A. Vallejos

Factors which determine the hydrogeochemical behaviour of karstic springs. A case study from the Betic Cordilleras, Spain

The Cabra-Alcaide karstic massif situated in the south of Spain constitutes an important part of the so-called Natural Park of the Subbetic Sierras. This aquifer system is drained by various springs which supply a population of some 100,000 inhabitants. The feed areas of these springs show very different characteristics with respect to their geological structure, size of the drainage area, thickness of the vadose zone, elevation and degree of karstification. In addition, the carbonate rocks lie over a clayey substratum which contains large masses of intercalated evaporites. Due to these conditions, the hydrochemical composition of the springs is relatively variable. In this study a hydrogeochemical characterization of the aquifer in both space and time is undertaken and the factors that determine it are discussed. To achieve this, 19 monthly samples were taken from the 6 most significant springs of the hydrogeological system. The commencement of sampling coincided with the transition from a period of several years of severe drought and a very wet two-year period, which amplified considerably the hydrochemical and hydrodynamic response of the springs to the recharge. Identification of hydrogeochemical processes was performed by studying hydrographs, the temporal evolution of physico-chemical parameters, ionic ratios (mainly Mg/Ca) and by means of simple and multivariate statistical analyses. The saturation status was established using the WATEQF program and the mass transfer was quantified using PHREEQC. With the exception of the epikarstic subsystem (i.e. the Zarza spring), the majority of the results indicate that the aquifer exhibits a diffuse flow model, in which piston flow phenomena are seen, closely linked to the most intense precipitation. Along the direction of flow hydrochemical trends are seen as the water type changes from Ca–HCO3 to Ca–Mg–HCO3; at the same time enrichment in some ions, derived from the dissolution of evaporitic minerals of the impermeable substratum, and dedolomitization processes occur. In this way, almost 90% of the water samples were oversaturated in calcite, the majority of cases being a consequence of the dissolution of the gypsum of the substratum. Only in the epikarstic springs can it be considered that the oversaturation in calcite is due to loss of CO2 from the emerging groundwater. It is concluded that hydrodynamic aspects together with hydrogeochemical characteristics need to be taken into account to correctly explain the hydrochemical evolution of the karstic springs. Moreover, the use of both approaches permits a more accurate establishment of the degree of aquifer karstification, which in turn needs to be known in order to assess its vulnerability to contamination and to protect recharge zones.

Hydrogeochemical Characteristics of Processes in the Temara Aquifer in Northwestern Morocco

The physico-chemical characteristics of the groundwater of the Temara aquifer were studied by means of piezometric mapping and determination of the ionic composition of the groundwater. In general, the agricultural activity is intense in the area, with water being pumped from numerous wells. Two aquifer formations can be distinguished which, over a wide area, are separated by layers of low permeability. The increased salinity at some points of the coastal zone is probably linked to the combined action of the washing out of Miocene marls, dissolution of carbonate rocks, agricultural pollution and seawater intrusion.

Geochemistry of thermal springs, Alhama de Granada (southern Spain)

Abstract The waters of the thermal springs at Alhama de Granada vary in temperature between 27 and 45°C. Temporal changes in the composition of the principal spring (Banos Viejos) indicate that a small degree of mixing may occur between deep thermal waters and shallow groundwater. Slight compositional variations also occur between the various thermal springs in the study area. These spatial variations are due to the different local hydrodynamic conditions in the springs. Towards the north in less hydraulically transmissive rocks, cooling of the rising water is more noticeable, as are ion exchange and processes of SO 4 reduction. The chemical composition of the water is related to the dissolution of evaporites (SO 4 and Cl salts), carbonates and silicates, and to the possible existence of sources of S within the rock. Estimates of the mean residence times have been obtained based on 14 C DIC and T. The state of thermodynamic equilibrium at the spring discharge was calculated using the SOLMINEQ.88 program. The results indicate that all the samples are supersaturated with respect to quartz, chalcedony, cristobalite, calcite, aragonite and dolomite, and undersaturated with respect to gypsum, anhydrite and halite. The use of different geothermometers and modelling of saturation indices for quartz, albite and anhydrite indicate temperatures of about 110°C.

Geometry and dynamics of the freshwater-seawater interface in a coastal aquifer in southeastern Spain

Abstract The contact between freshwater and seawater in coastal aquifers is studied using a relatively simple model for homogeneous aquifers. However, for real aquifers it is not so simple. The desalination plant built to supply water to the city of Almería is situated over the aquifer in the southern part of the River Andarax Delta. Its design capacity is 1100 L s−1, and it is supplied from boreholes pumping water from beneath the freshwater—seawater contact in this aquifer. Well logs kept over a period of two years have allowed us to accurately define the interface geometry of the freshwater—seawater contact. Lithological data collected from 31 boreholes have also indicated the existence of strata with low hydraulic conductivity, within others of high conductivity. During a simultaneous pumping test of six wells with 690 L s−1 total discharge, electrical conductivity measurements showed the influx of seawater 6–10 m below sea level and a drawdown of the interface in the piezometers closest to the pumping wells.

Geostatistical Analysis to Identify Hydrogeochemical Processes in Complex Aquifers: A Case Study (Aguadulce Unit, Almeria, SE Spain)

Abstract The Aguadulce aquifer unit in southeastern Spain is a complex hydrogeological system because of the varied lithology of the aquifer strata and the variability of the processes that can take place within the unit. Factorial analysis of the data allowed the number of variables to be reduced to 3 factors, which were found to be related to such physico-chemical processes as marine intrusion and leaching of saline deposits. Variographic analysis was applied to these factors, culminating in a study of spatial distribution using ordinary kriging. Mapping of the factors allowed rapid differentiation of some of the processes that affect the waters of the Gador carbonate aquifer within the Aguadulce unit, without the need to recur to purely hydrogeochemical techniques. The results indicate the existence of several factors related to salinity: marine intrusion, paleowaters, and/or leaching of marls and evaporitic deposits. The techniques employed are effective, and the results conform to those obtained using hydrogeochemical methods (vertical records of conductivity and temperature, ion ratios, and others). The findings of this study confirm that the application of such analytical methods can provide a useful assessment of factors affecting groundwater composition.

The anthropogenic impact on Mediterranean karst aquifers: cases of some Spanish aquifers

Mediterranean karstic aquifers are a major source of water supply for drinking water and agricultural use. In semiarid areas, the risk of causing an intensive exploitation is high, leading to degradation processes of water quality, not only due to limited agricultural activities developed on the karstic rocks—being generally poorly developed soils—but to the presence of deep evaporates which can be mobilised, or because of being coastal aquifers where seawater intrusion can progress rapidly. Moreover, karstic massifs constitute often positive reliefs that can generate barriers for civil works, more and more saved by building sophisticated tunnels; such works can affect the quantity and quality of the waters from the karst. Five examples of human impacts on some karst aquifers in SE of Spain are shown in this paper, three of them with impacts on water quality and the other two correspond to the impact of tunnels in high-speed trains drilling below the water table.

ArcE: A GIS tool for modelling actual evapotranspiration

This paper introduces ArcE, a GIS tool for modelling actual evapotranspiration (EA) from an undefined number of meteorological stations. From daily data of precipitation and temperature, ArcE uses ArcObjects as the programming language to incorporate equations and hydrological boundary conditions, in order to calculate EA at monthly and yearly time steps. Because weather data are often missing, ArcE is programmed to use non-global models such as Hargreaves for potential evapotranspiration (EP) and Budyko for EA. In arid regions, where results from global and non-global models are expected to deviate, ArcE allows for the segregation of low-divergent areas suitable for interpolating EA from those that should be excluded for mapping the variable. In the semiarid Almanzora River basin, a heterogeneous region with contrasting climate in SE Spain, divergence in lowlands with a higher aridity index was about 15% with respect to an accurate estimate of EA from the Penman–Monteith equation. Evaluating EA is a first step for mapping the non-evaporative fraction of precipitation as the difference in P and EA.

Erratum to ArcE: A GIS tool for modelling actual evapotranspiration [Comput. Geosci. 37(9), 1468-1475]

Erratum to ‘‘ArcE: A GIS tool for modelling actual evapotranspiration’’ [Comput. Geosci. 37(9), 1468–1475] Salvador Espana , Francisco J. Alcala , Angela Vallejos , Antonio Pulido-Bosch a a Departamento de Hidrogeologia, Universidad de Almeria, 04120 Almeria, Spain b Geo-Systems Centre/CVRM, Instituto Superior Tecnico, 1049-001 Lisbon, Portugal c Estacion Experimental de Zonas Aridas (EEZA-CSIC), 04120 Almeria, Spain

An oceanographic survey for the detection of a possible Submarine Groundwater Discharge in the coastal zone of Campo de Dalias, SE Spain

The Campo de Dalias, in south-eastern Spain, is an area of important economic activity linked to agriculture and tourism, both of which have exacted fierce exploitation of aquifer water. The recovery of one of these aquifers in recent years has even triggered fresh water discharges into the sea. An oceanographic survey was undertaken along the coastline in order to detect possible Submarine Groundwater Discharge (SGD). Salinity and temperature data were collected on the seasurface, as well as in 51 vertical profiles. These results suggest the existence of a thermohaline anomaly in the area of the port of Aguadulce possibly due to submarine groundwater discharges.

Impact of irrigated agriculture on groundwater-recharge salinity: a major sustainability concern in semi-arid regions

Intensive irrigated agriculture substantially modifies the hydrological cycle and often has major environmental impacts. The article focuses upon a specific concern—the tendency for progressive long-term increases in the salinity of groundwater recharge derived from irrigated permeable soils and replenishment of unconfined aquifers in more arid regions. This process has received only scant attention in the water-resource literature and has not been considered by agricultural science. This work makes an original contribution by analysing, from scientific principles, how the salinisation of groundwater recharge arises and identifies the factors affecting its severity. If not proactively managed, the process eventually will impact irrigation waterwell salinity, the productivity of agriculture itself, and can even lead to land abandonment. The types of management measure required for mitigation are discussed through three detailed case histories of areas with high-value groundwater-irrigated agriculture (in Spain, Argentina and Pakistan), which provide a long-term perspective on the evolution of the problem over various decades.RésuméL’irrigation agricole intensive modifie considérablement le cycle hydrologique et a souvent des impacts environnementaux majeurs. L’article porte sur une préoccupation spécifique—la tendance à l’augmentation progressive à long terme de la salinité de la recharge des eaux souterraines provenant des sols perméables irrigués et de la reconstitution des niveaux piézométriques des aquifères libres dans les régions plus arides. Ce processus n’a reçu que peu d’attention dans la littérature sur les ressources en eau et n’a pas été pris en compte par les sciences agricoles. Ce travail apporte une contribution originale en analysant, à partir de principes scientifiques, comment se produit la salinisation de la recharge des eaux souterraines et identifie les facteurs affectant sa sévérité. S’il n’est. pas géré de manière proactive, le processus aura éventuellement une incidence sur la salinité des puits utilisés pour l’irrigation, sur la productivité de l’agriculture elle-même et peut même mener à l’abandon de terres. Les types de mesures de gestion requises pour l’atténuation sont discutés à travers trois cas détaillés d’agriculture irriguée (en Espagne, en Argentine et au Pakistan), qui offrent une perspective à long terme de l’évolution du problème sur plusieurs décennies.ResumenLa agricultura intensiva con regadío modifica sustancialmente el ciclo hidrológico y a menudo tiene importantes impactos ambientales. El trabajo se centra en una preocupación específica—la tendencia a incrementos progresivos a largo plazo en la salinidad del agua subterránea en la recarga derivada de la irrigación de suelos permeables y de la recarga de acuíferos no confinados en regiones más áridas. Este proceso ha recibido escasa atención en la literatura de los recursos hídricos y no ha sido considerada por la ciencia agrícola. Este trabajo realiza una contribución original al analizar, desde principios científicos, cómo surge la salinización de la del agua subterránea en la recarga e identifica los factores que afectan su severidad. Si no se gestiona de manera proactiva, el proceso eventualmente impactará en la salinidad de los pozos de agua para riego, la productividad de la agricultura en sí misma, e incluso puede llevar al abandono de la tierra. Los tipos de medidas de gestión requeridas para la mitigación se discuten a través de tres casos detallados de áreas con alto valor de la agricultura con riego de agua subterránea (en España, Argentina y Pakistán), que proporcionan una perspectiva a largo plazo sobre la evolución del problema durante varias décadas.摘要集中灌溉农业大大改变了水循环,常常产生重要的环境影响。文章特别关注的问题就是—在比较干旱的地区灌溉的渗透性土壤和非承压含水层补给导致的地下水补给盐度长期连续增加的趋势。这个过程只在水资源文献中受到关注,并没有被农业科学所考虑。从农业原理上通过分析地下水补给造成的盐化是怎样引起的以及确定影响其严重程度的因素,本研究工作作出了创造性的贡献。如果不能受到积极的管理,过程最终将会影响灌溉水井的盐度以及农业自身的生产力,甚至可导致土地的废弃。通过高价值地下水灌溉农业区(西班牙、阿根廷和巴基斯坦)三个详细的案例探讨了缓解所需的管理措施类型,这些管理措施类型为过去几十年问题的演化提供了长期的观察视角。ResumoAgricultura intensiva irrigada modifica substancialmente o ciclo hidrologico e frequentemente tem grandes consequencias ambientais. O artigo centra-se em um conceito específico—a tendência para o aumento progressivo de longo prazo na salinidade da recarga da água subterrânea derivada de solos permeáveis irrigados e reabastecimento de aquíferos confinados em regiões áridas. Este processo recebeu pouca atenção na literatura sobre recursos hídricos e não foi considerado pela ciência agrícola. Este trabalho faz uma contribuição original para analisar, a partir de principios cientificos, como a salinização da reacarga de água subterrâneas ocorre e identificar os fatores que afetam sua severidade. Se não for gerenciado de forma proativa, o processo eventualmente terá impacto na salinidade do poço de irrigação, na produtividade agrícola e pode até levar ao abandono da terra. Os tipos de medidas de manejo necessárias para a mitigação são discutidos através de três históricos detalhados de áreas com agricultura irrigada de alto valor por água subterrânea (na Espanha, Argentina e Paquistão), que fornecem uma perspectiva de longo prazo sobre a evolução do problema ao longo de várias décadas.