| Popis: |
Availability of reactive nitrogen (Nr; mainly ammonium, NH4+, and nitrate, NO3−) via precipitation and upwelling groundwater affects carbon (C) accumulation in peat deposits and biological greenhouse gas emissions. Isotope composition of Nr was studied at Wolf Swamp (WS) and The Glades (GL), two peatlands located in western Maryland (U.S.), to provide a more robust understanding of N cycling at the ecosystem level. In recent years, both sites experienced a moderate atmospheric pollution (3–9 kg of deposited Nr ha−1 yr−1), and possible additional Nr inputs via groundwater contaminated by fertilizers/livestock. Sampling of living Sphagnum, vertical peat profiles, atmospheric deposition, and surface bog water was carried out on October 22–24, 2017. The δ15Nr signatures of vertical precipitation were negative (mass-weighted means of −7.2 and −8.1‰ at WS and GL, respectively) despite reports that NOx emitted by coal-burning power plants, a precursor of deposited nitrate, had been extremely positive (up to +26‰). Mean δ15N values at both sites increased in the order: vertical precipitation |
