Environ Geol (2006) 51: 349–361 DOI 10.1007/s00254-006-0331-0
A. Kallioras F. Pliakas I. Diamantis
Received: 1 March 2006 Accepted: 4 May 2006 Published online: 24 June 2006 Springer-Verlag 2006
A. Kallioras (&) Æ F. Pliakas I. Diamantis Department of Civil Engineering, Democritus University of Thrace, Xanthi 67100, Greece E-mail:
[email protected] Tel.: +30-25410-79692 Fax: +30-25410-79695
ORIGINAL ARTICLE
Conceptual model of a coastal aquifer system in northern Greece and assessment of saline vulnerability due to seawater intrusion conditions
Abstract This paper refers to the development of a conceptual model for the management of a coastal aquifer in northern Greece. The research presents the interpretation and analysis of the quantitative (groundwater level recordings and design of piezometric maps) regime and the formation of the upcone within the area of investigation. Additionally it provides the elaboration of the results of chemical analyses of groundwater samples (physicochemical parameters, major chemical constituents and heavy metals and trace elements) of the area which were taken in three successive irrigation periods (July–August 2003, July–August 2004 and July 2005), in order to identify areas
Introduction With the fact that almost 90% of the available freshwater resources with the exception of polar ice occurs in hydrogeological systems, groundwater management appears as a key issue for the management of water resources from a holistic view. A very common and widespread negative environmental impact regarding the qualitative degradation of aquifer freshwater resources is the increase in salinity of groundwaters. Kallergis (2000) quotes that groundwater salinisation may occur due to: • The presence of brines (especially within petroleum fields) • The presence of gypsum • The anhydrite or mineral salts within the aquifer material
of aquifer vulnerability. The study identifies the areas where ion exchange phenomena occur, as well as the parts of the aquifer where the qualitative degradation of the aquifer system is enhanced. The paper, finally, assesses the lack of any scientific groundwater resources management of the area by the local water authorities, as well as the current practices of the existing pumping conditions scheme as applied by groundwater users. Keywords Conceptual model of coastal aquifer Æ Groundwater resources management Æ Seawater intrusion Æ Saline aquifer vulnerability
• Intense irrigation which causes evapotranspiration increase • The presence of connate water in low aquifer depths However, one of the most common sources of fresh groundwater salinisation is seawater encroachment caused mostly by anthropogenic activities. Essink (2001) quotes that almost 50% of the world’s population lives within 60 km of the shoreline. The above fact enhances the necessity of integrated groundwater resources management in coastal aquifers, as the phenomenon of seawater intrusion poses serious social as well as economic threats to the local communities of coastal zones. Seawater intrusion is a widespread environmental problem in many European and Mediterranean coastal aquifers, which include Spain (Pulido-Bosch et al. 1999; Iribar et al. 1997; Gimenez and Morell 1997; Calvache
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and Pulido-Bosch 1997), Portugal (Stigter et al. 1998), Italy (Chiocchini et al. 1997; Barazzuoli et al. 1999), Israel (Yakirevich et al. 1998), Turkey (Karahanoglou 1997), Egypt (El-Bihery and Lachmar 1994), Libya (El Asswad 1995) and Morocco (Pulido-Bosch et al. 1999). Seawater encroachment also appears within the majority of the coastal aquifers in Greece, which are under hydrogeological investigation, and is responsible for their qualitative degradation (Fig. 1). Today, all scientific evidences lead to the conclusion that the encroachment of seawater into coastal aquifers is a phenomenon that regards the majority of the coastal area of northern Greece (especially within the coastal area of Eastern Macedonia
Fig. 1 Areas of groundwater salinisation in Greece (Kallioras et al. 2006)
Fig. 2 Geographical position of the study area in Greece
and Thrace). Seawater intrusion takes place either at typical coastal aquifers due to over-pumping of freshwater quantities such as the study aquifer in question (Kallioras 2002; Kallioras and Pliakas 2005; Kallioras et al. 2006) and the aquifer of Nea Peramos (Diamantis and Petalas 1989) or within the delta regions of the Rivers Evros, Nestos and Lissos (Pliakas et al. 2004) due to overpumping as well as drainage of the deltoid areas and reduction of the river flow.
Description of the study area The study area is located in Thrace, Greece (Fig. 2), and covers an area of approximately 120 km2, while the coordinates of its boundaries range from 025.171825 to 025.341932 (longitude in WGS 1984) from W to E and from 41.078614 to 40.961278 (latitude in WGS 1984) from N to S. The surface relief of the study area is geomorphologically characterised as flat, semi-hilly and hilly at several parts. Diamantis (1985) quotes that the geomorphological relief has been stringly affected by the alterations of sea level. Tectonic changes as well as the heave of the shoreline have given rise to the formation of the local potential aquifer of investigation which appears mostly confined, whereas it is connected with the unconfined system along the coastline. The main geological material which composes the aquifer system of the study area is sandstone as well as marly limestone of upper Miocene origin (Fig. 3). The aquifer base is exclusively composed of grey-green clay and its depth ranges between )80 and )170 m (Fig. 4). The aquifer system of the study area consists of semiconfined and unconfined layers, which are all developed within an alluvial environment. The geological framework of the confined aquifer layer consists of coarsegrained alluvial materials of upper Miocene origin and is covered by formations of siltstones, sandstones, small conglomerates and clays which appear in successive
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Fig. 3 Geological map of the study area
across the beds of small torrents of the study area, giving rise to the vertical movement of water and enhancing infiltration of rainwater as well as the surface outflow which appears periodically. In general terms these formations are of low storage capacity while their width ranges widely from a few to some tens of meters. There is also a phreatic aquifer having a small area of extent, which gives rise to natural groundwater recharge by either rainfall infiltration, percolation or irrigation returns. The unconfined aquifer is mainly observed across the shoreline and extends up to a few kilometres towards the mainland. Figure 5a–c shows some of the most typical geological sections of the study area. Figure 5a shows the stratigraphy of the study aquifer across the section A–A¢, as shown in the geological map of Fig. 3, whereas Fig. 5b, c shows the stratigraphy of the study aquifer based on the geological sections from groundwater wells relating to sections B–B¢ and C–C¢ of Fig. 3, respectively. It should be noted that the points of Fig. 5b (section B–B¢ of the geological map of Fig. 3) refer to locations where geophysical investigations took place. According to Diamantis et al. (1994), the hydraulic characteristics of the investigated aquifer system are as follows: (a) the upper Miocene aquifer layer has a K which ranges between 8.3 · 10)4 and 8.7 · 10)2 m/s and S which ranges between 1.55 · 10)5 and 1.18 · 10)3 while (b) for the semi-confined aquifer layer the values of K range between 3.5 · 10)4 and 2.4 · 10)3 m/s and the values of S range between 1.25 · 10)5 and 3.4 · 10)3. The recharge of the study aquifer system is a result of the following hydrogeological procedures: • Direct infiltration from rainfall • Percolations from the torrents and rivers of the area (mainly Vozvozis and Aspropotamos) • Recharge from irrigation returns • Lateral recharge (percolation) from the alluvial cone of Kompsatos River (at the northern boundaries) • Lateral recharge (percolation) from the northern mountainous zone of Rhodope
Fig. 4 Contour map of the clayey basement of the investigated aquifer
layers of small thickness. The above formations limit the vertical movement of groundwaters and enhance the confining conditions of the aquifer system. The above relatively confining unit is locally weakened, especially
The whole study area is highly cultivated and characterised by an irrational agricultural development mainly during the last three decades. This irrational and systematic groundwater abstraction for irrigation purposes of the area has resulted in the aggressive intrusion of seawater wedge, particularly during the last decade. The fluctuation of the groundwater levels from selected wells of the study area (Fig. 6) reveals a constant negative absolute value fact which enhances the continuous encroachment of seawater. The groundwater level decline, during the irrigation periods, ranges from 5 to 15 m for the majority of groundwater wells of the study area. The fact that the piezometric surface of the area is a few tens of meters below mean sea level (both before and
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Fig. 5 a Aquifer layer profile based on geological sections of groundwater wells, referring to section A–A¢ of the geological map (Fig. 3). b Aquifer layer profile based on geological sections of groundwater wells and geophysical investigations, referring to section B–B¢ of the geological map (Fig. 3). c Aquifer layer profile based on geological sections of groundwater wells, referring to section C–C¢ of the geological map (Fig. 3)
observed that the centre of the study area is characterised by the presence of a wide upcone, with a piezometric surface which enhances the phenomenon of seawater intrusion within the area of investigation.
Methods of investigation after the irrigation period) shows that the hydrogeological regime is related to an irreversible upconing due to seawater intrusion conditions (Fig. 7a, b). It is easily
As already mentioned, the study area is a hydrogeological aquifer system which is subjected to seawater
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Fig. 6 Fluctuation of groundwater levels (relative to mean sea level) of the study aquifer and trendline for the period June 2001– October 2005
intrusion conditions, due to extensive over-pumping of groundwater for irrigation purposes. A typical hydrogeological study for coastal aquifers subjected to seawater intrusion conditions should be framed according to Fig. 8. The collection of the so-called prerequisite data is essential for the beginning of the investigation. This stage includes the collection of geological and hydrogeological data (geological maps, aquifer geometrical characteristics, groundwater wells section diagrams, identification of aquifer boundary geological and hydrogeological conditions, aquifer hydraulic characteristics), hydrological and climatic data (satisfactory time series of rainfall heights, temperature, etc.) and finally
some general data which will be collected mostly by the farmers of the area who always provide needful information regarding the beginning and the end of the irrigation period, the type of cultivation, the property regime of each parcel. The collection of geographical data is another essential amount of data, as they provide the geographical characteristics of the study area, and therefore the basis of the research in spatial terms. Aerial or satellite images (which should be as recent as possible) are found to be of paramount importance in order to identify the current land uses, built-up areas, types and area of cultivations, extent and status of surface water bodies in every season of the hydrological year. This part of investigation is also related to the development of a complete groundwater wells inventory, together with the development of an integrated groundwater wells database, which contains essential elements for
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Fig. 7 Piezometric map of the study area based on groundwater level recordings (relative to mean sea level) on a April 2005 (prior to irrigation period), b October 2005 (after the irrigation period)
each well such as depth of well, stratigraphy, location and depth of well filter, coordinates, topographic level, etc. After the inventory is completed, the researcher should develop the monitoring well network for the area of investigation, in order to initiate schedule of measurements for the recordings of groundwater levels as well as sampling of groundwater. This will form the basis for the quantitative and qualitative monitoring of the study area and provide the data for the design of piezometric maps as well as pollutant (physicochemical parameters) distribution. The next stage for the integration of the hydrogeological management assessment for the coastal aquifer will be the development of mathematical models
(groundwater flow model, pollutant transport, managerial and optimisation model), which will be based on the conceptual model as developed from the earlier stages which were previously discussed. It is understood that there are always some serious difficulties which often arise and are related to data acquisition. Additionally, most of the cultivated lands are irrationally irrigated, under irregular and uneven pumping schemes. The exact location of each groundwater well in this study area has been recorded by the use of GPS instruments (Fig. 9a), with real coordinates (in longitude/latitude WGS 1984 projection system). During this research, 612 groundwater wells have been recorded (Fig. 9b) and identified according to their operation status (e.g. productive or abandoned and irrigation or water supply purpose). It has been estimated that approximately 8% of the above (50 wells) are abandoned, and all of them are located at the west and southwest boundaries of the study area where severe seawater intrusion conditions exist. The network also includes some wells which are used for water supply purposes, located at the northern part of the study area. The exact register of the groundwater extraction points has been achieved by the use of GPS TrackMaker version # 13.0 in association with Google Earth V. 3.0.0762, which provided all the satellite images appearing within this research paper. All geostatistical analyses were made with the use of MapInfo Professional v. 8.0 SCP and Vertical Mapper v. 3.1, while the grid interpolation was made using the advanced natural neighbour geostatistical method. The groundwater level recordings took place between June 2001 and October 2005, while the groundwater sampling took place during three successive irrigation periods (irrigation periods 2003, 2004, 2005). The sampling methods included in situ measurements of physicochemical parameters such as temperature, pH and electrical conductivity, while the rest of the chemical analyses for the major ions Ca2+, Mg2+, Na+, ) ) ) ) ) K+, Fe2+, NH+ 4 , HCO3 , Cl , SO4 , NO3 , NO2 and 3) PO4 were analysed on the same day of sampling.
Groundwater qualitative regime The quality monitoring of the study aquifer includes the chemical analyses of major chemical constituents of groundwaters as well as the estimation of heavy metals. The presentation of the physicochemical parameters [specific electrical conductivity (lS/cm), temperature (C) and pH] of the groundwater samples from the study aquifer system is related to 375 groundwater samples (Table 1) which were sampled during the irrigation period of July 2003, from which it is revealed that the value of specific electrical conductivity is inversely related to the value of pH (Fig. 10).
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Fig. 8 Basic research elements for the investigation of coastal aquifers subjected to seawater intrusion regime
Figure 11 shows the distribution of specific electrical conductivity (lS/cm) during the irrigation period of July 2003, for 375 groundwater samples, distributed evenly throughout the whole study area, showing with bold contour the distribution of the seawater wedge at the southern and western parts of the aquifer (indicative bold contour line with value of 1,500 lS/cm). This study also includes the chemical analyses of heavy metals and trace elements for 43 groundwater samples during the irrigation period of July 2003, as shown in Table 2. The chemical analyses of 125 groundwater samples (Table 3) in three successive irrigation periods (July 2003, July 2004 and July 2005) has shown that the majority of the groundwater samples that have western or southern origin (i.e. across the western and southern coastline), and hence in connection with the seawater, are highly polluted from chloride ions. Figure 12a, c, e presents the ionic distribution of chemical composition of the groundwater samples of the study aquifer, which reveals that the samples are grouped into two main categories according to their chemical composition and the ions domination. They are polluted from seawater intrusion, and therefore their most dominant ions are chlorides, while the samples from the northern part show a tendency to appear on the freshwater region of the Piper diagrams that follow. Figure 12b, d and f shows the domination of chloride ions (in meq/L) against the concentration of sodium ions (in meq/L) for the seawater-intruded regions, which again show the categorised groundwater sample groups into the ones originated from the northern part and therefore fresh, and the ones originated from the southern and western areas which are highly salinised. When seawater intrudes in a coastal fresh water aquifer an exchange of cations takes place:
1 1 Naþ þ Ca X2 ! Na X þ Ca2þ ; 2 2 where X indicates the soil exchanger (Appelo and Postma 1993). The same authors quote that the reverse process takes place with refreshening, i.e. when fresh water flushes a salt water aquifer: 1 2þ 1 Ca þ Na X ! Ca X2 þ Naþ ; 2 2 where Ca2+ is taken up from water, in return for Na+, with a NaHCO3-type water as result. Figures 13, 14 and 15 show the spatial distribution of the hydrochemical types of the groundwater samples, throughout the area of investigation. It is revealed from the above figures (Figs. 13, 14, 15) that the main aquifer replenishment zones are at the southern and middle parts of the area, where CaHCO3 and MgHCO3 water types are dominant, whereas the groundwater samples which reveal a CaCl and NaCl hydrochemical type are related to contamination from seawater intrusion and ion exchange phenomena. The almost negligent (in terms of spatial distribution) presence of NaCl and CaCl hydrochemical type groundwaters at the northern area is attributed to the presence of fossil groundwaters according to relevant studies of Diamantis and Petalas (1989). Therefore it could be argued that the type of recharge (i.e. freshwater or saline water recharge conditions) of the aquifer system is highly related to the alteration of the hydrochemical facies of the groundwater of the area and is based on the sequence of Fig. 16. The above hydrochemical regime is present during at least the period 2001–2005 independently of the rainfall intensity or the groundwater abstraction rates. Even when the extraction rates are far below the safe yield,
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Fig. 10 Values of pH versus specific electrical conductivity (lS/cm) during the irrigation period of 2003 from 375 groundwater samples
Fig. 9 a Groundwater wells network for groundwater samples and level recordings. b Inventory of groundwater wells of the investigated aquifer Table 1 Physicochemical parameters of 375 groundwater samples during the irrigation period of 2003 N = 375
Specific electrical conductivity (lS/cm)
Temp (C)
pH
Min Max Ave SD
598.00 17,350.00 2,026.73 2,276.59
16.90 29.20 21.77 1.71
6.89 9.93 7.64 0.31
mainly due to increase of rainfall heights, the groundwaters of the northern and western region of the study area appears saline.
Fig. 11 Distribution of specific electrical conductivity (in lS/cm) (Kallioras and Pliakas 2005)
Figure 17 shows the chloride concentration (in mg/L) profile (section A–A¢ of Fig. 3) based on sampling recordings made during the three successive irrigation periods of 2003, 2004 and 2005. It can be observed that the concentration of chloride ions has values which intimate high salinity hazards for the irrigation of the area. It can be observed that during the irrigation periods between 2004 and 2005, the values of chloride concentrations are significantly lower than the ones of 2003. Figure 18, shows the concentration (in mg/L) of Ca2+, Mg2+ and Na+ ions profile (section A–A¢ of Fig. 3) based on sampling recordings made during the irrigation period of 2005. The large initial increase of Ca2+ as the seawater front intrudes the aquifer is quite clear, leading to the expected CaCl hydrochemical type.
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Table 2 Statistical data of heavy metals and trace elements (concentrations in ppb) of 43 groundwater samples during the irrigation period (July) 2003
N = 43
As
Ba
Be
Cd
Cr
Cu
Fe
Min Max Ave SD
0.486 54.616 13.840 15.223
25.907 702.496 294.818 142.195
0.000 4.232 0.217 0.657
0.000 3.152 0.137 0.493
0.000 29.897 3.373 5.113
0.000 184.600 12.888 38.376
24.000 9,179.865 1,169.871 1,858.657
Min Max Ave SD
Min Max Ave SD
Ni
Pb
Rb
Se
Sr
U
V
0.249 2,709.181 539.877 757.888
0.000 11.692 1.345 2.645
0.182 30.435 4.249 6.084
0.000 46.147 6.565 11.669
131.024 27,984.033 3,870.546 5,749.009
0.503 30.657 10.629 8.108
0.000 46.474 6.415 12.392
Ga
Li
Mn
Zn
B
Co
Mo
0.960 20.741 9.049 3.885
0.000 248.274 42.865 46.829
0.000 410.829 19.341 68.387
0.000 1,006.862 117.714 166.592
0.000 444.644 94.777 108.662
0.000 4.155 0.486 0.937
0.000 10.899 1.088 2.520
Table 3 Statistical analysis of some of the major chemical constituents from 125 groundwater samples during the irrigation periods (July) 2003, 2004 and 2005 (concentrations in mg/L) SO2) 4
PO3) 4
NO)3
NO)2
102.70 396.50 226.43 58.46
9.10 651.30 101.20 128.57
0.00 1.17 0.14 0.22
1.00 121.50 15.76 21.94
0.00 0.14 0.01 0.02
1,559.56 85.10 10,120.00 2,188.72
318.20 32.33 1,049.20 180.27
91.85 0.00 590.00 103.37
0.47 0.09 3.20 0.53
10.18 0.00 109.86 20.58
0.00 0.00 0.05 0.01
75.18 2,694.96 800.55 807.74
189.10 2,440.00 344.17 362.93
2.50 313.50 81.57 82.65
0.31 0.54 0.39 0.08
0.00 15.60 2.04 3.47
0.00 0.04 0.01 0.01
Cl)
Na+
K+
Ca2+
Mg2+
Fe2+
NH+ 4
2003 Min Max Ave SD
2.08 1,023.80 237.77 248.06
0.76 14.10 3.53 2.60
8.01 2,180.40 364.68 478.24
2.90 476.10 89.71 109.08
0.00 1.30 0.09 0.24
0.00 2.73 0.09 0.42
7.30 5,591.30 1,059.08 1,342.01
2004 Min Max Ave SD
319.51 19.10 1,780.00 383.69
4.81 1.00 24.00 4.86
511.49 14.43 4,328.64 832.90
128.29 9.72 962.28 181.83
0.68 0.00 9.69 1.74
0.28 0.00 1.81 0.43
2005 Min Max Ave SD
8.40 580.00 160.47 119.06
1.10 6.10 2.95 1.18
21.64 1,026.05 287.52 301.37
8.20 311.60 102.26 80.38
0.02 0.52 0.14 0.11
0.00 4.16 0.95 1.28
Conclusions Coastal aquifers are quite sensitive sources of groundwater resources, partly because they are directly connected to the seawater and therefore susceptible to salinisation and partly because they are highly overpopulated and hence their freshwater resources are always under overexploitation for the satisfaction of anthropogenic needs. In Greece, seawater intrusion is one of the most common environmental problems, and definitely the most serious groundwater qualitative degradation of coastal aquifer resources. The problem becomes more severe especially in small islands, where the groundwater resources of the coastal aquifers is most of the times the only source of freshwater.
HCO)3
The fact that the Greek shoreline is very long dejects any application of pilot techniques for the prevention of seawater wedge such as the installation of biofilms, biological barriers, construction barriers, soil mixing and others. The area of investigation, for instance, has a shore length of 21.68 km, a fact which imposes the alteration of the groundwater pumping scheme or the artificial recharge of the groundwater (provided there will be enough alternative sources of freshwater of high quality) as the only feasible seawater intrusion countermeasure technique. Another critical aspect for discussion is the information of water users, and particularly the farmers, who always install new groundwater wells without any prior environmental impact assessment, at regions close to the
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b
Fig. 12 a Piper diagram for the groundwater samples of 2003. b Chloride versus sodium concentrations (meq/L) for the groundwater samples of 2003. c Piper diagram for the groundwater samples of 2004. d Chloride versus sodium concentrations (meq/L) for the groundwater samples of 2004. e Piper diagram for the groundwater samples of 2005. f Chloride versus sodium concentrations (meq/L) for the groundwater samples of 2005
coastline where the seawater has already intruded into the mainland. A typical characteristic of the area of investigation is the installation of groundwater wells at distances of a few tens of meters from the abandoned saline ones. The area of investigation is fortunately constantly recharged from the northern part, and particularly from the alluvial cone of Kompsatos River (Figs. 7a, b, 11) through lateral recharge. A recent environmental problem related to groundwater salinisation is the construction of defective works, specifically at the area where Aspropotamos torrent enters Vistonida Lake, where a drainage channel has been constructed and allows the migration of brackish waters from the saline Vistonida Lake to encroach the freshwater aquifer of the alluvial cone of Kompsatos River. Although the values of chloride concentration are low for irrigation purposes, the increase in salinisation of an aquifer that was always fresh is an issue that should be raised with the water resources management authorities. The interpretation of the piezometric results (Fig. 7a, b) in combination with the quality pattern maps (Figs. 13, 14, 15) reveals that the areas of freshwater
Fig. 14 Quality patterns of groundwaters of the study aquifer during the irrigation period of July–August 2004
Fig. 15 Quality patterns of groundwaters of the study aquifer during the irrigation period of July 2005
Fig. 13 Quality patterns of groundwaters of the study aquifer during the irrigation period of July 2003
recharge of the aquifer system are related to CaHCO3 and CaHCO3 water types (indicating recharge from the northern alluvial cone of Kompsatos River) or CaCl
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Fig. 16 Alteration of groundwater quality patterns according to the type of recharge (freshwater or saline water recharge) Fig. 18 Ca2+, Mg2+ and Na+ ion concentration profile, based on section A–A¢ of the geological map of Fig. 3, according to chemical analyses of the irrigation period 2005
Fig. 17 Chloride ion concentration profile, based on section A–A¢ of the geological map of Fig. 3, during the three successive irrigation periods of 2003, 2004 and 2005
and NaCl water types (at specific parts of the aquifer indicates the influence from entrapped groundwaters), where ion exchange phenomena take place. The southern and western parts of the investigated aquifer are mainly related to CaCl type of groundwater due to direct seawater intrusion (as the seawater encroaches, calcite which is contained in montmorillonitic clay is exchanged as chloride intrudes). The study of the above figures (Figs. 7a, b, 13, 14, 15) shows that ion exchange phenomena also occur at the western boundaries of the area, as saline-degraded groundwater enters the investigated aquifer system at the area of Pagouria (Fig. 11).
The problem of seawater intrusion in Greece is a matter not only of insufficient or lack of groundwater resources management but also of poor legislation enforcement. Most of the legislative documents regarding the management of water resources are characterised by generalities (Kallioras et al. 2004), and the enforcement of environmental law is rather questionable. Even the recently enacted legislation which harmonises the national water resources legislation with the European water framework directive (Directive 2000/60/EC) assigns the Ministry of Environment, Planning and Public Works for the management of water resources rather than the Ministry of Agricultural Development and Food, as more than 80% of the groundwater consumption in Greece is used for agricultural purposes. The area of investigation is a typical example of lack of scientific groundwater resources management of coastal aquifers, which has resulted in the aggressive intrusion of seawater wedge at the mainland freshwater aquifer. The continuous over-pumping conditions and the overexploitation of the aquifer resources enhance the qualitative degradation of the aquifer and pose threats for a variety of factors of the area such as environmental, social, economic and agricultural development. Acknowledgements The results of the paper in question is part of the research of the Doctoral Dissertation (third year, last stage of PhD) of Mr. Andreas Kallioras, Department of Civil Engineering, School of Engineering, Democritus University of Thrace, Greece. The satellite images, which appear in Figs. 4, 7a, b, 9a, b, 13, 14 and 15, are provided by Google Earth v. 3.0.0762 ( 2005 Google).
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