The assurance of drinking water supply is one of the biggest emerging global challenges, especially in urban areas. In this respect, groundwater and its management in the urban environment are ...gaining importance. This paper presents the modeling of nitrogen load from the leaky sewer system and from agriculture and the impact of this pressure on the groundwater quality (nitrate concentration) in the urban aquifer located beneath the City of Ljubljana. The estimated total nitrogen load in the model area of 58 km2 is 334 ton/year, 38% arising from the leaky sewer system and 62% from agriculture. This load was used as input into the groundwater solute transport model to simulate the distribution of nitrate concentration in the aquifer. The modeled nitrate concentrations at the observation locations were found to be on average slightly lower (2.7 mg/L) than observed, and in general reflected the observed contamination pattern. The ability of the presented model to relate and quantify the impact of pressures from different contamination sources on groundwater quality can be beneficially used for the planning and optimization of groundwater management measures for the improvement of groundwater quality.
Legislation addressing the quality of groundwater and increasing concerns over public health calls for the development of analytical methods that can produce accurate and precise results at the ppt ...level. Passive sampling has been recognised as a helpful tool in identifying various organic pollutants in groundwater, even when their presence had not yet been identified through conventional groundwater quality monitoring. The article presents an analytical method involving a simple and cost-effective passive sampling device using Zorflex® activated carbon fibres (ACFs) for the qualitative monitoring of a broad range of organic pollutants in water in a single run. The applicability of the method developed was tested in three hydrogeological studies. In the first case, we present a non-targeted qualitative screening and a list of 892 different contaminants detected in the groundwater in Slovenia. In the second case, we discuss the presence and origin of organic compounds in the groundwater from a pilot area of the urban aquifer, Ljubljansko polje. The third case presents a comparison of results between passive and grab sampling. Passive sampling with ACFs confirmed the presence of a pollutant, even when it had not been previously detected through a quantitative method.
Urban water supply systems (WSS) are complex and challenging to manage since the properties of water in the WSS change from source to the end user over time. However, understanding these changes ...requires a more profound knowledge of the WSS. This study describes the urban water cycle within the WSS of Ljubljana, Slovenia, where different water parameters such as temperature, electrical conductivity, total alkalinity, δ2H, δ18O, and δ13CDIC were monitored from September to November 2018. Altogether 108 samples were collected, including from the source (3) and at different levels of the WSS: wells (41), joint exits from water pumping stations (7), reservoirs (22), water treatment locations (2), drinking fountains (13), taps (19) and wastewater system (1). The data show that although the ranges of δ2H and δ18O values were small, each well is represented by a unique fingerprint when considering additional parameters. A statistically significant difference was observed between sampling months, and temperature and most parameters showed higher variability within the wells than across the WSS, suggesting a more unified WSS. Finally, based on δ13CDIC values, a distinction could be made between river/groundwater interactions within the WSS and between shallower and deeper wells and their distance from the river bank.
The isotope and elemental composition of tap water reflects its multiple distinct inputs and provides a link between infrastructure and the environment over a range of scales. For example, on a local ...scale, they can be helpful in understanding the geological, hydrogeological, and hydrological conditions and monitor the proper functioning of the water supply system (WSS). However, despite this, studies examining the urban water system remain limited. This study sought to address this knowledge gap by performing a 24 h multiparameter analysis of tap water extracted from a region where the mixing of groundwater between two recharge areas occurs. This work included measurements of temperature and electrical conductivity, as well as pH, δ2H, δ18O, d, δ13CDIC, and 87Sr/86Sr ratios and major and trace elements at hourly intervals over a 24 h period. Although the data show only slight variations in the measured parameters, four groups were distinguishable using visual grouping, and multivariate analysis (Spearman correlation coefficient analysis, hierarchical cluster analysis, and principal components analysis). Finally, changes in the mixing ratios of the two sources were estimated using a linear mixing model. The results confirm that the relative contribution from each source varied considerably over 24 h.
The fauna in the hyporheic zones of rivers has been relatively well studied but that from the phreatic zone remains comparatively unknown and there are few investigations into deeper intergranular ...aquifers (over 30 m in depth) due to technical difficulties. Two shallow boreholes of 29 m depth and two deep boreholes of 100 m depth, both near Ljubljana (Slovenia), were sampled more than 30 times between 14 January 2008 and 3 March 2009. On each occasion 14.4 to 18.0 m3 of water were abstracted using a high-capacity pump, then filtered by means of a plankton net with a mesh size of 60 µm. Organisms larger than 2 mm were damaged by the pump rotors, but their identification was still possible, while smaller representatives of the Copepoda (Crustacea) passed the rotors without damage. A near-by artesian borehole was sampled on 6 occasions. Water chemistry, physical properties and faunal composition analyses were carried out for each borehole. A total of 32 taxa, 24 of which were stygobites, were identified. Copepoda alone were represented by 16 species, 15 of which were stygobites. The shallow boreholes differ from the deep boreholes in their higher temperatures and higher concentrations of K+, Na+, Ca2+, Mg2+ and SO42- ions. The copepod communities in samples from the shallow boreholes differ sharply from those from the deep boreholes. There were also clear differences between shallow boreholes in two aquifers located a few kilometres apart, in physical and chemical characteristics as well as in fauna composition. Taxa with different ecological affinities, collected from groundwater, are indicators of hydraulic connections between different parts of an aquifer as well as of communication between surface and subsurface water bodies. The present study suggests that subterranean fauna, as well as epigean fauna, can provide effective support for classical dye/salt tracing experiments.
Water isotope investigations are a powerful tool in water resources research as well as in understanding the impact that humans have on the water cycle. This paper reviews past hydrological ...investigations of the Ljubljansko polje and Ljubljansko barje aquifers that supply drinking water to the City of Ljubljana, with an emphasis on hydrogen, oxygen and carbon stable isotope ratios. Information about the methods used and results obtained are summarised, and the knowledge gaps identified. Overall, we identified 102 records published between 1976 and 2019. Among them, 41 reported stable isotope data of groundwater, surface water and precipitation and were further analysed. Isotope investigations of the Ljubljansko barje began in 1976, while groundwater and surface water investigations of the Ljubljansko polje and along the Sava River began as late as 1997. Isotope investigations of carbon started even later in 2003 in the Ljubljansko polje and in 2010 in the Ljubljansko barje. These investigations were performed predominantly in the frame of short-term groundwater research projects at five main wellfields and sites along the Sava River. Almost no large-scale, long-term stable isotope studies have been conducted. The exceptions include groundwater monitoring by the Union Brewery in Ljubljana (2003- 2014) and precipitation in Ljubljana since 1981. Since 2011, more detailed surveys of the Ljubljansko barje were performed, and in 2018, the first extensive investigation started at wellfields and objects that form part of the domestic water supply system. Given the number of available studies, we felt that publishing all the numerical data and appropriate metadata would allow for a better understanding of the short and long-term dynamics of water circulation in the urban environment. In the future, systematic long-term approaches, including the appropriate use of isotopic techniques, are needed.
•Monthly water isotope assessment for tracing the contribution of various water sources to drinking water supply.•We identify the contributions of local precipitation and surface water to the ...groundwater of two aquifers.•Stable water isotope data reviled longer MRT than previously reported.
In cities experiencing rapid urbanization, we must continually update our understanding of the partitioning of drinking water sources concerning its supply if it is to be managed sustainably. This need is especially crucial given the pressure on water resources arising from evolving land use patterns and climate change. For this reason, a city-wide study of stable water isotopes (δ2H and δ18O) in precipitation, surface water and groundwater across Ljubljana, Slovenia, was undertaken. The goal was to characterise the temporal dynamics of urban water cycling and trace the various sources contributing to the city’s drinking water supply. Monthly water sampling, combined with hydrogeochemical and in-situ data, permitted the identification of local precipitation and surface water contributions to its two groundwater supply aquifers. In addition, a re-examination of the mean residence times (MRT) of surface waters revealed an MRT of 3–4 years, which is much longer than previously reported. Also, changes in the contributions of surface water and precipitation to groundwater were observed compared to previous studies. These findings improve our understanding of local water partitioning and provide valuable insights for water managers addressing future urban water resource management.
From the hydrogeological point of view Sorško polje area is a sink, filled with conglomerate,sandand gravel,where large quantities of groundwater are accumulated. Sorško polje aquifer is one of the ...richest regions of groundwater and represents an important reserve water source for the central part of Slovenia.The performed hydrochemical and isotope investigations present an independent completion of the previous hydrogeological investigation of Sorško polje. The results of research give more reliable information about the water origin, as well as about the influence of the local precipitation and Sava river water on the dynamics of the groundwater restoration in the aquifer. The research defines the characteristics of oxygen isotop ecomposition of groundwater in the Sorško polje aquifer and determines the volume share of aquifer recharge from the Sava river and from local precipitation.
The presence of nitrates, an important pollutant of drinking water sources, at present doesn’t represent an environmental burden that would demand immediate remedial measures in the aquifer of ...Ljubljansko polje. Nevertheless their presence indicates an anthropogenic influence that can not be neglected.The article discusses the spread of nitrates in the aquifer of Ljubljansko polje and gives an estimation of the influenceoftwoimportantnitrate sources, the agricultural and urban land use. The distribution of nitrates in the area is also discussed and the concentration changes with time are examined closely. The most important nitrate source in the groundwater is determined on the basis of nitrate-nitrogen isotope study. The results are correlated to the known land use of the urban area.Sampling for the present study was performed from the autumn 2002 to the summer 2004. The sampling locations were active wells of the public water supply, industrial wells, sampling wells of the existing monitoring network and the Sava river. The results show an uneven distribution of nitrates in the Ljubljansko polje aquifer. Areas with a concentration of up to 40 mg/l can be found, whereas the values in the river bank are low and comparable to those in the river water. On the average the concentration ranges from 20 to 25 mg/l. The nitrate concentration depends largely on the location in the aquifer and does not show significant changes during the time of the research projects,with some exceptions which confirmalocal input of nitrates from the surface in the vicinityofthesamplingsite.The most positive groundwater nitrate δ15N values were found in the area where the groundwater flows from the densely populated area.The least positive values are foundin the groundwater, where the sampling site is surrounded by entirely agricultural land. The spatial variation of the nitrogen source is important. The δ15N values seem to be more sensitive to nitrate input than the nitrate concentration itself and show changes with time. When the sampling site is far away from the source of contamination the amplitudes of NO3 concentration and δ15N are lower. The reason can be found in the homogenization of the groundwater flow.
Results of the study show that a combination of isotopic and hydrochemichal methods can be used to obtain new hydrogeological data about the properties of waters in individual aquifers of the ...Ljubljansko barje. An unambiguous distinction was made betweenwaters flowing into the aquifer from the Krim mountains and waters originating in the Gradaščica. It was also possible to identify waters deriving from the karst basin of the Ljubljanica river. The mean altitude of individual waters’ recharge areas was estimatedon the basis of isotopic analyses. The combination with chemical analyses was used to assess the approximate share of carbonate rocks in the aquifer’s recharge area and determine its lithological composition. On the basis of annual changes in the amplitude ofthe isotope signal, also the recharge dynamics of aquifers and the age of observed ground and surface waters were estimated.
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