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

Philip Schuler,L Stoeckl,P.-A Schnegg,L Gill,C Bunce

doi:10.1007/s10040-019-02082-0

Philip Schuler, L Stoeckl + Show 3 more

Open Access

https://doi.org/10.1007/s10040-019-02082-0

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Abstract

Knowledge about the hydraulic connections between submarine groundwater discharge (SGD) and its terrestrial coastal catchment is relevant with regard to the management of marine and coastal waters in karst areas. This study applies different methods and monitoring approaches to trace SGD between the Burren Limestone Plateau and Galway Bay in western Ireland, via an excavated sinkhole shaft and deep conduit. Areas of potential SGD were first delineated based on sea surface temperature anomalies using Landsat satellite images. Two fluorescent dyes and solid wood chips were then used as tracers. Solid wood chips were tested as potential means to circumvent the problem of high dispersion in the sea, impacting on the fluorescent dyes to yield readings below the detection limits. Sampling was conducted at 10 different terrestrial locations and in the sea at Galway Bay. Offshore sampling was conducted in transects over a period of four successive days onboard of a vessel using an automated field fluorometer and a conductivity-temperature-depth sensor. No wood chips were recovered in the sea but both fluorescent dyes were successfully sampled. The estimated travel times are in the order of 100 to 354 m/h, and localised tracer readings correlate well in space and time with low conductivity readings. By confirming hydraulic connections between the two karst features and Galway Bay, the study substantiates the hypothesised importance of Variscan veins with regard to regional groundwater flow in the region.

Highlights

Localised cold temperature anomalies were interpreted as potential influence of submarine groundwater discharge (SGD), which change in position over the 4 months of the year shown in the images
This may be caused by the presence of multiple SGD locations, currents and different mixing dynamics in the sea over the year, and between years
Submarine groundwater discharge (SGD) is recognized as an important pathway for contaminant transport into the coastal environment; it is of relevance in the context of coastal karst catchments

Summary

Introduction

Artificial tracer tests are common methods in karst hydrogeology (Kaess 1998; Benischke et al 2007) to study conduit parameters (Geyer et al 2007; Luhmann et al 2012), the transportation characteristics of potential contaminants (Flynn and Sinreich 2010), or more generally to establish hydraulic connections and estimate transit timesAlbillia Co., CH2000 Neuchâtel, Switzerland 4 Burren Outdoor and Education Centre (BOEC), Turlough, Clare, Ireland (Lauber and Goldscheider 2014; Margane et al 2018). Artificial tracer tests are common methods in karst hydrogeology (Kaess 1998; Benischke et al 2007) to study conduit parameters (Geyer et al 2007; Luhmann et al 2012), the transportation characteristics of potential contaminants (Flynn and Sinreich 2010), or more generally to establish hydraulic connections and estimate transit times. Fluorescent dyes are commonly used such as uranine (sodium fluorescein), rhodamines or optical brightener, as are physico/chemical tracers such as chloride and temperature (Luhmann et al 2012) or particulate bacteriophages (Sinreich and Flynn 2006; Maurice et al 2010). Many karst catchments are coastal, discharging via submarine springs. Karst morphology extends beyond the shore into the sea, as is the case for the Burren Plateau (Kozich and Sautter 2018)

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