Origin and cycling of riverine inorganic carbon in the Sava River watershed (Slovenia) inferred from major solutes and stable carbon isotopes

Abstract

The Sava River and its tributaries in Slovenia represent waters strongly influenced by chemical weathering of limestone and dolomite. The carbon isotopic compositions of dissolved inorganic carbon (DIC) and suspended organic carbon (POC) fractions as well as major solute concentrations yielded insights into the origin and fluxes of carbon in the upper Sava River system. The major solute composition was dominated by carbonic acid dissolution of calcite and dolomite. Waters were generally supersaturated with respect to calcite, and dissolved CO 2 was about fivefold supersaturated relative to the atmosphere. The d 13 C of DIC ranged from -13.5 to -3.3%. Mass balances for riverine inorganic carbon suggest that carbonate dissolution contributes up to 26%, degradation of organic matter *17% and exchange with atmospheric CO 2 up to 5%. The concentration and stable isotope diffusion models indicated that atmospheric exchange of CO 2 predominates in streams draining impermeable shales and clays while in the carbonate-dominated watersheds dissolution of the Mesozoic carbonates predominates.

Hydrogeochemical and Stable Isotope Characteristics of the River Idrijca (Slovenia), the Boundary Watershed Between the Adriatic and Black Seas

“…The average estimated total diffusive loss of inorganic carbon in the autumn is 1.93 9 10 5 mol/day and 2.51 9 10 2 mol/ day in spring. The River Idrijca showed seasonal patterns of CO 2 diffusive evasion that are similar to the River Sava in Slovenia (Kanduč et al 2007b) in the autumn sampling season. The evasion CO 2 flux is much lower in spring due to the lower pCO 2 pressure.…”

Isotopic composition of carbon in atmospheric air; use of a diffusion model at the water/atmosphere interface in Velenje Basin

“…A water sample (1 ml) was then injected into the tube and CO 2 measured directly from the headspace. Two standard solutions of Na 2 CO 3 (Carlo Erba and Scientific Fisher), with known δ 13 C DIC values of -10.8 ± 0.2 ‰ and -4.8 ± 0.2 ‰, were used to calibrate δ 13 C DIC measurements (SPötL 2005;KAndu^ et al, 2007). When sampling surface waters, pCO 2 immediately above the surface water was measured in an open system and in a closed system.…”

“…Both models (concentration and isotopic) should provide same values of time of equilibration, but in our case they do not. However, it has been shown that equilibration of CO 2 between water/air boundaries is more significant in impermeable silicate drainages (KAndu^ et al, 2007). Therefore equilibration of atmospheric CO 2 does not influence the value of δ 13 C DIC in surface waters significantly, which is a consequence of low discharge conditions in the catchment area.…”

“…Concentrations of dissolved inorganic carbon, DIC, and its isotopic composition (δ 13 C DIC ) in freshwater environments have been widely investigated (AmiottE-SuchEt et al, 1999;AtEKwAnA & KriShnAmurthy, 1998;mArfiA et al, 2004;KAndu^ et al, 2007) and groundwater/ surface water interactions, with evaluation of biogeochemical processes, have been reported for Velenje Basin (KAndu^ et al, 2010). …”

Characterisation of suspended matter in river systems: River Sava in Slovenia case study

“…Based on carbon isotope mass balance calculations at the border with Croatia, it was also calculated that degradation of organic mat-er is more pronounced in the late summer season. Among the biogeochemical processes in the River Sava degradation of organic matter is the most important process after dissolution of carbonates, contributing to carbon isotope dissolved inorganic carbon values (kanDu~ et al, 2007a).…”