Regional scale assessment of Submarine Groundwater Discharge in Ireland combining medium resolution satellite imagery and geochemical tracing techniques

Abstract

This paper sets the foundation for the use of freely available Landsat Enhanced Thematic Mapper (ETM+) thermal infrared (TIR) imagery in a regional scale assessment of submarine groundwater discharge (SGD) to coastal waters. A comprehensive, tiered, three-step approach is proposed as the most effective and affordable means to determine the spatial extent and scale of SGD from coastal aquifers to the coastal margin. As the preliminary step, Sea Surface Temperature (SST) values derived from Landsat ETM+ TIR are used to successfully detect plumes of colder water eventually associated with SGD in close proximity to the shoreline. Subsequently, potential sites of SGD are linked to geological features on land acting as possible sources, by combining within a Geographical Information System (GIS), mapped temperature anomalies with ancillary on-shore spatial datasets describing bedrock geology including aquifer fault lines. Finally, nearshore surveys mapping the activity of 222Rn (radon) and salinity are carried out to verify the presence of SGD and provide a qualitative assessment of fresh groundwater inputs to the coastal zone.Practical application of the complete approach in the context of coastal zone management is illustrated through a case-study of the Republic of Ireland. As part of this study, over 30 previously unidentified links between aquifers on land and the sea are shown along the Irish coast, hence illustrating the tight coupling between coastal waters and groundwater inputs at an unprecedented spatial scale. The study demonstrates the potential of the combined applications of remote sensing methods and geochemical tracing techniques for a cost-effective regional-scale assessment of groundwater discharge to coastal waters.