You are here:
BIOLOGICAL SINKS FOR N ADDITIONS TO A FORESTED CATCHMENT
Citation:
Nadelhoffer, K., M. Downs, B. Fry, J. Melillo, AND J. Aber. BIOLOGICAL SINKS FOR N ADDITIONS TO A FORESTED CATCHMENT. U.S. Environmental Protection Agency, Washington, D.C., EPA/600/A-92/292.
Description:
The goal of our research is to identify and quantify sinks for experimental Nitrogen (N) additions to a forested catchment at the Bear Brooks Watershed in Maine (BBWM) where background N deposition rates are low (< 4 kg ha-1 yr1). itrogen is added bimonthly to an experimental catchment (10ha) at the BBWM site as ammonium sulfate fertilizer using a helicopter. imonthly and annual N application rates are 4.2 and 25.2 kg ha", respectively. itrogen applied to the watershed in April, June, August and October (16.8 kg ha-') 1991 was labeled with a 15N tracer that increased the abundance of 15N label from about 0.3663 atm % to 0.4366 atm %, or, in natural abundance units, from 0 o/oo to 192 o/oo o15N. We used the 15N label to trace the fate of N added to the watershed during the 1991 growing season into soil and vegetation compartments. urface soil was the most important sink for the isotopically labelled N additions. oil (0-5cm) o15N values at 5 of 6 locations increased by 1 to 3 o/oo over pre-treatment values. ood was also a sink for N additions with o15N values of red spruce, beech, yellow birch and maple wood all increasing by about 4 o/oo after the catchment was amended with isotopically labelled N. oliar o15N values also increased by 2 to 4 o/oo by mid August. e estimate using 15N mass balancing that about 3/4 of the 16.8 kg N added during the 1991 growing season was retained in catchment soil and aboveground vegetation with soils being the dominant sink.