Box 1 – Height of Domed Peatlands
Peat accumulates in a saturated environment because of the slow rate of decay of organic material in the catotelm. Away from the lagg (interface between bog and adjacent mineral terrain), toward the center of the peat massif, the horizontal hydraulic gradients are lower, thus drainage is slower, so more peat accumulates. This may be exacerbated by the central massif’s isolation from minerotrophic water, unlike nearer the lagg where solute-rich water may accelerate decomposition and support vascular plants less resistant to decay than Sphagnum. These gradients and flows are illustrated in Figure 6.
The height of a bog dome can be greater in large systems—areas of higher precipitation excess over evapotranspiration—and where saturated hydraulic conductivity of the peat is low (slower drainage). Ingram (1982) provided a simplistic analytical model relating these parameters to bog dome height, although its simplicity is perhaps too much to be of practical importance (Belyea and Baird, 2006). In practice, the height to which a dome can reach is finite, because slow decomposition of a very thick peat deposit, even though saturated, eventually degrades an equivalent amount of organic matter as is added annually (Clymo, 1984).
Clymo (1987) estimates a range of heights between 0.5 to 10 m for temperate or boreal peatlands, although most are < 5 m. In tropical peatlands, where rainfall can be much higher, peat deposits of ~20 m can occur (Anderson, 1983), thus greater dome heights are possible.