Current conditions of saltwater intrusion in the coastal Rhodope aquifer system, northeastern Greece

The geological, hydrogeological and hydrochemical regimes of the coastal Rhodope aquifer system, northeastern Greece, are described. The aquifer system includes two aquifers within coarse grained alluvial sediments. Both vertical and lateral saline water intrusion occurs, usually caused by over pumping. Water has been pumped from the aquifer system at an ever-increasing rate for many years. Water samples for chemical analyses were obtained from 36 productive wells and from 5 research wells at several depths to cover the entire study area. The EC and chloride concentration distribution clearly illustrate the large extent of saline water intrusion in the aquifer system of the study ! area. Although the ionic content of groundwater of the study area is highly variable, the dominant anions are HCO3 ! + 2+ and Cl and the dominant cations are Na and Ca . Water in the saline parts of the confined aquifer is generally of the Ca2+-Cl! type. Evidence of cation exchange and reverse cation reaction between fresh and saltwater in the Rhodope aquifer system are reflected in the Piper diagram and the expanded Durov hydrochemical diagram, respectively, both for productive and research wells. The results of this study show that the development of a strategy for managing the aquifer system is vitally necessary.

Groundwater salinization is one of the most common environmental problems in Greece, and definitely the most serious groundwater quality degradation factor of coastal aquifers. The overexploitation of the Rhodope coastal aquifer system for the satisfaction of anthropogenic needs and especially for irrigation has resulted in dramatic decline of groundwater level and thus in saltwater intrusion mainly from the inlet of Vistonis lagoon. The hydraulic head is seriously reduced and a permanent regional cone of depression has been formed in the potentiometric surface of the aquifer system, western of Porpi. High hydraulic heads at the western boundary of the aquifer system show an increased recharge of the upper Miocene aquifer system. Additional field information and well monitoring, which is gained from the research wells, are needed to model the behaviour of the zone of saltwater intrusion more satisfactorily and to estimate the rate of movement of the freshwater/saltwater interface. Use of data gained from the construction of the five research wells resulted in a well defined conceptual approach of the Rhodope aquifer system. The horizontal distribution of EC and chloride concentration in groundwater samples from productive wells, as well as the vertical distribution of groundwater samples from the five research wells, illustrates clearly the saltwater intrusion in the aquifer system of the study area. The assumption that the main point of entry of saltwater into the Rhodope aquifer system is the inlet of the Vistonis lagoon seems valid because of the fact that, in the productive wells of the western part of the study area and at the first research well, EC and chloride concentration values were significantly higher. Evidence of cation exchange and reverse cation reaction between fresh and saltwater in the Rhodope aquifer system are reflected in the Piper and expanded Durov diagrams, respectively, constructed for both productive and research well groundwater samples.