Nitrogen Deposition And Increased Carbon Accumulation In Ombrotrophic Peatlands In Eastern Canada

Recent and long-term accumulation rates of carbon (C), using ²¹⁰Pb- and ¹⁴C-dating, were examined in 23 ombrotrophic peatlands in eastern Canada, where average 1990–1996 atmospheric wet nitrogen (N) deposition ranged from 0.3 to 0.8 g N m⁻² yr⁻¹. The average recent rate of C accumulation (RERCA) over the past 150 years was 73 ± 17 (SD) g C m⁻² yr⁻¹, ranging from 40 to 117 g C m⁻² yr⁻¹. The difference in RERCA between hummocks (78 g C m⁻² yr⁻¹) and hollows (65 g C m⁻² yr⁻¹) was significant. Increased RERCA over the past 50 years was found in hummocks and hollows in regions of higher N deposition and related to both elevated N deposition and growing degree-days above +5°C. There was a statistically significant positive relationship between N deposition alone and present-day C accumulation in both hummocks and hollows (R² = 0.28 and 0.38, respectively). Recent N accumulation was significantly larger in high N deposition regions. The total average aboveground vegetation biomass of hollows and hummocks did not differ significantly with N deposition. However, a significantly larger vascular plant leaf biomass was found in both hollows and hummocks of the high N deposition class than in the low N deposition class (>0.6 and <0.4 g m⁻² yr⁻¹, respectively). The average long-term apparent rate of C accumulation (LORCA) at 15 sites was 19 ± 8 (SD) g C m⁻² yr⁻¹, with no significant difference due to age of peat inception, latitude, or continentality.