The unknown role of karst aquatic systems for terrestrial–atmospheric carbon transfer (KarLoss)

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Inland aquatic systems transport terrestrial carbon to the oceans, but also emit CO2 to the atmosphere. Some studies argue that rivers from karst terrains might act as carbon sinks and others show that they are highly oversatured with respect to CO2. Due to the large inorganic carbon reservoir of carbonates, rivers and streams in karst terrains can potentially act as strong CO2 emitters to the atmosphere. However, the role of karst catchments and their respective springs and low-order streams in the global carbon cycle remains largely unknown. In addition, the role of diel changes in CO2 patterns are so far only poorly understood. Recent developments in portable laser-based analyzers allow to measure concentrations and stable istope ratios of evading CO2 directly in the field. This allows to unravel origins, pathways and transformation processes during carbon transfer from inland aquatic systems. The application of this technique will also help to overcome limitations of mathematical models for the assessment of CO2 evasion fluxes. This study aims to enhance our understanding of the role of temperate karst aquatic systems within the global carbon cycle with focus on CO2 evasion from low-order streams and their springs. We plan spatial and temporal quantifications by direct field measurements, to disentangle and understand physical and biogeochemical processes that drive CO2 gradients in karstic headwater catchments. This aim will be reached by detailed investigations of the Wiesent karst pilot catchment in Northern Bavaria, Germany and by comparisons to nearby headwaters of two granite- and sandstone-dominated catchments. We plan regular monthly field campaigns, diel and event-based samplings. Concentrations and stable isotopes of CO2 will be measured directly in the field. This will be complemented by laboratory analyses of all carbon phases (DIC, DOC and POC) for both, isotopes and concentrations. Such a multi-parameter approach opens new modelling perspectives of CO2 evasion via isotope ratio changes. These new approaches have the potential to better constrain current CO2 transfer rates from inland aquatic systems and could establish a basis for upscaling carbon fluxes to regional or global estimates.