The precarious freshwater resources of Sable Island, Nova Scotia, Canada: Occurrence and management considerations

Abstract

This paper presents an overview of the hydrogeology and the freshwater resources of Sable Island, Nova Scotia. The role of the sand deposits, morphology and dynamics of the dune structures and systems, precipitation, and tidal influences are discussed. The distribution, quality, and importance of both surface water and groundwater resources of the island are also presented. Fresh groundwater on the Island occurs in an unconfined sand lens aquifer. Studies to date on the hydrogeology of the island have shown highly variable rates of precipitation, both seasonally and annually, which in combination with the influence of shifting dune structures contribute to a dynamic freshwater /saltwater balance. Infiltration rates into the permeable aquifer system are greater than precipitation rates, precluding surface water flow.The chemical quality of water in the freshwater lens aquifer is generally good and meets the Guidelines for Canadian Drinking Water Quality. The aquifer is vulnerable to surface contamination, however, due to its shallow, unconfined nature, and any water supply wells are highly likely to be classified as being ‘under the direct influence of surface water’ (GUDI). Under these conditions a multi-barrier source water protection plan is considered essential for managing future public drinking water supplies on the Island. Recommendations for future studies, including long-term monitoring of water level trends, are provided to support the sustainable use of groundwater on the Sable Island.

The Stable Isotope Hydrology of Sable Island, NS, Canada

“…These measurements support the model of Hennigar (1976) that groundwater on Sable Island consists of an elongated discontinuous freshwater lens that is recharged by infiltration of rainfall and diffuses out to the sea at the edges of the island. That direct mixing between groundwater and seawater may occur either by direct incursion or flooding of seawater during severe weather (Parker, 2018) In contrast to shallow groundwater, groundwater from the deep well at the main station has a relatively constant hydrogen and oxygen stable isotopic composition with δ 2 H and δ 18 O values of -41 ± 1.3 and -6.7 ± 0.3 per mil respectively.…”

“…Because of this unique and isolated environment, Sable Island has been the focus of many scientific studies. These have mainly focused on the peculiar ecology of the feral horse population, but other investigations have ranged from traditional hydrology (Hennigar & Kennedy, 2016;Hennigar, 1976) to plant ecology (Tissier et al, 2013;Richardson et al, 2009). Sable Island's climate is classified in the updated Köppen-Geiger climate classification as Dfb (cold with a warm summer, but lacking a dry season) (Eamer et al, 2021).…”

“…Sable Island receives approximately 1460 mm of precipitation, mainly rain, annually (Environment and Climate Change Canada, 2021). This relatively large amount of rainfall along with high infiltration and no run-off results in an island-wide discontinuous unconfined freshwater aquifer, essentially a fresh water lens, diffusing into the sea at the lateral margins of the island (Hennigar & Kennedy, 2016). Vegetation consists mostly of marram grass (Ammophila arenaria) however as many as 224 species of vascular plants have been identified, both native and introduced (Stalter & Lamont, 2006).…”

“…For Sable Island, where the delta values of mean winter precipitation are essentially identical to the groundwater values, the denominator of this calculation ap-proaches zero, indicating that almost all of the groundwater is recharged by winter precipitation with little or no contribution from summer precipitation. The groundwater system on Sable Island has large discharge rates by which approximately 75% of the available reservoir is lost into the sea annually by diffusion (Hennigar, 1976).…”

“…Island results in standing pools, essentially surface exposures of the groundwater system (Hennigar, 1976). These pools are typically ephemeral and can dry out completely if the water table drops below the pond elevation.…”