Rivers are important contributors to the global carbon cycle as they actively cycle terrestrial organic matter (OM) during transport to the oceans. However, what controls the degradation of OM, especially at the river network scale, remains largely unknown. OM chemical composition is certainly relevant in this process, yet difficult to describe across the entire OM size continuum from dissolved OM (DOM) to large particulate OM (POM). This is likely needed, however, as OM size likely acts as a master trait, that mediates the retention and transport of OM and selects the target consumer community. At larger network scale, this should give rise to OM size-specific patterns of OM composition in dependence on the dendritic nature of a river network and the diversity of land cover types in its terrestrial matrix. Here, we examined the longitudinal patterns and drivers of OM chemical composition along two river networks differing in topology and land cover. We characterized OM chemical composition by mass spectrometry for DOM and by infrared spectroscopy for individual POM particles. Preliminary results showed an overall less degraded OM in headwaters than main stems and in river sections draining forested sub-catchments compared to those draining agriculture-dominated sub-catchments. However, the OM composition patterns across the river network varied with OM size.

Primary Presenter: Edurne Estévez, University of Innsbruck (edurne.estevez-cano@uibk.ac.at)

Authors:

Edurne Estévez, University of Innsbruck  (edurne.estevez-cano@uibk.ac.at)

Sophia Mützel, University of Innsbruck  ()

Rubén del Campo, University of Innsbruck  ()

Aitor Larrañaga, University of the Basque Country  ()

Gabriel Singer, University of Innsbruck  ()