『Abstract
　Storm losses of N via tile-drainage in the US Midwest are a major concern for water quality in the Mississippi River Basin (MRB). This study investigates the impact of precipitation characteristics of NO3^-, NH4⁺ and DON concentrations and fluxes for spring storms in tile-drains in a Midwestern agricultural watershed. Bulk precipitation amount had little impact on solute median concentrations in tile-drains during storms, but clearly impacted Mg²⁺, K⁺ and NO3^- concentration patterns. For large storms (＞6 cm of bulk precipitation), large amounts of macropore flow (43-50％ of total tile-drain flow) diluted Mg²⁺ and NO3^- rich groundwater as discharge peaked. This pattern was not observed for NH4⁺ and DON or for smaller tile-flow generating events (＜3 cm) during which macropore flow contributions were limited (11-17％ of total tile-drain flow). Precipitation amount was positively (P＜0.01) correlated to NO3^- and NH4⁺ export rates, but not to DON export rates. Limited variations in antecedent water table depth in spring had little influence on n dynamics for the storms studied. Although significant differences in flow characteristics were observed between tile-drains, solute concentration dynamics and macropore flow contributions to total tile-drain flow were similar for adjacent tile-drains. Generally, NO3^- represented ＞80％ of N flux during storms, while DON and NH4⁺ represented only 2-14％ and 1-7％ of N flux, respectively. This study stresses the non-linear behavior of N losses to tile drains during spring storms in artificially drained landscapes of the US Midwest, at a critical time of the year for N management in the MRB.

Keywords: Tile drainage; Nitrate; Ammonium; Dissolved organic nitrogen; Precipitation characteristics; Export rates』

Introduction
Materials and methods
　Experimental site description
　Hydrological measurements and water quality analysis
Results
　Storm characteristics, antecedent water table depth and tile flow response to precipitation
　Nitrogen and cation concentrations during storms
　Nitrogen and cation concentration patterns during storms
　Nitrogen fluxes and nitrogen export rates during storms
Discussion
　How do precipitation amounts and antecedent water table depth impact NO3^-, NH4⁺ and DON concentration patterns?
　How do NO3^-, NH4⁺ and DON fluxes and export rates vary in relation to changes in precipitation characteristics? Are they consistent with other published data?
　Are inter-drain variations in n export dynamics significant?
Conclusion
Acknowledgements
References