REPOSITORY > RESULTS

Abstract

Rapid population growth and increasing water demand places a serious strain on both quantity and quality of available local water resources. Climate change puts additional pressure by altering the water balance, affecting recharge conditions, and contributing to pollution and water degradation. Addressing these issues requires water management strategies that enhance both quality and availability of water sources. Understanding of the urban water cycle is necessary, including knowledge of water sources, distribution networks, and various components of the water supply system. The urban water cycle is complex and heterogeneous. It involves natural and engineered systems that vary spatially and temporally. One way to address these challenges effectively is by applying environmental tracers like stable water isotopes. This thesis uses stable water isotopes, along with hydrochemical and hydro-meteorological data, to evaluate the spatio-temporal patterns of water sources and flow paths, and to characterize the isotope signatures of different components within the urban water cycle. Sampling was conducted from 2018 to 2021 in Ljubljana’s aquifers, covering the entire journey from source to tap.
Firstly, a review of previous isotope investigations had been performed to identify key knowledge gaps. A preliminary investigation was performed in 2018, collecting samples from source to tap. Following this, a two-year sampling of water sources (i.e. precipitation, surface water and groundwater) was conducted. Additionally, extensive tap water sampling was carried out across Ljubljana. It was complemented by a 24-hour sampling experiments to analyse temporal variations in tap water composition.
Key findings include the characterization of water sources, changes in source contributions and the influence of climate on water isotopes. The study revealed unique isotopic fingerprints of different sources, despite the isotopic signal range being narrow due to the limited size of the Ljubljana catchment. Isotopic and hydro-chemical analyses revealed dynamic interactions between precipitation, surface water and groundwater. Source contributions were shown to vary over time. Isotopic data correlated with climate variations, indicating that future climate projections could significantly impact the isotopic composition of water sources. Potential changes in groundwater recharge dynamics were implied by observation of longer mean residence times of surface water. The study also found that the isotopic composition of tap water reflected the mixed contributions from different wellfields, providing insights into the water supply system's structure and operation. Seasonal and hourly variations in tap water isotopes highlighted the dynamic nature of water distribution and the influence of management practices. The research identified the potential for using isotope data in combination with concentration of certain elements as proxies for water source mixing ratios.
The research provides valuable data for water managers by offering insights into water dynamics in urban areas and contributing to strategic planning of water infrastructure. The thesis also emphasizes the need for continuous, long-term monitoring of water sources and the publication of data to ensure transparency and reproducibility in scientific research.