INVESTIGATION OF STORM GENERATED SALINITY AND CHEMICAL CHANGES IN A COASTAL AQUIFER

Changes in salinity and aquifer chemistry that result from sea spray, surface flooding and overwash following coastal storms were studied by collecting geochemical and physical data from a sandy coastal aquifer in southeastern Mississippi, preceding and following several coastal storm events during the period of September 14, 2007 to February 21, 2009. Water chemistry, stable oxygen and hydrogen isotopes, and conductivity profiles were collected from two 12.2 meter deep, 5 centimeter diameter, continuously screened wells in Gulfport, Mississippi. The wells are located 1.02 km (MDOT-1) and 0.51 km (MDOT-2) from the shoreline. We expected to find either freshening due to enhanced coastal precipitation or increased salinity from sea spray and/or storm surge-related processes. The results show increased conductivity in the upper portion of the profiles following storm events; however, MDOT-2 was increasingly disturbed by surface construction during the study period and some of the conductivity changes may be related to this disturbance. Isotopic data indicate mixing between fresh and sea water, but chemical data do not show a clear mixing relationship. No major storm surge events occurred during this period; therefore, the impact of overwash could not be assessed. The data, however, suggest minor salinity impacts following coastal storm events may occur in shallow coastal aquifer systems even in the absence of infiltration of storm surge overwash.