Temporal and Seasonal Variations of Silicate Svratka River and Sediment Characterization, Czech Republic: Geochemical and Stable Isotopic Approach

This study investigated weathering and hydrobiogeochemical processes in a silicate dominated watershed (Svratka river) in the Czech Republic in comparison with nearby carbonate dominated catchments. Elemental and isotopic analysis of river waters, particulates and sediments provided a more holistic view of weathering contributions, anthropogenic contamination, biological activity and evasion or sinks of CO₂ to the atmosphere. In water samples, we determined total alkalinity after Gran 1974, and cations and anions were determined with inductively coupled plasma–optical emission spectrometer and ion chromatograph. δ ¹³C_DIC in water samples was determined with isotope ratio mass spectrometer. pCO₂ and saturation indexes of calcite and dolomite were calculated with PHREEQC speciation program. Evasion fluxes were calculated after Broecker, 1974. Isotopic composition of carbon and nitrogen in particulate matter and sediments were determined with isotope ratio mass spectrometer. Mineral composition of sediments was determined with XRD method and elements with XRF method. Further enrichment factors of elements were calculated. The Svratka river, which is the major tributary of the Dyje river, is dominated by Ca²⁺ > Na⁺ > Mg²⁺ > K⁺ and HCO₃⁻ (as total alkalinity). Partial pressure (pCO₂) concentrations range from close to 0–572-fold of atmospheric pressure. Isotopic composition of carbon in dissolved inorganic carbon (δ ¹³C_DIC) value ranged from − 13.3 to − 8.0‰ reflecting degradation of organic matter and exchange with the atmosphere. Bicarbonate weathering intensity for the Svratka river at its mouth is 11.8 mol/(l⋅km²⋅s), more on par with silicate terrains and lower than nearby carbonate watersheds. Isotopic composition of carbon (δ ¹³C) and isotopic composition of nitrogen (δ ¹⁵N) values of river sediment reflect soil and temperate plant (C3 plant) values, while higher δ ¹⁵N values could be attributed to application of organic fertilizers in lower reaches. The river sediments, which came from weathering of crystalline rocks, are dominated by silt size, geochemically less mature quartz, feldspar and muscovite particles. All the stream sediments examined revealed slightly increased amounts of Zn, Cu and Pb. However, using Al as the normalization element to calculate enrichment factors, Zn, Cu and Pb are only elevated downstream, related to industrial contamination. This study is important for local and global level since it deals with contribution of weathering rates and contribution of CO₂ to the atmosphere in silicate watershed.