Nitrogen Deposition to and Cycling in a Deciduous Forest

Abstract

The project described here seeks to answer questions regarding the role increased nitrogen (N) deposition is playing in enhanced carbon (C) sequestration in temperate mid-latitude forests, using detailed measurements from an AmeriFlux tower in southern Indiana (Morgan-Monroe State Forest, or MMSF). The measurements indicate an average atmosphere-surface N flux of approximately 6 mg-N m^-2 day^-1 during the 2000 growing season, with approximately 40% coming from dry deposition of ammonia (NH₃), nitric acid (HNO₃), and particle-bound N. Wet deposition and throughfall measurements indicate significant canopy uptake of N (particularly NH₄+) at the site, leading to a net canopy exchange (NCE) of –6 kg-N ha^-1 for the growing season. These data are used in combination with data on the aboveground C:N ratio, litterfall flux, and soil net N mineralization rates to indicate the level of potential perturbation of C sequestration at this site.