Griselda Galindo

Contribution of volcanic ashes to the regional geochemical balance: the 2008 eruption of Chaitén volcano, Southern Chile.

The environmental geochemical behaviour of the rhyolitic ashes from the 2008 eruption of Chaitén volcano, Southern Chile, has been studied. After the bulk characterisation, the potential contribution to the regional geochemical fluxes was examined using: i) single batch leaching tests to provide a rapid screening of the implied major and trace elements; and ii) column experiments to evaluate the temporal mobility of leached elements. The environmental concerns of these ashes are related to the fine grained component present in each sample (independent of distance from the source), in particular the presence of cristobalite, and the geochemical hazards posed by ash-water interaction. Leaching experiments show the fast dissolution of surface salts and aerosols, which dominate over glass dissolution during the first steps of the ash-water interaction. Chaitén ashes could transfer to the environment more than 1×10(10)g or 10,000 metric tonnes (mt) of Cl, S, Ca, Na, Si, and K; between 1000 and 10,000 mt of F, Mg, and Al; between 100 and 1000 mt of As, Pb, P, Fe, Sr, Zn, Mn, and Br; between 10 and 100 mt of Ba, Li, Ti, Ni, Nb, Cu, Rb, Zr, V, Mo, Co, and Sc; and less than 10 mt of Cr, Sb, Ce, Ga, Cs, and Y. These results show the fertilising potential of the ashes (e.g., providing Ca and Fe) but also the input of potentially toxic trace elements (e.g., F and As) in the regional geochemical mass balance. The Chaitén results evidence lower potentials for poisoning and fertilising than low silica ashes due to the lower contents released of practically all elements.

Electrical conductivity and depth of groundwater at the Pergamino zone (Buenos Aires Province, Argentina) through vertical electrical soundings and geostatistical analysis

Abstract In the humid Pampean region of Argentina, a rich agricultural zone, the periodic occurrence of droughts of different intensity is one of the most important factors in the variability of crop yield. Because complementary irrigation is a highly efficient resource to increase such yields, an understanding of groundwater resources is important. This knowledge is limited in topographically smooth zones by the absence of outcroppings and observation boreholes. Water conductivity is another limitation factor if the goal is to avoid soil degradation by irrigation and negative effects for animal and human consumption. The aquifers of the northeastern zone of the Buenos Aires province have been studied regionally, but information at the local scale is limited to sparse boreholes. In this work, a survey using vertical electrical soundings was carried out to determine the depth, thickness, and continuity of shallower aquifers. Both a mapping of the water table and the electrical conductivity distribution of free aquifers were achieved from well data and geophysical results using geostatistical techniques. Recharge areas of the aquifer were recognized as those areas with low conductivity and topographic highs. The discharge areas, mainly at the bed of the Pergamino River, have higher values of conductivity; two zones north and south of the city of Pergamino have conductivities greater than 2000 μS cm−1. Isolines of depth to the fresh-salty water interface showed different values over the Pergamino River, with some local maxima at the swamp zone and near Pergamino.

Water Resources in the Salado River Drainage Basin, Buenos Aires, Argentina: Chemical and Microbiological Characteristics

Abstract Buenos Aires Province is located in the region of greatest agrarian importance in Argentina. Studies that have been carried out up to now are mainly hydrogeological, geological, and limnological and focused on localized specific problems. The aim of this article is to determine the chemical composition, including trace elements and the microbiological characteristics, of surface and shallow ground waters at a regional scale as a basis that may allow the relation of the dynamics of the natural systems with that of the economically productive systems. Groundwater and surface water were sampled in stations located with a global positioning system (GPS). Chemical and microbiological analyses were carried out using reference analytical methods. A representative group of samples was also analyzed with ICP-MS techniques for the determination of trace elements. Shallow groundwater is alkaline to strongly alkaline. The high sodium content is due to a cationic exchange process taking place in the clays of pampean loess. Surface waters, strongly alkaline and of sodium-chloride or sodium-sulfate type, come in part from the discharge of groundwater. The concentration of trace elements in shallow groundwater, does not respond strictly to the conditions of regional flow. Rather, their distribution is related to the morphology and distribution of several types of soils in the region. The microbiological analysis showed that in surface waters the number of total heterotrophic bacteria is within the usual ranges, fluctuating between 1 x 103 and 1 x 105 CFU/ml. The values of total coliforms and thermotolerant coliforms are in accordance with international established parameters for recreational waters.

GEOFÍSICA APLICADA A LA EVALUACIÓN DE LA VULNERABILIDAD A LA CONTAMINACIÓN EN ZONAS RURALES

Agricultural and cattle activities are considered to be the source of high risk of contamination of groundwater. The contamination is the result of the interaction between the contaminant charge and the aquifer vulnerability. The aim of this work was to evaluate the vulnerability of the Pampeano aquifer at some rural zones of the highly productive area of Pergamino-Arrecifes river basin. The traditional method of indexation was used taking into account the principal factors which influence: the depth of free groundwater level, the degree of confinement of the aquifer and the lithology of non saturated zone. The first one was obtained through geoelectrical prospecting, due to the lack of well information at some places. The last factors were estimated based on hidrogeological features known from some wells. The influence of the edaphic zone (soil) was incorporated as a new index by means of texture properties of soils sampled at each site and soil maps. Even if vulnerability was moderate for all the studied sites, some places along both margins of the Pergamino river had higher indexes than the surroundings of Arrecifes town. The small urban centers had greater risk of contamination of groundwater due to their intrinsic vulnerability (higher indexes) and the potential contaminant charge that intensive agricultural and cattle activities, which are developed around these sites, may generate. Higher values of nitrate concentrations were found at these places with a sharp increasing tendency during the last years, indicating the need of stronger control over the effect of these activities on groundwater contamination.