Biological Sinks for Nitrogen Additions to a Forested Catchment

摘要

The goal of our research is to identify and quantify sinks for experimentalNitrogen (N) additions to a forested catchment at the Bear Brooks Watershed in Maine (BBWM) where background N deposition rates are low (< 4 kg/ha/yr). Nitrogen applied to the watershed in April, June, August and October (16.8 kg/ha) 1991 was labeled with a (15)N tracer that increased the abundance of (15)N label from about 0.3663 atm % to 0.4366 atm %. Surface soil was the most important sink for the isotopically labelled N additions. We estimate using (15)N 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.