The Nitrogen Cycle in Boreal Peatlands

Abstract

It is nearly impossible to describe the relative importance of the inputs and outputs of nitrogen (N) to peatlands without first distinguishing among peatland types. As discussed in Vitt (Chap. 2), one way to classify peatlands is to group them according to their main nutrient sources; bogs mainly depend on the atmosphere as a nutrient source (ombrotrophic), whereas fens are fed mainly by surface water or groundwater (minero- trophic). At the local scale, the division between minerotrophy and ombrotrophy is fairly easy to make. At the landscape level, however, the distinction becomes increasingly difficult, as exemplified by the so-called mixed mires or patterned peatlands that may be composed of both minerotrophic and ombrotrophic elements. Another complicating factor relevant to describing the N cycle for peatlands is the influence of humans. The N dynamics in drained peatlands or in peatlands subject to elevated N deposition may be very different from that of undisturbed ecosystems. We have focused this chapter primarily on the N dynamics of undisturbed peatlands that are mainly ombrotrophic, with at most a few minerotrophic elements, such as a lagg zone. After a concise review of the main N inputs, N outputs, N pools, and within-ecosystem N flows, we will elaborate in our discussion on the human influence on the N cycle in peatlands, paying special attention to the disruptive effects of N deposition.