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: Kleče, Hrastje and Jarški 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 Kleče 8, Kleče 12 and Jarški prod 3 the low δ15NNO3 and high δ18ONO3 values result from pristine nitrate sources, while in Hrastje 3 and Kleče 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 Kleče 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.
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•Groundwaters in Ljubljansko polje aquifer are Ca2+-Mg2+-HCO3− waters.•The main sources of nitrate are atmospheric deposition, fertilizers and soil nitrogen.•Sewage-manure nitrate is important at locations where precipitation is the main source of groundwater.
The response of coastal systems to global acidification depends strongly on river inputs, which can alter the total alkalinity (AT) and dissolved inorganic carbon (DIC) in seawater. The northern ...Adriatic Sea (NAd) is a shallow continental shelf region that currently receives about 15% of the total freshwater input in the Mediterranean Sea, where the role of riverine discharges on the carbonate system has been poorly studied. In particular, river discharges can alter the carbonate system in the sea, affecting both the equilibrium chemistry and biological processes. For the main rivers flowing into the NAd (the Po, Adige, Brenta, Piave, Livenza, Tagliamento, Isonzo, Timavo and Rižana), data were collected for the pH, concentrations of the total alkalinity (AT), Ca2+ and Mg2+ and the isotopic ratio of stable carbon in the dissolved inorganic carbon (δ13CDIC). The DIC fluxes were estimated using the THINCARB (THermodynamic modeling of INOrganic CARBon) model for the compilation of the AT and pH data. The results show that the total transport of the AT in the rivers was 205 Gmol yr−1 while the transport of the DIC was 213 Gmol yr−1, of which about 70% was from the Po River. About 97% of the DIC in the river waters was in the form of bicarbonates. The high Mg2+/Ca2+ ratios indicate that dolomite weathering is predominant in the Adige, Piave, and Livenza river basins, while lower ratios in the Timavo and Rižana rivers indicate a greater proportion of calcite. The mean δ13C-DIC value was estimated to be −10.0 ± 1.7 ‰, a value nowadays considered typical for the DIC flux inputs in oceanic carbon cycle modeling. The DIC flux depends on the mineral weathering and biological activity in each river basin. However, these natural processes can be modified by anthropogenic disturbances that should be better quantified.
Nitrogen concentrations and isotopic composition were used to identify nitrate sources and processes in the catchments of two Slovenian coastal rivers, Rižana and Dragonja, and to investigate whether ...they have any notable influence on the Gulf of Trieste. The sampling was performed from May 2010 to March 2011. The data indicated that δ15NNO3 values in rivers provided mainly information about sources of riverine nitrate derived from soil nitrification, sewage, and/or manure. The load weighted δ15NNO3 values of 4.3‰ and 9.4‰ determined at the mouth of Rižana and Dragonja, respectively, were largely controlled by land-use in the riverine catchment. Phytoplankton nitrate assimilation was found to be significant mainly at the mouth of Dragonja. The combined use of salinity, nutrient concentrations, and nitrate, particulate nitrogen and carbon isotopic compositions revealed that the seawater surface was influenced by mixing with different sources including seawater, rivers and sewage effluent. The site influenced by sewage effluent is relatively spatially isolated, which suggests that NO3− is not widely distributed by this point source. Besides mixing, phytoplankton uptake was the main process controlling the distribution and isotopic composition of NO3− in the marine system and was more extensive in spring 2010, while in autumn NH4+, not NO3−, was the dominant source of N for phytoplankton. In addition, our results are consistent with the occurrence of nitrification in the water column in autumn and winter. The nitrification activity was higher in autumn, while in winter it occurred in parallel to phytoplankton uptake. This study demonstrates how stable isotopes of nitrogen in nitrate along with concentration measurements can be relevant when trying to identify the sources and key processes such as assimilation and nitrification in rivers and coastal areas.
•Load weighted δ15NNO3 in rivers were controlled by land-use in their catchments.•Manure fertilizers and/or sewage inputs were a source of nitrate at the rivers mouths.•δ15NNO3 in the Gulf of Trieste was a result of source mixing and assimilation.•Nitrification in the marine system was present in autumn and winter.
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