Nitrous oxide production in riparian zones and its importance to national emission inventories

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Riparian zones, which sit at the interface between terrestrial and aquatic components of the landscape, often receive and process large amounts of excess nitrogen (N) that moves out of agricultural fields towards streams. These areas thus have the potential to be 'hotspots' of nitrous oxide (N2O) production in the landscape. However, current Intergovernmental Program on Climate Change (IPCC) methodologies for calculating national N2O emission inventories do not explicitly account for riparian N2O production. In this paper, we examine the nature and extent of N2O production in riparian zones, present some new data on N2O production in these areas, and propose a modification to the current IPCC methodology for quantifying N2O emissions from agriculture. We also present an example of how large-scale riparian restoration efforts to achieve agricultural water quality objectives could cause significant changes in regional N2O budgets. Although current data are inadequate to propose a quantitative emission factor for riparian N2O emissions, they suggest that these emissions are likely to be significant in many regions. Specific data on riparian N2O emissions should be collected in association with detailed watershed mass balance studies that allow for evaluation of several aspects of the IPCC methodology at once and provide constraints on the magnitude of fluxes that are difficult to measure, e.g. N2O flux, N2O:N2 ratio. Riparian and wetland restoration projects to reduce NO3/- delivery to coastal waters are being considered in many areas of the world. These projects may affect regional and global N2O budgets, but only if they alter the N2O:N2 ratio during denitrification. (C) 2000 Elsevier Science Ltd.

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Chemosphere - Global Change Science