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In the Ajó coastal plain, which occurs in the south of the Samborombón Bay, Argentina, certain sectors of the wetland are influenced by the tidal flow, whereas others are not. In the tidally restricted Ajó wetlands, the evapotranspiration process is one of the most important components of the water balance due to fact that the flat morphology and low soil permeability make the flow of surface and groundwater difficult. Although evaporation is an important component of evapotranspiration, a quantitative estimation of this process is still lacking or poorly known. In this work, we quantify the evaporation term in the tidally restricted wetlands by applying isotopic modelling and assessing the hydrological response of the wetland by means of other methodologies, such as satellite imaging and level measurements. The results show that during deficit periods, the total evaporation ranges between 10 and 33 % of the local precipitation. In groundwater samples, it fluctuates between 2 and 13 %, whereas in surface water it varies between 8 and 20 %. Analyses of the water budget, satellite images and water level time series provide evidence on how evaporation processes regulate the hydrology of the wetland. The water balance suggests the occurrence of a deficit period, in which the satellite images show a reduction of the waterlogged areas and lakes, and a lowering in surface and groundwater level is recorded. [ABSTRACT FROM AUTHOR]

We report on the hydrologic and morphologic setting of the Samborombon Bay, Argentina, which is expected at the end of the 21st century as a consequence of possible scenarios of relative sea level rise (RSLR). The geomorphological analysis of the Samborombon coastland points out only minor changes occurred over the last 40 yr. The modifications are mainly related to the construction of canals to enhance the floodplain drainage. A digital elevation model (DEM) obtained by the Shuttle Radar Topography Mission (SRTM) data archive, ad hoc calibrated/validated for the study area, highlights that about 3000 km² of coastal plain present a morphological setting at high risk of sea flooding. The analysis of sea level and storm surge events recorded from 1905 to 2010 in Buenos Aires provides the RSLR rate and the return period of extreme floods. In addition, vertical land movements (VLM) measured by the permanent GPS stations of Buenos Aires and La Plata allow for the quantification of the eustatic component of the RSLR and estimating a plausible RSLR rate in the Samborombon Bay. Taking into account possible RSLR scenarios at the end of 2100 as resulting from the statistical analysis of (i) tide gauge and GPS time series and (ii) Intergovernmental Panel on Climate Change (IPCC) predictions, the potential effect of the increased sea level on the Samborombon coastland is simulated. The results show that the combined rise of sea levels, surficial waters and groundwater will lead to a new morpho-hydrologic setting of the coastal area, especially in the low-lying southern sector. Here, a coastline retreat up to 40 km is expected, with temporary submersion up to 4000 km² during storm surges. [ABSTRACT FROM AUTHOR]

Runoff, groundwater recharge and discharge, and surface water-groundwater interaction are the main driving forces of wetlands. The quantification of such flows is crucial information in the restoration and management of groundwater-dependent wetlands. The objective of this work is to quantify groundwater inflow at the level of the hydrogeological basin, which discharges into the wetland in the coastal plain of the Río de la Plata (Argentina). It also aims at evaluating whether such inflow is affected by groundwater exploitation in the high plain adjacent to the wetland. On the basis of water level data, a model of hydrological behaviour was developed and then a numerical simulation to quantify groundwater inflow was carried out. The evolution of groundwater levels was analyzed considering three situations: one of them in natural conditions and two others under different groundwater exploitation conditions. In the first case, the inflow originates in the recharge from precipitation, in the local groundwater discharge from the adjacent high plain and in the regional one from the semi-confined aquifer. The exploitation of the semi-confined aquifer in the high plain causes the formation of a cone of depression which modifies the hydrodynamics of the wetland in the area adjacent to the extraction wells. The quantification of flows shows that groundwater exploitation in areas of the basin located out of the wetland may cause the volume of water flowing into the wetland through groundwater discharge to decrease by approximately 25 %. The importance of considering discharge wetlands as part of regional hydrogeological systems should be highlighted, mainly as regards the management of natural resources. [ABSTRACT FROM AUTHOR]

Spatial variations of fluoride concentration in groundwater in the town of Saldungaray, Argentina affect water quality for human supply and decrease the aquifer reserves. The study region is a piedmont area, located near a hill area (west) and the fluvial valley of the Sauce Grande River (east). Two hydrogeological units can be identified: bedrock and clastic sediments. These sediments consist of sandy silt with a variable amount of calcium carbonate. Its greatest thickness occurs near the river where it is 60 m. Groundwater flow coincides with topography. Fresh water is exploited from this unit and it has low salt contents (dissolved solids 400 to 800 mg/l). Fluoride concentration varies between 0.2 and 5 mg/l. The groundwater flow and hydrogeological characteristics related to spatial variations of fluoride content are analyzed. The quality of water is a critical parameter in determining the overall quality of human lives, and the occurrence of high fluoride concentrations can have a pronounced impact on groundwater quality. [ABSTRACT FROM AUTHOR]

Mar Chiquita is a coastal lagoon located in the Argentine Buenos Aires province in South America. The aim of this study is to estimate the annual contribution of inland waters to the carbon cycle in this lagoon's catchment by estimating the corresponding local carbon budget. Fifteen pairs of water samples were chosen to carry out hydrogeochemical modeling using PHREEQC software. Groundwater samples were considered as recharge water (initial solutions), while streamwater samples were taken as groundwater discharge (final solutions for inverse modeling/reference solutions for direct modeling). Fifteen direct models were performed, where each groundwater sample was constrained to calcite equilibrium under two different carbon dioxide partial pressure (PCO2) conditions: atmospheric conditions (log PCO2 (atm) = -3.5) and a PCO2 value of log PCO2 (atm) = -3. Groundwater samples are close to calcite equilibrium conditions. The calcite precipitation process is kinetically slower than gas diffusion, causing oversaturation of this reactant phase in streamwater samples. This was accompanied by a pH increase of approximately two units due to a PCO2 decrease. From the fifteen inverse models it was estimated that, of the total carbon that enters per year in the hydrological cycle of the study area, about 11.9% is delivered to the atmosphere as CO2 and around 6.7% is buried in sediments. This would indicate that 81.4% of the remaining carbon is retained in equilibrium within the system or discharged into the Mar Chiquita lagoon and/or directly to the ocean through regional flows. [ABSTRACT FROM AUTHOR]