Alkalinity and dissolved inorganic carbon transported by rivers into the northern Adriatic Sea

The northern Adriatic is a shallow continental shelf region strongly impacted by rivers discharges, which currently receives about 21 % of the total freshwater input of the Mediterranean Sea. The effects of river nutrients on the trophic state of this coastal marine ecosystem have been largely analysed, but, to date, the knowledge on the riverine transport of dissolved inorganic carbon (DIC) is still limited. Land-borne DIC contributes to the increase of the total alkalinity in the coastal waters, counteracting the acidification process due to the absorption of CO? from the atmosphere. The estimates of DIC river loads were obtained by applying THINCARB model (THermodynamic modelling of INOrganic CARBon) to a compilation of total alkalinity and pH data provided by Research Institutes and Regional Environmental Protection Agencies. The data were collected from 2010 to 2018 for the main rivers flowing into the northern Adriatic Sea (Po, Adige, Brenta, Piave, Livenza, Tagliamento and Isonzo). The overall river transport of total alkalinity was 205 Gmol yr?¹, whereas the transport of DIC was 213 G mol yr?¹, of which around 70 % originates from the Po River. About 97 % of the DIC in river water is present in the form of bicarbonate. The mean ?¹³C-DIC was estimated to be -10 ?, that is considered today as representative of the DIC riverine inputs in oceanic carbon cycle modelling. Its flux mainly depends by mineral weathering in each river drainage basin, but this process does not exclude the presence of anthropogenic disturbances that should be better analysed.