Ra isotopes and Rn as a tool for the water management resources : the Alberquillas aquifer (Málaga-Granada)

Universitat Autònoma de Barcelona - Facultat de Ciències Llicenciatura de Ciències Ambientals PROJECTE DE FINAL DE CARRERA 2011 Ra isotopes and Rn as a tool for the water management resources: the Alberquillas Aquifer (Málaga-Granada) JosepOriol López Plana Directors: Dr. Jordi Garcia-Orellana Valentí Rodellas Vila 2 3 Quan surts per fer el viatge cap a Itaca, has de pregar que el camí sigui llarg, ple d'aventures, ple de coneixences. Has de pregar que el camí sigui llarg, que siguin moltes les matinades que entraràs en un port que els teus ulls ignoraven, i vagis a ciutats per aprendre dels que saben. LLUÍS LLACH 4 5 ACKNOWLEDGEMENTS / AGRAÏMENTS Primer de tot m’agradaria donar les gràcies al meu director de projecte, el Jordi Garcia-Orellana per haver-me donat la oportunitat de conèixer en el món de l’oceanografia de costa perquè estar qualsevol dimarts pel matí damunt d’una barqueta no té preu. Donar-te les gràcies per ensenyar-me tot el que he après en radioactivitat i el “Hola què tal?” que val molt! També agrair al co-director, el Valentí pels viatgets i les respostes a les múltiples preguntes que m’heu provocat durant aquesta estada al LRA. Agrairte també que em deixis fer barca quasi sempre i siguis tu qui et banyi a mes de Novembre i Gener. D’una manera molt especial, donar les gràcies als companys del Laboratori de Radioactivitat Ambiental (LRA). Al Pere per la campanya del FAM3 que mai oblidaré, al JoanManel pels debats a taula, a la Núria per empentar-me quan ha calgut, a la Patri perquè he après molt de tu, a la Viena per la quantitat de moments passats (buf!) i també a la Mercè (Famosillos!) per ajudar-me tant escoltant i discutint, a la Carol per les expedicions de l’estiu, a la Karina d’una manera molt especial per totes les aventures que hem visut, a la Teresa pels riures al despatx i a la Ester per haver passat tota la carrera junts i ara coincidir al laboratori. Agradecer a la Universidad de Málaga su colaboración para la redacción de este proyecto, a l’Institut de Ciències del mar (ICM) i al Centre Mediterrani d’Investigacions Marines i Ambientals (CMIMA) i a l’Institut Mediterrani d’Estudis Avançats (IMEDEA) per les diferents campanyes efectuades durant aquest temps. Per altra banda, donar mil gràcies a la gent del meu entorn. Al rugbi per deixar-me desfogar quan més ho necessito, a tota la colla d’Ambientals ja ho sabeu, per la vostra amistat i la quantitat de moments que hi ha hagut amb cada un de vosaltres i a la gent del barri per tots els divendres i la infinitat de futbolins que hem fet. Visu i Miri, gràcies especialment! !نركش نساج اي ةيبرعلا مسيك، انا ديعس نركشو اي ةلواب، انا ُتبحا Finalment, agrair sempre el recolzament incondicional de la meva familia des del primer fins a l’últim moment i en tot el que faci. Gràcies 6 7 PREFACE The aim of this project is to evaluate the importance of submarine groundwater discharge sector in order to improve the water balance in MálagaGranada region. The approach of this study arose from the the geology and the aquifers that indicate that there could be some discharge to the sea between Maro (Málaga) and Almuñécar (Granada) and the Andalusian’s Government and its Water Agence were really interested in evaluating it because there is a lot of population and few water available and the magnitude of groundwater discharge has generated controversy. Is well known that water is a scarce resource in this area and it’s very important for the society and for the environment. The legislation, the water policies, the knowledge of the aquifer and the geology, the water dynamics, the land use and the water perception in the society might help the management of this resource not just in Andalusia but in all the Mediterranean basin. The main objective is to evaluate the submarine groundwater discharge from the Alberquillas Aqufier to the sea by measuring 222 Rn and Ra isotopes. Specific objectives have been established to achieve the main objective: - Reveal the importance of water resources in the Mediterranean basin. - Learn radiometric techniques for the study of groundwater discharge to the sea. - Learn of sampling techniques of water samples for the measurement of Ra and Rn. - Learn the techniques for measuring Ra (RaDeCC) and Rn (RAD7). - Interpretation and discussion of results. During this semester, and in addition of the present study in MálagaGranada region, the author has participated in the initial phase (sampling, analysis and interpretation of preliminary results) of other research projects focused on the study of submarine groundwater discharges through the use of Ra isotopes and 222 Rn. These studies have been developed in different areas, including Alt Empordà (Roses and Sant Pere Pescador), Maresme with CMIMA’s group (Mediterranean Center for Marine and Environmental Research), Delta de l’Ebre, Peñíscola and Mallorca with the IMEDEA’s group (Mediterranean Institute for Advanced Studies). 8 9 INDEX ACKNOWLEDGEMENTS PREFACE INDEX 1. INTRODUCTION - - - - - - - - 12 1.1. WATER MANAGEMENT - - - - - - 12 1.1.1. MANAGEMENT OF WATER RESOURCES IN THE MEDITERRANEAN BASIN - - - - 12 1.1.2. MANAGEMENT OF WATER RESOURCES IN SOUTHEASTERN SPAIN - - - - - - 20 1.2. SUBMARINE GROUNDWATER DISCHARGE TO THE SEA - 23 1.2.1. DEFINITION AND IMPORTANCE OF THE SUBMARINE GROUNDWATER DISCHARGE - - - - 23 1.2.2. DETECTION AND QUANTIFICATION - - - 25 1.2.3. QUANTIFICATION WITH Ra AND Rn ISOTOPES - 31 2. STUDY AREA - - - - - - - - 34 2.1. HYDRIC SITUATION IN MÁLAGA-GRANADA REGION - 34 2.2. THE AQUIFER - - - - - - - - 35 2.2.1. DESCRIPTION AND TYPES - - - - 35 2.2.2. THE AQUIFER OF THE HYDROGEOLOGICAL SUBUNIT OF “LAS ALBERQUILLAS” - - - - - 36 3. MATERIAL AND METHODS - - - - - - 41 3.1. SAMPLING METHODOLOGY - - - - - 41 3.1.1. WATER SAMPLES - - - - - - 41 3.2. ANALYSIS PROCEEDING - - - - - - 43 3.2.1. Ra - - - - - - - - 43 3.2.1.1. Short-lived isotopes - - - - 43 3.2.1.2. Long-lived isotopes - - - - 43 3.2.2. Rn - - - - - - - - 43 3.3. DETECTION SYSTEMS - - - - - - 43 3.3.1. RaDeCC - - - - - - - 43 3.3.2. GAMMA SPECTROMETRY - - - - 44 3.3.3. RAD7 - - - - - - - - 44 4. RESULTS AND DISCUSSION - - - - - - 47 4.1. Rn - - - - - - - - - 47 4.2. Ra - - - - - - - - - 47 5. CONCLUSIONS AND FURTHER PERSPECTIVES - - 58 5.1. CONCLUSIONS - - - - - - - 58 5.2. FURTHER PERSPECTIVES - - - - - - 58 6. REFERENCES - - - - - - - - 60 16 Table 3: MEDA water projects (MEDA program). Acronym Countries Themes Coordinators ADIRA EG, ES, GR, JO, MA, TR V George Papadakis Description: Integrated management of local water supply and sanitation; wastewater reuse; use of non conventional water resources EMPOWERS EG, GB, JO, NL, PS I, II, III, V, VI Peter Laban Description: Improvement of decision-making in rural water supply and sanitation, and drought management EMWATER DE, IT, JO, LB, PS, TR I, IV Ismail Al Baz Description: Integrated management of local water supply and sanitation; wastewater reuse; use of non conventional water resources IRWA ES, IT, JO, LB II, IV Maria Teresa Calabrese Description: Irrigation water management ISIIMM EG, ES, FR, IT, LB, MA II, IV Michel Soulié Description: Irrigation water management MEDAWARE CY, ES, GR, JO, LB, MA, PS, TR I, V Maria Loizidou Description: Integrated management of local water supply and sanitation; wastewater reuse; use of non conventional water resources MEDROPLAN CY, ES, GR, IT, MA, TN III, V Dunixi Gabina Description: Improvement of decision-making in rural water supply and sanitation, and drought management MEDWA AT, ES, JO, PS II, IV, V, VI Hanan Salah Description: Irrigation water management ZER0-M AT, DE, EG, IT, MA, TN, TR I, V Martin Regelsberger Description: Integrated management of local water supply and sanitation; wastewater reuse; use of non conventional water resources EMWIS AT, BE, CY, DZ, EG, ES, FR, GR, IL, IT, JO, LB, LU, MA, MT, PS, PT, SY, TN, TR VI Eric Mino Description: EMWIS is an information and knowledge exchange tool on water among the Euro-Mediterranean Partnership countries (1) The ADIRA Project: “Autonomous Desalination System Concepts for Sea Water and Brackish Water in Rural Areas with Renewable Energies – Potential, Technologies, Field Experience, Socio-Technical and Socio-Economic Impacts” aims to develop suitable concepts and to install a number of desalination units around the Mediterranean, for fresh water supply in rural areas. In the focus of this project are environmental friendly, autonomous desalination units powered by renewable energy sources with fresh water output in the range of half to ten cubic meters per day. In the framework of the ADIRA project ten new desalination units were installed in Morocco, Jordan, Cyprus and Turkey. The experience and knowledge gained from planning, installing and monitoring the implemented technologies and from the evaluation of the potential of such systems, gives more light in the performance and cost issues of a clean but expensive technology. (2) The EMPOWERS Partnership is a regional partnership of 15 different national and international partners working together in Egypt, Jordan and Palestine to develop practical participatory methodologies that influence bottom up planning, and that lead to improved local water governance. Also working regionally, EMPOWERS supports a Regional Information Program to 17 disseminate the Partnership’s work and create links with other actors involved in improving local water management across the region. The EMPOWERS Partnership is a 4 year program (2003-2007) that is mainly funded by the EC’s MEDA Water Program with a total budget of 8.4 M€. Our main objective is to improve long-term access and rights to water and water related services by vulnerable populations in MEDA Zone through participatory water planning & management processes with all stakeholders. (3) EMWater: “Efficient Management of Wastewater, its Treatment and Reuse in the Mediterranean Countries” is a mainly EU-funded project that encourages reuse-oriented wastewater management. The EMWater project promotes innovative wastewater treatment and reuse solutions in its four partner countries Jordan, Palestine, Lebanon and Turkey through: - Trainings of staff involved in water resources management, - Development of a guide for decision-makers and water resources planning engineers, - Applied research and demonstration of innovative solutions by the implementation and operation of pilot plants, and - Dissemination and awareness raising activities. Experts from the field, decision-makers, interested citizens, and civil organisations are involved in all stages of project implementation. (4) EMWATER: “Efficient Management of Wastewater, its Treatment and Reuse”. Given the fact of water shortage crisis in the Mediterranean countries the EMWATER project aims to highlight innovative solutions in wastewater treatment and wastewater reuse. With this goal in mind experts from the field, decision-makers, interested citizens and civil organizations should be sensitized to these issues. A more specific aim is the strengthening of regional co-operation through the creation of networks among the experts as well as through cross-border knowledge transfer. Additionally the project aims at strengthening capacity building through local and regional training programs, the development of regional policy guidelines for wastewater treatment and reuse in the region. The improvement of the security and safety of water supply in the Mediterranean countries is the best recipe for social, economic and political stability in the region and is, thus, the foremost goal of the project. (5) IrWa: “Improvement of Irrigation Water Management in Lebanon & Jordan”. It’s objectives are improve irrigation water quality, increase crop production and farmers’ income, improve on-farm irrigation and fertilization efficiencies and enhance flood prevention to increase the agricultural area. (6) ISIMM: “Institutional and Social Innovations in Irrigation Mediterranean Management”. The overall objective is overcoming current contradictions associated with local water management in Mediterranean river basins through 18 innovative institutional solutions, based on common understanding of six key axes: social, institutional, territorial, historical, agricultural and hydrologicalhydraulic. (7) MEDAWARE Project: “Development of Tools and Guidelines for the Promotion of the Sustainable Urban Wastewater Treatment and Reuse in the Agricultural Production in the Mediterranean Countries”. The highest priority in the wastewater management sector in every country has to be given to setting up an effective wastewater management system which will include: - Maximization of collection of wastewater, - Upgrading the existing wastewater collection systems, - Rehabilitation or upgrading of existing wastewater treatment plants or the construction of new treatment plants, - Establishment of proper standards for influent and effluent wastewater quality, - Education of the farmers. (8) MEDROPLAN: “Mediterranean Drought Preparedness and Mitigation Planning”. The project contributes to the objectives of the MEDA WATER Program by enhancing regional co-operation in the areas of sustainable and integrated management of water resources. The objectives are: - Develop guidelines for drought preparedness plans that, o Minimize the impacts of drought providing a risk management approach. o Include the physical and socio-economic characteristics of Mediterranean countries. o Respond to the actual situation of institutional and civil stakeholders - Set up a drought preparedness network for the Mediterranean countries. (9) MEDWA: “Stakeholder Participatory Sustainable Water Management at farm Level”. The project objective is strengthen the interactive stakeholder capacity in irrigation water management in Jordan & Palestine by: - Implementation of efficient water demand management. - Implementation of efficient water supply management - Establishment of effective fore for experience exchange to strengthen interactive stakeholder capacities in irrigationwater management. (10) The Ec’Eau Sebou project, financed by the European Union has been implemented by the Sebou Water Basin Agency (ABHS) and WWFMediterranean Program, with the support of ACTeon, an environmental consultant based in France. It aims at displaying the importance of economic approaches for integrated water resources management in Morocco. The project attempts to: 19 - Introduce the role of the economic methodologies and tools in integrated water resources management. - Test economic analysis and tools in the Sebou basin. - Draw lessons from these tests concerning the relevance of economic analysis methodologies and tools for water resources management in Morocco. (11) Zer0-M: “Sustainable Concepts towards a Zero Outflow Municipality Objective”. Zer0-M aims at concepts and techniques to achieve optimised close-loop usage of all water and nutrient flows in small municipalities or settlements including tourism facilities. Zer0-M is about abandoning the concept of waste water. Blue Plan On the same direction but from another organisation, the Blue Plan is one of the stakeholders involved in the cooperation between the 21 states bordering on the Mediterranean and the European Community. This plan is an original mechanism for environmental regional cooperation within the framework of the United Nations Environment Program’s Mediterranean Action Plan (UNEP/MAP). One of the main tasks is to produce information and knowledge in order to alert decision-takers and other stakeholders to environmental risks and sustainable development issues in the Mediterranean, and to shape future scenarios to guide decision-taking processes. All of the Blue Plan’s work is structured around its four main strategic objectives, which are: - To identify, collect and process on an on-going basis environmental, economic and social information of use to the stakeholders and decisionmakers - To evaluate the interaction between the environment and economic and social development in order to measure what progress is being made towards sustainable development - To conduct analyses and prospective studies to help shape visions for the future and back-up decision-taking - To broadcast and circulate products and outcomes in the manner bestsuited to the target public. INECO INECO (Institutional and Economic Instruments for Sustainable Water Management in the Meditteranean Region) is a Coordination Action Project supported by the European Commission. The aim of INECO is defined as “to establish a Mediterranean network of research institutes, public authorities and stakeholders for coordinating research, and to analyse decision making practices regarding the application of institutional instruments in the water sector”. 20 INECO encompasses a series of coordination activities aiming to: - Promote the exchange and dissemination of best available water management practices through the systematic exchange of information and research among the participating parties and the consideration of institutional and socio-economic instruments improving sustainable, equitable and efficient water use. - Perform studies for the assessment of the efficiency, effectiveness and equity of currently applied water management practices, as well as the role of public involvement in planning and implementing alternative actions. - Promote capacity building for constructively engaged Integrated Water Resources Management, with emphasis on socio-economics and policy considerations. 1.1.2. MANAGEMENT OF WATER RESOURCES IN SOUTH-EASTERN SPAIN. The hydric management is directly influenced by legislation. In Europe there is the “Directive 2000/60/EC of the European Parliament and of the Council of 23 October 2000 establishing a framework for Comunity action in the field of water policy”. This Directive has as its object as it is stated, getting the good ecological and chemical status of all waters, continental, transitional, coastal and groundwater. In some ways, it is assumed that the most important issues related to the provision in Europe are well targeted. The main problems affecting the waters at this time are related to the quality of them, with consequent negative implications for both human health and aquatic ecosystems and rivers. In terms of SGD, this Directive has a special interest because of the emphasis that it gives to the groundwater. In the introduction it ensures “The quantitative status of a body of groundwater may have an impact on the ecological quality of surface waters and terrestrial ecosystems associated with that groundwater body” and it talks about the desire of a good groundwater quality. On this way, the “Directive 2006/118/EC of the European Parliament and of the Council of 12 December 2006 on the protection of groundwater against pollution and deterioration” sets out principles and good statements for groundwater. This policy gives more weight to integrate water planning with other environmental protection concepts, especially the figures of protected natural areas and gives priority to the establishment of participatory processes and public information plans during different stages of development. In Spain, the Directive 2000/60/EC is transposed to the Water Law approved by Royal Legislative Decree 1/2001 of 20 July, whereby the process of water planning culminates with the publication of river Basin Management Plans of the various demarcations in December 2009. 21 In addition to the general objectives set out in the Water Law, Basin Management Plans should ensure the environmental objectives established in the art. 92 and 92 bis of the Water Law, that are: For surface water (including transitional and coastal): 1. Prevent deterioration of surface water bodies. 2. Protect, improve and restore all surface water bodies in order to reach the good state. 3. Progressively reduce pollution and gradually eliminate discharges, emissions and losses of priority hazardous substances. For groundwater: 1. Avoid or limit the entry of pollutants into groundwater and prevent the deterioration of the of all groundwater bodies. 2. Protect, improve and restore bodies of groundwater and ensure a balance between the extraction and recharge in order to get good status of groundwater. 3. Progressively reduce the concentration of any pollutant resulting from human activity This work focuses on two basins in Andalucia (Southern Spain): the Mediterranean Coast (called Sur) and the Guadalquivir’s Basin (Figure. 2). 22 Figure. 2: The different basins in Spain. (Sistema de Información del Agua Subterránea. (IGME, 2002)). Those two basins have Hydrological Plans but they are olders than the Directive 2000/60/EC. Another administrative problem is that those basins were Spanish Government competence but after the Directive implementation they became competence of the Andalusian Water Agency. So, they have to elaborate new plans but untill then, the ancient Hydrological Plans are valid. The new Basin Management Plans will have a wider focus than a management approach based largely on infrastructure work. There are already experiences with planning and coordination at the subregional and sub-basins, such as Coordinated Plans. Coordinated programs come from the initiative of social groups, environmentalists, neighborhood, government, etc. which are presented to the Parliament of Andalusia in the form of Proposal not of law. Once adopted, the Government of the Junta de Andalucía is asked to write a program that serves as an operational tool where the objectives and the most priority actions are established to achieve, as well as check its viability. The program is designed with a regional character that seeks the recovery and development of the basin, considering all the possibilities of water resources and optimization of operations, rationalization of water resources and environmental protection. In order to do this, agencies should constitute to ensure the management of water 23 in the basin and the effective coordination of actions arising from the program and the participation of all stakeholders. 1.2. SUBMARINE GROUNDWATER DISCHARGE TO THE SEA. 1.2.1. DEFINITION AND IMPORTANCE OF THE SUBMARINE GROUNDWATER DISCHARGE Directive 2000/60/CE (Water Framework Directive) defines in the 2 nd article that "Groundwater" means all water which is below the surface of the ground in the saturation zone and in direct contact with the ground or subsoil. Groundwater is recharge (infiltration from rainfall, runoff and evapotranspiration) and discharge as extractions anthropogenic sources, rivers, lakes and to the sea. Submarine Groundwater Discharge (SGD) is the flow of water through continental margins from the seabed to the coastal ocean, with scale lengths of meters to kilometers, regardless of fluid composition or driving force (Burnett et al., 2003). Flow may be induced by the terrestrial hydraulic gradient as well as by marine processes such as wave set-up, tidally driven oscillations, densitydriven convection, and thermal convection (Figure. 4). The mix will be different in different regions, depending, for instance, on the hydraulic conductivity, hydraulic head, groundwater catchment area and recharge rates. Figure. 4: Schematic depiction (no scale) of process associed with submarine groundwater discharge. Arrows indicate fluid movement. (Taniguchi, M. et al., 2002). But, why is SGD important? SGD represents circa 5-10% of global freshwater sources to oceans, in the Atlantic total SGD (freshwater plus recirculated seawater) is up to 80-160% of the river flux entering the Atlantic Ocean (Moore et al., 2008), dissolved material transports is much more important that water itself and SGD may be a major pathway for micronutrients 24 (e.g. iron, molybdenum). In the Mediterranean basin, while the main rivers (Rhone, Po, Nile, Ebro, Tiber, Adige) discharge 158 km 3 /y, the freshwater SGD might be between 45 km 3 /y (Plan Bleu, 2003) and 68 km 3 /y (Zektser et al., 2007). On one side, the flux of freshwater due to SGD may be important because it can represent an exploitable freshwater resource. Moreover, this flux constitutes a required parameter for the hydrological balances to be closed and, thus, an estimation that water administration agents and decision makers would make profit from. When considering discharging groundwater as an exploitable resource, this quantitative importance can be more or less restricted to some specific areas (e.g. karstic zones). Even though, a SGD flux estimation can be helpful in taking decisions on hydrological policies such as installation of desalinization plants in coastal areas or restrictions in groundwater exploitation in a given area. On the other side, biogeochemical implications of SGD may go even farther. SGD could also drive an input of chemical compounds (nutrients, metals, etc.) into the coastal areas (Moore 1996; Rama and Moore 1996; Krest et al., 1999, 2000; Charette et al., 2001). These fluxes may affect the biogeochemical cycles of the sensitive coastal environments where they take place, likely inducing ecological effects like water eutrophication (Valiela and D’Elia, 1990). Many researchers have already recognized the biogeochemical importance of groundwater discharge through coastal sediments. Transport of nutrients to coastal waters may trigger algae blooms, including harmful algae blooms, having negative impacts on the economy of coastal zones (LaRocheetal, 1997). Figure. 5: Magnitude of SGD in each country of the Mediterranean basin. (Plan Bleu, 2003). 25 1.2.2. DETECTION AND QUANTIFICATION There are different methods in quantifying SGD (1) HYDROGEOLOGICAL MODELS To understand the regulatory mechanisms of coastal systems and for a proper efficient management of water resources in areas like the Mediterranean Sea, characterized by a traditional lack of resources and high punctual demand, is necessary to establish the water balance, which involves a precise quantification of the different water flows. A model can be understood as the representation of an object, process or real system. In hydrogeology, models are used with two purposes: firstly we use them to simulate a particular observed behavior and to predict how the flow system will behave in the future and secondly the models can be used to reproduce flow hypothetical situations and to understand as well the type of flow system we have (Anderson and Woessner, 1992). They are, therefore, a tool that allows a greater understanding of flow systems. However, a model determines the mass balance of a system (inputs - outputs = change in mass) thus becoming an important tool for managing water systems. At the same time, models are instruments of integration as they allow to join a variety of information (geology, geophysics, geochemistry, etc.).. Groundwater models are usually applied to four types of problems: - Groundwater flow. - Transport of solute. - Heat flow. - Deformation of the aquifer. In this work we are interested in studying the models that allow the estimation of the groundwater flow. The development of a hydrogeological numerical model simulation is a sequential process that begins with developing a conceptual model that describes and explains the main features of the system. Conceptual models can be understood as a series of hypotheses that describe the geology, hydrogeology, and hydrodynamics of a system and how these are related and structured in order to know its effects on the flow phenomena. Numerical models are understood as the mathematical expression of this conceptual model. Consequently, the elaboration of a conceptual model is necessary to define the geometry, the processes and the properties of the medium. However, there are many difficulties associated with the definition of these three parameters, such as knowing the geological contours and which will be the hydrogeological behaviour and knowing whether the properties can be thoroughly measured and are always reliable and representative. 32 Krest et al. (1999) concluded that radium desorption is essentially complete at a salinity of about 5 ppt, so adopting a conservative behaviour once released in sea water. All these radium isotopes derive from decay of Th parents which are tightly bound to particles whichever the salinity is. Thus, radium is especially useful for SGD studies where subsurface mixing of fresh and salty waters occur. Ideally, radium isotopes should be greatly enriched in groundwater relative to coastal waters (1-2 orders of magnitude) (Moore, 1996) due to the increased ratio between surface of solid aquifer material (containing immobile U and Th) and the amount of water seeping through them. The isotopes accumulate through the processes of dissolution, ion-exchange and alpha particle recoil (Kraemer and Genereux, 1998). The short-lived isotopes, 223 Ra (T 1/2 = 11.4 days) and 224 Ra (T 1/2 = 3.66 days), are continually regenerated from decay of their thorium parents, which are perpetually bound to particle surfaces. On the other hand, the long-lived isotopes, 226 Ra (T 1/2 = 1600 yrs) and 228 Ra (T 1/2 = 5.75 yrs), require considerable time for regeneration (Moore, 2003). With the mentioned range of half-lives, Rama and Moore (1996) concluded that this quartet of isotopes can provide powerful constraints on salt marsh hydrology and chemical exchange. The differences in regeneration rates lead to differences in fluxes of each of these isotopes. The short-lived Ra isotopes can be used to constrain the mixing time of near-shore waters across the shelf. The long-lived ones are useful to evaluate either radium sources or fluxes (Moore, 1999) to the coastal zone under study. These fluxes must be sustained by input from rivers, sea sediments, SGD, or other sources. If we can measure or eliminate all other sources and establish the radium concentration in the groundwater, the radium flux can be directly related to the SGD (Moore, 2003). 222 Rn 222 Rn (T 1/2 = 3.83 days) is a gas produced by the decay of 226 Ra. 222 Rn is considered a very good tracer to identify areas of groundwater discharge (Burnett and Dulaiova, 2003), mainly due to groundwater is significantly enriched in 222 Rn in relation to surface water (3 orders of magnitude or more) and 222 Rn is a non-reactive element. Moreover, the fact that the gas 222 Rn rapidly exhale into the atmosphere, allows differentiation between groundwater discharges from surface inputs. The use of continuous 222 Rn to assess the groundwater discharge is a relatively new technique (Burnett and Dulaiova, 2003) that allows to acquire results in a very short time and continuously throughout the study area or period relatively short (as opposed to the methodology based on discrete sampling technique Ra). This allows the characterization of large areas in an acceptable time and integrating the entire sampling area, which makes this technique ideal for the location of areas of groundwater discharge. Thus, this technique has great potential for the location of continental water seeps into the sea, particularly in karst areas where groundwater discharges usually occur in focused ducts of dissolution in carbonate rock. 33 2. STUDY AREA 34 2. STUDY AREA 2.1. HYDRIC SITUATION IN MÁLAGA-GRANADA REGION Given the difficulty of building new dams and the inconvenience of further increasing pressure on coastal aquifers, many of them already exploited in unsustainable conditions, water policy has had to redirect the one hand, to improve management and implementation of actions to encourage savings, particularly in the agricultural sector, and secondly, to promote the generation of unconventional resources. In this line, in recent years, the reuse of treated effluent for irrigation of golf courses has taken a special boom, and there are currently several ongoing initiatives, which focus on the coastal strip and the Guadalhorce Valley to expand this type of use and extension to agricultural irrigation and urban and industrial uses less stringent. In terms of desalination, the installation of Marbella is at full performance, whose annual 20hm 3 obtained from marine waters are vital to ensure the provision of the Costa Sol, and also of the Atabal, allowed to produce up 60hm 3 /year water resources by treating brackish water, and whose role will be essential for the supply of the capital while the resolution of the problem of salt contamination in Guadalhorce reservoir and alluvial aquifer isn't solved. To these plants, the second floor of the western commonwealth will be added in a relatively short time, to be located in Mijas, close to the city of Fuengirola, which is projected with an initial capacity, expandable, similar to that of Marbella. Looking to overwhelming perspectives for growth in water demand (according to statements drawn up for the Mediterranean area, in 2000 the net resources available hm 3 stood at 525 hm 3 , while the demand forecast for 2018 amounted to 675 hm 3 ), with the forecast (which match the various climate change scenarios) that in the next 20 years, the reduction of inputs will be of 10%, increasing the hydrological irregularity peninsular, and accentuating the imbalances in Mediterranean Basins, the solution in a medium - long term to increase water availability in the province of Málaga needs to look for new surface infrastructure regulation, complemented by desalination of sea water to supply the population near the coast, and to maximize (mostly in the same geographical area) reuse of treated wastewater for uses compatible with its quality, especially for agricultural irrigation, urban and golf courses. Only this way can guarantee the future needs without causing severe impacts, or even critical, on the water environment, impacts that otherwise would be incompatible with the objectives of the Water Framework Directive. This strategy will also entail additional benefits, including the recovery of aquifers nowadays exploited in an abusive way, and its rehabilitation as strategic reserves. But perhaps the positive effect of greater significance for society of Malaga would be their contribution to a more balanced territorial development. The use of unconventional resources in the coastal strip and surrounding areas would free up the reservoirs of some of the demands assigned to them, which would create surpluses that could be utilized in the inland municipalities whose growth is now mortgaged by the high consumption of the littoral. 35 2.2. THE AQUIFER 2.2.1. DESCRIPTION AND TYPES An aquifer is that geological formation, consisting of one or more layers of rocks (gravel, sand, limestone, etc.) that can store and transmit water through them in significant quantities, so that it can be extracted by headworks. The aquifers have very different surface dimensions and thickness. Aquifers can be classified according to the type of materials they contain or as hydraulic and structural circumstances. In the first case aquifers generally could be: - Porous aquifers when the permeability is due to intergranular porosity (e.g. gravel, sand). In general all detrital material with sand grain size minimum. - Karst and fissured aquifers whose permeability is due to cracks and fissures of both origin mechanical and dissolution. These include limestone, dolomite, granite, basalt, etc.., being the first two the major types. Figure. 9: Aquifer types according to their texture. (Libro Digital del Agua. Ministerio de Medio Ambiente y Medio Rural y Marino. Gobierno de España). Depending on hydraulic and structural circumstances, aquifers can react in three different ways (Figure. 10 and 11): - Free aquifer: are those in which the water level is below the permeable formation. The water flow is the drainage from the pores. - Confined aquifer: are those covered by an impermeable confining layer. The water level in captive aquifers is above the aquifer formation. The water flow is due to the expansion of water and decompression of vertical permeable structure, when depression occurs in the aquifer. Also they are called captive aquifers. - Semiconfined aquifers: can be considered a special case of captive aquifers, in which wall, ceiling, or both are not completely waterproof, but allow vertical movement of water. Actually semiconfined aquifer can be physical system composed of well-fed upper aquifer, semi-permeable package and lower semiconfined aquifer. The difference in levels 36 between the upper and lower aquifer leads to a vertical transfer of water that feeds the lower aquifer. Free aquifer Confined aquifer Figure. 10: Aquifer types depending on their structure and functioning. Figure. 11: Aquifer types according to their hydrodynamic characteristics 2.2.2. THE AQUIFER OF THE HYDROGEOLOGICAL SUBUNIT OF “LAS ALBERQUILLAS”. In the “Proyecto de Plan Hidrológico de la Demarcación Hidrográfica de las Cuencas Mediterráneas Andaluzas” there are summary sheets of the different water bodies. There, is also explained that in the Hydrographic Mediterranean District 67 acuifers have been identificated (Figure. 12), 7 of which are in low permeable land, but where there are significant deposits for human consumption. Those 67 acuifers are classified in five systems (Figure. 13). 37 Figure. 12: The 67 acuifers in the Hydrographic Mediterranean District Figure. 13: Location of the Hydrographic Mediterranean District and the five systems. The name of the subsurface water body is “Sierra Alberquillas” and it’s the number 060.063. It has an area of 11.714 ha. and an outcrop of 77,3 km 2 . The acuifer is non confined and belongs to the system II and III and the subsystems II-3 and III-1 (Figure. 14). Figure. 14: Location of the acuifer “Sierra de Alberquillas”. Source: Junta de Andalucía. Consergería de Medio Ambiente. Agencia Andaluza del Agua. 38 There are fourteen areas protected to supply: And seven networks of control: In this study is analised the quantitative, chemical and global state and it’s concluded that is BAD because of (1) Over-explotation of aquifers, saltwater intrusion and other processes of salinization and (2) Urban pollution. The solutions they found are (1) Constitution of users community and develop a business plan, (2) Implementation of connection and distribution infrastructures and (3) Promotion of reusing resources for agricultural irrigation and (4) Improvements in the sewerage system. The environmental objective is to rise the best state of the aquifer in 2021. 39 In a work from Malaga’s University and the Instituto Geológico y Minero de España (IGME) they explain that in Sierra Almijara-Alberquillas aquifer (Figure. 15) is taken 15hm 3 /year for water supply in the Malaga’s region (Figure. 16). Although this acuifer is bigger than Sierra Alberquillas, a global view could be taken. Figure. 15: Sierra Almijara (north) Alberquillas (south) aquifer separation with water flow arrows. (Modified from Carrasco, F. et al., 1988) Figure. 16: Hydric resource and degree of explotation. (Atlas Hidrogeológico de Málaga. Univ. de Málaga and IGME). 40 3. MATERIAL AND METHODS 41 3. MATERIAL AND METHODS 3.1. SAMPLING METHODOLOGY There have been sampled a total of 48 stations in the sea for the analysis of Ra isotopes and distributed between Maro and Almuñécar and 12 stations in wells, piezometers and springs in the area (Figure 17). It has also been made specific continuously sampling in Rn, drawing parallels at various distances from the coastline (along the isobaths of 5 m, 20 m, 30 m and 50 m from the coast). The field work was conducted in four sampling campaigns: 14-15 September 2006, 19-20 September 2006, 11-13 November 2009 fully tailored to Rn, and 21-24 September 2010 . The study area for the determination of Rn are shown in Figure 17. 3.1.1. WATER SAMPLES Radium isotope activities are typically present at such low levels in natural waters, especially in seawater, that their measurement requires preconcentration from large samples. This can be accomplished by passing large volumes (20 to 100 L) of water through a cartridge loaded with MnO 2 - impregnated acrylic fiber, which quantitatively extracts radium isotopes by adsorbing them onto the MnO 2 particles (Moore, 1976). The MnO 2 -impregnated acrylic fiber (Mn-Fiber) is prepared by immersing the raw acrylic fiber for about 15 minutes in saturated KMnO 4 solution (64 g·L -1 ) heated to 75ºC. The KMnO 4 oxidizes specific sites on the acrylic molecule and deposits MnO 2 at these sites. This process produces Mn-fiber having submicrometer sized particles of MnO 2 chemically bonded to the fiber. The process of Mn-fiber preparation is carried out under continuous stirring and the temperature is strictly controlled. Keeping a good mixing is needed to maintain the KMnO 4 permanently dissolved so that a homogeneous impregnation of the fiber is achieved. Temperature control is also a key issue. At temperatures lower than 75ºC, more time is required; for example, several days are needed at temperatures of 30-35ºC (Michel et al., 1981). The exothermic reaction proceeds very rapidly at temperatures over 80ºC, and the Mn-fiber can be destroyed due to strong oxidation. When the fiber turns black, it is quickly removed from the bath and rinsed thoroughly (Moore, 1976). Radium-free water, prepared by passing deionized water through previously prepared Mn fiber is used along all the procedure. After a final rinse in radium-free water, the fiber is hand-squeezed and stored in plastic bags until use. In the field, approximately 150 cm 3 (~50 g wet weight or ~25 g dry weight) of Mn-fiber is loosely introduced into a cylindrical PVC column. Loosing the fiber is important to maximize the active surface for radium adsorption. 48 -3.86 -3.84 -3.82 -3.80 -3.78 -3.76 -3.74 -3.72 0.0 0.4 0.8 1.2 1.6 2.0 2.4 35.6 35.8 36.0 36.2 36.4 36.6 222 Rn (dpm·L -1 ) Longitud (º) Prof = 5m Prof = 20m Prof = 30m Prof = 50m Salinidad (‰) Alberquillas Maro Cantarriján Cerro Gordo La Herradura Río Miel Figure. 21: a) Transects described for the determination of the concentration of 222 Rn during the November 2009 campaign. The different colors indicate isobaths along transects (5m, 20m, 30m and 50m) and the arrows of the legend the direction in which transects were conducted. b) Activities of 222 Rn measured along the transects, in different colors representing the different transects. It is also represented the salinity along the transect closest to the coast, following the 5m depth contour. a) b) 49 Table 4: Activity of Ra isotopes ( 224 , 223 , 226 , 228 Ra) of all stations sampled in September 2006 campaigns, together with the salinity, temperature and time of sampling. Temp Sal Latitud (N) Longitud (W) ºC ‰ Mar CerroGordoMar 14/9/2006 15:15 36.7315 3.7710 22.0 37.0 5.1 ± 0.6 1.2 ± 0.2 <MDA PlVelilla 14/9/2006 12:40 36.7355 3.6685 22.6 36.8 18.7 ± 1.2 1.4 ± 0.2 25.4 ± 1.0 <MDA CuevaCantRij 14/9/2006 18:00 36.7378 3.7781 25.7 37.0 7.0 ± 0.7 1.5 ± 0.2 <MDA <MDA PlayaCantRij 14/9/2006 19:15 36.7361 3.7748 23.9 37.1 12.1 ± 0.9 1.1 ± 0.2 16.9 ± 0.3 <MDA CañueloEste 15/9/2006 10:30 36.7397 3.7812 17.6 37.3 6.4 ± 0.6 0.3 ± 0.1 30.6 ± 0.4 <MDA Herradura 15/9/2006 15:15 36.7320 3.7627 17.4 37.5 5.3 ± 0.5 0.7 ± 0.1 5.7 ± 0.2 <MDA Continental CT_PozoSeverino 14/9/2006 18:30 36.7364 3.7730 22.4 2.5 86.8 ± 6.0 1.7 ± 0.4 355.1 ± 1.3 99.7 ± 1.6 CT-10 14/9/2006 14:25 36.7333 3.7686 24.0 2.2 125.9 ± 9.4 102.1 ± 5.2 818.8 ± 2.5 125.8 ± 2.3 CT-2 15/9/2006 10:00 36.7502 3.7751 22.8 0.6 102.4 ± 7.7 9.0 ± 1.3 90.2 ± 1.1 108.8 ± 3.0 ManAlberquillas 15/9/2006 8:40 36.7503 3.8055 22.5 0.3 58.5 ± 2.9 4.8 ± 0.4 Mar CGordoSifon 19/9/2006 13:06 36.7297 3.7649 16.8 37.0 2.8 ± 0.4 0.3 ± 0.1 12.4 ± 0.2 3.6 ± 0.3 CuevaCantRij 19/9/2006 13:16 36.7381 3.7783 16.8 37.0 6.0 ± 0.5 0.3 ± 0.2 7.7 ± 0.2 MarAbierto 19/9/2006 13:26 36.7257 3.7822 17.6 37.0 2.7 ± 0.3 0.7 ± 0.2 12.3 ± 0.3 Continental CV-1 20/9/2006 12:55 36.7625 3.8434 21.2 0.4 18.2 ± 1.3 1.6 ± 0.2 35.0 ± 0.3 14.2 ± 0.6 ManMaro 20/9/2006 10:14 36.7628 3.8369 19.3 0.4 57.0 ± 2.2 7.3 ± 1.0 1781.3 ± 3.1 43.3 ± 1.1 14-15 Septiembre 2006 226 Ra 228 Ra Muestra 224 Ra 223 Ra 19-20 Septiembre 2006 N.A. N.A. N.A. Fecha y Hora N.A. N.A. Cordenadas (dpm·100L -1 ) N.A. No analised MDA. Minimum detectable activity 50 For the September 2006 campaign, the concentrations of 224 Ra in seawater measures range from 18.7 ± 1.2 dpm·100L -1 in Velilla Beach and 2.7 ± 0.3 dpm·100L -1 in the sample of open sea. It suggests that the measure of Velilla Beach came after a stormy day in which there were contributions from sea water from surface streams. For 223 Ra the maximum concentration in the sea is 1.5 ± 0.2 dpm·100L -1 in the cave of Cantarriján and 0.3 ± 0.2 dpm·100L -1 at several stations. The 226 Ra concentration varied between 30.6 ± 0.4 dpm·100L -1 on the beach of Cañuelo and 12.3 ± 0.3 dpm·100L -1 in the open sea station. Table 5: 224 Ra activity of samples taken in the campaign in September 2010, together with the salinity, temperature and time of sampling. Temp Sal Latitud (N) Longitud (W) ºC ‰ Mar MLG03 21/9/2010 8:15 36.7515 3.8170 21.86 36.49 2.1 ± 0.2 MLG09 23/9/2010 8:10 36.7362 3.7585 22.05 36.44 3.1 ± 0.3 MLG13 21/9/2010 8:35 36.7495 3.8176 21.69 36.25 5.6 ± 0.4 MLG14 22/9/2010 15:40 36.7468 3.8083 22.87 36.37 1.6 ± 0.2 MLG15 22/9/2010 17:12 36.7441 3.7989 22.94 36.50 1.3 ± 0.2 MLG16 22/9/2010 9:45 36.7414 3.7896 22.26 36.36 2.0 ± 0.2 MLG17 22/9/2010 9:02 36.7386 3.7802 21.80 36.36 5.1 ± 0.4 MLG17prof 23/9/2010 9:25 36.7386 3.7802 22.88 36.40 2.3 ± 0.3 MLG19 23/9/2010 10:24 36.7335 3.7609 22.11 36.41 2.0 ± 0.2 MLG22 22/9/2010 16:20 36.7487 3.8286 23.35 36.35 1.5 ± 0.2 MLG23 21/9/2010 8:50 36.7460 3.8193 21.95 36.49 0.8 ± 0.1 MLG24 22/9/2010 15:50 36.7433 3.8099 22.77 36.36 1.4 ± 0.2 MLG25 22/9/2010 17:02 36.7406 3.8006 23.23 36.35 1.1 ± 0.1 MLG26 22/9/2010 11:09 36.7379 3.7911 22.28 36.37 2.2 ± 0.2 MLG27 22/9/2010 9:17 36.7352 3.7817 22.11 36.39 1.4 ± 0.2 MLG29 23/9/2010 9:50 36.7293 3.7616 22.07 36.42 1.7 ± 0.2 MLG32 22/9/2010 16:25 36.7453 3.8302 23.94 36.31 1.1 ± 0.1 MLG33 21/9/2010 9:10 36.7426 3.8208 22.02 36.49 1.2 ± 0.2 MLG34 22/9/2010 16:05 36.7399 3.8114 23.21 36.35 0.8 ± 0.1 MLG35 22/9/2010 16:47 36.7371 3.8020 23.20 36.34 0.8 ± 0.1 MLG36 22/9/2010 0:00 36.7345 3.7927 22.50 36.37 1.5 ± 0.2 MLG37 22/9/2010 9:25 36.7318 3.7833 22.27 36.37 1.2 ± 0.2 MLG38 22/9/2010 8:10 36.7291 3.7740 22.25 36.36 2.3 ± 0.2 MLG38prof 23/9/2010 10:05 36.7291 3.7740 20.43 36.48 1.9 ± 0.2 MLG39 21/9/2010 14:34 36.7264 3.7647 22.38 36.45 2.0 ± 0.2 MLG43 21/9/2010 9:20 36.7392 3.8223 22.13 36.49 0.8 ± 0.1 MLG46 22/9/2010 11:32 36.7311 3.7943 22.27 36.37 0.9 ± 0.1 MLG47 22/9/2010 8:34 36.7284 3.7849 22.26 36.35 1.4 ± 0.2 MLG48 22/9/2010 8:20 36.7256 3.7754 22.23 36.37 1.2 ± 0.2 MLG49 21/9/2010 14:56 36.7230 3.7660 22.30 36.45 1.5 ± 0.2 MLG53 21/9/2010 9:30 36.7357 3.8239 22.09 36.49 1.0 ± 0.2 MLG59 21/9/2010 15:07 36.7195 3.7676 22.04 36.44 1.7 ± 0.2 MLG63 21/9/2010 9:45 36.7324 3.8255 21.93 36.45 0.5 ± 0.1 MLG83 21/9/2010 11:50 36.7253 3.8286 22.52 36.42 0.8 ± 0.1 MLGOPEN 21/9/2010 11:30 36.7067 3.8211 22.67 36.47 0.6 ± 0.1 MLG_MONA1 23/9/2010 8:30 36.7191 3.7351 22.62 36.44 1.6 ± 0.2 MLG_MONA2 23/9/2010 7:55 36.7190 3.7281 22.75 36.42 1.3 ± 0.2 MLG_MONA3 23/9/2010 8:21 36.7155 3.7353 22.78 36.47 1.4 ± 0.2 MLG_MONA4 23/9/2010 8:10 36.7153 3.7282 22.50 36.44 1.9 ± 0.2 Continental CT_PozoSeverino 21/9/2010 17:30 36.7383 3.7771 21.73 1.63 65.8 ± 2.8 MLG_Pz_CT1 21/9/2010 20:00 36.7380 3.7776 22.10 14.90 224.5 ± 18.9 MLG_Pz_CT2 22/9/2010 9:00 36.7380 3.7776 22.50 6.62 78.5 ± 5.5 MLG_Pz_CT3 22/9/2010 10:00 36.7380 3.7776 23.87 12.19 129.2 ± 8.3 MLG_Pz_CT4 22/9/2010 0:54 36.7380 3.7776 24.80 31.07 550.5 ± 43.2 MLG_Pz_CT5 22/9/2010 13:45 36.7380 3.7776 25.57 24.21 397.4 ± 16.0 21-23 Septiembre 2010 Muestra Cordenadas (dpm·100L -1 ) Fecha y Hora 224 Ra 51 Regarding the concentrations of 224 Ra in the sea of September 2010 campaign, the concentration of 224 Ra varies between 5.6 ± 0.4 dpm·100L -1 in MLG13 station, in front of the mouth of Rio Miel, and 0.6 ± 0.1 dpm·100L -1 in MLGOPEN station offshore. The average concentrations in the ocean is 1.7 ± 1.2 dpm·100L -1 . As in the case of 222 Rn, 224 Ra highest value corresponds to the mouth of Rio Miel, suggesting that these high values of Ra are linked to river discharge. 223 Ra concentrations in samples of sea is less than the detection limits of the technique (0.3 dpm · 100L -1 ). There is a significant difference in the results of measurements of salinity and 224 Ra activities carried out in September 2006 and September 2010. In general, samples from September 2006 are more active than 2010 because the samples are taken directly from the beach where the concentrations are higher due to the possible direct influence sediment. There is also a difference between open water samples taken in both campaigns. The activity in open sea in September 2006 is 2.7 ± 0.3 dpm·100L -1 with a salinity of 37.0 ‰ while in September 2010 the activity of the sample MLG47 (which coincides geographically with the above) is 1.4 ± 0.2 dpm·100L -1 with a salinity of 36.35 ‰. Is also noteworthy the low salinity and 224 Ra activity measured in the sample of open water in September 2010 (MLG-OPEN: 0.6 ± 0.1 dpm·100L -1 with a salinity of 36.50 ‰) compared with the measured activities in the Western Mediterranean (e.g. 1.7 ± 0.5 dpm·100L -1 in the waters of Menorca with a salinity of 38.1 ‰ (Garcia-Solsona et al., 2010a). This difference is likely due to the coast of Malaga is influenced by the mixing of waters from the Atlantic Ocean (salinity 36.2 ‰) with Mediterranean Sea (38.2 ‰). 224 Ra activities in boreholes, springs and piezometers at different campaigns, range from 18.2 ± 0.3 dpm·100L -1 (sounding of the Cave of Nerja, salinity 0.4 ‰) and 550 ± 40 dpm·100L -1 (piezometer made in Cantarriján beach, salinity 31.1 ‰). Figure. 23 shows and compares the concentrations of 224 Ra in water from the piezometers, springs and boreholes and the concentrations in samples of seawater. 224 Ra concentration of probes and piezometers is clearly influenced by water salinity, as the Ra desorbs from the particles due to cation exchange processes in seawater (Krest et al., 1999, Moore et al., 1995, Webster et al., 1995). There are different methods for calculating the groundwater discharge into the sea based on a mass balance of Ra isotopes (Moore, 1996, Hwang et al., 2005; Moore, 2003; Krest and Harvey, 2003). The methods, based on different boundary conditions require, in general, the calculation of flow balance Ra ( 224 Ra, in this study) from the mainland to the sea through groundwater discharges ( 224 Ra xs ) and estimate of Ra in the groundwater aquifer ( 224 Ra SGD ) that discharges to the sea ("end-member") so that the discharge is determined by the equation (6): [ ] [ ] [ ] 3 gw 224 1 xs 224 13 mBqRa yBqRa ymSGD − − − ⋅ ⋅ =⋅ (6) 52 0 1 2 km0 1 2 km 224 Ra (dpm·100L -1 ) Alberquillas Maro Cantarriján Cerro Gordo La Herradura Río Miel Figure. 22: Activities of 224 Ra (dpm · 100L -1 ) in sea and inland stations (piezometers and boreholes) sampled during the campaign in September 2010. The dashed line indicates the area used for the calculation of groundwater discharge. The study area has been delimited on the basis of bathymetry and Ra and 222 Rn concentrations observed. 54 The calculation of 224 Ra xs is based on determining the contribution of 224 Ra of potential sources of 224 Ra to the sea (e.g. rivers and sediment) and attributing to the SGD the excess of 224 Ra that can not be provided by them, taking into account the baseline of 224 Ra open sea water. Considering that all contributions of 224 Ra come exclusively from groundwater discharge, 224 Ra xs would be determined by the difference between the average activity of 224 Ra in the study area and the activity of 224 Ra in open sea. In the September 2010 sampling, the mean activity of 224 Ra (weighted according to depth) in the study area (dashed line in Figure. 22) is 1.5 ± 0.8 dpm·100L -1 , while the activity 224 Ra in the sample of open ocean is 0.6 ± 0.1 dpm·100L -1 , which implies a 224 Ra xs activity of 0.9 ± 0.8 dpm·100L -1 , assuming a 1σ uncertainty. Given small excess of 224 Ra on the coast (close to 0, statistically), and considering that the entire 224 Ra proceeds of SGD, the results indicate that the discharge is low or not detectable by the technique of Ra isotopes. This conclusion would be supported by another tracer like 222 Rn, which is enriched by a different geochemical processes, and reveals qualitatively that the discharge of groundwater in the area is minimal. However, if we consider this difference ( 224 Ra xs ) as statistically significant, we could estimate the maximum SGD in the area of September 2010 from a model mixture of different isotopes of Ra. This mixture model developed by Moore (2003), is based on a binary mixture between SGD and sea water (sea), and allows to calculate the fraction of groundwater (f SGD ) from the equations (7): f sea + f SGD = 1 f sea 224 Ra sea +f SGD 224 Ra SGD = 224 Ra average ⋅e λ 224 ⋅T (7) where λ 224 is the decay constant of 224 Ra (0.1894 d -1 ), 224 Ra average the average activity of 224 Ra (weighted according to depth) in the study area in September 2010 (1.5 ± 0.8 dpm·100L -1 ), 224 Ra sea activity in the offshore sample (0.6 ± 0.1 dpm·100L -1 ) and 224 Ra SGD activity measured in groundwater discharge to the sea. Given the piezometers made, from the linear regression shown in Figure. 23 and assuming that the groundwater discharge to the sea with a maximum of 36‰ salinity, the activity of 224 Ra in this groundwater that discharges to the sea (salinity 36‰) and that could be used as "end-member" in the calculation, the groundwater discharge to the sea would be of 580 ± 30 dpm·100L -1 . 55 Figure. 23: Activities (dpm·100L -1 ) of 224 Ra in water from different springs, boreholes and piezometers sampled. 224 Ra activities measured at sea are differentiated. The dashed red line represents the linear fit of 224 Ra versus piezometers salinity. It should be noted that the residence time (T) of water from continental origin in the study area is another important parameter of Equation 2, which can be estimated from the differences in decay between 223 Ra and 224 Ra (Moore , 2000). However, considering that 223 Ra levels measured in this study are below the detection limit of the technique, it requires an alternative estimation of this parameter. Considering a water residence time in the study area of 1 day (minimum residence time that can be calculated with Ra isotopes and allows a maximum SGD flow in quantifying (Garcia-Solsona et al., 2010b), the maximum fraction of SGD (f SGD ) in the study area is less than 0.0023, with an uncertainty similar to its own value, because the concentrations of 224 Raaverage and 224 Rasea are statistically equal. However, and considering the fraction of continental water (f SGD = 0.0023) like a maximum value, the discharge of groundwater in the study area can be determined from the equation (8) described by Moore (2003): SGD m 3 ⋅d −1 [ ] =f SGD ⋅ V m 3 [ ] T d [ ] (8) where V is the volume of water in the area studied (3.11 m3 · 10 8 m3, the zone outlined in Figure 22) and T is the minimum residence time of water in area of interest (1 day for Ra method). From this equation, the estimated maximum discharge SGD (mixture of fresh and salt water) into the sea is 130 hm3·y -1 . 56 Given that the salinity of the water considered is 36 ‰, only a small fraction of this is fresh water. Knowing minimum salinity of the wells sampled (0.4 ‰), the salinity of seawater (36.5 ‰) and those of groundwater that discharges to the sea (36 ‰), we can determine the fraction of freshwater in SGD (f gw = 0.013). From this value, and from the total discharge is obtained by equation 3 in September 2010, a maximum flow of fresh groundwater discharge to the sea of 1.7 hm 3 ·y -1 is extrapolated. It should be noted that this flow only refers to the defined area (between Maro and Cerro Gordo). However, the results of the analysis of 224 Ra in the tip of the Mona and 222 Rn transect between Punta de la Mona and Cerro Gordo, suggest that groundwater discharge to the sea that could take place in this area is also very low. Nevertheless, it is important to note that the calculated flows derived from a sampling punctual on time, from which, discharge flows were extrapolated over a year. To obtain more precise measurements more continuous sampling should be prompt in time. The maximum value of 1.7 hm 3 ·y -1 obtained in this study is much lower than the 7.9 – 11.5 hm 3 ·y -1 reported in Andreo et al. (2010) and Carrasco et al. (1998) at 100m over the sea level. From the management point of view, although the extraction of groundwater for drinking or turistic pruposes could be considered, could be prioritare to manegament the Maro spring or in any case supply water from the desalination plant of Marbella (55 km souther than Málaga) that, at full performance, obtains 20 hm 3 ·y -1 from seawater and Atabal’s plant (next to Málaga) is allowed to produce up to 60 hm 3 ·y -1 water resources. The urban water supplies in Málaga are estimated to 156.93 hm 3 ·y -1 (Durán Valsero, JJ., 2007) so that maximum value of 1.7 hm 3 ·y -1 is the insignificant 1% of the total. Moreover the explotaion of the coastal aquifers could be an environmental risk from two points of view. From the one hand, nutrients inputs from groundwater to the sea will be reduced and the biodiversity of this marine ecosystem area, which is protected by the Junta de Andalucia as an environmental reserve, could be affected and on the other hand the extraction of water from a coastal aquifer could be reduced the piezometric level favoring the seawater intrusion that is always an important hydrogeological and environmental problem. On the same way, it has to be thought that in the “Proyecto de Plan Hidrológico de la Demarcación Hidrográfica de las Cuencas Mediterráneas Andaluzas” is analised the quantitative, chemical and global state of Andalucian aquifers and it is concluded that they are not healthy due to the over-explotation of aquifers, saltwater intrusion and urban pollution. 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