Factors Contributing to Spatial Variability of N2O Fluxes in a Virginia Salt Marsh

Salt marshes are heralded for their capacity to denitrify terrestrially-derived nitrogen, but a byproduct of this is the emission of nitrous oxide (N 2 O), a potent greenhouse gas. In this study I seek to characterize physical and biogeochemical factors that contribute to spatial variability of N 2 O emissions within a marsh. A flow-through steady-state (FT-SS) chamber and trace gas analyzer were used to measure fluxes within a small mid-Atlantic salt marsh. Fluxes of N 2 O were low (<29.9 µg N 2 O -N m -2 h -1 ) with the exception of one emission hotspot (158.4 µg N2O-N m -2 h -1 , average) that became the focus of the investigation. Factors thought to contribute to N 2 O production including exogenous nitrate (NO - 3 ) delivery and denitrifying microbial activity were evaluated within the context of the measured fluxes. There is evidence that bioturbation promotes N 2 O emission by influencing both NO - 3 delivery and denitrifying activity through enhanced infiltration, water residence time, and surface area that support elevated levels of microbial N2O production. At the low and high density burrow sites (42 and 328 burrows m -2 , respectively), burrows expanded sediment surface area for gas and solute exchange by 7% and 59%, respectively, and overwhelmed saturated hydraulic conductivity as the primary infiltration pathway for exogenous NO - 3 . N 2 O production within the marsh was typically below the detection limit (29.9 µg N 2 O-N m -2 h -1 ) and was limited by either NO - 3 delivery or the potential to support elevated microbial activity.

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