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Spatial and temporal assessment of groundwater quality indicators and hydrogeological characterization of a karstic aquifer in Western Turkey

[1]Alper ELCI, [2]Orhan GUNDUZ, [3]Celalettin SIMSEK [1] Dokuz Eylul University, Dept. of Environmental Eng., Tinaztepe Campus, 35160 Buca-Izmir, TURKEY, e-mail: alper.elci@deu.edu.tr [2] Dokuz Eylul University, Dept. of Environmental Eng., Tinaztepe Campus, 35160 Buca-Izmir, TURKEY, e-mail: orhan.gunduz@deu.edu.tr [3] Dokuz Eylul University, Torbali Vocational School, Dept. of Drilling, 35860 Torbali-Izmir, TURKEY, e-mail: celalettin@deu.edu.tr

Abstract A case study is presented that characterizes the hydrogeology of a karstic aquifer system nearby the city of Izmir, Turkey. The main objective of this study is to provide an assessment on the spatial distribution of specific groundwater quality parameters, and to gain insight into their temporal evolution. The study area is the Nif Mountain karstic aquifer system located to the southeast of the city of Izmir that is an important recharge source for the densely populated surrounding area. The 1000 km2 study area is within the boundaries of the third largest city, and in the vicinity of one of the most industrialized areas of Turkey. Therefore, it is under significant environmental stresses due to residential, industrial and agricultural activities. Field work was conducted as a series of field excursions to study the hydrogeology, and to mark sampling points for consecutive groundwater sampling. A total of 59 sampling points were selected constituting of 25 wells and 34 springs. Sampling was performed in April and September 2006, during the wet and dry season of the year to assess possible temporal changes in water quality and isotopic composition. Samples were analyzed for several groundwater quality parameters including major ions, arsenic, boron, heavy metals and isotopic composition. In addition to geochemical characterization, discharge rates of some springs were measured. It is found that the hydrogeological structure is fairly complex with springs having a wide range of discharge rates. High-discharge springs originate from allochthonous limestone units and surface outcrops of conglomerate and sandstone units. On the other hand low-discharge springs are formed at the contacts of claystone and limestone units, and at the contact zones of allochthonous limestone and flysch units. High-discharge springs typically have rates higher than 200 L/s in the winter months, with a maximum of about 1000 L/s. However, a 65% decrease was observed for the summer months. Based on stable isotope analysis data, an oxygen18-deuterium relationship is obtained that lies somewhere between the Mediterranean meteoric and mean global lines. Tritium analyses confirm that low-discharge springs originating from contact zones have longer circulation times compared to high-discharge karstic springs. Isotopic composition of groundwater does not change throughout the year, except for tritium. Furthermore, spatial assessment of geochemical data revealed a correlation of sampling elevation with nitrate, chloride and electrical conductivity (EC). This result implies that groundwater quality significantly deteriorates as water moves from the mountain to the plains. The same “elevation effect” was also observed for the CaCO3 concentrations, therefore indicating continuous rock dissolution as groundwater flows through the system. Heavy metal, arsenic and boron concentration are generally below drinking water quality standards with a few exceptions occurring in residential and industrial areas located at the foothills of the mountain. Comparative evaluation of winter and summer quality data shows an overall increase in electrical conductivity values. Nitrate contamination was more sporadic and concentration changes in time were less predictable. Although lower contaminant concentrations due to dilution effects were expected for the winter months, the internal hydrodynamics and the ongoing dissolution processes in the karstic aquifer system are suspected to seclude any temporal trends. It is concluded that the Nif Mountain overall has a significant potential to provide high quality water, although the available groundwater quantity is expected to drop significantly for the summer months, due to decrease in discharge and also because of deterioration of groundwater quality. From a water quality point of view, direct consequences of anthropogenic activities were observed, which requires close monitoring of Nif Mountain’s pristine water resources. The study revealed that less groundwater recharge in the dry period of the year does not always translate to higher concentrations for all groundwater quality parameters. It was also evident from the study results that water circulation times, lithology, quality and extent of recharge also play an important role on the alteration of groundwater quality. Keywords: stable isotopes, groundwater quality, nitrate, boron, arsenic

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1. Introduction Karstic limestone formations in the Mediterranean basin are potential water resources that can meet a significant portion of groundwater demand. The water supply potential of a karstic aquifer is not only dependent on the hydrogeologic properties of the area, but also on its geochemical characteristics. Due to unique water circulation patterns that are typical of karstic aquifers, these systems are more susceptible to groundwater contamination. Therefore, it is necessary to thoroughly study the hydrogeology and geochemistry of karstic mountain regions. This paper presents a hydrogeological characterization of the Nif Mountain karstic aquifer system located to the southeast of the city of Izmir in western Turkey that is an important recharge source for the densely populated surrounding area. With a total drainage area of more than 1000 km2, the Nif Mountain karstic aquifer system is considered to be an important resource for the domestic water supply system of the city of Izmir, the third largest metropolitan area of Turkey. Furthermore, the karstic structure in Nif Mountain recharges the surrounding Bornova, Kemalpasa and Torbali plains, where intense agricultural and industrial production takes place, as well as the Cumaovasi plain where the Tahtali Dam Reservoir of the Izmir water supply system is situated. In this regard, the quality of subsurface drainage originating from Nif Mountain is considered to be an important factor that determines the overall water quality pattern around the Izmir metropolitan area. Furthermore, this study aims to provide a spatial and temporal assessment of the groundwater quality parameters nitrate and electrical conductivity since it is often of interest for water resource managers how the spatial distribution of certain groundwater pollutants change with time. The impact of decreasing groundwater recharge in the summer months on groundwater quality indicators is investigated. It is also determined, if there are any temporal change in isotopic composition of groundwater in the study area.

2. Study area 2.1. General description The study area is located to the southeast of the city of Izmir, which is on the Aegean coast in western Turkey (Fig. 1). From a geomorphologic point of view, the study area mainly consists of Nif Mountain and the surrounding plains. The selected study area is delineated such that Nif Mountain is situated at the center and a number of low level plains in all directions surround the mountain. The study area of slightly more than 1000 km2 is located in a region that demonstrates typical characteristics of the Mediterranean climate with mild, rainy winters and hot, dry summers. Based on the data collected at the Bornova Meteorological Station between 1979 and 2005, the region receives a mean annual precipitation of 594 mm. The highest precipitation amounts are observed in November, December and January, with long-term monthly averages of 100, 120 and 106 mm, respectively. The lowest precipitation values are observed in July and August with long-term monthly averages of 2.3 and 1.8 mm, respectively (DMI 2006). During winter months, the precipitation typically occurs in the form of snow around the summit of Nif Mountain (1,450 m) but no permanent snow cover occurs due to moderate temperatures with a mean above 0°C. Being situated within the administrative boundaries of the third largest city and in the vicinity of one of the most industrialized areas of Turkey, Nif Mountain is under immense environmental stresses due to residential, agricultural and industrial development. In particular, the fertile agricultural plains are being converted to organized industrial zones and/or residential lots in Bornova, Cumaovasi, Kemalpasa and Torbali plains. This transformation is the main reason for the increase in population density in the region. In addition to the city of Izmir, Bornova, Kemalpasa, Buca, Menderes and Torbali are among the major counties of Izmir that are situated around Nif Mountain. According to the 2000 census data, about 850,000 inhabitants live within these counties at the lower elevations of Nif Mountain. The population density decreases with proximity to Nif Mountain, on which only a few small villages exist on the hillslopes. A wide network of streams and creeks has developed in and around the vicinity of Nif Mountain as seen in Fig. 1. Among the most important of these streams, the perennial Hirsiz and Gurlek creeks originate from the southwestern slopes of the mountain and later merge to form the Tahtali stream, which flows through the heavily populated Cumaovasi plain. The Tahtali stream is the major tributary of the Tahtali reservoir that was constructed in the 1990s to meet the water demand of the Izmir metropolitan Area. The Kapuz and Kestane creeks originate from the northeastern slopes of the

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mountain and later merge to form the Nif stream, which flows into the industrialized Kemalpasa plain before merging with the Gediz River. Finally, the Visneli stream originates from the southeastern slopes of the mountain and is mainly fed by two karstic springs (P-14 and P-15). The Visneli stream flows into the Torbali plain, which is considered to be an important agricultural production area and an industrial development region. With long-term mean daily flow values of about 10 m3/s, the Tahtali, Nif, and Visneli streams are important recharge sources for their corresponding underlying surficial aquifers.

2.2. Geological setting Basically, four different rock types are observed in and around the study area: (1) the Paleozoic-aged Menderes metamorphics, which mainly consist of schists, (2) the Mesozoic-aged Bornova flysch that mostly contains meta-sandstones, shales, ophiolites as well as the Upper Cretaceous-aged allochthonous limestones, (3) the Neogene-aged conglomerates, claystones and clayey-limestones, which are collectively known as the Visneli Formation, and (4) the Quaternary-aged alluviums. Of these units, the Menderes metamorphics are considered to be the foundation rock, on which Bornova flysch lies nonuniformly via a thrust fault. In general, Menderes metamorphics are observed mainly as schists with limited spatial extent in eastern parts of the study area. The western and southern portions of the mountain are mostly characterized by the Neogene series including conglomerates, sandstones, claystones and limestones. Finally, the northern and southwestern parts of the study area are mostly covered by alluvial layers. The thickness of the alluvial layer ranges from 40-120 m in the Bornova and Kemalpasa plains and from 20-80 m in the Torbali and Cumaovasi plains (Simsek 2002).

3. Field work and water sampling The characterization of the Nif mountain karstic aquifer system is a two-stage process that involves (1) field work and (2) sample analysis. The field work was conducted as a series of field excursions for the general assessment of regional hydrogeology, where in-situ measurements of several water quality parameters were done and samples were collected for analyses in the laboratory. Furthermore, logs pertaining to boreholes in the study area and a regional geology map were together evaluated in order to identify aquifers and to supplement the hydrogeological characterization process of the study area. Field work was conducted as a series of expeditions to Nif Mountain and its vicinity in 2005 and 2006. This stage was initiated with a preliminary field exploration that was conducted with the aid of a 1/25,000 scaled topographic basemap and a handheld GPS device. During this exploration, potential sampling locations within the study area (i.e., natural springs and accessible wells screened in the unconfined aquifer) were designated and marked on the basemap. The type of sampling location (well or spring) and its spatial coordinates (X, Y, Z) were recorded. Several other additional details were also noted such as the depth and the average production capacity in cases of wells, and the mechanism of water outflow and discharge rate in cases of springs. The database was then shortlisted to a total of 59 sampling points (Fig. 1) by considering a fairly homogeneous spatial distribution of the points within the study area. The data collected from the field work were then transferred into a database that was hosted by a GIS platform for spatial analysis and data visualization. The selected 59 data points (25 wells and 34 springs) were later revisited in several other field trips for sample collection and further analysis. In order to assess temporal changes in water quality and isotopic composition, sampling was performed in April and September of 2006, which roughly marked the end of the wet and dry period of the year. Some basic physicochemical parameters such as pH, electrical conductivity, water temperature and salinity were measured in-situ with portable multiparameter probes. For other parameters of interest, the water samples were collected into 50-, 500- and 1000 mL polyethylene bottles from each sampling location. These bottles were temporarily stored in portable coolers and were then transferred to refrigerators located in the Water Quality Laboratories of Dokuz Eylul University at the end of each sampling day for further sample analyses.

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Fig.1. Map of study area showing topography and locations of sampling points

3.1. Sample analyses The water samples collected from 59 sampling points were analyzed for major anions, heavy metals and trace elements. The 50-mL sample collected from each point was acidified in the field with nitric acid to drop the pH level below 2. This pretreated sample was then analyzed by inductively coupled plasma mass spectrometry (ICP-MS) for heavy metals and several trace elements such as arsenic, boron and iron at Canadian ACME Laboratories. The 500-mL sample collected from each sampling point was used to analyze major anions such as chloride, bromide, nitrate, nitrite, fluoride, sulfate and bicarbonate ions. Of these, only the bicarbonate analysis was performed by titrimetric techniques; the remaining anions were analyzed by ion chromatography (IC) in Dokuz Eylul University laboratories. Finally, the 1000-mL samples collected from 14 selected karstic springs were tested for stable isotopes δ18O (oxygen-18), δ2H (deuterium) and δ3H (tritium) in the isotope laboratories of Hacettepe University, Turkey, and University of California, USA. The oxygen-18 and deuterium analyses were performed using a Finnigan MAT 251 Isotope Ratio Mass Spectrometer, and the tritium analysis was done using a liquid scintillation counter. All measurements and chemical analysis results from both sampling periods were eventually compared and then presented on maps in order to reveal any spatial patterns of groundwater quality deterioration.

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Fig.2. Geological map of the study area with discharge rates of major springs (only April 2006 data is shown)

4. Results 4.1. Hydrogeological characterization and evaluation of isotope data Four major aquifer units have been identified in the area: (1) the allochthonous karstic limestones located within the flysch units, (2) the conglomerate and sandstone units of the Visneli Formation, (3) the clayey limestone units of the Visneli Formation and, (4) the alluvium layers. A geological map of the study area is shown in Fig. 2. A detailed assessment of the regional geology and the above-mentioned aquifer systems reveals that the most important water-bearing unit in the study area is the allochthonous karstic limestone aquifer. The Neogene series (conglomerate-sandstone and clayey-limestone) aquifers and Quaternary alluvial aquifer systems are in general of secondary importance for the region, as they have a relatively lower water supply potential compared to the karstic limestone units. In this regard, wells that are drilled in the allochthonous limestone units have been proven to provide significant amounts of water (i.e., as high as 50 L/s from a typical well depth of less than 300 m). It must also be mentioned that all of these aquifer systems are recharged by Nif Mountain via infiltration from surface runoff and horizontal seepage from subsurface interflow. The complex geological structure and the aquifer formations in the Nif Mountain area and its vicinity resulted in the formation of numerous natural springs. These springs can be classified into four major categories depending on the parent rock, the formation mechanism, and the rate of discharge: (1) high-discharge springs that emerge from the outcropping fractures and cracks of allochthonous limestone units, (2) high-discharge springs that emerge from the surface outcrops of conglomerate and sandstone units of the Visneli formation, (3) medium- to low-discharge springs that are formed at the contact zones of allochthonous limestone and flysch units, and (4) low-discharge springs that are formed at the contact zones of claystone and clayey-limestone units of the Visneli Formation. Spring discharge rates

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measured at selected sampling locations are presented along with the regional geology in Fig. 2. The high-discharge springs originating from allochthonous limestone units have discharge rates higher than 50 L/s, which can sometimes reach up to 300 L/s depending on the annual precipitation pattern. Typical examples of this category are the Visneli (P-14 and P-15) and Gurlek (P-22) springs located in the southeast and west of the study area, respectively. The springs with high discharge rates emerging from the conglomerates and sandstone units have discharges in excess of 200 L/s. The seasonal discharge at these locations could occasionally reach up to 1000 L/s during winter and spring seasons when recharge rates are at maximum. These springs usually have larger recharge areas and are observed at lower elevations of the study area. The Oglananasi (P-33) and Ayrancilar (P-34) springs are considered to be typical examples of this category. On the other hand, low-discharge springs originating from the contact zones of Neogene-aged claystone and clayey-limestone units typically have discharge rates less than 1 L/s. The springs in the Altindag (P-1) and Kiriklar (P-18) region of the study area belong to this category. Finally, the medium- to low-discharge springs that emerge from the contact zones of allochthonous limestone and flysch units have discharge rates that differ considerably and are generally higher than 1 L/s but typically less than 10 L/s. The rate depends on the spatial extent of the limestone interface at the contact zone. Typical examples to this category are Sekeroluk (P-24) and Esoluk (P-32) springs located in the central portions of the study area. In general, spring discharge rates in the study area decreased on average 65% from April to September based on the comparison of discharge rate measurements in the field. A subset of karstic and contact springs was also sampled in April and September 2006 to determine the isotopic composition of the Nif Mountain karstic aquifer system. Based on the comparison from results of both sampling periods it can be concluded that the isotopic composition of spring water in the study area does not change seasonally (Fig. 3). It can be seen that the δ18O values range from -7.91 to -5.49‰ and the deuterium δ2H values range from -42.7 to -29.8‰. In this regard, the values for all water samples lie between the mean global (δ2H=8⋅δ18O+10) and the Mediterranean meteoric lines (δ2H=8⋅δ18O+22). A correlation analysis was performed and the following relationship was obtained between δ18O and δ2H values for the study area representing both winter and summer seasons (designated as Izmir coastline in Fig. 3):

2 18δ H = 5.94 δ O + 2.86 (1) It should be noted that this relationship is similar to the data fit for the Antalya station that is given by IAEA (2002) (designated as Antalya coastline in Fig. 3):

2 18δ H = 6.52 δ O + 6.78 (2) In a comparable study conducted in central Anatolia (Gunay 2006), it was shown that the isotopic composition of groundwater in a karstic aquifer was much closer to the mean global meteoric line than to the relationship found in this study. The relationship between δ18O and δ2H in spring water from the karst aquifer in central Anatolia is given by the following equation (Gunay 2006):

2 18δ H = 8.0 δ O + 14.5 (3) The differences between these studies could be explained by the drastic differences in the climatic conditions of the central Anatolian and Aegean/Mediterranean regions. Even if the two karstic aquifers have similar hydrogeological characteristics, the differences in recharge mechanisms and climatic conditions would ultimately yield distinct isotopic compositions as shown above. In another study conducted on the Syrian coast, Charideh and Rahman (2006) present the following relationship between δ18O and δ2H:

2 18δ H = 6.0 δ O + 4.6 (4)

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This relationship is similar to Eq. (2) that was written for Antalya station, thus implying a representative relationship for the eastern Mediterranean Sea. For the same set of samples, tritium analysis was performed to estimate the circulation times of the groundwater in the study area. Unlike the stable isotope analysis results presented above, tritium values changed from April to September; the range for the winter sampling period was 3.27−4.82 TU, and the range for the summer sampling period was 2.53−5.21 TU. The mean tritium values were 4.18 and 3.83 TU for the winter and summer periods, respectively. Lower tritium values for the summer demonstrate longer circulation times of groundwater, whereas higher values for the winter indicate rapid replenishment of groundwater by precipitation. The tritium values range from 3.27−3.96 TU for P-7, P-18, P-30, P-31 and P-32, all of which occur at the contact zones of two different geologic layers. On the other hand, the water samples from karstic springs P-4, P-6, P-9, P-10, P-14 and P-15 have tritium concentrations varying from 4.05−4.82 TU, which clearly indicates that these springs have shorter circulation times compared to the contact springs. Furthermore, the water samples from two major springs in the south of the study area (P-33 and P-34) have distinctly different tritium concentrations of 3.27 and 4.01 TU, respectively. It is noteworthy that these springs are only about 2.5 km apart. Moreover, P-34, the spring with the highest recorded discharge rate of 877.5 L/s (April 2006) in the study area, has a fairly short circulation time. The travel and circulation times for P-33 are probably longer, which further implies distinct differences in aquifer permeability values for both spring locations. The spring with the shortest circulation time indicated by the second highest tritium value is located to the east of the mountain and is called the Visneli spring, P-14. This spring is a typical karstic spring in the form of an open-conduit gravity spring where groundwater emerges from an open cave mouth. It also has a relatively high discharge rate of 256 and 50.5 L/s for April and September 2006, respectively. Another spring in the east, P-15, is of the same type, and its water has a tritium concentration of 4.21 TU. Conclusively, tritium analyses demonstrate clearly that springs originating from contact zones have longer circulation times compared to the high-discharge-rate karstic springs in the same area.

Fig.3. Relationship between δ18O and δ2H values for sampled spring water

4.2. Spatial and temporal assessment of groundwater quality indicators Well and spring samples collected from the Nif Mountain karstic aquifer system were assessed based on several water quality parameters: pH, temperature, electrical conductivity (EC), nitrate, fluoride, bromide, chloride, sulfate, bicarbonate, hardness, calcium, magnesium, sodium, potassium, arsenic, boron, iron, aluminum, zinc, manganese and copper. However, within the scope of this paper, only EC and nitrate were evaluated.

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The range of EC for all samples was 212−1583 µS/cm, and 243−1780 µS/cm for April and September sampling periods, respectively. The spatial distributions of EC values for each sampling period, which were calculated using the inverse distance weighted interpolation method, are depicted in Fig.4. It is evident that samples taken from springs in the mountain have the lowest electrical conductivity values. In contrast samples taken from locations that lie closer to the city center (northwest of study area) and in agricultural areas (southwest of study area) had clearly the highest EC values. Furthermore, the correlation between EC and elevation was evaluated (Fig. 5). It can be observed that the EC of samples was lower at higher elevations of the mountain and increased in a non-linear fashion as one travels towards the plains. This “elevation effect” is typical for areas like Nif Mountain where the levels of anthropogenic activities and rock-water interactions (i.e., shale, ophiolites and clays) increase as groundwater travels down from the uplands. This trend was also observed in chloride values and in hardness values of water samples to a certain extent (data not shown). The hardness values ranged from 28.2−662.8 mg/L CaCO3, with mean and standard deviation of 348.41 ± 137.22 mg/L CaCO3.The high standard deviation value is indicative of the continuously ongoing carbonate mineral dissolution processes in the karstic aquifer. Furthermore, heavy metal, arsenic and boron concentration were generally below drinking-water quality standards with a few exceptions occurring in residential and industrial areas located at the foothills of the mountain (data not shown). Elevated arsenic concentrations at three sampling points were probably related to local geologic formations, which are likely to contain oxidized sulfite minerals in claystones. The occurrence of nitrate at all sampling locations is also shown in Fig.4. The mean concentrations were 16.83 and 18.91 mg/L for the April and September sampling periods, respectively. There are sporadic occurrences of high nitrate concentrations in certain parts of the study area, e.g. the northwest and southwest corners of the study area, which are residential or farming areas. Furthermore, when EC values are compared with nitrate concentrations (Fig. 4), high nitrate concentrations do not necessarily occur at locations with high EC values or vice versa, although a correlation between both parameters was observed to some extent. Fig. 6 illustrates changes of EC from April, the end of the wet season, to September, which marks the end of the dry season. An increase in EC values was observed for 45 out of 59 sampling points from wet to dry season. While most of the increase was less than 25%, a limited number of sampling locations exhibited more than 25% increase. This generally increasing trend in EC can be attributed to reduced groundwater recharge fluxes during summer months, and consequently to relatively longer retention time of groundwater within the karstic formation. However, in limited parts of the study area, EC decreased in the summer, e.g. south and southeast of Nif Mountain. With respect to nitrate contamination, the spatial distribution varied significantly over time, as it is illustrated in Fig. 7. Concentrations remained basically unchanged at higher elevations of the Nif Mountain, where the population density is low and limited agricultural activities exist. About 35% of all sampling locations had nitrate concentration changes less than 0.5 mg/L. In contrast, nitrate concentration increases and decreases occurred sporadically without any concrete spatial pattern. At about 30% of the sampling points an increase in nitrate concentration was observed, whereas at 35% of the sampled locations a significant decrease was observed. More than 25 mg/L increase in nitrate concentration occurred in two monitoring wells located close to the industrialized Kemalpasa plain, and the Cumaovasi plain, which hosts many farms and greenhouses. On the other hand, sampling locations, where nitrate concentrations dropped more than 25 mg/L do also exist.

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a)

(b)

Fig.4. Spatial distribution of nitrate concentrations and electrical conductivity in (a) April 2006, and (b) September 2006. (P: spring sample, K: well sample)

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Fig.5. Correlation of electrical conductivity (EC) with sampling elevation (curve represents a logarithmic regression fit, regression coefficient r2 =0.55)

Fig. 6. Change in electrical conductivity values from April to September 2006. (P: spring sample, K: well sample)

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5. Conclusions The hydrogeological characterization of the Nif Mountain karstic aquifer system confirmed its importance as a recharge source for the densely populated surrounding area. It is also evidenced by the isotopic and chemical analyses of groundwater samples that the alluvial aquifer systems around Nif Mountain have some degree of hydrological interaction. The springs of Nif Mountain, which originate from these aquifers are classified into four major categories including: (1) high-discharge springs that emerge from the outcropping fractures and cracks of allochthonous limestone units, (2) high-discharge springs that emerge from the surface outcrops of conglomerate and sandstone units of the Visneli Formation, (3) medium- to low-discharge springs that are formed at the contact zones of allochthonous limestone and flysch units, and (4) low discharge springs that are formed at the contact zones of claystone and clayey-limestone units of the Visneli Formation. In particular, the high-discharge springs provide significant amounts of high-quality water and thus demonstrate potential for future use. A study by Biondic et al. (2006) provides similar insight into the relationship of spring discharge rates with the geological features of their catchment areas for a site in Slovenia. Assessment of groundwater quality data revealed a negative correlation between sampling elevation and groundwater quality. This correlation is a direct consequence of the increasing level of anthropogenic activities and rock-water interactions as groundwater flows from the uplands to the plains. Spatial assessment of EC values and nitrate concentrations indicated a dependence on land-use patterns, e.g. higher values in low-populated areas versus higher values at certain hotspots of the studied area. Also, groundwater quality data for the winter and summer sampling periods were comparatively evaluated. There was an overall increase in EC values from winter to summer that can be attributed to decreased groundwater recharge and slower groundwater circulation, thus implying that internal aquifer hydrodynamics and ongoing karstic dissolution processes are more dominant in EC occurrence. However, from a nitrate pollution point of view, groundwater quality deteriorated in some parts, in other it improved. Nitrate occurrences in the studied system are believed to originate either from fertilizer application or from sewage leakages, as concentrations are sporadically very high. Therefore, the temporal evolution of nitrate pollution is more difficult to predict, as anthropogenic factors play also a role besides natural dilution and dissolution processes. From a groundwater quality point of view close monitoring of Nif Mountain’s pristine water resources are required. More frequent sampling is required to better evaluate any temporal trends of groundwater quality data. It is evident from the study results, however, that less groundwater recharge in the dry period of the year does not always translate to higher concentrations for all groundwater quality parameters because water circulation times, lithology, quality and extent of recharge also play an important role on the alteration of groundwater quality. Finally, the unique properties of a karstic aquifer system complicate the assessment of spatial and temporal distribution of groundwater contaminants, and therefore more research to elucidate dispersion and hydrodynamics in these systems must be conducted.

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Fig. 7. Change in NO3 concentrations from April to September 2006. (P: spring sample, K: well sample)

Acknowledgements This study was funded by the Scientific and Technological Research Council of Turkey (TUBITAK), project no. 104Y290 and the Marie Curie International Reintegration Grant MIRG-CT-2005-029133 within the 6th European Community Framework program. The authors are thankful to Yetkin Dumanoglu and Rahime Polat for their assistance in anion analyses by ion-chromatography.

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