Abstract
Peat formation is a slow process and the formation of thick peat layers in large parts of e.g. Russia, Canada and Indonesia has generally taken thousands of years. Due to degradation of peatlands throughout the world, as a result of changed land use and pollution, many ecosystem services provided by peatlands have disappeared. It is therefore necessary to restore degraded systems or create new peat-forming wetlands. Information on the early stages of peat formation is scarce, however, and the biogeochemical conditions that stimulate the transition of mineral sand to growing peatland (which would have happened thousands of years ago in e.g. Russia, Canada and Indonesia) remain largely unknown. In this thesis, several pathways of peat formation are studied using three model species: Stratiotes aloides, which grows in the aquatic phase, Typha spp., which grow in the semi-terrestrial phase, and Sphagnum mosses, which grow in the terrestrial or floating mire stage. Using a combination of lab studies, mesocosm experiments and field measurements, the biogeochemical conditions and biotic interactions (such as facilitation) that stimulate or limit growth of these ecosystem engineers were studied. Furthermore, for each of these species, the contribution to the net C sequestration rate of a system -or the net build-up of an organic layer that can form peat- was determined. We found that there is a huge difference between starting peat formation “from scratch” (on mineral soils) or restoring peat formation in a degraded peatland. In this latter case, secondary peat formation can be started after habitat conditions are suitable for growth of Sphagnum mosses (e.g. by topsoil removal and rewetting). For primary peat formation, on the other hand, the main concern is the low colonisation rates of low-nutrient, mineral soils. Therefore, modifying habitat conditions to suit the requirements of target species and harnessing inter- and intraspecific facilitation is essential to transform such a system into a net C sink without having to wait a thousand years.
