To determine if the distinct deuterium (D) and oxygen-18 (18O) signature of precipitation from a tropical storm or hurricane
could be used as a natural tracer in a springshed, isotope analyses of water samples from Wakulla Spring in north Florida were done over
the course of two Atlantic hurricane seasons. Water samples were collected between Feb. 10, 2012 and Aug. 27, 2012 and between March 19
and Oct. 21, 2013. Additionally, water samples and water quality data from a total of 20 springs in north and central Florida were
collected between Jan. 14 and Feb. 18, 2012 during a period of prolonged drought; the springs were sampled again between Sept. 20 and Nov.
9, 2012 after rains in the summer and fall increased groundwater levels. The δD and δ18O values of the samples from the 21 springs,
including Wakulla Spring, showed that the springs during non-baseflow conditions have much more variability in isotope composition than
they had have during baseflow conditions. Comparison between the two sets of samples provided a range in isotope values for springs fed by
the Upper Floridan aquifer. The 2012 hurricane season had one major storm, Tropical Storm Debby from June 23 to 27, which brought over 500
mm (20 in) of rain to the Wakulla Springs study area. A clear signal of the tropical storm was observed in the Wakulla Spring water
samples as isotopically light rain recharged the aquifer and emerged at the spring. A minimum in δD (of -30‰)and δ18O (of -5.1‰)on July 4
to 5 indicated a mean transit time of nine days from the heavy rainfall that occurred on June 25 and 26. The average isotope values during
baseflow prior to the storm were -17‰ δD and -3.3‰ for δ18O. The transit time was similar to travel times found by dye trace studies of
the sinking streams in the springshed. The exact isotope composition for Tropical Storm Debby was not known, so there was not enough data
to apply isotope-based hydrograph separation to the streamflow record for Wakulla River. The maximum measured streamflow was documented at
2,600 cfs by an acoustic Doppler current profiler measurement on June 26, 2012. During the 2013 hurricane season, rainfall was recorded
and collected for isotope analysis. No major storms reached the study area during the 2013 Atlantic hurricane season except for a weakened
Tropical Storm Andrea which brought a small amount of rain on June 6 (2.27 in, 58 mm). The precipitation had very negative isotope values
(δD = -109‰ and δ18O = -14.7‰). A minimum δ18O value of -4.1‰ was seen in Wakulla Spring samples 29 and 33 days later but it was not clear
if these values could be attributed to the very small amount of isotopically light precipitation since precipitation samples from a few
other intense summer storms during the month had values slightly more negative than -4.1‰. The use of tropical storm precipitation was
shown to be an effective and simple method for studying the hydrology of a springshed with the potential for very light isotope
composition of rainfall distributed over a large land area and a very distinct signal in springflow. The drawbacks are that the
opportunities to apply the method are limited by the unpredictable occurrence of tropical storms and hurricanes and that a two-component
mixing model for hydrograph separation may not provide enough information for watersheds with complex hydrology. The use of tropical storm
or hurricane precipitation as a natural tracer in a springshed would work well in ongoing studies of springs, where the information it
provides could be added to geochemical tracer data and isotope data for other components of aquifer storage. / A Thesis submitted to the Department of Earth, Ocean and Atmospheric Science in partial fulfillment
of the Master of Science. / Spring Semester 2016. / March 21, 2016. / isotopes, Wakulla Springs / Includes bibliographical references. / Yang Wang, Professor Co-Directing Thesis; Jeffrey P. Chanton, Professor Co-Directing Thesis;
William M. Landing, Committee Member.
| Identifer | oai:union.ndltd.org:fsu.edu/oai:fsu.digital.flvc.org:fsu_360426 |
| Contributors | Rau, Erica (authoraut), Wang, Yang (professor co-directing thesis), Chanton, Jeffrey P. (professor co-directing thesis), Landing, William M. (committee member), Florida State University (degree granting institution), College of Arts and Sciences (degree granting college), Department of Earth, Ocean, and Atmospheric Science (degree granting department) |
| Publisher | Florida State University, Florida State University |
| Source Sets | Florida State University |
| Language | English, English |
| Detected Language | English |
| Type | Text, text |
| Format | 1 online resource (154 pages), computer, application/pdf |
| Rights | This Item is protected by copyright and/or related rights. You are free to use this Item in any way that is permitted by the copyright and related rights legislation that applies to your use. For other uses you need to obtain permission from the rights-holder(s). The copyright in theses and dissertations completed at Florida State University is held by the students who author them. |
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