Geokolloqium, Dr. Anna-Neva Visser

- GEOSCIENTIFIC COLLOQUIUM -

Geochemical and Isotopic Gradients in Tufa Channels: Insights into Carbonate Dynamics and Microbial Potential

Presentation from Dr. Anna-Neva Visser
Friedrich-Alexander-Universität (FAU)

 
Abstract

Tufa channels (“Steinerne Rinnen”) are carbonate-precipitating freshwater systems in which hydrological, geochemical, and biological processes interact over short spatial scales. Despite their local relevance for carbonate formation and carbon cycling, the relative importance of physicochemical versus biologically mediated processes along active flow paths remains poorly constrained. Here, geochemical and isotopic gradients were investigated in three morphologically distinct tufa channels in Bavaria, Germany. Results combine in-field parameters, dissolved organic/inorganic carbon (DOC/DIC) concentrations and hydrochemistry with natural abundance measurements (δ¹³C-DIC, δ¹³C-DOC, δ¹⁸O-DO, δ¹⁸O and δD-H₂O). Distinct downstream trends in carbonate system parameters (alkalinity, DIC, pCO₂, δ¹³C-DIC) indicate strong CO₂ degassing and carbonate precipitation as dominant controls on channel-scale carbon dynamics, with channel morphology exerting a clear influence on the magnitude and expression of these gradients. In contrast, DOC concentrations and δ¹³C-DOC exhibit smaller but notable spatial variability. Conservative ions remain largely constant along flow paths, supporting the dominance of in situ processes over external mixing. These results highlight a channel- and morphology-dependent development of geochemical and isotopic gradients. The interpretation of subtle isotopic variations, particularly in DOC and dissolved oxygen, remains ambiguous and will be discussed in the context of physicochemical versus biological controls.