SI2023 – A-7 – Pairing remote sensing and in-situ monitoring to track pond dynamics on Sable Island – Sarah Hall

Small, low-lying islands, are particularly vulnerable to climate change, as rising seas and more frequent and intense coastal storms can temporarily flood coastlines, damage infrastructure, and salinize fresh groundwater resources that support island ecosystems and serve as a critical drinking water supply. Sable Island is a small, low-lying island with dynamic sand dunes. The island’s unique ecosystem of wild horses, grey seals, and endangered sea birds relies on approximately 20 freshwater ponds that exist in topographic depressions where the groundwater table rises above the land surface. The freshwater ponds are intrinsically tied to the groundwater resources; thus, short-term and long-term changes in groundwater levels impact pond water levels and aerial extent. During large storms, flooding can overtop or erode Sable Island’s foredunes and salinize freshwater ponds. To monitor ocean-aquifer-pond interactions, we installed stilling wells and piezometers equipped with water level loggers in five ponds and a transect of beach wells equipped with conductivity, temperature, and depth loggers. The near-infrared band of satellite images was used to quantify pond area and beach flooding in over 80 images during the three-year monitoring period that included events such as Hurricane Teddy (2020), Larry (2021), Fiona (2022), and several winter Nor’Easters. For each pond, a volume-area-depth relationship was created and compared to pond areas extracted from satellite images. We used meteorologic and hydrodynamic data to determine factors that control beach flooding and pond area. Results show that pond area responds not only to variable climate conditions but also to seawater flooding.