Chemical Dynamics and Evaluation of Biogeochemical Processes in Alpine River Kamniška Bistrica, North Slovenia

Abstract

Biogeochemical processes were investigated in alpine river—Kamniska Bistrica River (North Slovenia), which represents an ideal natural laboratory for studying anthropogenic impacts in catchments with high weathering capacity. The Kamniska Bistrica River water chemistry is dominated by HCO3 −, Ca2+ and Mg2+, and Ca2+/Mg2+ molar ratios indicate that calcite weathering is the major source of solutes to the river system. The Kamniska Bistrica River and its tributaries are oversaturated with respect to calcite and dolomite. pCO2 concentrations were on average up to 25 times over atmospheric values. δ13CDIC values ranged from −12.7 to −2.7 ‰, controlled by biogeochemical processes in the catchment and within the stream; carbonate dissolution is the most important biogeochemical process affecting carbon isotopes in the upstream portions of the catchment, while carbonate dissolution and organic matter degradation control carbon isotope signatures downstream. Contributions of DIC from various biogeochemical processes were determined using steady state equations for different sampling seasons at the mouth of the Kamniska Bistrica River; results indicate that: (1) 1.9–2.2 % of DIC came from exchange with atmospheric CO2, (2) 0–27.5 % of DIC came from degradation of organic matter, (3) 25.4–41.5 % of DIC came from dissolution of carbonates and (4) 33–85 % of DIC came from tributaries. δ15N values of nitrate ranged from −5.2 ‰ at the headwater spring to 9.8 ‰ in the lower reaches. Higher δ15N values in the lower reaches of the river suggest anthropogenic pollution from agricultural activity. Based on seasonal and longitudinal changes of chemical and isotopic indicators of carbon and nitrogen in Kamniska Bistrica River, it can be concluded that seasonal changes are observed (higher concentrations are detected at low discharge conditions) and it turns from pristine alpine river to anthropogenic influenced river in central flow.