Storm nitrogen dynamics in tile-drain flow in the US Midwest

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 on 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 ( 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.