Frequent Storm Surges Affect the Groundwater of Coastal Ecosystems

Abstract

Recent studies have focused on the effect of large tropical cyclones (hurricanes) on the shore, neglecting the role of less intense but more frequent events. Here we analyze the effect of the offshore tropical storm Melissa on groundwater data collected along the North America Atlantic coast. Our meta‐analysis indicates that both groundwater level and specific conductivity significantly increased during Melissa, respectively reaching maximum values of 1.09 m and 25.2 mS/cm above pre‐storm levels. Time to recover to pre‐storm levels was 10 times greater for groundwater specific conductivity, with a median value of 20 days, while groundwater level had a median recovery time of 2 days. A frequency‐magnitude analysis indicates that the percent of time with salinization is higher for Melissa than for energetic hurricanes. Given the high frequency of these events (return period of 1–2 years), and the long time needed for groundwater conditions to return to normal levels, we conclude that increasingly frequent moderate storms will have a significant impact on the ecology of vegetated shorelines.

Morphologic, Atmospheric, and Oceanic Drivers Cause Multi‐Temporal Saltwater Intrusion on a Remote, Sand Island

“…Our observations on Sable Island indicate that large waves and strong winds from the south pushed a large volume of seawater onto the low‐elevation flat south beach, and the subsequent infiltration and salinization of groundwater were greatest in localized depressions (e.g., MS2 at the toe of the dune), similar to observations of Terry and Falkland (2010). This spatial pattern differs from the observations from coastal aquifers underlying higher or steeper coastlines that report the greatest increases in groundwater level and salinity along the coast and minimal impact inland (Nordio et al., 2023). In the days following the storm, infiltrated seawater caused high horizontal hydraulic gradients and high rates of submarine groundwater discharge, causing the beach groundwater levels to drop.…”

“…This causes prolonged salinization over the winter when sea levels and winds are elevated. These results suggest that the return time between events may be more important for aquifer recovery than hydrogeological characteristics (Nordio et al., 2023). Furthermore, results indicate that sustained sea‐level anomalies (Sallenger et al., 2012; Yin et al., 2009) and more frequent storms may cause vertical SWI at timescales that preclude groundwater recovery.…”

Storm Surges and Sea Level Rise Cluster Hydrological Variables Across a Coastal Forest Bordering a Salt Marsh

“…Storm surge events homogenize hydrological conditions, increasing groundwater conductivity and soil WC in the high forest. The effects of storm surge are likely felt until 40 days after flooding, similarly to what reported in Nordio et al (2023). According to our results, storm surge events do not increase the differences in hydrological conditions among sites, and are not directly responsible of vegetation zonation.…”

Biophysical Drivers of Coastal Treeline Elevation

“…Both flood extent inland and subsurface salinization decrease with increasing distance from open water to uplands (Guimond & Michael, 2021), as wider marshes reduce exposure of the marsh‐forest ecotone to storm surge and mitigate saltwater intrusion. Less permeable systems, such as those with clay‐rich soils, reduce drainage after inundation events, and thus increase root exposure to saline and/or hypoxic conditions (Nordio et al., 2023). Shallow groundwater tables support saturated soil conditions and reduced seaward groundwater flow with SLR (Guimond et al., 2020), which can extend the time it takes saltwater pulses from storms to dissipate, increasing the likelihood of tree mortality.…”