Storm‐driven groundwater flow in a salt marsh

Abstract

[1] Storms can cause significant groundwater flow in coastal settings, but prior studies of the effects of storms on groundwater flow and transport have largely focused on very large storms and used salinity as a tracer. We have little information about the effects of smaller storms on coastal flow and how storm-induced variability affects key tidal wetlands like salt marshes, which may remain saline throughout a storm. Here we show that even the distant passage of a moderate storm can strongly increase groundwater flow and transport in salt marsh ecosystems and adjacent barrier islands. Groundwater monitoring and radium isotope tracer analyses revealed significant influx of saline creek water into the confined aquifer below the marsh platform, driven by storm surge. This pulse of fluids reached depths exceeding 5 m, and surge-enhanced tides propagated through the aquifer to affect flow in the upland >100 m from the creek bank. Groundwater discharge from the marsh varied significantly prior to the storm, doubling during inundating tides compared to a period of noninundating neap tides. Storm surge then caused groundwater discharge to decline $50% compared to similar inundating tides. Ra-and nutrient-poor creek water that entered the confined aquifer below the marsh was quickly enriched in nutrients and carbon, even on 12 h tidal cycles, so that nutrient discharge was likely proportional to groundwater discharge. Storm-related flow could also drive significant contaminant discharge from developed coastlines. The enhanced transport and variability observed here likely affected hundreds of kilometers of the coastline impacted by the storm.

What time scales are important for monitoring tidally influenced submarine groundwater discharge? Insights from a salt marsh

“…In addition to daily variations in SGD associated with tidal cycles, field studies have documented variations in SGD on spring-neap [Robinson et al, 2007a;de Sieyes et al, 2008de Sieyes et al, , 2010Santos et al, 2009b], seasonal [Michael et al, 2005;de Sieyes et al, 2010;Gonneea et al, 2013b], and interannual [Anderson and Emanuel, 2010;Gonneea et al, 2013a] time scales. Storms can also cause significant groundwater exchange in submarine groundwater flow systems [Moore and Wilson, 2005;Hu et al, 2006;Smith et al, 2008;Santos et al, 2009a;Wilson et al, 2011;Xin et al, 2014]. Most of these studies have focused on a single time scale, so it has been difficult to determine the relative importance of variations that occur over different time scales.…”

Numerical modeling and sensitivity analysis of seawater intrusion in a dual-permeability coastal karst aquifer with conduit networks

“…Likewise, high tides associated with hurricanes or tropical storms have been found to temporarily affect the extent of seawater intrusion in a coastal aquifer (Moore and Wilson, 2005;Wilson et al, 2011).…”

Quantifying tidal contribution to submarine groundwater discharges: A review

“…The terrestrial driving force of SGD is determined by the inland hydraulic gradients in the coastal aquifers which may have both temporal and spatial variations. The marine driving forces of SGD include various sea level variations such as tides [2][3][4][5][6][7][8][9][10][11], waves [12][13][14], and storms [15][16][17], etc. The differences in salinity and temperature between seawater and groundwater may cause significant pore water density gradients in coastal aquifers which may in turn result in seawater-groundwater circulation [6,[18][19][20][21][22].…”