Nitrogen deposition and increased carbon accumulation in ombrotrophic peatlands in eastern Canada

Abstract

Recent and long‐term accumulation rates of carbon (C), using 210 Pb‐ and 14 C‐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 (R 2 = 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.