Groundwater and Stream Water Dynamics in a Premontane Transitional Rainforest Using Stable Isotope Techniques
Monday, May 5, 2014
Andrea DuMont
,
Civil Engineering, Texas A&M, College Station, TX
Gretchen Miller
,
Zachry Department of Civil Engineering, Texas A&M University, College Station, TX
Brendan Roark
,
Texas A&M, College Station, TX
Hydrologic, geologic, and biologic processes are critical to understanding the ecosystem in the tropical forests of Costa Rica. Precipitation is significantly lower during the dry season, and incoming rainfall can be completely intercepted and re-evaporated by the forest canopy during light events. Thus groundwater supplies the majority of water for streamflow, making it important for downstream use for drinking water and hydropower facilities. By using stable isotope signatures, we were able to reliably and precisely characterize the nature of these ecohydrologic processes to determine the influences on the groundwater system in a challenging environment with limited accessibility and complex subsurface conditions.
This study focuses on research conducted at the Texas A&M Soltis Center for Education and Research, near San Ramón, Costa Rica. We have monitored a 2.2 ha watershed there, measuring precipitation (averaged 4.4 m/yr) and transpiration rates for over two years (averaged 1.2 mm/day), and groundwater levels and stream flow (runoff, spring flow, baseflow) rates for nearly one year (averaged 0.09 m3/sec). Over a 40-day span during summer 2013, we collected a combination of daily and rain-event based samples throughout the watershed. Sources included: the main stream, two small tributaries, groundwater, pore water, throughfall and stemflow, and xylem water from 8 tree species across the watershed.
We then measured stable isotope fractions (δ18O and δD) in the water using a Picarro L2120i CRDS. Isotope ratios for surface water averaged -5.50‰ for δ18O and -28.00‰ for δD; baseflow was measured at -5.45‰ for δ18O and -29.18‰ for δD. Results of baseflow partitioning confirm that groundwater is the dominant source for stream water even in the wet season. We additionally conclude that in this watershed, groundwater transport to the stream is characterized by short residence times attributed to macropore flow in the subsurface, despite a low permeability of the andisol clay.
Andrea DuMont, Civil Engineering, Texas A&M, College Station, TX
Andrea DuMont is a graduate student in civil engineering-water resources at Texas A&M University, studying groundwater and stream water interactions in a premontane transitional rainforest of Costa Rica. She received her B.S. degree from the Missouri University of Science and Technology (formerly University of Missouri-Rolla) in geological engineering.
Gretchen Miller, Zachry Department of Civil Engineering, Texas A&M University, College Station, TX
Gretchen Miller is an assistant professor in the Zachry Department of Civil Engineering at Texas A&M University, where she teaches fluid mechanics, water resources engineering, and groundwater engineering. She completed her B.S. and M.S. degrees in geological engineering at the Missouri University of Science and Technology (formerly University of Missouri- Rolla), and her Ph.D. in civil and environmental engineering at the University of California, Berkeley. Her research focuses on groundwater resource sustainability, and includes studies of groundwater-ecosystem interactions and modeling across the groundwater-plant-atmosphere continuum.
Brendan Roark, Texas A&M, College Station, TX
Brendan Roark, Ph.D., is an assistant professor at Texas A&M University and director of the Stable Isotopes Geosciences Facility.
