[Eoas-seminar] Reminder: MS Defense

[eoas-seminar at lists.fsu.edu]

Hello all,

Please join us for Riley Thomason’s MS Defense on Wednesday, November 5 @ 2:00 pm in EOAS 3067.


Title: Tracing Storm Runoff from Hurricane Idalia in Two Springs in North Florida Using Oxygen and Hydrogen Isotopes

Name: Riley Thomason
Date: Wednesday, November 5, 2025, at 2:00 pm EST
Advisor: Yang Wang
Location: EOAS 3067

Abstract: Recharge in karst aquifer systems, such as the Floridan Aquifer, can occur rapidly through sinkholes, sinking streams, and conduits in underground limestone, making these systems susceptible to contamination from surface water. Analyses of various chemical and isotopic tracers in water samples from major springs in North and Central Florida have yielded a wide range of transit times, making it difficult to reliably assess how long it might take for contaminants to move through the aquifer and affect water quality at the springs. This study used time-series water isotope data collected before and after Hurricane Idalia to investigate the impact of storm runoff in Wakulla Spring and Sally Ward Spring in North Florida.
Between August 28, 2023, and October 27, 2023, water samples from Wakulla Spring had δ18O and δD values ranging from -3.8 to -3.6‰ and -19.0 to -13.5‰, respectively, while samples from Sally Ward Spring had δ18O and δD values ranging from -4.3 to -2.7‰ and -22.3 to -15.2‰, respectively. The δ18O and δD values of rainwater from Hurricane Idalia, which passed through the study area on August 30, 2023, were -15.2‰ and -108.5‰, respectively, considerably lower than those of normal rainfall in the region. This distinctive isotopic composition provided a valuable hydrologic tracer for tracking storm-derived water in the regional groundwater system. Following the hurricane, event water was detected at Sally Ward Spring within one day, whereas it took 10-12 days for the event water to appear at Wakulla Spring. A second isotopic signal was observed at Sally Ward Spring 12-19 days later, indicating complex recharge and flow dynamics. These observations suggest that although the two springs are closely located, they respond quite differently to major storm events.
At Wakulla Spring, the estimated 10-12-day transit time for event water agrees with previous estimates based on dye tracing and stable isotope measurements. Both springs showed elevated particulate matter concentrations following Hurricane Idalia. USGS records also documented a five-day period of increased gauge height at Wakulla Spring, consistent with enhanced runoff and aquifer discharge. However, isotope mass balance calculations indicate that even at peak discharge, event water made up less than 1% of total discharge at Wakulla Spring and about 7% at Sally Ward Spring. These results demonstrate that discharges at both Wakulla and Sally Ward Springs are dominated by pre-event water stored in the aquifer, even following a major storm.

Best,
Adea


Adea Arrison
Sr. Academic Program Specialist
Department of Earth, Ocean & Atmospheric Science
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