Hydrogeochemical Evolution of Groundwater in a Mediterranean Coastal Aquifer, Mersin-Erdemli Basin (Turkey)
Total Page：16
File Type：pdf, Size：1020Kb
Environ Geol (2006) 49: 477–487 DOI 10.1007/s00254-005-0114-z ORIGINAL ARTICLE Zeynel Demirel Hydrogeochemical evolution of groundwater Cu¨neyt Gu¨ler in a Mediterranean coastal aquifer, Mersin-Erdemli basin (Turkey) Abstract In this study, hydrogeo- silicate weathering reactions; (2) Received: 25 July 2005 Accepted: 16 September 2005 logic and hydrochemical informa- dissolution of salts; (3) precipitation Published online: 11 November 2005 tion from the Mersin-Erdemli of calcite, amorphous silica and ka- Ó Springer-Verlag 2005 groundwater system were integrated olinite; (4) ion exchange. As deter- and used to determine the main mined by multivariate statistical factors and mechanisms controlling analysis, anthropogenic factors the chemistry of groundwaters in the show seasonality in the area where area and anthropogenic factors most contaminated waters related to presently affecting them. The fertilizer and fungicide applications PHREEQC geochemical modeling that occur during early summer Z. Demirel Æ C. Gu¨ ler (&) demonstrated that relatively few season. Department of Geological Engineering, phases are required to derive water Engineering Faculty, Mersin University, chemistry in the area. In a broad Keywords Coastal aquifer Æ 33343 Mersin, Turkey E-mail: [email protected] sense, the reactions responsible for Water–rock interaction Æ Principal Tel.: +90-324-3610001 the hydrochemical evolution in the components analysis Æ Cluster Fax: +90-324-3610032 area fall into four categories: (1) analysis Æ Mersin Introduction In the MEB area, urban and agricultural expansions have caused an ever-growing need for fresh water. In The development of groundwater resources for water this region, water supply for most municipalities, supply is a widespread practice in the Mediterranean domestic use water for urban developments and irriga- coastal region of Turkey, favored by the existence of tion water for agricultural activities is almost exclusively basins with thick Quaternary deposits that form aquifers provided through hand dug or drilled wells. In addition with good-quality water (Demirel 2004). The Mersin- to obvious primary uses of water for domestic use (e.g., Erdemli basin (MEB) is particularly productive (Fig. 1). washing and bathing) the quantities required have been The Mediterranean coastline stretching from the city of greatly increased by secondary demand, principally for Mersin to the Erdemli region is heavily populated with gardening, landscaping, and water for swimming pools recent (last 15 years) urban developments (e.g., villas, of the villas, apartment complexes, etc. These supplies apartment complexes, and multi-storey buildings), which are mostly required during the main holiday season, are mostly occupied during summer season for vacation which coincides with the driest period. Therefore, water purposes. Due to an increased population influx from the resources in the MEB area are subject to intensive de- surrounding cities, especially during the peak season mands, stresses and pollution risks (Demirel 2004) and (May to September); the population of this region in- similar problems were reported in the other Mediterra- creases several folds (e.g., 2–4 times). The MEB is not nean countries (e.g., Pulido-Leboeuf 2004). only an urban area but it is also surrounded by densely Population dynamics and agricultural activities in cultivated orchards (mostly citrus), traditional vegetable this region have important implications from the farms and greenhouse cultivations, where farming groundwater chemistry standpoint, especially in the activities continue all year long due to favorable climate. near-shore area, for local communities who rely upon 478 coastal aquifers directly for their water supply. Despite Ophiolithic me´lange also contains substantial amounts its importance, little is known about the natural phe- of chromite mineralizations with chromite (Cr2O3) nomena that govern the chemical composition of contents ranging between 52–60% (Yaman 1991). groundwater in this region or the anthropogenic factors Tertiary units are composed of oligo-miocene gildirli that presently affect them. This study tries to answer formation, lower-middle miocene karaisali formation mainly these questions. The main objectives of this pa- and gu¨ venc¸formation, middle-upper miocene kuzgun per are: (1) to assess the chemistry of groundwater and formation, and upper miocene-pliocene handere forma- (2) to identify the anthropogenic factors that presently tion (Fig. 1). Tertiary rocks consist of a succession of affect the water chemistry in the region by using multi- marine, lacustrine, and fluvial deposits, which display variate statistical and geochemical modeling techniques. transitional characteristics both vertically and areally in the study area (Senol 1998). The Quaternary basin-fill deposits are a heteroge- Site description neous mixture of metamorphic, volcanic, and sedimen- tary rock detritus ranging from clay to boulder size. The The MEB is situated in the Mediterranean Sea region of mixture includes stream alluvium, stream-terrace the southeastern part of Turkey and extends from deposits, fan deposits, delta deposits, shore deposits, 36°30¢–36°45¢ of latitude north to 34°15¢–37°30¢ of lon- caliche (calcrete), and Terra Rosa deposits (Mediterra- gitude west (Fig. 1). The MEB area is bounded by the nean red soil) (Senol 1998). The basin-fill deposits vary Taurus Mountains on the northern side and by the greatly in lithology and grain-size, both vertically and Mediterranean Sea on the southern side. The southern areally. Accordingly, the hydraulic properties of these portion of the MEB area is a delta plain made up of deposits can differ greatly over short distances, both sediments mainly from Alata River in the west and laterally and vertically. partly by Tece, Arpac¸, and Mezitli creeks in the east direction. The flow regimes of these creeks are strongly dependent on the seasonal rains. These creeks flow only Materials and methods 3–4 months in a year and their average discharges are 2– 3m3/s. Topographic structure in the north of the Sample collection and analytical techniques investigated area (Taurus Mountains) is rugged with altitudes ranging from 300 to 1,100 m. For chemical analysis, a total of 32 water samples from In the MEB area, climate is characterized by hot and the MEB (from 6 springs, 11 wells, and 1 seawater dry periods in summer and by warm and wet periods in sampling locations) were obtained during 2002 from two winter, which is typical for the coastal zones around the separate sampling campaigns (May and August) at the Mediterranean Sea. According to 30-year monthly sampling points shown in Fig. 1. This period was chosen averages, lowest mean temperature occurs in January because it coincides with the maximum water abstrac- (10°C) and highest mean temperature in August (28°C). tion from the MEB aquifer and minimum precipitation The mean annual temperature in this area is 18.6°C. and recharge in the area. Table 1 summarizes the Showers start in October, and continue till mid April chemical analysis results for water samples collected and the maximum rainfall occurs in December. The from the MEB. One spring (sample no. 7) was sampled MEB area receives slightly higher than 500 mm of pre- only once in August and two wells (samples 13 and 14) cipitation annually, and extended periods (i.e., 3– were sampled only once in August and May, respectively 4 months) without precipitation are common. Monthly due to various reasons. Mediterranean Sea water was average atmospheric temperatures and precipitation for sampled only once in May. Therefore, there are only 14 a 30-year period (1961–1991) at the Erdemli station are locations that were sampled twice during both May and presented in Fig. 2. August 2002 sampling campaigns. Rocks and unconsolidated deposits in the area can be Water samples obtained from the wells are from divided into three geologic units (Senol 1998): (1) upper various depths because the wells in the area vary greatly Cretaceous mersin ophiolithic me´lange; (2) Tertiary in depth. Average well depth is 15 m for hand dug wells units; (3) Quaternary basin-fill deposits. A simplified and 87 m for drilled wells. Electrical conductivity (EC) stratigraphic column showing associations between all and pH were monitored during pumping, and samples rocks and unconsolidated sediments is shown in Fig. 3. were collected only when values stabilized or after at Mersin ophiolithic me´lange (upper cretaceous) is gen- least three well volumes had been purged. Water samples erally found in the northern part of the study area within obtained from the springs were collected at the spring deep canyons and shows serpentinization (Fig. 1). orifice. Measurements of EC and pH were made in the Ophiolithic me´lange contains various rocks with differ- field using a pH/Cond 340i WTW meter. For the pH ing compositions including gabbro, harzburgite, verlite, measurements the electrode was calibrated against pH dunite, clinopyroxenite, diabase, and radiolarite. buffers at each location. Two aliquots were taken from 479 Fig. 1 Map showing the water sampling locations and geology of the study area each sampling location; one for cation and the other for anion analysis. Aliquots were filtered through a 0.45-mm Millipore cellulose type membrane and stored in HDPE bottles. The sample bottles were rinsed three times with the filtered sample water before they were filled. Then, 0.25 ml/L of HNO3 (nitric acid) was added to the first aliquot to prevent precipitation.