Supervisors info:
Ιωάννης Παπανικολάου, Αναπληρωτής Καθηγητής, Τμήμα Αξιοποίησης Φυσικών Πόρων και Γεωργικής Μηχανικής, Γεωπονικό Πανεπιστήμιο Αθηνών
Γεώργιος Σταμάτης, Καθηγητής, Τμήμα Αξιοποίησης Φυσικών Πόρων και Γεωργικής Μηχανικής, Γεωπονικό Πανεπιστήμιο Αθηνών
Στυλιανός Λόζιος, Επίκουρος Καθηγητής, Τμήμα Γεωλογίας και Γεωπεριβάλλοντος, Εθνικό και Καποδιστριακό Πανεπιστήμιο Αθηνών
Summary:
The study area is located in the southern part of the Euboea Island, specifically in the Ochi mountain complex. Two high-pressure tectonic units of the Cycladic Blueschist Unit (CBU), the Styra and the overlying Ochi nappe, are separated by the Ochi thrust. The mountain complex is dominated by crystalline formations of relatively gray and white colour (marbles) with silicate intercalations (silex) of phyllosilicate minerals (sipolines), a variety of schists (mica, glaucophane, quartz, hornblende, epidote), gneisses and meta-ophiolitic mélange composed of metasediments, metabasic and meta-ultrabasic rocks. Many types of folds (isoclinal, inclined, periodic, sheath, ptygmatic, chevron), faults and joints that have been distinguished in the South Evia have been forced by both, the ductile and brittle regime. Two main fold axes and three systems of faults characterize the eastern block of the NNE-SSW detachment fault – Attica/Octhonia fault. The main fold axis is trending NE-SW, parallel to the Ochi’s mega-anticline structure, but also in certain positions fold axis of NNW-SSE direction are also traced. The scope of this thesis is to study the hydrogeological conditions and the hydrochemistry of springs in relation to the tectonic pattern. More than 80 springs were mapped at the south-eastern limb of the Ochi’s mega-anticline, with the overwhelming majority of them being embedded in schists, while the rest are located in the contact between marbles and schists. Groundwater flow is governed by the NE and NW trending faults as evidenced by the location of the springs, while their discharge rate is controlled by the small-scale tectonic structures, such as, folds and fractures. 22 springs with the highest discharged rates have been studied regarding their hydrological characteristics. Temperature (°C), pH, redox potential (mV), electrical conductivity (μS/cm) and total dissolved solids (mg/l) were measured in situ. Ηardness (total, calcium and temporal), primary and secondary ions were analyzed by the methods of titration, spectrophotometry and flame photometry. Heavy metals and selected trace elements were analyzed by the method of inductively coupled plasma optical emission spectrometry (ICP-OES) in four representative samples. The springs are associated with two main types of aquifer systems. Karst aquifer is highly productive groundwater system, often associated with conduit flow. Springs 1, 3, 4, 5, 6, 7, 13, 14 and 15 belong to this aquifer system and they have Ca-HCO3 type of water- fresh water with natural enrichment and renewal. The lowest discharge rates correspond to the fissured rock aquifer, where the secondary porosity forms a low permeability to schists, ophiolites and gneisses. This aquifer system has a mixed water type (Na-Ca-Mg-HCO3-Cl). Ca++ and Na+ are the dominating cations and HCO3- and Cl- are the dominating anions. The sampling water is characterized as alkaline because of 7.2 - 8.4 pH values. According to the hydrogeochemical analysis, element enrichment of the water is mainly the result of the geological background effect (carbonate and silicate minerals) and in a lesser extends to anthropogenic factors (agricultural activities, pastures, quarries). There is an exception to the southern springs of Metochi – Platanistos (11, 12 and 16), where high concentrations of sodium, chloride and sulphate ions indicate proximity to the sea (aerosols). The trace elements (Mn, Fe, Al, Ni, Co, Cr, As, P) concentrations of the spring 18 show the effect of the mineral composition and ore deposits in the ophiolitic rocks of Ochi. Τhe water quality through the Richards chart and compared with E.C. limits indicates suitability both for irrigation and human consumption. The geological cross sections are intended to connect lithology and tectonic structure with the type and discharge rate of the springs. Finally, the combined use of geological data, in situ measurements, tectonic analysis and hydrogeological study contribute to extract the relation between the hydrochemical and hydrolithological conditions and the way that the tectonic pattern of fissured rocks affects the groundwater flow, storage and occurrence.
