Evaluation of geochemical processes and nitrate pollution sources at the Ljubljansko polje aquifer (Slovenia): A stable isotope perspective.

The Ljubljansko polje aquifer, which is the main supply of drinking water for the local population in Ljubljana, Slovenia is highly vulnerable to anthropogenic pollution. In this study, the geochemistry of major constituents including nitrate concentrations and the dual isotopes of nitrate were used to ascertain the spatial distribution of processes and nitrate sources in the groundwater from seven wells at three different water supplies: Klece, Hrastje and Jarski prod. The groundwater is of the Ca2+-Mg2+-HCO3- type approaching equilibrium with respect to dolomite and are moderately supersaturated with calcite. The groundwater nitrate concentrations ranged from 5.32 to 50.1 mg L-1 and are well above the threshold value for anthropogenic activity (3 mg L-1). The δ15NNO3 values ranged from 1.4 to 9.7‰, while δ18ONO3 values were from 6.3 to 34.6‰. Based on isotope mixing model three sources of nitrate were identified: atmospheric deposition, fertilizers and soil nitrogen. At Klece 8, Klece 12 and Jarski prod 3 the low δ15NNO3 and high δ18ONO3 values result from pristine nitrate sources, while in Hrastje 3 and Klece 11 equal amounts of nitrate derived from soils with mixed fertilization and sewage. The data also indicate that the main sources of high nitrate concentrations in groundwater are from fertilizers and sewage-manure (comprising up to 64%). Such levels occurred in the Hrastje and Klece 11 wells where precipitation is the main source of groundwater. Nitrate derived from atmospheric deposition accounted for approximately 10% of the nitrate in the groundwater. The message from this study is that to reduce the nitrogen load and improve water quality will involve containment and the careful management of sources from urban and agriculture inputs such as sewage-manure and fertilizers.

Hydrological system behaviour of an alluvial aquifer under climate change.

In this paper, we present an assessment of the sensitivity of groundwater-surface water interactions to climate change in an alluvial aquifer, located in the Ljubljansko polje, Slovenia. The investigation is motivated by a recent assessment of climate change pressures on the water balance in the Sava River Basin (Gampe et al., 2016). The assessment was performed using a comprehensive hydrological modelling approach, which is based on the direct/indirect communication between FEFLOW and WaSiM/MIKE 11. This modelling framework provides a precise simulation of the critical processes in the study domain, which are the main drivers influencing the interactions between precipitation, river water and groundwater under different future climate scenarios. Climate projections were based on the results of the three regional climate models SMHI-RCA4, KNMI-RACMO22E and CLMcom-CCLM4. The results show that there will be higher levels of local precipitation during 2036-2065, the projected river discharge will be larger in the future compared to 2000-2014, and it is unlikely that the Ljubljansko polje will suffer from water scarcity. In addition, amongst the various sections of the Sava River the section between Crnuce and Sentjakob is the one most sensitive to climate change. By running the models under different climate scenarios a deeper insight into aquifer system functioning was obtained. Investigating impacts of climate change on groundwater and interactions between surface water and groundwater on the local scale is a basis for applying such a study on the global scale, which was still not very well investigated.

Determination of the sources of nitrate and the microbiological sources of pollution in the Sava River Basin.

Coupled measurements of nitrate (NO3-), nitrogen (N), and oxygen (O) isotopic composition (δ15NNO3 and δ18ONO3) were used to investigate the sources and processes of N cycling, while the microbial source tracking (MST) method was used to identify microbiological pollution in the surface water of the Sava River Basin (SRB) in autumn in 2014 and 2015 during high and low water discharge. Atmospheric nitrate deposition or nitrate-containing fertilizers were found not to be significant sources of riverine nitrate in the SRB. The ranges of isotope values suggest that NO3- in the SRB derives from soil nitrification, sewage, and/or manure, which were further supported by MST analysis. Microbiological indicators show the existence of hotspots of fecal pollution in the SRB, which are human associated. Long-term observations indicate persistent fecal contamination at selected locations caused by continuous discharge of untreated wastewaters into the SRB.