Marine and human activity influences on the groundwater quality of southern Korinthos area (Greece)

In this paper the groundwater quality of the southern part of Korinthos region (north‐east Peloponnese) is discussed. The geology is characterized by a thick sequence of Neogene marls alternating with sandstones, overlain by superficial Quaternary deposits. The latter consist of a mixture of loose materials such as conglomerates, marly sandstones, sands and clay to silty sands. The area is crossed by a fault system parallel to the coastline, and the Quaternary sediments have formed extended Tyrrhenian marine terraces. Two aquifers have been identified in the area. The first is unconfined and occurs within the Quaternary sediments whereas the other is a deep confined aquifer occurring within the underlying Neogene marl series. Analysis of hydrochemical evolution over the past 30 years has indicated significant deterioration of quality owing to seawater intrusion and nitrate pollution. The various sources of pollution have rendered, to a large extent, shallow groundwater unsuitable not only for potable water supply but also for irrigation purposes. However, this is not the case for the deeper confined aquifer. Statistical analysis was used to explore the evolution of salinization during the years 1968 and 1998. In view of the alarming conditions caused by the documented groundwater quality deterioration, the need for integrated water resources management is stressed to maintain the socio‐economic growth of the region studied. Copyright © 2003 John Wiley & Sons, Ltd.     

Groundwater quality in the semi‐arid region of the Chahardouly basin,West Iran

Chahardouly basin is located in the western part of Iran and is characterized by semi‐arid climatic conditions and scarcity in water resources. The main aquifer systems are developed within alluvial deposits. The availability of groundwater is rather erratic owing to the occurrence of hard rock formation and a saline zone in some parts of the area. The aquifer systems of the area show signs of depletion, which have taken place in recent years due to a decline in water levels. Groundwater samples collected from shallow and deep wells were analysed to examine the quality characteristics of groundwater. The major ion chemistry of groundwater is dominated by Ca²⁺ and HCO₃^?, while higher values of total dissolved solids (TDS) in groundwater are associated with high concentrations of all major ions. An increase in salinity is recorded in the down‐gradient part of the basin. The occurrence of saline groundwater, as witnessed by the high electrical conductivity (EC), may be attributed to the long residence time of water and the dissolution of minerals, as well as evaporation of rainfall and irrigation return flow. Based on SAR values and sodium content (%Na), salinity appears to be responsible for the poor groundwater quality, rendering most of the samples not suitable for irrigation use. Copyright © 2007 John Wiley & Sons, Ltd.     

Environmental isotopes and hydrochemical study applied to surface water and groundwater interaction in the Awash River basin

An environmental isotope and hydrochemical study was carried out to conceptualize the surface water and groundwater interaction and to explore the groundwater flow pattern in relation to the geological setting. More emphasis is given to the Afar Depression where groundwater is a vital source of water supply. Conventional field hydrogeological study and river discharge records support the isotope and hydrochemical analysis. The region is tectonically active, comprising rift volcanic terrain bordered by highlands. The result revealed that recent meteoric water is the major source of recharge. Three distinct groundwater zones were identified associated with the highlands, transitional escarpment and the rift. Towards the rift, the ionic concentration and isotopic enrichment (δ²H and δ^18degO) increases following the groundwater flow paths, which is strongly controlled by axial rift faults. The groundwater flow converges to the seismically active volcano–tectonic depressions with internal drainage and to the Awash River. Within the Afar Depression, at least four groundwater regimen are identified: (1) fresh and shallow groundwater associated with alluvial deposits ultimately recharged by isotopically depleted recent highland rainfall and the evaporated Awash River; (2) cold and relatively younger groundwater within localized fractured volcanics showing mixed origin in axial fault zones; (3) old groundwater with very high ionic concentration and low isotopic signature localized in deep volcanic aquifers; and (4) old and hot saline groundwaters connected to geothermal systems. The study demonstrated that dependable groundwater can only be obtained from the first two aquifer types in aerially restricted zones in flat plains following river courses, local wadis and volcano–tectonic depressions. The conventional hydrogeological survey and discharge records indicate substantial channel losses from the Awash River, which becomes a more dominant source of recharge in central and lower Awash valleys. Copyright © 2007 John Wiley & Sons, Ltd.     

Characterization and evaluation of processes governing the groundwater quality in parts of the Sabarmati basin,Gujarat using hydrochemistry integrated with GIS

Intense agricultural and industrial activities in any area are likely to make groundwater vulnerable with respect to its quality. In one such area which is a part of Sabarmati river basin of Gujarat, factors influencing the groundwater hydrochemistry in pre‐ and post‐monsoon season were evaluated. Groundwater samples were collected from 5 km × 5 km grids on the basis of spectral signature of vegetation and soil, observed on satellite image. Integration of Conventional graphical plots, Piper plot, saturation index values (estimated using PHREEQC) and GIS was helpful not only to create the database for analysis of spatial variation in respective water quality parameters but also to decipher the hydrogeochemical process occurring in such a large area. USSL diagram and % sodium were used to characterise the suitability of groundwater for irrigation. It was observed that leaching of wastes disposed from anthropogenic activities and agrichemicals is the major factor influencing the groundwater quality, in addition to the natural processes such as weathering, dissolution and ion exchange. Sea water relics are also impacting the groundwater quality. Control of indiscriminate and unplanned exploitation of groundwater, application of fertilizers and disposal of industrial wastes in the affected areas can possibly ensure groundwater protection from further pollution and depletion. Copyright © 2011 John Wiley & Sons, Ltd.     

Hydrological and isotopic characterization of river water,groundwater, and groundwater recharge in the Heihe River basin,northwestern China

We used hydrochemistry and environmental isotope data (δ¹⁸O, δD, tritium, and ¹⁴C) to investigate the characteristics of river water, groundwater, and groundwater recharge in China's Heihe River basin. The river water and groundwater could be characterized as Ca²⁺? Mg²⁺? HCO₃^?? SO₄^2? and Na⁺? Mg²⁺? SO₄^2?? Cl^? types, respectively. Hydrogeochemical modelling using PHREEQC software revealed that the main hydrogeochemical processes are dissolution (except for gypsum and anhydrite) along groundwater flow paths from the upper to middle Heihe reaches. Towards the lower reaches, dolomite and calcite tend to precipitate. The isotopic data for most of the river water and groundwater lie on the global meteoric water line (GMWL) or between the GMWL and the meteoric water line in northwestern China, indicating weak evaporation. No direct relationship existed between recharge and discharge of groundwater in the middle and lower reaches based on the isotope ratios, d‐excess, and ¹⁴C values. On the basis of tritium in precipitation and by adopting an exponential piston‐flow model, we evaluated the mean residence time of shallow groundwater with high tritium activities, which was around 50 years (a). Furthermore, based on the several popular models, it is calculated that the deep groundwaters in piedmont alluvial fan zone of the middle reaches and in southern part of the lower reaches are modern water, whereas the deep groundwaters in the edge of the middle reaches and around Juyan Lake in the lower reaches of Heihe river basin are old water. Copyright © 2010 John Wiley & Sons, Ltd.     

Basin structure and water quality of the Oligocene aquifer in the Sebkhet El Behira basin (central Tunisia)

ABSTRACT

The Sebkhet El Behira–Garaat El Majdoul multilayer aquifer system is composed of Mio-Plio-Quaternary and Oligocene groundwater exploited in Sidi Bouzid and Kairouan governorates. Annual withdrawal volumes from El Behira Oligocene groundwater were about 0.37 hm³ in 2005 and 0.36 hm³ in 2008. The present study of the Oligocene reservoir in the Sebkhet El Behira–Garaat El Majdoul basin is based on various data including 2D seismic sections, petroleum wells, field geological cross-sections and geochemical analysis. The gathered data allowed us to establish the tectonic framework and to define its influence on the structure of the aquifers seated in the deep Oligocene sandstone reservoirs. Three Oligocene sub-basin aquifers are defined showing different depth, thickness and petrophysical characteristics: lower salinity (<1.5 g/L) and higher porosity (30%). Two field sections in the northern and in the southern parts of Cherahil anticline exhibit the presence of four to five sandstone levels. The anticlines limit the Sebkhet El Behira–Garaat El Majdoul basin. In addition, the morphostructural configuration controls the piezometry of underground flows in the Oligocene and Mio-Plio-Quaternary unconfined aquifers.

Editor D. Koutsoyiannis; Associate editor M. Besbes     

Methods of groundwater recharge estimation in eastern Mediterranean—a water balance model application in Greece,Cyprus and Jordan

Groundwater recharge studies in semi‐arid areas are fundamental because groundwater is often the only water resource of importance. This paper describes the water balance method of groundwater recharge estimation in three different hydro‐climatic environments in eastern Mediterranean, in northwest Greece (Aliakmonas basin/Koromilia basin), in Cyprus (Kouris basin and Larnaka area) and in Jordan (northern part of Jordan). For the Aliakmonas basin, groundwater recharge was calculated for different sub‐catchments. For the Upper Aliakmonas basin (Koromilia basin), a watershed‐distributed model was developed and recharge maps were generated on a daily basis. The mean annual recharge varied between 50 and 75 mm/year (mean annual rainfall 800 mm/year). In Cyprus, the mean groundwater recharge estimates yielded 70 mm/year in the Kouris basin. In the Larnaka area, groundwater recharge ranged from 30 mm/year (lowland) to 200 mm/year (mountains). In Jordan, the results indicated recharge rates ranging from 80 mm/year for very permeable karstified surfaces in the upper part of the Salt basin, where rainfall reaches 500 mm/year to less than 10 mm/year and to only about 1 mm/year in the southernmost part of the basin. For the north part of Jordan, a watershed‐distributed model was developed and recharge maps were generated. This water balance model was used for groundwater recharge estimations in many regions with different climatic conditions and has provided reliable results. It has turned out to be an important tool for the management of the limited natural water resources, which require a detailed understanding of regional hydro(geo)logical processes. Copyright © 2007 John Wiley & Sons, Ltd.     

Insights into groundwater salinization from hydrogeochemical and isotopic evidence in an arid inland basin

In the Manas River basin (MRB), groundwater salinization has become a major concern, impeding groundwater use considerably. Isotopic and hydrogeochemical characteristics of 73 groundwater and 11 surface water samples from the basin were analysed to determine the salinization process and potential sources of salinity. Groundwater salinity ranged from 0.2 to 11.91 g/L, and high salinities were generally located in the discharge area, arable land irrigated by groundwater, and depression cone area. The quantitative contributions of the evaporation effect were calculated, and the various groundwater contributions of transpiration, mineral dissolution, and agricultural irrigation were identified using hydrogeochemical diagrams and δD and δ¹⁸O compositions of the groundwater and surface water samples. The average evaporation contribution ratios to salinity were 5.87% and 32.7% in groundwater and surface water, respectively. From the piedmont plain to the desert plain, the average groundwater loss by evaporation increased from 7% to 29%. However, the increases in salinity by evaporation were small according to the deuterium excess signals. Mineral dissolution, transpiration, and agricultural irrigation activities were the major causes of groundwater salinization. Isotopic information revealed that river leakage quickly infiltrated into aquifers in the piedmont area with weak evaporation effects. The recharge water interacted with the sediments and dissolved minerals and subsequently increased the salinity along the flow path. In the irrigation land, shallow groundwater salinity and Cl^? concentrations increased but not δ¹⁸O, suggesting that both the leaching of soil salts due to irrigation and transpiration effect dominated in controlling the hydrogeochemistry. Depleted δ¹⁸O and high Cl^? concentrations in the middle and deep groundwater revealed the combined effects of mixing with paleo‐water and mineral dissolution with a long residence time. These results could contribute to the management of groundwater sources and future utilization programs in the MRB and similar areas.     

Isotopes and geochemistry in a managed aquifer recharge scheme: a case study of fresh water injection at the Damascus University Campus,Syria

A combination of stable isotopes (¹⁸O and ²H) and hydrochemistry has been applied to investigate storage processes in relation to aquifer storage and recovery (ASR) of the shallow alluvial Quaternary aquifer in Damascus basin. The stored water, entirely taken from the Figeh springs during flood periods, was injected in a single well having a brackish groundwater. Water samples were collected from four observation wells drilled in the Damascus University Campus (DUC) site during a 3‐year period (2006–2008). The injectant water, which deviates in its chemical and isotopic signatures from that of the ambient groundwater, shows that the stored water plume remains within close proximity to the injection well (IW) (<≈ 100 m). Thus, only two wells (W13 and W14) located at a distance less than 80 m from the injection point were affected by this injection. The observation wells located at longer distances from the IW (≈145 m and ≈ 600 m for wells W15 and WHz, respectively) were completely unaffected by the injection. Although most of the chemical and isotopic parameters usefully reflected the mixing process that occurs between the injectant water and ambient groundwater, the stable isotope (¹⁸O) and chloride (Cl⁻) were the most sensitive parameters that quickly reflect this signature. Using a simple mass balance, the calculated proportion of injectant water reaching the well W13 was in the range of 50–90%. This proportion was even lower (30–55%) in the case of well W14. Although the drought event prevailing during this study did not much help to inject further amounts of water, higher than the injected volume (0·2416 M m³) and also not favourable to better evaluate the fate and subsurface hydrological processes, these findings offer encouragement to continue the ASR activities, as an alternative way for better management of water resources in this basin facing intensive problems. Copyright © 2010 John Wiley & Sons, Ltd.     

Evolution study of a regional groundwater system using hydrochemistry and stable isotopes in Songnen Plain,northeast China

Groundwater is often a critical source of water for municipal, industrial and agricultural uses, especially in arid and semi‐arid environments. Songnen Plain, located in the central part of northeast China, is such a region, it being an important productive base of commodity grain in this country. In the past two decades, groundwater quality in the region, especially salinization, has deteriorated under natural changes and human activities, and has become a crucial factor restricting sustainable eco‐environmental and socio‐economic development. In this paper, The Taoer River catchment, situated in the middle of the region, was selected as the study area for the groundwater quality evolution study using hydrochemistry and stable isotopes to obtain a better understanding of the system. Fifty‐two groundwater samples were collected with systematic design during the low‐water and high‐water periods in 2003. A series of comprehensive quality data interpretations, e.g. statistics, ratios of ions and Piper diagrams, together with stable isotope data, have been used to gain an insight into the spatial and temporal variations and evolution laws of groundwater hydrochemistry. The following main hydrochemical processes were identified as controlling the water quality of the groundwater system: weathering–dissolution, evaporation–condensation, ion‐exchange reactions and groundwater salinization. This latter process, salinization, is the most important process and is caused by the leaching of superficial or near‐surface salts from the saline–alkaline soil into shallow groundwater. Copyright © 2006 John Wiley & Sons, Ltd.     

Alluvial sediment sources in a glaciated catchment: The voidomatis basin,Northwest Greece

X-ray diffraction (XRD) of the fine matrix component of four alluvial units and modern channel sediments in the Voidomatis River Basin of northwest Greece shows that fine sediment sources have changed considerably during the late Quaternary. The matrix fraction of the modern channel sediments is derived predominantly from erosion of local flysch rocks and soils. During the last glaciation, however, the fine sediment load of the Voidomatis River was dominated by glacially-ground, finely comminuted limestone materials. Limestone-derived fine sediment is not produced in significant amounts under modern climatic conditions. By combining this XRD work with a detailed programme of clast lithologic 1 analysis we have reconstructed former bedload and fine sediment load composition. The lithological properties of both the coarse (8-256 mm) and fine (< 63 μm) elements of the sediment load have varied markedly during the late Quaternary. A simple, semiquantitative assessment of fine sediment mineralogy, using diffractogram peak-height data, has provided a valuable complement to the information gathered from more traditional clast lithological techniques. Together, in favourable geological settings, fine fraction mineralogy and clast lithological analysis can provide a valuable tool for the reconstruction of late Quaternary alluvial environments.     

Pollution mechanisms in a Ramsar wetland: Delta of the River Evros,Greece

The pollution mechanisms affecting the protected wetland of the river Evros delta, were investigated during an one year survey (1992–1993). The eastern part of the wetland was mainly influenced by river transported pollution which is generated in the greater catchment basin of the river Evros, in Bulgaria, Turkey and Greece. In this part of the wetland, the highest concentrations of organic matter were found during summer, but nutrients concentrations increased during the early winter months. Nitrogen concentrations remained high throughout spring but SRP concentrations decreased considerably during the same period. In the western part of the wetland, the watercourses were mainly influenced by local activities (agriculture and animal breeding) but pollutant concentrations were lower than in the river stations. These preliminary results indicate that river transported pollution is the major factor for the quality degradation of the wetland's waters.     

Modelling of the groundwater hydrological behaviour of the Langueyú creek basin by using N‐way multivariate methods

The groundwater hydrochemical behaviour of the Langueyú creek basin (Argentina) has been evaluated through a systematic survey, followed by application of hydrological and chemometric multivariate techniques. Ten physicochemical parameters were determined in groundwater samples collected from 26 wells during four sampling campaigns (June 2010; October 2010; February 2011 and June 2011), originating a tridimensional experimental dataset X . Univariate statistical and graphical hydrochemical tools (contour maps and Piper diagrams) applied to individual campaigns, allowed to reach some preliminary conclusions. However, a best visualization of the aquifer behaviour was achieved by applying Principal Component Analysis (MA‐PCA) and N‐way PCA procedures, Parallel Factor Analysis and Tucker3. Results were consistent with two‐term models, being Tucker3 [2 2 1] the most adequate, explaining a large amount of the dataset variance (50.7%) with a low complexity. The first Tucker3 [1 1 1] interaction (38.2% of variance) is related with (i) calcium/magnesium versus sodium/potassium ion exchange processes; (ii) an increase of ionic concentration and (iii) a decrease of nitrate pollution, all processes along the direction of the groundwater flow. The second [2 2 1] interaction (12.5% of variance), accounts for the predominant role played by conductivity, bicarbonate and magnesium in the dataset. The seasonal variations are closely related to concentration/dilution phenomena originated by the variations of the phreatic levels, although this point will require additional sampling to establish a definitive hydrochemical model. Copyright © 2013 John Wiley & Sons, Ltd.     

A study of interaction between surface water and groundwater using environmental isotope in Huaisha River basin

The surface water and groundwater are important components of water cycle, and the interaction between surface water and groundwater is the important part in water cycle research. As the effective tracers in water cycle research, environmental isotope and hydrochemistry can reveal the interrelationships between surface water and groundwater effectively. The study area is the Huaisha River basin, which is located in Huairou district, Beijing. The field surveying and sampling for spring, river and well water were finished in 2002 and 2003. The hydrogen and oxygen isotopes and water quality were measured at the laboratory. The spatial characteristics in isotope and evolution of water quality along river lines at the different area were analyzed. The altitude effect of oxygen isotope in springs was revealed, and then using this equation, theory foundation for deducing recharge source of spring was estimated. By applying the mass balance method, the annual mean groundwater recharge rate at the catchment was estimated. Based on the groundwater recharge analysis, combining the hydrogeological condition analysis, and comparing the rainfall-runoff coefficients from the 1960s to 1990s in the Huaisha River basin and those in the Chaobai River basin, part of the runoff in the Huaisha River basin is recharged outside of this basin, in other words, this basin is an un-enclosed basin. On the basis of synthetically analyses, combining the compositions of hydrogen and oxygen isotopes and hydrochemistry, geomorphology, geology, and watershed systems characteristics, the relative contributions between surface water and groundwater flow at the different areas at the catchments were evaluated, and the interaction between surface water and groundwater was re- vealed lastly.     

Characterization of the aquifers of the Bangui urban area,Central African Republic,as an alternative drinking water supply resource

Abstract

This paper presents the results of a survey carried out in 2010 aimed at evaluating the type and quality of the groundwater resources of the Bangui region of the Central African Republic. This work is the first step towards the development of groundwater resources in the Central African Republic in order to find alternatives to direct pumping from the Ubangi River and provide the population of the suburbs with a safer drinking water supply from deep boreholes. By combining both geological and hydrogeochemical approaches, it appears that the geology of Bangui is favourable to the development of a secure and sustainable water supply from groundwater provided that the conditions of exploitation would be constrained by the local authorities. The deep Precambrian carbonate aquifers, known as the Bimbo and Fatima formations, are identified as target resources in view of the relatively good quality of their water from the chemical point of view, and the semi-confined structure of the aquifers that prevents the mixing with shallow aquifers that are already strongly affected by domestic and industrial pollution. The main difficulty in terms of exploitation is to appreciate the depth of the resource and the more or less fractured/palaeo-karstified type of the porosity.

Editor Z.W. Kundzewicz

Citation Djebebe-Ndjiguim, C.L., Huneau, F., Denis, A., Foto, E., Moloto-a-Kenguemba, G., Celle-Jeanton, H., Garel, E., Jaunat, J., Mabingui, J., and Le Coustumer, P., 2013. Characterization of the aquifers of the Bangui urban area, Central African Republic, as an alternative drinking water supply resource. Hydrological Sciences Journal, 58 (8), 1760–1778.     

The role of bromide and iodide ions in the salinization mapping of the aquifer of Glafkos River basin (northwest Achaia,Greece)

Seawater intrusion causes many problems for groundwater quality, whereas natural remediation is time consuming. However, in cases where groundwater replenishment is feasible, groundwater quality remediation is possible and rapid. The alluvial aquifer in the lowland of the Glafkos River basin, which extends south of Patras city, was for over 30 years the major water source supplying the broader area. Groundwater quality has been degraded due to seawater intrusion, caused by overpumping and generally by inappropriate groundwater management. During the last decade, groundwater quality has been remedied due to diminished groundwater abstractions. The remediation rate was further higher because of rapid discharge of the brackish groundwater, through wells with freely flowing water in the coastal area, where, however, groundwater quality remains low. This paper deals with the hydrogeochemical processes that take place in the area. It is ascertained that ion exchange and mineral dilution processes are dominant. The ion relations between chloride, bromide and iodide, as well as the distribution maps of their concentrations, were used to determine the spatial distribution of the seawater intrusion front. In the lower part of the area in a distance from 1000 and 1500 m from the coast, the rBr^?/rCl^? ratio showed low values (<2·5 × 10^?3) similar to those of seawater. The rI^?/rCl^? ratio also presented low values (<7 × 10^?5), with the lowest one (2·7 × 10^?5) detected along the coastline. In the upper part of the area, a gradual change of those ratios was observed upstream, until they receive values similar to those of the surface waters of Glafkos River. Copyright © 2007 John Wiley & Sons, Ltd.     

Environmental isotopic and hydrochemical characteristics of groundwater systems in Daying and Qicun geothermal fields,Xinzhou Basin,Shanxi, China

The conceptual hydrogeological model of the low to medium temperature Daying and Qicun geothermal fields has been proposed, based on hydrochemical characteristics and isotopic compositions. The two geothermal fields are located in the Xinzhou basin of Shanxi, China and exhibit similarities in their broad‐scale flow patterns. Geothermal water is derived from the regional groundwater flow system of the basin and is characterized by Cl·SO₄‐Na type. Thermal water is hydrochemically distinct from cold groundwater having higher total dissolved solids (TDS) (>0·8 g/l) and Sr contents, but relatively low Ca, Mg and HCO₃ contents. Most shallow groundwater belongs to local flow systems which are subject to evaporation and mixing with irrigation returns. The groundwater residence times estimated by tritium and ¹⁴C activities indicate that deep non‐thermal groundwater (130–160 m) in the Daying region range from modern (post‐1950s) in the piedmont area to more than 9·4 ka BP (Before Present) in the downriver area and imply that this water belong to an intermediate flow system. Thermal water in the two geothermal fields contains no detectable active ¹⁴C, indicating long residence times (>50 ka), consistent with this water being part of a large regional flow system. The mean recharge elevation estimated by using the obtained relationship Altitude (m) = ? 23·8 × δ²H (‰ ) ? 121·3, is 1980 and 1880 m for the Daying and Qicun geothermal fields, respectively. The annual infiltration rates in the Daying and Qicun geothermal fields can be estimated to be 9029 × 10³ and 4107 × 10³ m³/a, respectively. The variable ⁸⁶Sr/⁸⁷Sr values in the thermal and non‐thermal groundwater in the two fields reflect different lithologies encountered along the flow path(s) and possibly different extents of water‐rock interaction. Based on the analysis of groundwater flow systems in the two geothermal fields, hydrogeochemical inverse modelling was performed to indicate the possible water‐rock interaction processes that occur under different scenarios. Copyright © 2010 John Wiley & Sons, Ltd.     

Spatial prediction of nitrate pollution in groundwaters using neural networks and GIS: an application to South Rhodope aquifer (Thrace,Greece)

Neural network techniques combined with Geographical Information Systems (GIS), are used in the spatial prediction of nitrate pollution in groundwaters. Initially, the most important parameters controlling groundwater pollution by nitrates are determined. These include hydraulic conductivity of the aquifer, depth to the aquifer, land uses, soil permeability, and fine to coarse grain ratio in the unsaturated zone. All these parameters were quantified in a GIS environment, and were standardized in a common scale. Subsequently, a neural network classification was applied, using a multi‐layer perceptron classifier with the back propagation (BP) algorithm, in order to categorize the examined area into categories of groundwater nitrate pollution potential. The methodology was applied to South Rhodope aquifer (Thrace, Greece). The calculation was based on information from 214 training sites, which correspond to monitored nitrate concentrations in groundwaters in the area. The predictive accuracy of the model developed reached 86% in the training samples, 74% in the overall sample and 71% in the test samples. This indicates that this methodology is promising to describe the spatial pattern of nitrate pollution. Copyright © 2008 John Wiley & Sons, Ltd.     

Integrated water management in shared water resources: The EU Water Framework Directive implementation in Greece

The political dimension of water becomes highly important not only because of its scarcity, but also as a result of its sharing across national boundaries. Approximately 40% of the global population lives in transboundary water basins, 55% of which are located in Europe, emphasizing the need for cooperation and harmonization of policies. In order to better handle major water problems Europe have adopted the new EU Water Framework Directive 2000/60 the implementation of which is further discussed. Especially in Greece, management of transboundary rivers is of major importance, since roughly 25% of the country’s renewable resources are “imported”. However, lack of integrated approaches and legal agreements as well as administrative shortcomings, make transboundary cooperation and management a hard task. This study refers to 4 shared basins in Northern Greece and demonstrates the problems that occur for their sustainable management.     

Helium and CO2 soil gas emission from Santorini (Greece)

Soil gas investigation is a useful tool to detect active faults. The sudden appearance of soil gas anomalies in zones of deep-reaching faults represents a promising potential precursor of earthquakes and volcanic eruptions. In volcanic areas the development of soil gas monitoring techniques is particularly important, as they can represent, together with remote sensing techniques, the only geochemical methods that can be safely applied during volcanic unrest, when it becomes impossible or too dangerous to sample crater fumaroles. A soil gas survey was carried out in June 1993 at the main island of Thera, in the Santorini volcanic complex. CO₂ flux and CO₂ and helium concentrations were measured at 50 cm depth for 76 points covering the entire island, with a spacing of 500 m or less. Several anomalous soil degassing sites have been detected. The main anomalies correspond to the Kolumbos line and to the Kameni line, two volcano-tectonic fault systems that controlled all the historic volcanic activity of Santorini. A third anomaly is related to a gas-leaking fault cutting the geothermal field of southern Thera. Soil gas data, together with geovolcanological and seismological evidence, indicate that the Kolumbos and Kameni lines are the most probable sites for future volcanic or seismic reactivation, and provide the basis for the establishment of a new geochemical monitoring technique at Thera.