Barometric pressure influence on water table fluctuations in coastal aquifers of partially enclosed seas: An example from the Adriatic coast, Italy

The water table level fluctuations in a coastal phreatic aquifer of the Adriatic coast (southern Po Plain – Italy) were recorded to characterize groundwater level response to sea level fluctuations. Tide-induced fluctuations, atmospheric pressure loading and recharge from rainfall have all been recognized in the measured water table changes. We also identified additional water table fluctuations that are not related to rain, atmospheric pressure or tides. We propose that these additional fluctuations are related to interaction of groundwater, seiche events and ‘inverted barometric effects’. Their amplitude is important, because at a distance of 70 m from the coast they have a magnitude of 0.07 m, whereas the local tide has a 1 m amplitude. Seiches are standing waves that create sea water fluxes which affect groundwater below the first row of dunes in the study area. We propose that this ‘inverted barometric effect’ is an important process in creating water fluxes in the coastal zone that may strongly affect the position and width of the mixing zone between salt and fresh water.