The high spatial and temporal variabilities of nitrous oxide (N2O) emissions from the soil surface have made it difﬁcult to predict ﬂux patterns at the ecosystem scale, leading to imbalances in nitrogen (N) budgets at all scales. Our research sought to quantify topographic controls on the sources or sinks of N2Oin the soil proﬁle to improve our ability to predict soil-atmosphere N2O ﬂuxes and their contribution to watershed N budgets. We monitored surface-to-atmosphere N2O ﬂuxes for 2 years in the Susquehanna Shale Hills Critical Zone Observatory in central Pennsylvania. Topographically convergent ﬂow path locations had signiﬁcantly higher surface N2O ﬂux rates than nonconvergent ﬂow path locations in the summer, but not other seasons. Overall, N2O ﬂuxes were a large percentage (~19%) of total ecosystem N losses, and nearly twice as large as stream N export. Surface N2O ﬂuxes were better correlated with concentrations of O2, N2O, and NO3- in shallow soil layers (<30 cm) than deeper soils. Following decades of anthropogenic atmospheric deposition and additional N from shale weathering, watershed N inputs (~8 kgN ha-1 yr-1) are greater than outputs (~3.7 kgN ha-1 yr-1). Our research revealed patterns of N cycling that are distinct from many other watersheds that have been extensively studied to understand N saturation; despite showing no other symptoms of N saturation, the watershed had high upland N2O losses, especially in convergent ﬂow paths during summer. High upland N gas losses may be a mechanism that maintains N limitation to biota in the Shale Hills catchment.
Weitzman, J. and Kaye, J.P. (2018): Nitrogen Budget and Topographic Controls on Nitrous Oxide in a Shale-Based Watershed. Journal of Geophysical Research: Biogeosciences, 123(6):1888-1908. DOI: 10.1029/2017JG004344
This Paper/Book acknowledges NSF CZO grant support.