IMPACTS OF URBAN REGREENING ON SOIL DENITRIFICATION

Many cities demolish abandoned homes and create regreened vacant lots (RVLs), and an increasingly popular, high-intensity use of RVLs is as urban agriculture. Urban agriculture may potentially result in higher nitrogen (N) runoff to aquatic ecosystems, but this potential has not been quantified. We examined the role that varying land reuse intensity plays in determining potential for N export in runoff, focusing on soil N availability and N removal capacity via denitrification. We contrasted undemolished vacant properties, turfgrass RVLs, and regreened urban agriculture lots (UA) in Buffalo, NY, examining soil N and C availability, denitrification potential, and isotopic evidence of denitrification.

Land reuse intensity only affected soil properties in surficial soil horizons. Total N was 2.5x higher in UA soils (mean: 0.51%) than non-UA (mean: 0.21%). Soil nitrate was 2.6x higher in winter (mean: 12.4 μg N*gds^-1) than summer (mean: 4.7 μg N*gds^-1) and was generally higher in UA soils. Despite increased soil N availability at UA sites, there were no differences in denitrification potential, and denitrification potential was low across all sites (mean: 0.62 μg N*gds^-1). Isotopic evidence further confirms that denitrification was not a major sink of N. The driver most strongly predicting denitrification potential was total N, followed by water extractable organic carbon, and then nitrate. Although UA had low denitrification activity and had high N availability compared to non-UA sites, UA likely only has moderate potential for runoff-driven N export, as nitrate levels were substantially lower than values typical for conventional agricultural soils.