Date of Award
2024
Degree Type
Dissertation
Degree Name
Doctor of Philosophy in Biological and Environmental Sciences
Department
Geosciences
First Advisor
Soni M. Pradhanang
Abstract
Submarine groundwater discharge (SGD) is the flow of water from continental shelves to coastal waterbodies and is an important transport vector of terrestrially-sourced waters and pollutants to coastal waterbodies. Subject to variabilities and forcings operating over numerous scales, SGD is particularly difficult to quantify at the spatial resolutions necessary to assess source characteristics, while obtaining the coverage necessary to understand its spatial controls. Small Unmanned Aircraft Systems-deployed thermal infrared sensors (sUAS-TIR) provide a means of identifying SGD source zones and quantifying SGD TIR thermal anomaly (“plume”) areas at very high spatial resolutions over large areas, though are unable to quantify SGD fluxes. Similarly, the RAD7 Rn222 monitoring system enables the quantification of surface water Rn222 activities and their associated SGD fluxes at high spatial resolutions with regional coverage; however, due to equilibrium response delays, the RAD7 is unable to accurately resolve Rn222 activities in temporally and/or spatially dynamic environments.
In chapter 1, we present a methodological construct for implementing a sUAS-TIR program for environmental data gathering, including the identification and characterization of SGD TIR. The methods we propose enable researchers to employ sUAS-TIR in a safe, technically rigorous, and systematic manner, promoting the use of this technology to overcome SGD scaling challenges.
In chapter 2, we couple fundamental fluid and thermal physics with well-established SGD TIR flux vs. plume area correlations to advance our understanding of controls on SGD. We find that, for both diffuse and spring SGD, benthic discharge geometry is likely the principal factor governing local variability of SGD flux and SGD TIR plume areas, while hydrogeologic parameters - hydraulic gradient, hydraulic conductivity, and channel friction factor - serve as regional controls on SGD.
In chapter 3, we derive inversion models that solve for the actual environmental Rn222 activities necessary to yield observed RAD7 Rn222 activities under two hypothetical environmental dynamics - punctuated (i.e., stepwise), and gradual (i.e., linear). We apply our models to high-resolution RAD7 Rn222 surveys, and, comparing both our model results and observed RAD7 Rn222 data to laboratory analyzed samples, we find that our results yield significantly improved representations of environmental Rn222 activities.
Finally, in chapter 4 we use our novel RAD7 Rn222 models to quantify high-spatial-resolution SGD fluxes across three coastal waterbodies in Rhode Island (RI) - Ninigret Pond (NIN), Green Hill Pond (GH), and Greenwich Bay (GB) - during four seasonal sampling campaigns. And, we employ our sUAS-TIR methods to obtain very-high-resolution TIR imagery of SGD TIR plumes across northern NIN and northern GH. Combined, these methods enable SGD assessments over multiple spatial and temporal scales, and they reveal: 1) highly heterogeneous SGD systems; 2) regional hydrogeologic and local benthic controls on SGD; 3) SGD temporal responses dominated by terrestrial forcings for NIN, and co-dominated by terrestrial and marine forcings for GH and GB; and 4) a significant correlation between SGD TIR plumes and anthropogenic structures, suggesting a causal relationship between SGD and nearshore benthic disturbances.
Creative Commons License
This work is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 4.0 License.
Recommended Citation
Young, Kyle S. R., "SEEKING CLARITY IN THE COASTAL ZONE: QUANTIFYING SUBMARINE GROUNDWATER DISCHARGE (SGD) BY THERMAL INFRARED (TIR) IMAGERY AND RADIONUCLIDE TRACER MODELING" (2024). Open Access Dissertations. Paper 1721.
https://digitalcommons.uri.edu/oa_diss/1721
