Impacts of Extratropical Cyclone Fiona on a sensitive coastal lagoon ecosystem

Abstract

Oceanic storms can strongly disturb the physical and biogeochemical conditions of transitional coastal waters. Impacts of extreme oceanic storms on coastal ecosystems have received limited attention worldwide, with no studies at higher latitudes (> 45°) where tropical cyclones have usually abated. This study investigates the combined impacts from marine and atmospheric forcing on a coastal lagoon in Prince Edward Island, Canada, during and after Extratropical Cyclone Fiona in September 2022. Physical (water levels and temperature) and biogeochemical (dissolved oxygen [DO], electrical conductivity, pH, nitrate–nitrogen concentrations, total suspended solids [TSS]) datasets from the lagoon and the watershed's tributaries, groundwater springs, and piezometers were used to assess ecosystem disturbance and recovery timelines following the storm. Fiona resulted in a 1.6 m storm surge into the lagoon that elevated water temperatures by up to 6°C, disturbed the density‐dependent stratification of salinity and temperature, and reduced the diel amplitude of DO, indicating a reduction in plant respiration due to ecosystem disturbance. The freshwater tributaries revealed sharp changes in flow (30‐fold increase), nitrate–nitrogen (NO3‐N) concentrations and loading (70‐fold increase), and TSS loading (40‐fold increase) to the lagoon during and immediately following the storm. The lagoon rapidly recovered (hours) from the hydraulic disturbance of the storm surge, but elevated nutrient levels persisted for months. The intensity and frequency of extratropical cyclones is projected to increase in the Northwest Atlantic, making field‐based studies of cyclone impacts on coastal waters critical for understanding future coastal ecosystem disturbance and recovery periods relative to the timing of future storms.

Intertidal spring dynamics and coastal nutrient loading revealed through geophysics, drone surveys, and in‐situ monitoring

“…Also, it is possible that the springs throughout the watershed (Figure S1) exhibit spatiotemporal variability in NO 3 -N concentrations not captured in the sporadic sampling reported here (Table 1). For example, extreme rainfall events have been shown to drive sustained increases in NO 3 -N levels in the Basin Head tributaries (Bonnington et al, 2023). However, this study was conducted during the baseflow season when This finding is consistent with other studies which reported that SGD can deliver a comparable (or sometimes higher) chemical load to coastal waters than rivers (Kim et al, 2003;Lecher et al, 2015;Lee et al, 2009;Santos et al, 2021;Slomp & Van Cappellen, 2004), even though SGD is rarely monitored.…”

“…The shallow (mostly <2 m deep) lagoon experiences a mixed semi-diurnal tide with a 0.8 m and 1.3 m tidal range at spring and neap tides, respectively, and a mean residence time of 2-7 days (Sharp et al, 2003). Tidal pumping occurs through a narrow channel (Figure 1), making the lagoon vulnerable to ecosystem disturbances from storm-surge-driven mixing during hurricanes and other coastal storms (Bonnington et al, 2023).…”

Interrelated Coastal Flooding, Erosion, and Groundwater Salinization on a Barrier Island During Hurricane Fiona

“…Extreme value analysis (Figure S2b in Supporting Information S1; Kamphuis, 2020) on 65 years of hindcast wave data for the modeled location revealed that the maximum significant wave heights observed during this storm have a relatively short return period (<3 years). However, water levels from the combined effect of waves and storm surge made this a historic event, significantly impacting coastal developments and ecosystems in PEI (e.g., Bonnington et al, 2023). Satellite imagery from Planet Team (2017) and images from the COASTIE citizen science program (coastiecanada.ca) revealed intensive beach/dune erosion and sediment transport (Figure 3b).…”