FRESHWATER CRISIS ON A REMOTE ISLAND: FIELD INVESTIGATIONS OF POND AREA DECLINE AND SALTWATER INTRUSION DYNAMICS ON SABLE ISLAND, NOVA SCOTIA

Small islands often support dense human populations and diverse ecosystems. However, the freshwater resources that support these environments are highly vulnerable to regime shifts that occur in their terrestrial, oceanic, and climatic systems. As a result, small islands have been highlighted by the WHO and the IPCC as one of four regions most vulnerable to climate change. Sable Island is a small, low-lying, barrier island located in the Northwest Atlantic Ocean that has been recently designated as a Canadian National Park Reserve due to its unique ecosystem of wild horses, endangered seabirds, and the world’s largest breeding population of grey seals. Sable Island is an ideal island groundwater observatory as the island is relatively pristine, has a long historical record of environmental data, has shrinking groundwater-fed freshwater ponds that sustain the ecosystem, experiences strong forcing from ocean processes and changing climate, and is particularly susceptible to seawater overwash and concomitant salinization.

Declining freshwater pond area on Sable Island has raised concern for the island’s ecosystem. To provide insight into the observed long-term decline in pond volumes, pond-aquifer connectivity is assessed by monitoring sediment temperature and water levels at the surface and within the sediment. Long term changes in subsurface freshwater lens volume and associated saltwater intrusion are assessed by comparing multiple 2D transects of subsurface resistivity performed using a WalkTEM to geophysical surveys from the 1970s. In addition, geophysical surveys performed at high and low tide reveal the dynamic nature of the subsurface freshwater, and in combination with data from a transect of multi-level piezometers equipped with conductivity, temperature, and pressure loggers to characterize the effect of oceanic forcing on the island’s groundwater dynamics. This transect captured episodic salinization and subsequent freshwater flushing dynamics of a low-lying freshwater lens during the 2019 hurricane season. Data from this groundwater observatory provides new insight into freshwater lens dynamics, and gradual and episodic salinization of freshwater resources on Sable Island. Such insights are critical to enhance the understanding freshwater resource vulnerability on small islands.