报告题目：The role of Hyporheic zone: From local to the continental scale N2O emissions from streams and river
报告人： Dr. Daniele Tonina, Department of Civil Engineering, Center for Ecohydraulics Research, University of Idaho
摘要：Riverine networks are a significant source of nitrous oxide (N2O) emissions to the atmosphere, contributing an estimated 10% of anthropogenically generated N2O. The main biogeochemical transformations that lead to N2O emissions are denitrification (NO3- to N2) and nitrification reactions (NH4+ to NO3-) that are mediated by microbes mainly living in benthic biofilms, subsurface sediments of the hyporheic zone, and within the riverine water column. These three zones form the riverine corridor, whose hydromorphological characteristics depend on land use land cover, biomes, climate and geological characteristics. Here, we present a simple dimensionless framework to analyze and predict N2O emissions from the riverine corridor and show the relative importance of each of these three zones along the river continuum. The model was developed with data collected by the 2nd Lotic Intersite Nitrogen eXperiment (LINXII) project and then validated with measurements taken in different reaches from 10 river networks across the world including headwater streams, medium and large rivers and a tidal system with different morphology, land cover, biomes and climatic conditions. The model shows the key contribution of hyporheic and benthic processes in small streams, contrasting with the dominant contribution of water column processes in rivers. Application of the model at the continental scale shows that streams are the main source or N2O emissions whereas large rivers contributes less than 30% of the total N2O emissions.