Groundwater dynamic, temperature and salinity response to the tide in Patagonian marshes: Observations on a coastal wetland in San José Gulf, Argentina

Abstract

The processes regulating the relationship between tidal fl ows and shallow groundwater dynamics, temperature and salinity in a coastal wetland in an arid climate are analysed in a detailed fi eld study carried out in the marsh located at Playa Fracasso (Argentina). The continuous records of groundwater level, temperature and electrical conductivity from a transect perpendicular to the coastline were studied during a period ranging from summer to winter, together with the information obtained in hydro- geomorphological fi eld surveys and soil pro fi les. An assessment of the processes conditioning marsh hydrology was carried out contemplating seasonal (summer e winter) and periodical variations caused by tidal fl ows. The study showed that the dynamics of groundwater in relation to tidal fl ows depends almost exclusively on the in fi ltration of tidal water when the marsh is fl ooded during spring tides (syzygy), with an increase in the groundwater discharge level at the onset of syzygy. The differences in temperature between sea and continental water were very useful in de fi ning the origin of the different contributions. Groundwater salinity is mainly associated with the leaching of the soil salts that enter with the sea water in fi ltrating during fl ood events. The presence of saline soils in the marsh is regulated by the evapo- transpiration predominating in arid zones. The conceptual hydrological model suggested may help in the understanding of the hydrological processes in other similar marshes of Patagonia, as well as in coastal wetlands of arid zones worldwide.