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TRANSPORT AND ATTENUATION OF NON-POINT SOURCE POLLUTANTS IN KARSTIC AQUIFERS

Final Activity Report Summary - KARSTANPS (Transport and attenuation of non-point source pollutants in karstic aquifers)

The principal objective of this research project was to investigate the effects of non-point source pollutant releases on groundwater resources in karst aquifers. Non-point source pollutants are released from sources that are by nature dispersed over a certain area, e.g. groundwater pollutants such as nitrate and pesticide originating from agricultural activities. Karst aquifers, which are major water resources in many parts of the world and in particular in the Mediterranean basin, are very susceptible to contamination due to their distinct hydrogeological features. Contaminants in karst aquifers can travel rapidly from their sources and have detrimental effects on distant receptor points, such as water supply wells, lakes or man-made reservoir lakes.

This study focused on the interaction of nitrate contamination with groundwater flow in a karst aquifer (Nif mountain karstic system) that is an important groundwater recharge source for the city of Izmir, located in western Turkey. A multi-disciplinary approach was utilised to characterise and investigate nitrate contamination patterns for the study site. The aquifer system was studied in detail with seasonal ground- and spring water sampling, groundwater level measurements, spring flow rate measurements, interpretation of the local geology, chemical analyses of collected samples, isotopic studies, data analyses using geographical information systems (GIS), and mathematical modelling. As a result maps illustrating the spread of groundwater contamination were produced. Contamination 'hotspots' in the studied area were identified.

Thus, contamination could be related with land-use patterns and groundwater recharge mechanisms of the aquifer. A relationship between groundwater contamination and site elevation could be established. Furthermore, temporal trends of nitrate contamination were not visible from a statistical point of view, thereby demonstrating the unpredictable occurrences of nitrate contamination due to the unique hydrological features of karst groundwater systems.

Patterns of nitrate contamination became more meaningful when compared to groundwater flow patterns at the study site. A mathematical model capable of simulating regional groundwater flow was developed. Magnitude and direction of groundwater flow were estimated using this model. Maps illustrating groundwater levels and directions of flow were produced to understand the flow system and to relate it to current nitrate contamination patterns. Results further revealed that the Nif mountain karst aquifer and the Tahtali reservoir, which provides 36 % of the Izmir metropolitan area water demand, are connected hydraulically, meaning that the Nif mountain karst aquifer feeds the water sources of this important reservoir. This result had important implications with respect to the vulnerability of this water resource for the city of Izmir.

Finally, protection zones for each water supply well were established using again numerical modelling methods. These zones represent vulnerable areas, where any voluntary or accidental contaminant releases at the ground surface potentially can affect groundwater quality of that well. It was found that protection zone boundaries for karst aquifers need to be set relatively wider in contrast to other types of aquifers.