Groundwater geochemistry in coastal wetlands: A case study in the Parque Costero del Sur biosphere reserve, Argentina

Abstract

Groundwater geochemistry and dynamics are both among the main controlling factors of environmental features in wetlands. Coastal wetlands in particular are complex environments in which groundwater geochemistry is linked to a large number of controls, such as tidal action, landforms and interactions between groundwater and surface water. The Parque Costero del Sur Biosphere Reserve is part of a larger wetland zone that extends along the right margin of the Río de la Plata estuary. The environmental characteristics present in such area are strictly connected to the geomorphological setting of the coastal plain. The aim of this study is to understand the hydrogeochemical processes which determine groundwater quality in this biosphere reserve. Major ions and environmental isotopes of groundwater were analyzed together with water balances, water table measurements and a geological and geomorphological characterization of the coastal plain in order to analyze the hydrogeochemical and hydrodynamic processes present in the wetland. Results point out that the groundwater hydrogeochemical and hydrodynamic characteristics vary over the different landforms that form the Río de la Plata coastal plain, with particular chemical facies for each one. The principal hydrogeochemical mechanisms acting in groundwater are controlled by processes which include rainfall recharge, dissolution of CO2(g), carbonates, halite and gypsum, and Na+/Ca+2 exchange. Water is one of the main conditioning factors in wetlands and this study is the first attempt to understand the mechanisms that rule groundwater geochemistry in this remote area. This research contributes to a better understanding both the hydrology and hydrogeochemistry of the biosphere reserve and future investigations will benefit from our results. In particular, this work provides the basic knowledges on surficial water - groundwater interaction necessary to develop an integrated coastal management plan aimed to guarantee the ecosystem protection through a sustainable use of the natural reserve.