Program: RESESS Boulder
Major: Earth Science & Astronomy
Academic Affiliation: Vassar College
Mentors: Dr. Holly Barnard
Alexander Nguyen is a rising junior undergraduate at Vassar College, and he is pursuing a dual major in Earth Science and Astronomy. At Vassar, he is a research assistant studying the eruptive histories of the Cosigüina and Momotombo-Monte Galán volcanoes in Nicaragua.
Alex’s RESESS research project entails the usage of subsurface topography and water availability to quantify the distribution of aboveground carbon and forest water stress and how this varies across landescapes in semi-arid forests.
After graduating, he hopes to be able to continue his passion of planetary geology and materials in graduate school. As a BIPOC and low-income student, Alex supports and strives to increase diversity, accessibility, and equity in the geosciences.
Rock moisture can be an important contributor to forest transpiration and growth.
Limited work has been done studying the effects of rock moisture (subsurface water stored in
fractured, weathered rock) on transpiration rates — especially in water-limited environments.
Semi-arid forests like the Gordon Gulch catchment (west of Boulder, CO) exhibit complex water
budget systems where water sources are not completely understood. Here, we compare
transpiration rates from plots on opposing aspects with regard to soil moisture and potential rock
moisture storage as inferred from shallow seismic refraction surveys. We calculated the
transpiration rates of ponderosa pine and lodgepole pine trees with sap flow data collected from
June to September 2014. Potential storage for rock moisture is estimated based on qualitative
analysis of shallow seismic refraction line data. While one would expect areas with higher soil
moisture on average to have higher transpiration rates, our results showed the contrary: the plot
with less soil moisture on average exhibited 25% higher transpiration rates. By qualitatively
analyzing the seismic line images, we found that this phenomenon could possibly be explained
by rock moisture. The plot with higher transpiration also had more fractured, weathered bedrock
below that could potentially store more water in rock moisture. Rock moisture is an important
component of the complex water budget system in Gordon Gulch. Further imaging of the
subsurface is key to advance our understanding on how water is being used and moved in similar
environments. Our research provides insight into rock moisture’s potential effects on water usage
via transpiration in water-limited environments.