2012


Breanna Skeets

Habib Bravo-Ruiz


Years participated in RESESS:
2010
2012


An Overview

Major: Hydrogeology
Academic Affiliation: West Virginia University
Research and Writing Mentor: Daniel H. Doctor, USGS


Biography

Habib grew up near a warm and beautiful beach west of the capital of Puerto Rico, where I learned to appreciate nature. His interest in geology was sparked by a fossiliferous limestone that he and his father gazed upon when we went to the beach. He wasn't sure what to study until his senior year in high school, when his appreciation for nature led him to study geology. In his free time, he enjoys watching documentaries, playing massive multiplayer online games, going to the beach, and caving. He is passionate about water, particularly precipitation rates of limestone as water emerges from springs, contaminant flow through karst aquifers, and wildlife and its habitat.


Abstract

Biogeochemical evaluation of diel cycles in a spring-fed travertine depositing stream in Clark County, Virginia

The diel cycles in temperature, electrical conductivity, and chemistry of Spout Run, a spring-fed stream in Clarke County, Virginia, were studied to determine biogeochemical factors that control the balance between calcite precipitation and dissolution. The gaging station at Spout Run is located above a travertine dam that forms a waterfall with a pool below. To assess the impact of the diel cycles on biogeochemical processes, laboratory measurements of major cations and anions, dissolved inorganic carbon (DIC), isotopic composition of the DIC, dissolved organic carbon (DOC), dissolved oxygen (DO), and dissolved CO2, were taken at two hour intervals for two days above (site A) and below (site B) the waterfall. Complementary field measurements of pH, conductivity, and temperature were taken at 30-minute intervals with light intensity measured at 15-minute intervals. Preliminary results reveal that temperature, conductivity, and the δ13C-DIC peak near midnight at both sites. The coincident cycles in δ13C-DIC values and temperature suggests that an increase in temperature caused a decrease in the solubility of CO2, and therefore an increase in δ13C-DIC values due to outgassing of CO2. The δ13C-DIC values also slightly increased from site A to site B, suggesting that outgassing occurred along the waterfall. This is supported by differences in pH and excess partial pressure of CO2 (ePCO2) between both sites. In the periods of high light intensity, an in-stream photosynthesis by aquatic plants and algae preferentially consumed 12CO2 while leaving the heavier 13CO2behind, adding DO to the water. There is a 2-hour time lag between the DO and δ13C-DIC peaks, however we considered that the changes in δ13C-DIC are likely controlled to some extent by photosynthetic activity. Future dissolved gas analyses and PHREEQC geochemical modeling results will provide the CO2 concentration and the saturation state with respect to calcite throughout the study period.