Controls on the seasonal exchange of CH3Br in temperate peatlands

Abstract

Measurements of CH3Br exchange at two New Hampshire peatlands (Sallie's Fen and Angie's Bog) indicate that net flux from these ecosystems is the sum of competing production and consumption processes. Net CH3Br fluxes were highly variable and ranged from net emission to net uptake between locations within a single peatland. At Sallie's Fen, net CH3Br flux exhibited positive correlations with peat temperature and air temperature during all seasons sampled, but these relationships were not observed at Angie's Bog where flux varied according to microtopography. The major CH3Br production process at Sallie's Fen appeared dependent on aerobic conditions within the peat, while CH3Br production at Angie's Bog was favored by anaerobic conditions. There was evidence of aerobic microbial consumption of CH3Br within the peat at both sites. In a vegetation removal experiment conducted at Sallie's Fen with dynamic chambers, all collars exhibited net consumption of CH3Br. Net CH3Br flux had a negative correlation with surface temperature and a positive correlation with water level in collars with all vegetation clipped consistent with aerobic microbial consumption. Vegetated collars showed positive correlations between net CH3Br flux and air temperature. A positive correlation between net CH3Br flux and surface temperature was also observed in collars in which all vegetation except Sphagnum spp. were clipped. These correlations are consistent with seasonal relationships observed in 1998, 1999, and 2000 and suggest that plants and/or fungi are possible sources of CH3Br in peatlands. Estimates of production and consumption made on two occasions at Sallie's Fen suggest that peatlands have lower rates of CH3Br consumption compared to upland ecosystems, but a close balance between production and consumption rates may allow these wetlands to act as either a net source or sink for this gas.