Eduardo Kruse

Saltwater contamination in the managed low-lying farmland of the Venice coast, Italy: An assessment of vulnerability.

The original morphology and hydrogeology of many low-lying coastlands worldwide have been significantly modified over the last century through river diversion, embankment built-up, and large-scale land reclamation projects. This led to a progressive shifting of the groundwater-surficial water exchanges from naturally to anthropogenically driven. In this human-influenced hydrologic landscape, the saltwater contamination usually jeopardizes the soil productivity. In the coastland south of Venice (Italy), several well log measurements, chemical and isotope analyses have been performed over the last decade to characterize the occurrence of the salt contamination. The processing of this huge dataset highlights a permanent variously-shaped saline contamination up to 20km inland, with different conditions in relation with the various geomorphological features of the area. The results point out the important role of the land reclamation in shaping the present-day salt contamination and reveal the contribution of precipitation, river discharge, lagoon and sea water to the shallow groundwater in the various coastal sectors. Moreover, an original vulnerability map to salt contamination in relation to the farmland productivity has been developed taking into account the electrical conductivity of the upper aquifer in the worst condition, the ground elevation, and the distance from salt and fresh surface water sources. Finally, the study allows highlighting the limit of traditional investigations in monitoring saltwater contamination at the regional scale in managed Holocene coastal environments. Possible improvements are outlined.

Recharge assessment in an urban area: a case study of La Plata, Argentina

Leakage from water mains, storm drainage and sewer systems in urban areas constitutes a source of recharge that is difficult to identify and quantify at a regional scale. The objective of this work is to apply a methodology that would make it possible to evaluate urban recharge at a regional scale, taking as a case study the city of La Plata (Argentina). In the study area, population growth and an increase in water demand has caused the intensive exploitation of groundwater with resulting alteration in groundwater flow. The methodology used was developed on the basis of a water balance and the simulation of the temporal evolution of the cones of depression and the volumes of water extracted from the aquifer. The method consists of adjusting the piezometry resulting from the numerical modelling to the measured piezometry, by means of the variation of the recharge parameter in the urban area. The results obtained make it possible to identify and quantify urban recharge, which in this case represents a volume of water similar to the recharge from precipitation.RésuméFuite de conduites maîtresses, drainage des orages et systèmes d’égouts en zones urbaines constituent des sources de recharge qu’il est difficile d’identifier et de quantifier à une échelle régionale. L’objectif de ce travail est d’appliquer une méthodologie qui rendrait possible l’évaluation d’une recharge urbaine à une échelle régionale, prenant comme cas la ville de La Plata (Argentine). Dans la zone d’étude, la croissance de la population et l’augmentation de la demande en eau ont causé une exploitation intensive de la nappe avec altération résultante du débit d’écoulement souterrain. La méthodologie utilisée a été développée sur la base d’un bilan d’eau et de la simulation de l’évolution temporelle des cônes de dépression et des volumes d’eau extraits de l’aquifère. La méthode consiste à ajuster la piézométrie résultant de la modélisation numérique à la piézométrie mesurée, au moyen de la variation des paramètres de la recharge dans la zone urbaine. Les résultats obtenus ont rendu possible l’identification et la quantification de la recharge urbaine, qui dans ce cas représente un volume d’eau similaire à la recharge des précipitations.ResumenLas pérdidas de las cañerías de aprovisionamiento de agua, de los drenajes pluviales y cloacas, constituyen una recarga urbana que es de difícil identificacion y cuantificación a escala regional. El objetivo del trabajo es aplicar una metodología que permita evaluar la recarga urbana a escala regional tomando como caso de estudio a la ciudad de La Plata (Argentina). El crecimiento poblacional y el aumento en la demanda de agua produjeron una explotación intensa de las aguas subterráneas con la consecuente alteración del flujo subterráneo. La metodología usada se desarrolló partir de un balance de agua y la simulación de la evolución temporal de los conos de depresión y los volúmenes de agua extraídos del acuífero. El método consiste en ajustar la piezometría resultante del modelo numérico a la piezometría medida, mediante la variación del parámetro de recarga en el área urbana. Los resultados obtenidos permiten identificar y cuantificar la recarga urbana la cual representa, para este caso, un volumen de agua similar a la recarga proveniente de las precipitaciones.ResumoAs fugas a partir de canalizações de águas de abastecimento, de águas pluviais e de águas residuais em áreas urbanas constituem uma origem de recarga que é difícil de identificar e quantificar a uma escala regional. O objetivo deste trabalho é a aplicação de uma metodologia que tornasse possível avaliar a recarga urbana a uma escala regional tomando como estudo de caso a cidade de La Plata (Argentina). Na área de estudo, o crescimento populacional e um incremento na procura de água causaram uma exploração intensiva da água subterrânea com a consequente modificação no escoamento da água subterrânea. A metodologia usada foi desenvolvida com base no balanco hídrico e na simulação da evolução temporal dos cones de rebaixamento com os volumes de água extraídos do aquífero. O método consiste no ajuste da piezométrica resultante da modelação numérica com a piezométrica medida, através da variação do parâmetro de recarga na área urbana. Os resultados obtidos tornam possível identificar e quantificar a recarga urbana, que neste caso representa um volume de água similar ao da recarga proveniente da precipitação.

Ionic exchange in groundwater hydrochemical evolution. Study case: the drainage basin of El Pescado creek (Buenos Aires province, Argentina)

The phreatic aquifer beneath the Pampean plain, in eastern central Argentina, constitutes a relevant source of water supply in the area. The objective of this work was to assess the significance of the cation exchange processes in the hydrochemical evolution of this aquifer, based on a study case located in the middle and upper basin of the El Pescado creek. Results indicate that Ca2+/Na+ exchange is the main process determining the evolution of groundwater from the recharge areas (Ca–HCO3) towards the local discharge areas (Na–HCO3), as well as representing a source of Na+ contribution to the water in the aquifer. This hydrochemical characteristic is central to the identification of local discharge areas within a plain environment which extends regionally. The ion exchange capacity of these discharge areas has environmental importance, due to its influence on groundwater quality and potential groundwater uses. These results may be applied to any aquifer sharing similar hydrogeological characteristics.

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.

Numerical and experimental study of a thermal probe for measuring groundwater velocity

A thermal method for a rapid measurement of groundwater velocity, particularly in aquifers with preferential flow where groundwater velocities over tenths of (m/d) are expected, was studied. Some instruments for measuring groundwater velocity are based on the application of heat. Those consisting of a central heater surrounded by several thermistors seem adequate for the above purpose, but their measuring range lies below 30 md (meters per day) and there are few works about their theory. Based on the diffusion-convection-dispersion equation, an electrical model is proposed for representing this type of instruments and a theoretical study is presented in an attempt to extend their measuring range. The model can be excited with any shape of power or temperature signals, allows the signals to be feedbacked for controlling the heaters excitation, and includes the thermal features of the heater and thermistors. The model was validated through laboratory tests with velocities of up to 100 md and extrapolated up to 1000 md. Numerical results suggest that exciting the heater with constant temperature allows the measuring range of these probes to be extended.

Surface water and groundwater response to the tide in coastal wetlands: Assessment of a marsh in the outer Río de la Plata estuary, Argentina

ABSTRACT Carol, E; Kruse, E and Tejada, M, 2013. Surface water and ground water response to the tide in coastal wetlands: Assessment of a marsh in the outer Río de la Plata estuary, Argentina On the coast of the outer Río de la Plata estuary (Argentina) there is a vast coastal wetland occurring in a marsh environment. The hydrodynamics of this wetland is subject to a semidiurnal microtidal regime which causes a wedge of estuary salt water to penetrate below the freshwater coming from continental discharge. This paper analyzes the hydrodynamics of surface and groundwater, and it assesses how anthropogenic changes affect the natural hydrological behavior of the coastal wetland in the southern sector of the outer Río de la Plata estuary. Water level and temperature measurements were carried out on water from the canals flowing into the estuary and the phreatic aquifer located in the marsh. The salinity of the water column was measured at one high tide which was above and one which was below the regional groundwater discharge level. The results show that in natural conditions the wetland has a complex hydrological behavior conditioned by the tidal flow. Surface and groundwater saline stratification is a distinctive characteristic, and the variations in level, temperature and salinity of groundwater depend on its interaction with estuary and continental water. At present, 47 % of the marsh is excluded from the tidal cycle due to anthropogenic action (levees, roads and canals with floodgates), causing a major alteration to the hydrological behavior and the environmental characteristics of the wetland.

Groundwater travel time in the freshwater lenses of Samborombón Bay, Argentina

Abstract The Samborombón Bay area (Argentina) is a coastal plain environment that contains groundwater resources with high salinity. In addition, there are local freshwater lenses associated with shell ridges and sand sheets in the region. In this work, the groundwater travel time in these freshwater lenses is estimated based on their geological conditions, which include hydraulic conductivity, recharge, morphology and discharge to surface freshwater or to saline groundwater. Groundwater travel times in the freshwater lenses were calculated from the equations developed by Chesnaux and Allen. The travel times estimated for the different scenarios were relatively short. The results indicate that the groundwater flow tends to be strongly dependent on the recharge conditions, with an excess of water in the water balance. The results can be applied to help design sustainable management methods to exploit this water resource system and also to assess the impact of contaminant plumes on this groundwater resource. Citation Carol, E., Kruse, E. & Roig, A. (2010) Groundwater travel time in the freshwater lenses of Samborombón Bay, Argentina. Hydrol. Sci. J. 55(5), 754–762.

The carbon budget of a large catchment in the Argentine Pampa plain through hydrochemical modeling

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 lagoons 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.

Hydrogeologic Behavior of an Alluvial Aquifer, Salta Province, Argentina: Simulations of Hydraulic Conductivity Field, Groundwater Flow, and Chloride Migration

This work was designed to analyze the hydrogeological behavior of an alluvial aquifer in the River Mojotoro basin site in the Province of Salta, Argentina. The study area presents coarse-grained sediments with high infiltration capacity. The hydraulic conductivity field is affected by the physical heterogeneity of the medium and a geostatistical method, kriging, was used to construct this field from local measurements. The groundwater flow velocity field is computed using a hybrid mixed finite-element method and small variations in the flow directions were determined. Given the existence of a point source of chloride in the region under study, the spatial distribution of the generated plume in the saturated zone is analyzed. The advection-diffusion equation describing the transport of chloride in vertical and horizontal cross-sectional planes of the aquifer is discretized employing a method of characteristics combined with a mixed finite-element procedure, which provides an efficient method to eliminate spurious numerical oscillations and handle the convective term in the equation. The migration of chloride shows patterns, which are affected by the litologic heterogeneities of the aquifer and the regional groundwater flow.

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.