Shallow groundwater temperature patterns revealed through a regional monitoring well network

Groundwater temperature is a critical control on groundwater quality, geothermal system efficiency and ecosystem dynamics in receiving surface waters. Despite the known importance of groundwater temperature, there is a lack of dedicated aquifer thermal monitoring across spatial and temporal scales. Pressure transducers and other sensors installed in groundwater monitoring well networks often record temperature as a secondary function, but these comprehensive groundwater temperature data sets are seldom analysed. In this study, we analysed seasonal, interannual and spatial patterns of shallow groundwater temperatures from a regional groundwater monitoring network in Nova Scotia, Canada and compared these subsurface temperature data to air temperature data from nearby climate stations using linear regressions and Fourier analysis. The results showed that seasonal groundwater temperatures were damped (with seasonal amplitudes 3.6%-42% of air temperature amplitudes) and lagged (phase shifted 43-145 days) compared to air temperature, with notable year-to-year variations in both damping and lagging. Results also highlighted the role of snowpack thickness on the lowest mean monthly groundwater temperatures. Given potential impacts of climate change, land cover change, urbanization and geothermal energy development on groundwater temperatures, we encourage water authorities and regulators to begin or enhance aquifer thermal monitoring and provide guidance for capitalizing on existing monitoring well infrastructure to track temperature dynamics and changes. Groundwater temperature exerts critical control on groundwater quality, geothermal system efficiency and ecosystem dynamics, yet dedicated aquifer thermal monitoring is lacking across spatiotemporal scales. In this study, we analysed seasonal, interannual and spatial patterns of shallow groundwater temperatures from a regional groundwater level monitoring network. We call on water authorities and regulators to begin or enhance aquifer thermal monitoring to track temperature changes and provide specific recommendations to consider when monitoring groundwater temperatures using more common groundwater level observation well networks.image