Denitrification in bottomland hardwood wetland soils of the Cache River

Denitrification rates were quantified in bottomland hardwood wetland soils of the Cache River. N¹⁵ labeled nitrate was added to columns containing wetland soils and river water. Over 40 days, nitrate-N in floodwater (approximately 9 mg N L⁻¹) decreased by between 82% and 59%, which gave estimates of N export from the water column of between 11.5 mg N m⁻² day⁻¹ and 7.5 mg N m⁻² day⁻¹. These values correlated directly with organic content of surface sediment, which included forest litter. Added glucose doubled rates of nitrate loss in these soils, which indicated that the process was carbon limited. Nitrification occurring simultaneously with denitrification was determined using isotopic dilution techniques. Contributions of nitrate to water from nitrification were estimated at between 5% and 12% of the total nitrate reduced. Rates of nitrogen transformation in these forest soils were likely limited by available soil carbon from tree litter and perhaps canopy leachate, rather than by nitrate concentration in inflowing floodwater.