Reviewing water types in Patagonia’s Atlantic seaboard

Abstract

The leading goal of this report is to recognize the chemical and isotopic compositions of the main water types, to infer mixing processes, and to present additional evidence of potential submarine groundwater discharge (SGD) in Argentina’s Patagonian coastal zone. The research, carried out in the Argentine provinces of Río Negro, Chubut and Santa Cruz (41°–48°S) during August–September 2014, involved approximately 2000 km of coastline. For such purpose, data on electrical conductivity-EC, Radon-222Rn activity, stable isotope values (δ18O and δ2H), and inorganic nutrient concentrations, in different types of ground- and surface waters (i.e. rivers, lagoons/ponds, permanent wells, marine coastal waters/seawater) were used. Groundwater is mainly supplied by eastern Patagonia rainfall and surface water infiltration, although some wells in estuarine zones evidence mixing with seawater during high tide. Andean precipitations and snowmelt are the main water sources of the Chubut River, whereas lakes/ponds showed the signature of evaporated eastern Patagonia rainfall. The highest nutrient concentrations were determined in groundwater > surface waters of lagoons/ponds > surface waters of rivers > seawater. High 222Rn concentrations measured in groundwaters at some coastal sites, which were higher than 222Rn concentrations measured in rivers and seawater, support the idea of the occurrence of SGD in Patagonia’s coastal zone. The obtained results corroborated the usefulness of multi-tracer studies to recognize, at regional-scale, different water types, mixing processes and likely sources of groundwater advection to the sea.