Exploratory study of groundwater infiltration in lough arrow using thermal imagery and geochemical tracers

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abstract: Groundwater dynamics were investigated in Lough Arrow in the north-west of Ireland. The lake is designated under the EU Habitats Directive (92/43/EEC) for its representative Annex I habitat from which charophytes are the main feature of interest. Groundwater interactions are considered a significant component of the lough's hydrology with its Annex I archetype deemed vulnerable to the pressures of nutrient pollution. This study utilised thermal imagery and geochemical tracers to detect and quantify groundwater inputs. Landsat 7 Thermal Infrared Imagery from two dates in both summer and winter was processed to investigate the potential occurrence of localised seepage points of groundwater captured as anomalous spatial plumes. In situ surveys of radon were undertaken in summer to confirm the presence of groundwater in the lake. Results were subsequently modelled to estimate the total groundwater discharge into the lake during the survey period. Additionally, a conceptual site model was created to characterise potential pressures to the lake from groundwater interactions within the catchment. Thermal imaging failed to conclusively identify thermal plumes consistent with localised groundwater inputs in Lough Arrow. However, the radon inventory applied to the mass balance estimated the lake was subject to 6,722m3 of groundwater influx per day at the time of the survey. The conceptual site model determined the lake was subject to potential pollution pressures from groundwater due to the catchment's physical attributes and land use activities. This is primarily due to the presence of a karst aquifer in the majority of the catchment coupled with significant agricultural and forestry practices. The vulnerability of the aquifer and the influx of groundwater to the lake highlights the potential threat groundwater contamination may pose to the favourable conservation condition of Lough Arrow's Annex I habitat.