Riverine ecosystem metabolism drivers and functioning across environmental and anthropogenic gradients

River and stream networks receive and transport carbon from terrestrial ecosystems to inland waters and ultimately to the oceans, while hosting a suite of biogeochemical processes that result in carbon dioxide (CO₂) emissions to the atmosphere. These fluxes are shaped by riverine ecosystem metabolism, defined by the interplay between gross primary production (GPP) and ecosystem respiration (ER). Advances in dissolved oxygen (O₂) sensor technology have enabled widespread estimation of daily GPP and ER from high‑frequency O₂ dynamics. However, the robust quantification of these metabolic rates remains challenging. In physically dominated, high‑energy environments such as steep channels and step‑riffle systems, continuous gas exchange between the water surface and the atmosphere complicates the estimation of gas transfer velocities and, consequently, metabolism. In addition, GPP is highly sensitive to short‑term variability in light availability, turbidity, and nutrient supply, factors that can fluctuate rapidly in response to hydrological disturbances and land use-land cover change.

Understanding how fluvial metabolism varies across environmental contexts and responds to hydrological and biogeochemical stressors is essential for assessing ecosystem functioning, resilience, and vulnerability. In this study, conducted within the BREATHE Water4All and C-NET projects, we monitored high-frequency O₂ dynamics across three sharply contrasting fluvial environments: (i) a high-mountain glacier-fed stream network, (ii) an agricultural drainage ditch, and (iii) a partially restored urban river. Continuous O₂ measurements were combined with ancillary variables, including CO₂, water temperature, solar radiation, water level, electrical conductivity, turbidity, nutrients, and colored dissolved organic matter (CDOM). This multi-sensor approach enabled detailed characterization of diel metabolic patterns and identification of the dominant physical and biogeochemical drivers shaping them. The selected case studies span strong gradients in hydrology, geomorphology, nutrient availability, and anthropogenic influence, providing a unique framework to compare site-specific metabolic regimes and ecosystem functioning. Preliminary results indicate marked differences in daily GPP and ER estimates across systems, reflecting the combined effects of nutrient availability, light limitation, hydrologic disturbance, and physically driven gas exchange.