『Abstract
　Experimental and theoretical work emphasize the role of plant nutrient uptake in regulating ecosystem, ecosystem disturbance, and continued inputs of atmospheric nitrogen (N) will increase watershed N export. In ecosystems where snowpack insulates soils, soil-frost disturbances resulting from low or absent snowpack are thought to increase watershed N export and may become more common under climate-change scenarios. This study monitored watershed N export from the Hubbard Brook Experimental Forest (HBEF) in response to a widespread, severe soil-frost event in the winter of 2006. We predicted that nitrate (NO3^-) export following the disturbance would be high compared to low background streamwater NO3^- export in recent years. However, post-disturbance annual NO3^- export was the lowest on record from both reference (undisturbed) and treated experimental harvest or CaSiO3 addition watersheds. These results are consistent with other studies finding greater than expected forest NO3^- retention throughout the northeastern US and suggest that changes over the last five decades have reduced impacts of frost events on watershed NO3^- export. While it is difficult to parse out causes from a complicated array of potential factors, based on long-term records and watershed-scale experiments conducted at the HBEF, we propose that reduced N losses in response to frost are due to a combination of factors including the long-term legacies of land use, process-level alternations in n pathways, climate-driven hydrologic changes, and depletion of base cations and/or reduced soil pH due to cumulative effects of acid deposition.

Keywords: Experimental watersheds; Frost event; Long-term monitoring; Nitrogen cycling; Watershed stream export』

Introduction
Methods
　Study site
　Climate and soil data
　Hydrologic flux measurements
　Stream sampling and analysis
　N fluxes
Results
　Climate and soil data
　Hydrologic fluxes
　Frost surveys
　Stream NO3^-
　Stream DOC and DON
Discussion
　Frost in the long-term record
　Challenges in linking soil frost and N dynamics
　Soil frost and watershed N export
　Potential mechanisms of reduced N losses
Conclusions
Acknowledgments
References