Aquest divendres tindrem amb nosaltres Angang Li (Civil and Environmental Engineering, Norhwestern University, USA) que ens parlarà de: «Upscaling the variations of flow and reaction of carbon and nitrogen in rivers – a modeling approach».

L'idioma del seminari serà l'anglès.

Resum

Human activities have substantially increased riverine fluxes of carbon and nitrogen. River-groundwater interactions facilitate retention and transformation of carbon and nitrogen, and therefore profoundly impact carbon and nitrogen cycles. River-groundwater processes involve extensive variations. For example, flow and reaction often co-vary over depth, and reaction rate often decreases over reaction time. While it is imperative that we understand how these variations affect whole-stream carbon and nitrogen dynamics, available whole-stream models are often over-simplified to consider space- and time-dependent variations in hydrological and biogeochemical processes. To bridge this gap, we developed a physically-based particle tracking model that directly simulates hydrological and biogeochemical processes at multiple scales. We first simulated whole-stream nitrogen dynamics under different denitrification profiles. By considering vertical covariation between flow and reaction, we found that it is the rapid flushing near the sediment-water interface that controls whole-stream nitrogen removal. We then simulated whole-stream dynamics for components of dissolved organic carbon whose reactivity changes differently over time. We found that the relative contribution of each component to whole-stream carbon uptake depends on how its reactivity changes over time. Our results highlight that variations in hydrological and biogeochemical processes are important and must be considered to accurately represent whole-stream carbon and nitrogen dynamics.