Isotopes help understand groundwater discharge in the Esteros del Iberá Wetland Area

ORTEGA, LUCÍA; MANZANO, MARISOL; ARAGUÁS-ARAGUÁS, LUIS; MILLER, JODIE; ZABALA, MARÍA EMILIA; DIETRICH, SEBASTIÁN; VIVES, LUIS

París

Congreso; Groundwater, key to the Sustainable Development Goals; 2022

IAH-CFH; UNESCO-IHP; The French Water Partnership, under the patronage of French National Commission for UNESCO and with the support of the Ministry for the Environment; Seine-Normandy Water Agency and Sorbonne University

Wetlands are critical productive ecosystems that support a wide variety of environmental processes from water quality protection, water storage, and flood protection to carbon  fixation in vegetation. In the context of climate change, increasing water demands and increased flood and drought risk, wetlands are more critical than ever to achieve sustainable development. Despite their importance, the existence of many wetlands around the world is seriously threatened by disruptions to the water cycle at a variety of scales. Understanding how wetlands are sustained is essential to both protect as well as restore water-related ecosystems, in line with SDG target 6.6. In this contribution, we look at how isotope tools can help understand hydrological behaviour in the Ibera wetland, in the province of Corrientes, the largest and most important wetland in Argentina, South America. Although there are numerous threats to the Ibera wetlands, the recent wildfires of the end-summer 2022 have highlighted the vulnerable state of the system to prolonged droughts, which is projected to be further exacerbated by climate change. The Ibera  wetland, which is mostly rainfed, is assumed to be partly sustained by groundwater, butthe exact location of groundwater discharge sites to the various surface water bodies in the wetland remains uncertain. A range of isotopes tracers including deuterium, oxygen-18 and radon-222 isotopes were analysed from water samples taken from lagoons, rivers, wells, and boreholes in or surrounding the wetland to understand groundwater-wetland connectivity. The isotopic signature (deuterium and oxygen-18) of the Ibera Lagoon is distinctly different from other surface water systems, but also clearly indicates an area ofconcentrated groundwater discharge in the south-eastern sector of the wetland. Radon-222 activities were key to locating these conduits of preferential deep groundwater discharge into the shallower groundwater system as well as the surface water systems. Radon-222 activities were also key to identifying patterns of groundwater connectivity in the major rivers surrounding the wetland. These results provided an enhanced understanding of the hydrological functioning of the Ibera wetland, the connection to the groundwater system and set the baseline to identify the impacts of anthropogenic activities in the wetland in the near future.