Submarine Groundwater Discharge at a Single Spot Location: Evaluation of Different Detection Approaches

Abstract

Submarine groundwater discharge (SGD) into the ocean is of general interest because it acts as vehicle for the transport of dissolved contaminants and/or nutrients into the coastal sea and because it may be accompanied by the loss of significant volumes of freshwater. Due to the large-scale and long-term nature of the related hydrological processes, environmental tracers are required for SGD investigation. The water parameters of electrical conductivity and temperature, the naturally occurring radionuclides of radon and radium as well as the stable water isotopes 18 O and 2 H have proven in previous studies their general suitability for the detection and quantification of SGD. However, individual hydrogeological settings require a site-specific application of this "tool box". This study evaluates and compares the applicability of the abovementioned tracers for investigating SGD from a distinct submarine source in a karst environment at Cabbé, southern France. The specific advantages and disadvantages of each individual parameter under the given hydrogeological conditions are discussed. Radon appeared to be the most suitable environmental tracer in the site specific context. The water temperature was less reliable due to the little temperature difference between seawater and groundwater and since the diurnal variation of the air temperature masks potential SGD signals. Radium isotopes are less OPEN ACCESSWater 2014, 6 585 applicable in the studied region due to the lack of a well-developed subterranean estuary. The stable water isotopes showed results consistent with the salinity and radon data; however, the significantly higher effort required for stable isotope analyses is disadvantageous. A multi-temporal thermal remote sensing approach proved to be a powerful tool for initial SGD surveying.

How to identify groundwater-caused thermal anomalies in lakes based on multi-temporal satellite data in semi-arid regions

“…These aspects need to be considered if the approach presented is to be applied to other areas and environments. However, the general suitability was already proven for the entire coastline of the Dead Sea and also for a rather humid karst environment at Cabbé on the Mediterranean Sea (Schubert et al, 2014). Particularity the latter points to further improvement with regard to the influence of geological-background-constrained discharge behaviour, which may result in low-to high-flow stages.…”

A combined-method approach to trace submarine groundwater discharge from a coastal karst aquifer in Ireland

“…Satellite imagery was used to identify offshore sampling areas based on expected temperature differences between the sea and emerging SGD (Roxburgh 1985;Schubert et al 2014).…”

“…Locating diffuse or point SGD and further determining the associated terrestrial catchment is a challenge in itself due to the inherent significant spatial and temporal variability in the flux (Burnett and Dulaiova 2003). Natural environmental tracers such as salinity, temperature or radon may be sampled in situ (Schubert et al 2014), while some tracers, like temperature, may be also remotely sensed from space (Zektser et al 2007;Johnson et al 2008;Wilson and Rocha 2012;Tamborski et al 2015). In all cases, the use of such parameters is constrained by ocean mixing and dilution, thereby weakening and spatially integrating the signal potential towards a limit of detection or below (Breier et al 2005).…”

Radon applications in geosciences – Progress & perspectives

“…[47]), groundwater interaction in marine (e.g. [48]) or freshwater environments (e.g. [49]), submarine groundwater discharge (e.g.…”