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 Ca-Mg-HCO 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 and are well above the threshold value for anthropogenic activity (3 mg L). The δN values ranged from 1.4 to 9.7‰, while δO 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 δN and high δO 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.

River inputs can significantly affect carbon dynamics in the costal ocean. Here, we investigate the influence of four rivers (Isonzo/Soča, Timavo/Reka, Rižana, and Dragonja) on inorganic carbon (C) in the Gulf of Trieste in the northern Adriatic Sea using stable isotope signatures of dissolved inorganic carbon (δ 13 C DIC ). In 2007, rivers exported 1.03×10 11 g C in the form of dissolved inorganic carbon (DIC) to the Gulf of Trieste with the lowest export observed in the Dragonja and the highest in the Isonzo/Soča. River plumes were associated with higher total alkalinity (TA) and pCO 2 values compared with Gulf of Trieste waters, but their inputs showed high spatial variability. The δ 13 C DIC values and the isotopic mass balance suggested that river input during the spring of 2007 represented about 16 % of DIC at our study site VIDA, located in the southeastern part of the Gulf of Trieste. During autumn of 2007, the riverine contribution of DIC was less pronounced (3 %) although the river export of C was higher relative to the spring season. Convective mixing with the Gulf of Trieste waters and bora wind events appear to reduce the riverine contribution to the DIC system. Our results suggest that river plumes play an important role in C cycling in the Gulf of Trieste by direct inputs of higher riverine DIC and by increased biological uptake of DIC promoted by the supply of riverine nutrients.

No abstract

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.

<p>      Our process-based understanding of stable isotope signals, as well as technological developments, has progressed significantly, opening new frontiers in marine interdisciplinary research. This has promoted the broad utilisation of carbon and oxygen isotope applications to gain insight into carbon cycling in marine ecosystems and their interaction with the atmosphere.</p> <p>Our study was performed in the Gulf of Trieste in the N Adriatic where the influence of biological processes, riverine loads and local climate conditions on the atmosphere-water CO<sub>2</sub> exchange and on the carbonate system equilibrium was investigated, in order to elucidate what drives the CO<sub>2</sub> exchange and to estimate the vulnerability of the Gulf of Trieste to acidification processes. On an annual scale, the Gulf of Trieste clearly acts as a sink of CO<sub>2</sub>, strongly controlled by the seasonal variability of water temperature, biological processes, wind speed and riverine inputs. The calculated air-sea CO<sub>2</sub> flux was estimated to be -1.47 ± 1.41 mol C m<sup>-2</sup> yr<sup>-1</sup>. The sink was generally stronger during the winter months, whereas during early summer and autumn the CO<sub>2</sub> fluxes were lower. It was interesting to note that the atmospheric CO<sub>2 </sub>concentrations exhibited large fluctuations on a daily basis, as well as on a seasonal time scale. The average atmospheric CO<sub>2</sub> concentration during our study in 2013 was 438 ± 16 ppm. This is significantly higher than the global average, which, at the time was around 400 ppm. Further The isotopic composition of carbon in atmospheric carbon dioxide (<em>δ</em><sup>13</sup>C<sub>CO2,air</sub>) values panned from -12.7‰ to -9.1‰ with an average value of -10.8 ± 0.9‰. This is considerably different to the “background” value of -8‰ (from NOAA/ESRL) and can most probably be attributed to the presence of fossil fuel emissions. The results are comparable with the data obtained in the Adriatic between Ravenna and Otranto.</p> <p>The presented study indicate that the quality and comparability of datasets is critical to improve the estimation of processes that influence the carbon dynamics in marine environment. Thus, the implementation of the principle in our laboratory, the monitoring of our measurement quality, validation and status of newly developed gas CO<sub>2 </sub>reference materials (SIRS1, SIRS2 and SIRS3) as a part of SIRS project will be also presented.</p>