I studied Landscape ecology and the protection of nature at the Ernst Moritz Arndt University in Greifswald
In my thesis (diploma) with the title "Ecological investigations on the decomposition of Phragmites australis on rewetted fen and at reference locations" I occupied myself intensively with humid areas, in particular fens. The thesis is part of the BMBF project "Ökosystemmanagement für Niedermoore".
During the last decades fens and bogs continue to win growing public interest. The global increase in consumption, mostly by use of peat or drainage for agricultural use focused the attention on the diverse and important natural resources the fens provide. There is as well an increasing importance for the material and water management, environmental and nature protection and for prehistorical questions (SUCCOW, 1988).
One of the most substantial characteristics of growing fens is the accumulation of peat and the reduced dismantling of dead vegetable substance, this is how the fens accumulate substances like carbon dioxide (CO₂). If the fens loose their functionality the peat bound material is mobilized and great quantities of carbon dioxide (climaticeffective gas) are released (SUCCOW und JESCHKE, 1986).
In former times peatlands were often drained for intensive agricultural use. The low water table in drained peatlands results in a higher microbial activity and consequently in larger peat decomposition losses, associated with large emissions of nutrients and greenhouse gases.

The emissions of materials and trace gases have a negative effect on the water resources and the atmosphere (KUNTZE, 1993, AUGUSTIN et al., 1996). The study of the material household of drained fens is therefore important in connection with the influence of human activities on the climate.
The fens held 4% to 10 % of the surface of the young- and old-pleistozaen before the start of the regular drainage at the beginning of the 20th century (PFADENHAUER, 1994). The question, in what respect the functionality of degraded fens can be restored by measures of renaturalization does not only play a role in the scientific, but also in the political discussion about the further handling of drained peatlands.

In the context of the BMBF - project „Ökosystemmanagement für Niedermoore“, subproject „Friedländer Große Wiese“ it is to be examined to what extent it is possible to reinitialize peat accumulation at a heavyly degraded fen. In order to determine optimal water regimes for renewed peat accumulation and minimal decomposition losses a set of management measures like e.g.. different variants of rewetting or removal of nutrients by cut were compared with one another. A goal of these measures is it to stabilize the material conversions on low level and to re-establish the functionality of the fens to a large extent.

In my thesis I concentrated on the influence of different types of rewetting management measures on the material conversions in the soil and the decomposition of reed stems and reed rhizomes. There are already numerous investigations to the dismantling of cellulose and leaf litter (UNGER, 1968; LUTHARDT, 1987; u.a.). In order to create conditions as close as possible to natural conditions HARTMANN (1995, 1997) worked with root material replacing cellulose. Based on this I exposed stems and rhizomes of Phragmites australis (CAV.) TRIN. EX STEUD.
Phragmites australis was selected because it is one of the potentiall peat accumulating species. The rhizomes were exposed because they are together with root material the macroscopically identifiable parts of reet peat. The stems were exposed to determin whether they would be suitable as reference material for the roots.

Results:
From the gathered location parameters only the temperature and the water content showed a direct influence on the decomposing behavior of the rhizomes and stems.
The other parameters were either not different enough on the various locations to make a difference or they showed no direct influence on the decomposing.
The investigations let the rhizomes appear as the more suitable material, since they reflect the results determined with the roots, the stems are not suitable as reference material.

The rewetting measures had an different effect than expected on the water content of the soil, e.g. the permanent overflowed location shows on the average the smallest water contents of the locations. Altogether the location differences were smaller than expected. This led to smaller differences in the decomposition rate. The permanently rinsed location shows a high decomposition despite high water contents. This stands in direct contrast to the original assumptions concerning the factors determining the decomposition in a rewetted fen. The fact that the two reference locations, which were not ploughed and thus still had an intact soil structure, exhibited the lowest decomposition, makes clear that the natural conditions of a fen cannot be restored at least at short notice through bare flooding. A regeneration might occur after over 100 years, before that it is only a revitalization (EGGELSMANN,1989).
In order to clarify the question, which rewetting measures are the most suitable, more long-term monitorings are necessary. A wide rewetted area before intensively agriculturally used will develop to a gradual mosaic with vegetation from Typha, Phragmites, Carex-Rieden und Alnus-forests (Wichtmann und Koppisch, 1998). The rise of water levels leads to nutrient changes in the soil, which release desired (nitrogen reduction) and on the other hand unwanted developments (methane release (Augustin, 1996)). There have to be long-term monitor programs and at least medium-term process orientated and ecological investigations in rewetted fens (Harter und Luthardt, 1997).