Ionic relations: a tool for studying hydrogeochemical processes in Pampean shallow lakes (Buenos Aires, Argentina) (original) (raw)
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Revista Brasileira de Recursos Hídricos, 2001
Chemical analyses of major ions performed in some of the Pampasic ponds located in the lower reach the Salado River showed a similar composition to that of shallow groundwater, i.e., the total dissolved solids ranged between 1 g/l and 2 g/l, sodium was the most abundant among the cations and accounted (meq/l) for 80.6%. Calcium amounts were 6.5% while magnesium was 9.9%. Potassium was less abundant with a mean value of 3.0%. Appreciable differences between summer and winter values were not observed. Since groundwater was the main source of surface water, a possible geochemical mechanism was proposed in order to achieve better understanding of the Pampasic pond's water chemistry. The processes that seem to be responsible for groundwater hydrochemistry are: cation exchange, ancient marine sediments dissolution and aluminosilicate weathering. The differences observed between surface water and shallow groundwater composition with respect to an additional enrichment in sodium may be attributed to the evaporation-crystallisation process promoting calcite precipitation.
Journal of Geochemical Exploration, 2015
The Pampean plain is one of the most extended regions of the world. In this plain there are numerous shallow lakes that have different origins associated with climate changes at the end of the Quaternary period. Chasicó Lake is the main waterbody in the southwest of the Chaco-Pampean plain. It shows some differences from the typical Pampean shallow lakes. The aim of this paper is to explain the geochemical process that determines the chemical composition of the water of Chasico Lake. The results show that the groundwater is sodium bicarbonate type. Chebotarev's diagram indicates that the catión-exchange takes place in groundwater. The surface water of Chasicó Lake is sodium chloride type. Gibbs's diagram shows that the geochemical processes that affects the Chasicó Lake are evaporation and crystallization, being the water of the lake similar to seawater. The BEI (Base Exchange Index) shows that the process of cation-exchange in the water is not relevant. As, F and V concentrations were studied in surface and groundwater showing significant correlations in groundwater between As vs. F (r = 0.99, p b 0.05), As vs. V (r = 0.99, p b 0.05) and V vs. F (r = 0.99, p b 0.05), while in surface water it was only found for As vs. F (r = 0.91, p b 0.05). The As, F and V concentration values were higher and more widely dispersed in surface water than in groundwater, as a consequence of evaporation. The fact that these elements do not correlate in surface water may also indicate a different origin.
International Journal of Salt Lake Research, 1994
Rivers and streams originating in the surrounding mountainous area are the major sources of salt in the Salinas Grandes basin (Crrdoba, Argentina). These rivers infiltrate when they reach the sandflat or in the fringes of the mudflat, feeding springs which often form shallow lakes. Presently, the lakes are distant from the playa edge, thus allowing inflow waters to dissolve ancient (Pleistocene?) evaporite beds. In the sandflat environment, two dominant types of water have been recognized (SO]--C1--HCO~--Na +, and C1--SO] --HCO~--Na +), both considered as original members of the brine in the saline complex. Two main sources of solutes were distinguished, one related to the waters supplied by the southern sector and another to waters of the eastern sector. As a result of the chemical evolution in the playa environment, all brines belong to the neutral type (C1--SO]--Na+). Following model, waters from the southern sector should evolve towards an alkaline brine (C1--SO 2--HCO~--Na+), whereas those from to the eastern sector should evolve towards a neutral one (C1--SO]--Na+). A computer simulation was carried out to model the chemical evolution of source waters. The results obtained by this methodology showed the same dichotomy (alkaline vs, neutral) established by model. The deficit in alkalinity could not be explained by any of the mechanisms published until now. Gypsum dissolution is the most likely mechanism which accounts for the chemical evolution of the waters investigated. When such a process is included in the computations, the Ca 2+ supplied by gypsum beds generates an increase in the ion activity product (aCa+2.aCO] -) and produces a significant change in the 2Ca+2/(2CO~ -+ HCO3) ratio, switching from values less than 1 to values greater than 1. This process determines the precipitation of calcite, and leads to a decrease in alkalinity, which in turn would explain the existence of a neutral brine in the saline complex. An intermediate salinity brine was detected in the mudflat, which, according to the model , should evolve towards a SO ]--free neutral brine (CI--Na+--Ca2+). The absence of this type of brine may be explained through mixing processes.
Environmental Earth Sciences, 2020
The chemical compositions of waters from the upper basin of the Ctalamochita River draining the Córdoba Pampean Ranges were analyzed to determine the chemical signature related to different forcings, geochemical processes, and solutes sources. The catchment has four sub-basins: Santa Rosa River, Grande River, Quillinzo River and De Los Sauces River. Most of the riverine chemical compositions are dominated by the HCO 3 −-Ca 2+-type to Ca 2+-Na +-Mg 2+. The specific conductivity is higher in the Santa Rosa and De Los Sauces rivers (347.59 and 409.00 μS/cm, respectively) than in the Grande and Quillinzo rivers (125.56 and 87.54 μS/cm, respectively). Mineral hydrolysis of andesine and oligoclase and the dissolution of calcomagnesian limestone, are the main dissolved solids contributors to the river waters. Higher contribution of bicarbonate ions is associated to those sub-basin having quarry mining activity. Saturation indexes show that the Santa Rosa and De Los Sauces rivers are saturated with calcite, dolomite, and talc.
Environmental Geology, 2008
The main ions were measured seasonally during two years at 13 sampling stations in the Salado River and its main tributaries. The importance of each ion was assessed by standard methods used to examine ionic composition and by multivariate methods. The K-means clustering and Principal Component Analysis were applied to the percentages of the major ions. The concentration of the major cations are in the order Na + > Mg 2+ > Ca 2+ > K + and the major anions, Cl-> SO 4 2-> HCO 3-> CO 3 2-, and the salinity was high (mean TDS 2,691 mg l-1) due to sodium chloride. Using the proportions of the ions was possible to identify seven types of water within the basin related to discharges of different river sub-catchments and from endorheic catchments (in a sand dune region) actually connected with the basin by canals. The chemical composition of the basin is consequence of surface waters receiving salts from groundwater, evaporation and weathering of Post-Pampeano materials, and of anthropogenic impact by diversion between subcatchments for flood control. These results allowed us to test the marked effects on the ionic balance of basin at the base of a diversion management from endorheic catchments characterized by high salinity waters.
Hydrochemistry of pampasic ponds in the lower stream bed of Salado River drainage basin, Argentina
Environmental Geology, 2000
Chemical analyses of major ions were performed in some of the pampasic ponds in the lower stream bed of Salado River drainage basin. Results indicated that total dissolved solids had a mean value of 1341 mg/l, where sodium was the most abundant of the cations (80.2%) and chloride (44.2%) and bicarbonate (37.4%) were the predominant anions. Saturation index showed oversaturation with respect to calcite and dolomite. Since groundwater is the main source of surface water, high sodium concentration in the ponds may be explained by a cation exchange process in the loessic sediments of the basin where calcium is replaced by sodium.
CATENA, 2018
The Pampean aquifer, in south east Argentina, is mainly constituted of loess-like sediments. These are clastic sediments mainly composed of quartz and aluminosilicates and calcrete concretions. Its hydrochemistry is generally studied assuming a chemical equilibrium between mineral phases and the aqueous fluids. The phases forming the matrix of this aquifer are considered to be the reactive phases responsible for the chemistry of the groundwater. In the present study, batch dissolution experiments were performed on calcrete and loess to better understand the source of the Pampean aquifer water chemistry and to measure the benefit of applying waterrock interaction models that use kinetic rate laws instead of thermodynamic equilibria. The different minerals composing the loess and calcrete samples were calculated using quantitative Rietveld refinement of X-ray powder diffraction (XRD) patterns. This analysis showed that the major phases of loess are quartz (~30 wt%) and feldspars (~70 wt%). The main components of calcrete are calcite (~95 wt%) and quartz (~5 wt%). Scanning electron microscopy with energy dispersive X-ray microanalysis (SEM/EDXS) was used to provide detailed information about the chemical composition of the powder samples, revealing the presence of traces of minerals like halite, barite and fluorapatite, which were not detected by XRD. The kinetic code KINDIS was used to carry out simulations using the minerals identified previously in their relative proportions to identify the signature of those geochemical phases on water chemistry. Experimental data from batch dissolution experiments were compared to simulated data. This investigation showed that water reached pseudo steady state concentrations due to the presence of fast dissolving phases like halite, barite, gypsum, plant phytolith. These phases appeared to be of major importance in controlling the chemical composition of the Pampean groundwater. Furthermore, this work showed that the KINDIS software can be used on all kinds of aquifers as it is very easy to modify the parameters of the simulation to adapt it to numerous situations. The modeling is a very important tool for thermodynamic and kinetic studies of groundwater chemistry; it enables the prediction of water quality and can help to understand the impact of anthropic or natural contamination on the groundwater.
Chemical behavior of the Salí River, Province of Tucumán, Argentina
Environmental Geology, 2001
Major ionic composition and other chemical parameters were determined at ®ve sampling stations on the Salõ Â River (Province of Tucuma Ân, Argentina). The heavy human usage of the river causes increased levels of dissolved ions, from the dissolution of halite and gypsum, and from the weathering of basic sediments. Correlations demonstrate that sodium chloride and sulphate, and calcium carbonate are the main contributors to dissolved ions in the river. In the polluted region, south of the Celestino Gelsi dam, the main source of calcium and sulphate is the dissolution of gypsum. Large amounts of halite are also dissolved. Weathering of biotite, K-feldspar and albite are suggested by the data. Conductivity, dissolved oxygen and organic matter all indicate severe contamination by organic matter (mainly from sugar-cane processing) in the lower course. The data also demonstrate a substantial improvement in water quality before the discharge of the river at the Rõ Âo Hondo dam. Data from the Colorado (a tributary of the Salõ Â River) and Medina rivers are also analyzed and compared.
Hydrochemistry of two adjacent acid saline lakes in the Andes of northern Chile
Chemical Geology, 2002
Numerous closed-basins in central Andes contain saline lakes and salt crusts (salars). Almost all of them are neutral or alkaline lakes. Only two lakes out of 84 studied in Bolivia and Chile are acid lakes. They are located in two adjacent intravolcanic basins in northern Chile. The origin of acidity is due to the juxtaposition of two factors: the very strong hydrothermal alteration of volcanic rocks in the drainage basins and the high sulfur content in the whole area. Primary minerals are replaced by amorphous silica, limonite, chlorite, white mica and elemental sulfur. The buffer capacity of the volcanic rocks has been considerably lowered and is no longer sufficient to neutralize the sulfuric acid generated by oxidation of native sulfur. Dissolution modeling of chlorite, white mica and sulfur in a neutral inflow water leads to a composition very much like that of the acid inflows. The modeled acid solution is oversaturated with respect to alunite by several orders of magnitude, exactly as observed in natural acid inflows. Some of the alunite reported in the altered zones of the drainage basins could be supergene in origin. The simulation of evaporation of acid inflows shows a good agreement between salar brines and computed brines, indicating that the acidic brines do not originate in the past hydrothermal activity, but result from recent supergene processes: the leaching of the severely altered volcanic rocks and the direct evaporation of the resulting acidic waters. Aluminium shows a conservative behavior in both salars reflecting the drastic lowering of the saturation index of Al-sulfate minerals in evaporating acid brines, which is confirmed by the lack of detection of alunite within both salars. D