Origin and recharge mechanisms of groundwater in the upper part of the Awaj River (Syria) based on hydrochemistry and environmental isotope techniques

摘要

The Barada and Awaj basin is the most important and extensively used water basin in Syria. Chemical and isotopic data of groundwater have been used to determine the spatial distribution of hydrogeological features in the upper part of Awaj River catchment area located southwest of this basin. Hydrogeochemical evolution of groundwater reveals the domination of dissolution/precipitation mechanisms in these very complex stratigraphic sequences. The dissolution of carbonate rocks as well as reverse cation exchange processes seem to be the main factors controlling groundwater mineralization. The isotopic composition of precipitation and groundwater indicate that the modern-day atmospheric precipitation is the main source of groundwater recharge before an important evaporation occurred. The isotopic data also imply an existence of hydraulic connection between the different aquifers system. The results obtained allowed us to delineate two main spatial groundwater zones within the study area with different flow components. The south, central and eastern parts are considered to be one zone which is characterised by a shallow horizontal flow associated with active interaction between groundwater and hosting rocks. The nitrate concentrations in this zone are attributed to anthropogenic sources. The second zone consists in south-western, western and north-western parts where the karstic features are well developed mainly in the Jurassic strata. This zone is characterized by a high vulnerability to pollution confirmed by high values of nitrate coming from sewage water. The deep vertical groundwater flow component seems to be dominant in this zone and is controlled by fractures and geological structures.