Elevated River Inputs of the Total Alkalinity and Dissolved Inorganic Carbon in the Northern Adriatic Sea

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.

Projected climate oligotrophication of the Adriatic marine ecosystems

“…The projected tendency confirms trends that have been observed in historical data on warming (e.g., Shaltout and Omstedt, 2014;Mohamed et al, 2019;Bonacci et al, 2021), oligotrophication (e.g., Mozetič et al, 2010;Coppini et al, 2013;Cerino et al, 2019;Novak et al, 2019;Ciglenečki et al, 2020;Penezić et al, 2022), acidification (Luchetta et al, 2010;Hassoun et al, 2015Hassoun et al, , 2022Giani et al, 2023), and corroborates the results of recent climate projections at Mediterranean scale (Reale et al, 2022). Our study provides a closer look at the diversification of the projected changes within the Adriatic basin.…”

The benthic-pelagic coupling affects the surface water carbonate system above groundwater-charged coastal sediments

“…The low pH of groundwater and SGD suggests a possible dissolution of CaCO 3 resulting in high values of values of DIC (Figure 3) (Deines et al, 1974;Winde et al, 2014;Wang et al, 2018;Liu et al, 2021). Freshwater end members that are enriched in A T and DIC, are a common phenomenon observed in limestone-rich catchments such as the Puck Bay catchment (Giani et al, 2023). For example, samples collected in Moreton Bay (Australia) showed average groundwater concentrations of A T and DIC 1.5 and 1.7 times higher than in the surface waters of Moreton Bay, respectively, which implies also that SGD may be a source of these solutes in surface waters (Stewart et al, 2015).…”