NCKRI) in Carlsbad, NM. NCKRI is home to scientists and staff that collaborate with faculty and students on teaching and research. Furthermore, New Mexico is home to world-class caves, including Carlsbad Caverns.
The field of hydrogeophysics focuses on the characterization of subsurface properties, groundwater flow and transport processes using a variety of shallow geophysical methods including direct current (DC) resistivity, electromagnetic methods including time domain electromagnetic methods (TDEM), audio magnetotelluric (AMT), seismometers, and magentotelluric methods.
New Mexico Tech hosts a wide variety of geophysical equipment that is being used in hydrologic studies include an 84 electrodes ABEM LS2 DC resistivity/induced polarization system, a 54 node SuperSting DC resistivity system, a Zonge MT-AMT-TDEM system, gravimeter, Temperature logging Truck.
At NM Tech, these geophysical tools are being used to understand the fate and transport of hydrocarbons contaminants (Fig. 1), the hydrogeologic properties of sedimentary deposits (Fig. 2) and fault zones, the distribution of fresh and brackish water in closed basins, and geothermal system characterization (Fig. 3). We are also developing novel inversion techniques to characterize the permeability of crystalline basement rocks.
River Corridor Science
Watershed research has been a focus at New Mexico Tech for over 25 years. We are proud to continue this research into the connection between humans, ecosystems, the hydrological cycle. Our current research faculty includes Dr. Jesus D. Gomez-Velez, Dr. Dan Cadol, and Dr. John L. Wilson (emeritus) who currently supervise six watershed-focused masters and doctoral students.
Watershed scale science is key to managing water resources for a growing population in a changing environment. Issues of runoff, evapotranspiration, groundwater-surface water exchange, and erosion all interact to create a dynamic, complex system. Much of the western US depends on runoff from these complex forested mountain watersheds to meet their water demands. We apply tools such as geostatistical models, remote sensing, coupled surface water-groundwater flow models, and surface energy balance models to interrogate watershed systems. Frequently the goal is to understand the response of these systems to disturbances such as wildfires, floods, and droughts so that land and water managers can both prepare for disasters and proactively treat their watersheds to reduce risk. Collaborators range from federal agencies such as the US Bureau of Reclamation and US Geological Survey, to state and local entities including the New Mexico Office of the State Engineer and Interstate Stream Commission, and the City of Santa Fe.
Active and recent projects include:
- Hydrologic and geomorphic effects of wildfire
- Interactions between surface water and groundwater over a wide range of spatio-temporal scales
- Controls on the rate and temporal distribution of water extraction and transpiration
- Sediment transport in ephemeral streams
- Modeled interaction between vegetation and flow to create floodplain vegetation mosaic
- Hydraulic effects of vegetation in flow
- The transport and fate of vegetative material such as large woody debris and post-fire debris
- Mountainous-watershed hydrology and mountain-block hydrogeology
Aqueous Geochemistry, Reactive Transport, and Tracers
Reactive transport involves physical and chemical processes that occur as fluids flow through geologic formations, resulting in complex feedbacks between flow and chemical reactions. Assistant Professor Andrew Luhmann and MS student Zhidi Wu are currently conducting flow-through fluid-rock interaction and mechanical experiments to assess coupled chemical-mechanical degradation in geologic carbon sequestration environments. Experiments at reservoir temperature and pressure are conducted on Pennsylvanian Morrow B Sandstone cores from the Farnsworth Field in Texas (Southwest Regional Partnership on Carbon Sequestration site), and will identify how cement composition and texture impact mechanical property changes due to reaction with CO2-rich brine.