Decomposition and Peat Accumulation in Rich Fens of Boreal Alberta, Canada

Fens are important components of Canada’s western boreal forests, occupying about 63% of the total peatland area and storing about 65% of the peatland carbon. Rich fens, dominated by true moss-dominated ground layers, make up more than half of the fens in the region. We studied organic matter accumulation in three rich fens that represent the diversity in structural types. We used in situ decomposition socks, a new method that examines actual decomposition throughout the upper peat profile over an extended period of time. We coupled our carbon loss data with macrofossil analyses and dated peat profiles using ²¹⁰Pb. Across the three rich fens and in the top 39 cm of the peat column, dry mass increases on average 3.1 times. From our dry mass loss measurements, we calculate that annual mass loss from the top 39 cm varies from 0.52 to 1.08 kg m². Vertical accumulation during the past 50 years has varied from 16 to 32 cm and during these 50 years, organic matter accumulation has averaged 174 g m⁻² y⁻¹ compared to 527 g m² y⁻¹ dry mass loss, with additional mass losses of 306 g m² y⁻¹ from peat between 50 and 150 years of age. Organic matter accumulation from our rich fens compares well with literature values from boreal bogs, whereas peat bulk densities increase about three times within the uppermost 40 cm, much more than in bogs. Hence, rich fens accumulate peat not because the plant material is especially hard to decompose, is acidic, or has the catotelm especially close to the surface, but because dense, rapidly produced inputs outweigh the relatively rapid decomposition process of the upper peat column. Author Contributions: DHV conceived study; KS, KW, SF, & DHV performed research; DHV, KW analyzed data; DHV, KW contributed new methods; DHV, KW wrote the paper.