Présentations Colloques

    Oral Presentation
    Session 8.05: Karst aquifers
    Schmidt Sebastian
    Regional assessment of contamination dynamics of a Eastern Mediterranean karst aquifer system
    In the Eastern Mediterranean (Levant) drinking water supply is heavily dependent on springs fed by karst aquifers since prehistoric times. Those springs are often located within growing built-up areas and therefore spring water quality is frequently affected by contamination, e.g. from wastewater disposal or livestock farming. The aim of this study is to enhance the understanding of pollution dynamics of spring water resources in order to optimise raw water management and treatment.**The analysis focuses on multiple parameters of 35 springs located in a study area of approx. 700 kmC – the central West Bank north of Jerusalem and Jericho- (1) repeated sampling of E.coli, nitrate and chloride to quantify microbiological and chemical contamination and (2) continuous high-resolution monitoring of electrical conductivity plus partly spring discharge and nitrate concentration for 13 individual springs in order to assess hydrological system variability and contamination dynamics. The sampling was conducted during (1) stable low flow conditions (after > 5 months without any significant precipitation), (2) stable high flow conditions (after the rainy season) and (3) dynamic conditions during single precipitation events. **Even adjacent springs with similar hydrogeological and land use settings display entirely different behaviour in terms of hydrological characteristics and dynamics of contaminants. Furthermore, on regional scale, there is no correlation between microbiological and chemical contamination. For example, some springs located in urban areas with a high wastewater borne flow fraction (nitrate concentration frequently ranges around or above 50 mg L) still display low quantities of faecal indicator bacteria, indicating a sufficient long residence time in the aquifer. Vice versa, several springs with a low chemical contamination load (low chloride and nitrate concentration) but high E.coli counts were detected.**Because of the observed spatial and temporal heterogeneity, each individual water source needs to be specifically investigated and characterised, preferentially by high-resolution monitoring, to ensure an appropriate assessment. Special attention should be drawn to small springs which are frequently used for local water supply without any purification measures.**


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