Impacts of Urbanization, Agriculture and Touristic Development on Groundwater Resources in the Eastern Part of Thermaikos Gulf

Impacts of urbanization, agriculture and touristic development on groundwater resources in the eastern part of Thermaikos Gulf (North Greece): An application of DPSIR model for sustainable development

P. Venetsanou, K. Voudouris*, N. Kazakis and C. Mattas Lab. of Engineering Geology & Hydrogeology, Dept. of Geology, Aristotle University, GR 54124, Thessaloniki, Greece * e-mail: [email protected]

Abstract: The eastern part of the Thermaikos Gulf is characterized by urbanization, touristic development and intensive agricultural activities. Water resources are characterized by high water demands for agriculture and tourism during the dry period (May- late September) when water availability is low. The main aquifers are within coarse grained Neogene and Quaternary deposits (porous aquifers). This study deals with the impacts of the aforementioned activities on groundwater resources in this area. Therefore, hydrometeorological, hydrogeological and hydrochemical data were collected, evaluated and compared with previous studies. The water demands for domestic and irrigation use are mainly covered by groundwater abstracted from aquifer systems via numerous boreholes. A continuous groundwater level decline has been recorded over the last 30 years and a negative water balance has been established in the coastal aquifer favoring sea water intrusion. The concentration values of chloride range between 400 mg/L and up to 700 mg/L at this area having as a result the degradation of groundwater quality. An additional pressure in the area is the intensified fertilization, as it is documented by the increased nitrate concentration. High nitrate values locally exceed the maximum admissible concentration of 50 mg/L set by EU Council for drinking water therefore rendering most groundwater unsuitable for human consumption. The DPSIR approach (Driver-Pressure-State-Impact-Response) was applied in order to be used as a useful tool for the selection of the most appropriate environmental indicators in order to construct a suitable monitoring network that will help decision makers and stakeholders to take the appropriate measures and to monitor the effectiveness of their implementation. In the present paper measures such as: the reuse of the treated wastewater for irrigation purposes, the construction of dams for exploitation of surface water, artificial recharge, public education, etc. are proposed in order to achieve an integrated and sustainable water resources management.

Keywords: Coastal aquifer systems, DPSIR technique, Nitrate pollution, Seawater intrusion, Thermaikos Gulf, Urbanization

1. INTRODUCTION

Greece is facing severe water stresses and is characterized by (Daskalaki and Voudouris, 2007): 1) long coastline that favors hydraulic communication between coastal aquifers and seawater; 2) intensive irrigated agriculture; 3) non-homogeneous spatial distribution of rainfall and water demands. Water resources are characterized by high water requirements for agriculture and tourism during the dry period (April-late October) when water availability is low. The major water use is in irrigation for agriculture: 86% of the total consumption. Water needs are mainly covered by groundwater abstracted from the aquifers via numerous boreholes. Irrational management (overexploitation) of the coastal aquifer systems has been led to a negative water balance triggering sea water intrusion which affects the socioeconomic development of these areas. For this reason, many coastal aquifers are reported to be affected by quality deterioration (salinisation and nitrate pollution) (Diamantis and Petalas, 1989; Lambrakis and Marinos, 2003; Voudouris, 2006a; Voudouris et al., 2010). The main applied fertilizers [NH4NO3, (NH4)2SO4 and mixed types of NPP (Nitrogen Phosphate Potassium)] in cultivated areas and the disposal of domestic and industrial wastewater through torrents are the most important sources of nitrates. In addition, in the urban areas the high nitrate concentrations are attributed to the direct disposal of untreated domestic wastewater in former wells that are presently used as septic tanks (Voudouris et al., 2004). 4 P. Venetsanou et al.

Several techniques such as SWOT analysis and DPSIR framework have been proposed for the assessment of the environment that can support and optimize an integrated water resources management (Diamantopoulou and Voudouris, 2008; Kagalou et al., 2012; Mattas et al., 2014). The Driver-Pressure-State-Impact-Response (DPSIR) framework was developed by the European Environment Agency in 1999 and is widely applicable in environmental studies (Zacharias et al., 2008; Carr et al., 2007). The DPSIR is a very useful tool because it links socioeconomic factors (drivers) and anthropogenic activities (pressures) with environmental parameters (states and impacts) and finally with the required measures that must be taken to improve the environmental status (Skoulikidis, 2009). In this paper, DPSIR was applied by using geographic information system (GIS) which is a useful tool of major importance since it depicts the current state of the environmental conditions and their spatial distribution in a specific area (Agyemang et al., 2007). Through GIS different thematic maps were combined relating the pressures with the drivers (e.g. groundwater quality with land use). All the observed changes of the environmental parameters during the past years were recorded and updated in a GIS database. Furthermore, thematic maps were used in order to compare past and present regarding the quality characteristics of groundwater resources in the eastern part of Thermaikos Gulf (Voudouris et al., 2014). A variety of data (hydrogeological, hydrochemical, hydrological, meteorological, land uses, population, etc.) were collected for the implementation of a reliable DPSIR framework. The DPSIR technique has been applied for the first time in this site and therefore its results can be used by the decision makers and stakeholders of the study area in order to design an integrated plan for water resources management and groundwater sustainability. Towards this direction further actions and measures were proposed including pressure monitoring programs (Song et al., 2012).

2. STUDY AREA

The research area is located in the Region of Central Macedonia, in northern Greece, and extends in the coastal zone of the eastern Thermaikos Gulf. It is part of the Municipality of Thermaikos, which includes the municipal community Peraia (former Municipality of Thermaikos), Epanomi and Michaniona and has a surface area of 137 km2. It is an agricultural and touristic region with continually increasing water demands. The urbanization of the area occurred because of its short distance (20 km) from the metropolitan city of Thessaloniki (the second largest city in Greece). The study site covers the Neogene and Quaternary sedimentary geological formations (Figure 1). The Neogene formations are mainly located in the hilly part and comprise the following series: § The Lower-Middle Miocene basic conglomerate series which is composed of gravels with small amounts of sand. § The Upper Miocene red clay series with a mean thickness of 50 m. Clay, silt, clay sand and silty clay are the main materials forming an impermeable formation. § The Upper Miocene sandstone marl series with a mean thickness of 100 m, which consists of sand, marl and sand-lens.

Quaternary sediments predominate in the coastal zone with a mean thickness of 30 m and consist of: § Coastal lake and lagoon sediments, which are sands and sandy clays § Beach ridges and sand dunes § Alluvial deposits of gravel, sand and sandy clay.

In the last years, a continuous increase in population is observed in the region due to internal migration of population from the neighboring Municipality of Thessaloniki to the study area. From 1991 to 2011 the total population increased by 150%. According to the census of 2011 (National Statistical Service of Greece), the total population is approximately 50,000 residents. However, during the summer months the population increases by 70% according to data from the local municipality. The municipal community of Peraia has by far the largest population in the research

European Water 51 (2015) 5 area. Population density ranges between 118 inhabitants/km2 in Epanomi and 1215 inhabitants/km2 in Peraia.

Figure 1: Morphological and geological map of the study area.

The land use of the study area is presented in Figure 2, as derived from the Corine Land Cover (2000) as well as groundwater quality degradation zones from major pollutants (nitrates and chlorides according to Pavlou et al., 2013). The irrigation areas represent about 54.7%. The cultivated land is 6800 ha and the main crops are olive trees, vineyards and cereals. The industrial area is located in the surrounding area of Mesimeri (southeastern part of the study area) and contains small sized industries. In the study region, there are three protected areas (Natura 2000).

Figure 2: Land use map of the study area and nitrate and chloride pollution of groundwater (Pavlou et al. 2013).

6 P. Venetsanou et al.

According to the climate data of the official meteorological station of the Hellenic Meteorological Service in “Macedonia” airport in Thessaloniki, the mean annual temperature is 15 oC, the total annual precipitation is 475 mm and the average relative humidity is 67%. According to the Thornthwaite-Mather method (1955), the coefficient of real evapotranspiration is 75% of the total annual precipitation. December and November are the months of precipitation peaks. On the contrary, July and August are the driest months. The lowest temperatures are reported during January (Voudouris et al., 2014). Wind direction is mainly northwest. Consequently, the climate of the study area is characterized as Mediterranean (Csa) according to Köppen (1954) classification. The surface runoff is temporal during the wet period (from November to April). The drainage network shows a dendritic pattern. The elevation of the area ranges between 0 to 213 m above mean sea level. The mean slope of the area is 1.85%.

3. DPSIR FRAMEWORK

The Driver-Pressure-State-Impact-Response (DPSIR) framework is a developed version of previous frameworks for environmental reporting and assessment, such as the Pressure-State- Response (PSR) framework that was adopted by the Organization for Economic Co-operation and Development (OECD, 1993). The effectiveness of the DPSIR relies upon the fact that it can reflect the relation between anthropogenic activities and environmental state changes that causes environmental impacts that lead to social and political responses (Smeets and Weterings, 1999). The components of the framework are briefly described in Kristensen (2004) and European Environment Agency (1999), as below. Driving forces are the ‘needs’ and can be classified in primary (shelter, food, drinking water) and secondary (entertainment, culture, etc). Pressures are the required human activities to cover a ‘need’ and they exert pressures on the environment. State represents the physico-chemical/biological environmental conditions and is affected by the pressures. Impacts are the manifestation of the state changes in the human well-being. Responses are the efforts to change the state in order to avoid undesired impacts. Although DPSIR is frequently applied for environmental clarification, especially in European countries (Rasi Nezami et al., 2013), it has been widely criticized for several shortcomings (Song et al., 2012; Rekolainen et al., 2003). The main criticism is that the framework is based on stable indicators and does not take into account the dynamics of the system. In addition, it cannot detect the trends unless it repeats the same indicators at regular intervals (Song et al., 2012; Carr et al., 2007). Another significant disadvantage is that the framework does not provide clear cause-effect relationships for complex environmental problems, since it provides linear unidirectional causal chains. According to Carr et al. (2007), the real aim of DPSIR is to select suitable indicators to be proposed for the construction and operation of an effective monitoring system in order to assess the environmental problems. The authors adopted this approach. In this paper, the DPSIR framework was used to relate socio-economic with qualitative/quantitative indicators and to assess the main factors that contribute to the water resources degradation in the coastal eastern part of Thermaikos Gulf, Northern Greece. The application of DPSIR approach was based on the data from the research project "Research of water resources in Thermaikos area" (Voudouris et al., 2014). The data were collected during the period 2008-2013. They include field measurements and chemical analyses, meteorological data, as well as information collected from previous studies. The disadvantage in the present study is the complexity of the existing environmental problems that were investigated only by using scientific environmental indicators and field observation. The main information acquired by this approach regards the identification of the main problems in the area and their cause in order the decision makers to set their priorities. The effectiveness of the applied measures can be monitored by using the environmental indicators (Karakos et al., 2003). A complete DPSIR implementation should be enhanced by one participatory research method (Hay, 2004; Cameron, 2000; Cook, 1997) since the human system and the environmental system are distinctive (Karakos et al., 2003), but it was not

European Water 51 (2015) 7 conducted in that case study. This causes a difficulty in identifying the relation between drivers and impacts. The selection of the appropriate groups involved in the area and the discussion with these groups can reveal facts that cannot be seen from the strict scientific approach and also can verify or contradict the results of the research (Agyemang et al., 2007). The participation of the direct involved stakeholders can always contribute to the proposal of the appropriate responses.

4. RESULTS

The DPSIR framework for the study area is shown in Figure 3, whereas a detailed analysis of Driver-Pressure-State-Impact-Response is presented below:

4.1 Driving forces

The population growth, the intense agriculture, the animal breeding, the touristic activities, and operation of small industries constitute the main driving forces in the area. According to the most recent censuses (1991 to 2011), a continuous population increase has been recorded during the last decades. This growth has intra-annual characteristics, with an increase of approximately 70% occurring during summer due to the touristic development (Voudouris et al., 2014).

4.2 Pressures

The major pressures from intensive agriculture, especially along the coastal part of the area, consist of the extensive use of fertilizers that causes nitrate pollution and increased concentrations of phosphorus compounds. The land use changes (from uncultivated land to cultivated) constitute an additional pressure. Significant amounts of nitrogen loads that pollute groundwater originate from livestock. Organic pollutants originate from the operation of mills and cattle farms. The uneven temporal distribution of rainfalls combined with the well overpumping in order to meet the increased irrigation and drinking water demands during summertime, is also an important pressure. The aforementioned pressures influence the water availability and are reflected in the groundwater quality degradation and the decline of groundwater table. More specifically, the quality degradation is related to the high concentrations of Na+ and Cl- due to the overexploitation of the coastal aquifer system that has led to seawater intrusion.

Figure 3: A generic DPSIR framework for water resources (Kristensen, 2004, modified by the authors).

8 P. Venetsanou et al.

4.3 State

Groundwater is the main source which covers water demands for both domestic and irrigation uses of the area. The water demands are covered by the exploitation of the coastal aquifer through numerous boreholes. According to data from the groundwater level measurements and sampling, the current state of groundwater resources is described in the next paragraphs. The total groundwater abstractions of the aquifer systems are about 25×106 (approximately 20×106 m3/yr are irrigation needs) (Voudouris et al., 2014; Venetsanou et al., 2016). This amount exceeds the natural recharge of the aquifer, which was estimated to be 23×106 m3/yr (Voudouris et al., 2014). So, the present abstractions are greater than the safe yield and the aquifers are overexploited. It is pointed out that safe yield is the rate at which groundwater can be withdrawn from an aquifer without causing an undesirable adverse effect (Heath and Spruill, 2003). Therefore, the continuously increasing requirements for water have led to the overexploitation of the coastal aquifer. As a result, a negative water balance is established and seawater intrusion in the research area is observed (Pavlou et al., 2013). The main aquifers are developed in the sandstone-marl series and the Quaternary deposits. The aquifers system is characterized by complexity and anisotropy. It is modulated by an upper unconfined aquifer with a mean thickness of 80 m and a deeper confined aquifer below 200 m. An impermeable layer of clay with mean thickness of 40 meters separates the two aquifers. The deeper confined aquifer consists of gravels and sand whereas the main material of the upper aquifer is medium size sand. The majority of the boreholes exploits the upper unconfined aquifer and meets the water demands of the area (Kazakis et al., 2013). The groundwater is classified as Ca-Mg-HCO3 type in the unpolluted zones in contrast to the areas affected by seawater intrusion which is of Na-HCO3 and Na-Cl hydrochemical types (Voudouris and Kazakis, 2011). The overexploitation of the unconfined aquifer is depicted in the decline of the groundwater table of the coastal area (Kazakis, 2014). According to Voudouris et al. (2014), the observed yearly drawdown of groundwater table is about 1 m. In addition, a maximum decline of 45 m has been locally observed over the last 30 years (Figure 4). As a result, an inversion of groundwater flow direction towards the mainland was observed in the coastal zone. Furthermore, the seawater intrusion inevitably has resulted in intense salinization of the coastal aquifer.

Figure 4: Water level fluctuation in the coastal area during the period 1978-2012.

The concentrations of chloride (Cl-) are up to 700 mg/L in the areas of Epanomi and Aggelochori (Voudouris et al., 2006b; Pavlou et al., 2013) whereas near Agia Triada are up to 400 mg/L (Kazakis et al., 2015). As demonstrated in Figure 5, there is a quite strong relation between Na+ and

European Water 51 (2015) 9

Cl-, indicating the common origin (seawater intrusion) of these ions. Furthermore, a decrease of electrical conductivity (EC) and chloride (Cl-) concentration is observed distancing from the sea (Figure 6). The Cl- concentration is higher at the end of the dry season (October). Seawater intrusion has been favoured by some preferential paths, depending upon the geological conditions of each area (Lambrakis and Marinos, 2003). - Nitrate (NO3 ) is a widespread inorganic pollutant in shallow aquifers (Galloway et al., 2008). Nitrate pollution is observed in the study area due to intense agriculture and the irrational use of fertilizers (Kazakis and Voudouris, 2015). Nitrate concentrations of the unconfined aquifer exceed 50 mg/L (the maximum admissible concentration set by EU Council for drinking water), near Epanomi, Peraia and Aggelochori (Figure 2), rendering most groundwater improper for human consumption in contrast to the confined aquifers in which the nitrate concentrations are up to 15 mg/L. Furthermore, high arsenic concentrations (≈10 µg/L) are locally recorded and can be associated with lithogenic origin and geothermal fluids (Voudouris et al., 2014) Based on results of the application of the DRASTIC method to assess the groundwater vulnerability (Voudouris et al., 2010), it is concluded that low values of vulnerability are found in the north-eastern part of the study area. Highest vulnerability values are recorded in the western coastal part and associated with shallow aquifers without a great depth of vadose zone (Voudouris, 2014).

4.4 Impacts

The overpumping of the wells in order to cover the increased irrigation and drinking water needs, causes reduction of the reserves. The seawater intrusion that comes as a result of the overpumping leads to a further loss of groundwater reserves, because the latter become improper for irrigation or human consumption. This might lead to the necessity of drilling new wells and to extend the water supply network, which, in turn, would cause an increase of the water price. Such price policy would act as a suspending factor for the development of the promising touristic sector. Land use changes might also result to a decrease of the water reserves. The shifting from rain-fed (e.g. wheat) to irrigated (e.g. maize) cultivations or to the construction of touristic or industrial facilities, may result to the pollution of the aquifers or to the groundwater level drawdown and, consequently, to the loss of additional groundwater quantities. The major source of pollution is the agricultural activities. The inconsiderate use of fertilizers makes groundwater improper for human consumption.

350

300

250

200

150 Na = 0,36 Cl + 11,2 Na (mg/L) Na R2 = 0,73 100

0 0 100 200 300 400 500 600 700 800 Cl (mg/L)

Figure 5: Correlation between Na+ and Cl- concentrations (mg/L).

10 P. Venetsanou et al.

Figure 6: Hydrochemical cross section of EC and Cl in the study area.

4.5 Responses

Appropriate measures and feedback policies are required to address the aforementioned pressures and improve the state of the water system. According to DPSIR analysis results, the following measures are suggested in order to improve the water quantity and quality in the research area (Voudouris et al., 2006b; Mattas et al., 2014): § Reduction of groundwater abstraction, pumping rates decrease and allocation of boreholes should be applied in the coastal area that is affected by seawater intrusion. § Reuse of the treated wastewater for irrigation purposes in order to reduce the groundwater abstraction. § Small dams should be constructed in the main torrents of the hilly region. The aim of these dams is the retardation of wintertime torrential flows contributing to the groundwater recharge increase and the improvement of the water supplies for the agriculture needs. Based on geological and hydrotechnical criteria, there are some sites suitable for construction of dams. § Introduction of water saving techniques in order to decrease the groundwater abstractions for irrigation purpose. § Integrated climate changes considerations into water resources management. § Information and awareness of citizens, farmers and students for rational water use. § Application of the Code for Good Agricultural Practice in order to reduce the nitrate groundwater pollution of agricultural origin through reduction and appropriate application of fertilization (Mattas et al., 2014). § Water pricing policies in accordance with the guidelines set by the Water Framework Directive, will reward the good consumers and will encourage the water saving practices.

Finally, a systematic monitoring of groundwater levels and groundwater quality should be applied in order to avoid the salinization of the coastal aquifer.

European Water 51 (2015) 11 5. DISCUSSION

Groundwater is globally under intense pressure, as it is in the studied coastal aquifer as depicted in the results of this study. The DPSIR approach revealed the main pressures of the coastal aquifer which can be the base of a sustainable groundwater management plan. In addition, the combativeness of the method with the GIS allows the allocation of the impacts in a specific area and can ensure targeted measures for the future addressing of these impacts. The DPSIR approach is flexibly and easily applicable in variable environments and can be used as a useful tool for groundwater management and protection (Mattas et al., 2014). Although this method has been frequently applied in various areas, it must not be forgotten that it has essential deficiencies (Rekolainen et al., 2003; Song and Frostell, 2014). The main disadvantage is its impotence to evaluate the dynamic of the system as it is based on stable indicators. Furthermore, a gap in respect to the inability to capture trends has also highlighted by Carr et al. (2007). Apparently, the proposed linear unidirectional causal chains of environmental problems are not a realistic solution owing to the complexity and variability of the environmental problems. Nevertheless, the quantification of a problem renders it more understandable to the decision makers and to local authorities. Additionally, the provided links between the nodes of DPSIR by applying specific socioeconomic and natural science based models describe the cause-effect dynamics in advance (Karageorgis et al., 2006a; b). In this framework the proposed action for the study area can prevent a further groundwater quality deterioration and quantity depletion without disturbing the socioeconomic balance of the area.

6. CONCLUSIONS

The aquifer systems in the eastern coastal part of Thermaikos Gulf (North Greece) are under pressures, due to urbanization, touristic development and intensive agriculture. These activities influence the regime of groundwater resources and will affect the future development of the region. The main aquifer is developed within the sandstone-marl series and the Quaternary deposits. This coastal part is characterized by increasing water demands for domestic and irrigation uses and negative groundwater balance due to overexploitation, as deduced from the decline of groundwater levels. The hydrochemical investigation of the coastal aquifer systems revealed salinity due to seawater intrusion. Furthermore, intensified fertilization has led to groundwater quality deterioration as shown by the increased nitrate concentration. Other sources of nitrate pollution are leaking septic tanks in urban areas. The DPSIR (Driver-Pressure-State-Impact-Response) approach was applied in order to assess the impacts of the aforementioned activities on water resources and propose measures to optimize the state of groundwater resources. These measures include the reuse of the treated wastewater for irrigation purposes, the construction of dams for exploitation of surface water, artificial recharge, water efficiency measures and public education.

ACKNOWLEDGMENTS

This scientific work was carried out within the framework of a research program (Lab. of Engineering Geology & Hydrogeology, Dept. of Geology, Aristotle University), funded by the Municipality of Thermaikos, during the period 2008-2013. The authors greatly appreciate the valuable contribution of Vasilios Marinos, Eirini Liami and Athanasios Pavlou, who worked in the field to collect hydrogeological data. Finally, the staff of Municipality of Thermaikos Thessaloniki, especially Sophia Papantoniou and Lambros Miaritis, are acknowledged for their contribution to this project.

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