| Fire on hillslope soils often increases soil nitrification rates and downstream nitrate
concentrations in perennial stream systems in the year following fire, yet fire responses in non-
perennial stream systems may differ because they dry for the part of the year. Drying results in
variable sediment moisture throughout intermittent stream networks. To determine the
magnitude of both fire and stream drying on nitrogen dynamics, we collected pre- and post-fire
stream sediments to obtain mean daily sediment temperatures, gravimetric water contents, pH,
available ammonium, nitrification rates, and available nitrate from a intermittent stream system
in southwestern Idaho that was subjected to prescribed fire. To investigate the driving factors
behind nitrification rates, we used mixed effects models and exploratory multivariate analyses,
including Principal Coordinates Analysis (PCoA) and regressed the first two dimensions against
nitrification rates and hydrologic variables. Our results indicate that decreases in sediment
acidity and mean daily sediment temperature lead to decreased nitrification rates within
intermittent streams, even prior to fire. These results contrast with previous studies on hillslope
soils in perennial stream systems that observed increases in nitrification rates, ammonium, soil
pH, and soil moistures following prescribed fire. We conclude that low to moderate severity
prescribed fire conducted in the fall does not increase nitrification rates. Rather, low sediment
temperatures and higher sediment pH inhibit nitrification rates within the channels.
Keywords: Nitrification, Prescribed Fire, Stream intermittency, Sediment pH, Ordination |