Abstract
Submarine Groundwater Discharge (SGD) represents a significant mode of chemical transport to water bodies, making it an important flux to understand. Small Unmanned Aircraft Systems-deployed thermal infrared sensors (sUAS-TIR) provide a financially and logistically inexpensive means of identifying SGD source zones and quantifying SGD thermal infrared (TIR) plume areas over regional scales at high spatial resolutions. sUAS-TIR additionally offers the unique capability of high temporal resolution measurements of SGD. As a developing science application, the use of sUAS-TIR to image SGD requires substantial background knowledge. We present a proposed methodological construct for implementing a sUAS-TIR program for SGD-TIR data gathering, with applications extending to other research fields that can benefit from airborne TIR. Several studies have used airborne TIR in combination with empirical SGD flux measurements to quantify SGD, reporting a consistently strong regression between SGD flux and SGD TIR plume area. We additionally discuss novel research opportunities for sUAS-TIR technologies, as applied to SGD flux. The combination of high spatial and temporal resolution capabilities, at relatively low costs, make sUAS-TIR a promising new technology to overcome the scaling challenges presented by empirical studies and modeling of SGD fluxes, and advance our understanding of the controls on SGD fluxes.
Highlights
Submarine groundwater discharge (SGD) is defined by Burnett et al (2003) as “any and all flow of water on continental margins from the seabed to the coastal ocean, regardless of fluid composition or driving force [1].” Though there are some differences in the driving forces of groundwater discharge to coastal estuaries, estuarine SGD can be defined as “any [flows from the estuary bed to the coastal estuarine waters], regardless of composition or driving force” [1]
As the SGD flux vs. SGD thermal infrared (TIR) plume area regressions and their controls are better understood, small Unmanned Aircraft Systems (sUAS)-TIR detection may provide a parsimonious means for scientists and resource managers to assess SGD fluxes in regions where in situ measurements are environmentally or logistically prohibitive—an important capability given the significance of SGD as a chemical and nutrient transport mechanism [4,8]
SGD flux and SGD TIR plume areas are sensitive to temporal dynamics that operate on seconds to annual timescales
Summary
Submarine groundwater discharge (SGD) is defined by Burnett et al (2003) as “any and all flow of water on continental margins from the seabed to the coastal ocean, regardless of fluid composition or driving force [1].” Though there are some differences in the driving forces of groundwater discharge to coastal estuaries (such as reduced wave action and salinity-driven buoyancy between pore and estuarine waters), estuarine SGD can be defined as “any [flows from the estuary bed to the coastal estuarine waters], regardless of composition or driving force” [1]. SGD is comprised of two primary components: terrestrially derived fresh waters (fresh SGD) driven by terrestrial groundwater hydraulic gradients; and saline waters that have mixed within the sub-estuarine aquifer via tidal, wave, and other marine-forcing processes, before returning to the marine environment (Figure 1) [2,3,4,5] The sum of these components, total SGD, constitutes a significant advective flux component in the hydrologic cycle, estimated at approximately 300 to 400% of total global runoff [6]. Natural radiometric tracers (such as radium and radon) and chemical are used used to to quantify quantify local localSGD, SGD,and andtheir theirresults results chemical tracers tracers (such (such as as methane) methane) are can be integrated to obtain estimates for regional fluxes. We provide an overview of existing SGD TIR studies and detail specific opportunities for the use of sUAS-TIR to advance knowledge in the field of SGD research
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