Climate change risk assessment for a confined, small-island aquifer off Prince Edward Island, Canada

Abstract

Aquifers on small islands are at risk of salinization due to the low topographies and small freshwater volumes, and present-day risks are expected to be exacerbated under projected climate change. To date, most studies addressing saltwater intrusion in small islands have focused on sandy barrier island environments, whereas the impact of geological heterogeneity in island bedrock aquifers has received little attention. The aim of this study is to use numerical modelling to investigate saltwater intrusion dynamics in a small-island setting under various climate change perturbations, and to consider how geological layering impacts the aquifer response. The Lennox Island First Nation, like the rest of Prince Edward Island, heavily relies on groundwater resources to supply their water demands. To determine how climate change influences groundwater dynamics on Lennox Island, observation well and geophysical resistivity data were used to calibrate a numerical model of coupled groundwater flow and salt transport to present-day, steady-state conditions. This was used as the initial conditions to simulate the impacts of climate change scenarios including sea-level rise (SLR), storm surge overtopping, changes in aquifer recharge, and coastline erosion. Results indicate that aquifer recharge and erosion have the largest influence on aquifer dynamics. SLR also resulted in relatively significant impacts, as the confined aquifer was not able to pressurize enough to prevent landward movement of the saltwater wedge (salinized groundwater). When these effects were considered in tandem, the model results show pronounced impacts on the freshwater aquifer. These results provide new insights for quantifying risks to island aquifers and for sustainably managing groundwater resources on islands.