Mires of Tierra del Fuego. With contributions of: Erwin Adema (RUG) Hans Joosten (Uni-Greifswald) John Couwenberg (Uni-Greifswald) Christiaan Fritz (Uni-Greifswald) Olivier Ogliati (Uni-Greifs.;fotos) Jan Sliva (Uni-Munchen; fotos). 1. 2. 3. 4. 5.
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With contributions of:
Erwin Adema (RUG)
Hans Joosten (Uni-Greifswald)
John Couwenberg (Uni-Greifswald)
Christiaan Fritz (Uni-Greifswald)
Olivier Ogliati (Uni-Greifs.;fotos)
Jan Sliva (Uni-Munchen; fotos)
This region practically has no forests and has a high grazing pressure. The precipitation is low and the evaporation rather high. We visited the fen in a very wet condition. Normally it is much dryer.
This fen is fed by groundwater with a relatively low EC 230-350. The surface water has very high EC values (900-1500 µS/cm), since it has dissolved many salts from the surface. At 1m depth we measured 3500 µS/cm.
Almost dry salty lake
The fen is fed by groundwater with different EC values. It is also fed by surface water from streams and from ditches along the road. The bog, which is only 60 cm, on top of the fen also stores rain water. So this bog development is very recent
The spring forest is situated on thin peat where much groundwater discharges. Shifting groundwater flows create opportunities for trees at one site, but may drown trees somewhere else. Strong winds can easily put these trees down.
The spring forest
This is the best preserved part of the spring mire. Further down a small rivulet from the hill cuts through the peat and at the end causes some erosion
The spring fen
This is an older erosion gully, which is now almost dry. These structures drained the mire upstream, so a forest vegetation could develop or a bog.
The spring area
The original spring mire could have looked like this, showing spring water coming in and proceeding through the fen peat to the river. Such a mire is extremely sensitive to erosion of inflowing surface water. The results of the German students show that the spring fen was later blocked by the bog expansion.
The bog has a small lagg zone and sometimes small rivulets are formed. Both have low values in EC (ca. 40 µS/cm). Only the rivulets that cross the bog have higher values of about 130 µS/cm
The bog margin
This bog complex is mainly fed by rain and surface water. Most of the surface water originates from rivulets from the slope
This lake is a local high point of a mire system. Sphagnum magellanicum is dominant here with EC between 60-95. Slightly under the top an Astelia mire is present with higher EC in the pools (125)
> 4 m deep
A lake on top
So Sphagnum magellanicum appears to be dominant at slightly lower EC then Astelia.
Hans Joosten made a boring in this Sphagnum and Astelia pumila vegetation: under the Sphagnum was over 60 cm of Sphagnum peat, while under the Astelia was 60 cm of Astelia peat, followed by Sphagnum peat. Apparently competition between Sphagnum magallanicum and Astelia can be a stable state for hundreds of years. In most situations Astelia is pushing Sphagnum back to the pool
EC = 126
In many pools algae appear to be dominant. The algae may compete with Sphagnum magellanicum for nutrients and CO2. EC values are always higher in the algae soup.
Further research on the competition for CO2 and nutrients would be very interesting (Sphagnum, Astelia and Algae). If the algae win, this could explain the lack of accumulation in the pools (over 50 cm deep).