Isotopic and hydrochemical investigation of groundwater salinisation in a coastal aquifer system; Milas Basin, SW Turkey


Barut İ., ALPAR Ş. B.

33rd International Geological Congress (33IGC), Norway, 1 - 04 August 2008, pp.1352329

  • Publication Type: Conference Paper / Full Text
  • Country: Norway
  • Page Numbers: pp.1352329

Abstract

Groundwater salinization (S=0.5-36.2 psu) in the coastal aquifer system of the Milas Basin, which is bordered with Mandalia Bay in the SW Turkey, is investigated. The samples collected from the natural mineral sources and wells were analyzed for geologic, hydrochemical and isotopical content. Geological setting of the sedimentary rocks which have been differentiated according to their sites of deposition in this study show impermeability limits significant differences. In the karstic areas the surface rain limit is different from the nutrition area of underground source water. The seawater observed in some sources located in the karstic salt systems (Ekinambari and Savranköy), which also show seasonal variation, has been explained by underwater sources. Hydrologic budget calculations indicated that a water inflow of 80 million cubic m per year penetrates from the Paleozoic and Mesozoic karstic limestone aquifers of more than 150 square km in area.
The evaporation is calculated as 51 per cent (640 million cubic m per year) of bulk precipitation in the catchment area. The total flows are realized in two ways; base flow (50 per cent) after infiltration and surface flow (50 per cent). Some sea springs have been observed in the sea, -5 m deep, and along the northern coastal zone of Mandalia Bay. The variations in the water budget have been estimated as discharges of sea springs and added to general discharge. The most important karstic springs in the investigation area have been defined. All samples collected in the study area stay between of the meteoric lines representing the Eastern Mediterranean and terrestrial types, respectively. A high "deuterium excess" value of the Milas meteoric line implies that the precipitation in the basin is affected, under a high evaporation ratio, by the atmospheric water vapor in the eastern Mediterranean.
Due to the position and distribution of the geological formations, the recharge to the groundwater is directly from infiltration from the precipitation and from the runoff in the polje areas. Test show that the groundwater movements are mainly controlled by active structural elements. The groundwater reserved in the autochthonous and allocthonous units in the east move west- and northwestward as evidenced in the karstic salt springs. The recharge in the carbonated rocks in the west, on the other hand, flows towards the alluvial plains and springs in the southeast. The impermeable units of the allocthonous sequences act as a barrier and seawater encroachment occurs as a result of tectonic activities. Seawater intrusion in carbonated rock aquifer reduces the economic value of the underground water used in irrigation and drinking.