oa Carbon Dynamics in Natural and Engineered River Systems: Insights from Lipid Biomarkers

Soil organic carbon (OC) fixed by plants through photosynthesis can be transported to rivers and ultimately buried in marine sediments, acting as a long-term carbon sink. However, rivers are not passive conduits, they act as dynamic systems where soil OC can be respired back into the atmosphere, stored in sediments, or further transported. Anthropogenic modifications to river systems have altered these processes, particularly affecting OC mobilization, degradation, and sequestration, yet their impact on the global carbon cycle remains poorly constrained.

This study addresses these challenges by tracing specific OC pools using lipid biomarkers to distinguish plant-derived (long-chain n-alkanes and fatty acids), soil bacteria-derived (branched GDGTs), and freshwater aquatic (e.g., riverine brGDGTs and long-chain diols) OC sources. Radiocarbon (¹4C) dating of these biomarkers will estimate OC residence time, while mineral association analyses will evaluate OC stabilization. The research focuses on two contrasting river catchments in northeast Germany: the quasi-natural Peene and the engineered Oder, both flowing into the Szczecin Lagoon. By analyzing distribution of brGDGTs and isotopic signatures of leaf waxes (d¹³Cwax, d²Hwax), the reconstructed vegetation, hydroclimate, and temperature changes can provide a climatic context to understand OC dynamics during transport and over time.