Silvina Carretero

Hydrogeochemical and isotopic characterisation of groundwater in a sand-dune phreatic aquifer on the northeastern coast of the province of Buenos Aires, Argentina

This contribution presents the hydrochemical and isotopic characterisation of the phreatic aquifer located in the Partido de la Costa, province of Buenos Aires, Argentina. In the sand-dune barrier geomorphological environment, groundwater is mainly a low-salinity Ca-HCO3 and Na-HCO3-type, being in general suitable for drinking, whereas in the continental plain (silty clay sediments), groundwater is a Na-Cl type with high salinity and unsuitable for human consumption. The general isotopic composition of the area ranges from−6.8 to−4.3 ‰ for δ18O and from−39 to−21 ‰ for δ2H, showing that rainwater rapidly infiltrates into the sandy substrate and reaches the water table almost without significant modification in its isotopic composition. These analyses, combined with other chemical parameters, made it possible to corroborate that in the eastern area of the phreatic aquifer, there is no contamination from marine salt water.

Linking patterns of freshwater discharge and sources of organic matter within the Río de la Plata estuary and adjacent marshes

We investigated carbon isotopic ratios (δ13C) v. carbon to nitrogen (C : N) ratios for surface sediments throughout a large estuarine system (Rio de la Plata, RdlP), combined with sediment cores from adjacent marshes to infer main carbon sources. We also evaluated the influence of the El Nino–Southern Oscillation (ENSO) and associated high freshwater-discharge events on the organic-matter transport within the estuary. The isotopic pattern in surface sediments of the RdlP showed the upper reaches to be influenced by riverine particulate matter (δ13C range: –24 to –26‰). Similarly, in the sediment cores from marshes of the upper reaches, δ13C values decreased from –24‰ in ancient sediments to –28‰ in recent sediments, reflecting an increased contribution of organic matter from land, including C3 plants and freshwater phytoplankton, during the past 50 years. However, the lower reaches represent a depositional environment of marine algae (δ13C range: –21 to –23‰), with no influence of detritus from adjacent marshes, indicating minor erosion of the marshes in the lower reaches operating as carbon-sink habitats. Our isotopic analysis showed that the transport and deposition of terrigenous organic matter within the RdlP and adjacent marsh habitat appear to be both temporally and spatially linked to hydrology patterns.

A typology of household-level adaptation to coastal flooding and its spatio-temporal patterns

The predicted sea-level rise and changes in storm surge regimes are expected to lead to an increasing risk of flooding in coastal regions. Accommodation can be an alternative to protection in many areas, with household-level adaptation potentially constituting an important element of such a strategy, as it can significantly reduce costs. To date, a systematic typology of household-level adaptation to coastal flooding does not exist. In order to bridge this gap, we conducted a series of quantitative surveys in different coastal areas in Denmark, Germany and Argentina. We applied a cluster analysis in order to categorise the adaptive behaviour of coastal households. Coastal households were found to cluster in four groups that we term: the comprehensives, the theoreticians, the minimalists and the structurals. With the exception of households focusing on the implementation of high-effort structural measures, our results show the affiliation to these groups to follow a specific temporal sequence. At the same time, large differences in category affiliation exist between the study areas. Risk communication tools can utilise our typology to selectively target specific types of households or to ensure that the information needs of all groups are addressed.

Impact of afforestation on coastal aquifer recharge. Case study: eastern coast of the Province of Buenos Aires, Argentina

The effects of afforestation on groundwater recharge—which is the only source of drinking water supply in the Pinamar District (Partido de Pinamar), located on the eastern coast of the Province of Buenos Aires, Argentina—are analysed. The study area is characterised by a sand-dune barrier parallel to the coast, where freshwater lenses accumulate. These are bounded to the west by the brackish water of the continental plain and to the east by the seawater. Soil texture makes it possible to infer the infiltration capacity. Methods associated with groundwater table fluctuations, hydrodynamics, hydrochemistry and the characteristics of stable isotopes (2H and 18O) in groundwater were used. In order to confirm the results, daily water balances were carried out. Recharge variations were quantified based on periodic groundwater table records and water balances. A decrease in recharge was verified in forested areas with respect to non-forested areas (bare soil). The groundwater flow (hydraulic gradients), the electrical conductivity of groundwater and the fractionation of stable isotopes indicate that the higher evapotranspiration in areas with tree cover leads to a decrease in water surplus and in the possibilities for groundwater table recharge. The effects of afforestation on recharge and, therefore, on good-quality shallow groundwater reserves constitute a key element in planning the sustainable use of the water resources.

Hydrological Variations Associated with Geomorphological Changes in a Sand Dune Barrier of the Partido de La Costa, Province of Buenos Aires

The evolution of land use in San Clemente del Tuyu and Santa Teresita (Partido de La Costa [La Costa District], Buenos Aires , Argentina ) is analysed in association with the increase in population and the presence or absence of a water supply service, in order to assess changes in the hydrological system through time. A multi-temporal analysis was undertaken on Landsat satellite images, differentiating types of land use . Water balances were estimated, and the recharge for each situation was evaluated. An increase in urbanized surface at the expense of the natural sand dune environment can be observed, which entails larger impervious surfaces that are unsuitable for the infiltration and recharge of the aquifer. In both areas, a decrease in groundwater reserves occurred; in Santa Teresita , there was even a deterioration in the chemical quality of water due to sea water intrusion . It can be concluded that the urbanization process has had a negative impact on the water system in the sand dune barrier area, affecting the infiltration and recharge processes. The presence of managed supply systems acquires relevance as a conditioning factor to avoid saltwater intrusion processes. It is essential to implement land-use planning strategies that would protect the areas unaffected by urbanization that may be of use as a reservoir for the future supply of freshwater .

Long-Term Trends and Variability of Water Levels and Tides in Buenos Aires and Mar del Plata, Argentina

We present an analysis of the long-term trends and variability of extreme water and tidal levels and the main tidal constituents using long-term records from two tide gauges in the wider region of the Rio de la Plata estuary: Buenos Aires (1905–2013) and Mar del Plata (1956–2013). We find significant long-term trends in both tidal levels and the main tidal constituents (M2, S2, K1, O1, and the overtide M4) from a running harmonic analysis in both locations. The tidal range decreased on average 0.63 mm y−1, as a result of an increase of the low water levels and a decrease of the high water levels. We also find a secular decrease in the amplitude of the semi-diurnal constituents and an increase of the diurnal ones, but of different magnitudes at each location, which suggests that different processes are producing these changes. In Buenos Aires, an increase of river discharge into the estuary seems to reduce the tidal range by hampering the propagation of the tidal wave into the estuary, whereas no influence of river discharge on water and tidal levels can be detected in Mar del Plata. We believe that other factors such as thermohaline changes or the rise of mean sea-level may be responsible for the observed tidal range decrease. Despite the tidal long-term trends, we find no significant trends in the meteorological component of the tide-gauge records other than an increase in the mean sea-level. In addition, we explore teleconnections between the variability of the meteorological component of the tide-gauge records and climate drivers.

Pseudokarst and Speleothems in the Chihuido Granite, Province of Mendoza, Argentina

The core of the Chihuido Anticline is located precisely at Cerro Chihuido, Malargue, southern Mendoza province, Argentina. This anticline represents the outcropping pre-Jurassic platform of the margin of the Neuquen Basin, which is composed of three volcano-sedimentary units separated by angular unconformities. The older unit corresponds to the volcano-sedimentary complex named as El Fortin, which concludes with the intrusion of a thick rhyolite-monzogranite dyke. The dyke, together with plutons corresponding to the Gondwana magmatism, is exposed on a paleosurface whose relief has been partly fossilized by much modern pyroclastic rocks. The thickness of the dyke varies from 0.2 km to almost 1 km. In this landscape, the dyke is the most remarkable topographic and geological characteristic, not only for its huge dimensions but also for its numerous weathering cavities that provide it with a quite peculiar aspect. Typical pseudokarst landforms are represented by tafoni cavities. The nature of pseudokarst is portrayed by selective erosion along joint planes and andesite composition blocks included in the dyke. In the wall of some cavities within the almost vertical dyke, opal speleothems have been formed from silica released by rock weathering. The speleothems were studied by means of optical microscopy, scanning electron microscopy (SEM), and X-ray diffraction. The study of these minor features of the granitic landscape, such as tafoni, and the associated speleothems, the description of their morphology, and the analysis of their composition are the main objectives of this chapter.