Graduation Year

2023

Document Type

Thesis

Degree

M.S.

Degree Name

Master of Science (M.S.)

Degree Granting Department

Geology

Major Professor

Patricia Spellman, Ph.D.

Committee Member

Jason Gulley, Ph.D.

Committee Member

Kai Rains, Ph.D.

Keywords

Analytical, Karst, Springs, Nitrate, Pollution

Abstract

The Upper Floridan Aquifer (UFA) is a highly transmissive and heterogeneous karst aquifer that makes it acutely susceptible to pollution. Rapid and extensive water quality changes in nutrients at springs draining the UFA have prompted intensive monitoring at several priority springs, including continuous and discrete water quality sampling. Springs, however, are a discrete discharge point of an often-expansive phreatic cave network that can intersect different land uses and thus drain distinct geographic areas of a springshed. The extensive network contains convergent passages from deep and shallow aquifer regions and may contribute to varying water chemistry across passages resulting in water from different conduits mixing before discharging, causing convoluted signals at springs. This raises the question of whether one single monitoring location in the spring basin, like the one currently installed at Peacock Springs, is collecting data that is holistically representative of the entire cave system.

This research is focused on spatial and temporal water chemistry variability at Peacock Springs in northern Florida in an attempt to compare the current readings at the spring basin with the cave system and the spring vent in order to see if the current sensor readings are an accurate reflection of water quality within the whole system. With the help of cave divers, a YSI EXO2 multiparameter sonde, which continuously records pH, dissolved oxygen (DO), temperature, and specific conductance, was used to collect water quality surveys through a planned dive path at Peacock Springs. Additionally, three locations, plus the main spring vent, were selected to examine how water quality parameters varied among conduits and the vent. The three locations intersected the dive path of the divers. At these locations, the divers also collected grab samples of water which were then analyzed for NO2-+NO3- as N (NOx-N), major ion chemistry, and dissolved organic carbon (DOC). Furthermore, a comparison was made between the spring vent discharging mixed water, and the current monitoring sonde installed in the spring basin.

Differences were observed in many water chemistry parameters at Peacock Springs both spatially and temporally. At discrete sampling locations, NOx-N varied over 1.5 mg/L among sampled passages after the rainy season (October 2022), but only by ~ 1.0 mg/L near the end of the dry season (March 2023). Overall, average NOx-N was higher at each site after the rainy season compared to before the rainy season. Much like NOx-N, DO and DOC were also highly variable between cave passages, and ranges between them were greater in the wet season compared to the dry season. Spatial variability in continuously collected parameters was also observed and showed distinct water chemistry signals emerging from different passages.

The results potentially show that different land uses are being drained by different conduits but more data needs to be collected to confirm this belief. Additionally, YSI EXO2 sensor comparisons between spring vent and external monitoring location showed different values for key physiochemical parameters most notably DO and temperature, but also, pH, and specific conductivity. The observable differences highlight the need for screening proper spring basin sampling locations. Our understanding of water chemistry variability in phreatic caves is currently limited but plays an important role in water quality change interpretation and remediation success for spring groundwater basin management.

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