Dwog

A dwog or dwog horizon (obsolete: "black cord" , "blue ray" ) is a former, humus terrain surface that was covered by sedimentation . The designation is only used for marsh soils . The Dwoghorizont is the diagnostic horizon for the Dwogmarsch .

Emergence

If the former seabed falls dry for a long time, marshy soils develop, which form a humus top soil. This process does not necessarily have to be of artificial origin ( embankment ), but also represents a completely natural process of coastal development. Just as some areas silt up due to sedimentation , floods can occur again due to changes in sea level or repeated storm surges . In these cases, the former terrain surfaces are covered with new marine deposits and a layer change in the soil occurs due to sedimentation.

Because of the superimposed silt cover, the organic matter could no longer be completely converted. After coalification or humification it is still present as a dark colored band in the soil. The former (fossil) topsoil horizons are therefore clearly visible in the profile. They are called Dwog (plural: Dwöge). Because the soils of the Jungmarschen are relatively well ventilated, the humus in them is subject to greater mineralization . Dwog horizons therefore occur mainly in Altmarschen.

In addition to the above-mentioned theory, which is represented in current specialist books, there was also a second view in older literature: The accumulation of humus in a certain location was attributed to a strongly varying air supply during a short phase of sedimentation. The air conditions would therefore be aerobic enough for humification but not sufficient for complete degradation. This would be the case in a sedimentation area with little movement and swamp vegetation. The dwog should therefore not represent a fossil topsoil horizon, but a fossil underwater horizon (soil type Gyttja ).

Dwog horizons

In marsh soils, the humus topsoil (Ah horizon) is always followed by an air-supplied and groundwater-influenced subsoil (Go horizon). After covering, these are referred to as fossil (f). The old topsoil is then a humusdwog (fAh). If there is a lot of iron in the old Go, it is called Eisendwog (fGo). A Dwog profile has a humusdwog and / or an iron endwog.

properties

Since dwarfs were once greened surfaces that were suddenly covered by new deposits, remnants of the old vegetation and humus layer can still be found in them. This can be seen in the dark brown, blue to black color in the otherwise brownish sub-floor. An old root penetration can often still be seen. These characteristic dark, thin layers are clearly visible in drill rods and profiles, which explains the trivial names “black cord” or “blue ray”.

The humus-rich subsurface horizon has a negative impact on the drainage, so soils frequently with close pending Dwögen waterlogging show. Sufficient drainage must be created for use.

Remarks

Just like a dwog, a kink is also a layer change in the soil profile caused by sedimentation. However, a kink is not a former surface, but a particularly clay-rich layer as a result of the deposits.

literature

Streif, H. (1990): The East Frisian coastal area - North Sea, islands, mud flats and marshes , Geological Guide Collection 57, 2nd completely revised edition, Brothers Borntraeger, Berlin, Stuttgart, ISBN 978-3443150518

Kuntze, Herbert (1965): The marshes - heavy soils in agricultural evolution; Opportunities for use and improvement of difficult locations; Paul Parey publishing house, Hamburg and Berlin

Ad hoc working group on soil; Federal Institute for Geosciences and Raw Materials in cooperation with the State Geological Services of the Federal Republic of Germany (Hrsg.) (2005): Bodenkundliche Kartieranleitung . 5. revised u. exp. Edition. Hanover, ISBN 3-510-95920-5