Mires of Tierra del Fuego

1
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)
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2
3
4
5
2
Maria Bahety fen (1)
Radicell/sedge peat
7m
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.
Sphagnum/radicell peat
Lake sediments
Sand
spring
3500
1500
270
980
220
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
3
Maria Cristina fen (2)
4
Maria Cristina fen
170
117
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
240
170
113
170
gt230
550
650
5
Andorra mire (3)
6
Andorra mire
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

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Andorra mire
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

160
75
150
140
35-40
140
75
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.
8
Andorra mire

• 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.
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Andorra mire

• The bog margin

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
7m
130
40
40
10
Rancho Hambre mire (4)
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Rancho Hambre mire
340
110
Sphagnum peat
35
100
14
50
radicel/sedge peat
Sphagnum/ radicell peat
Lake sediments
sand
This bog complex is mainly fed by rain and
surface water. Most of the surface water
originates from rivulets from the slope
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Moat mires (5)
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Moat mires
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)

• A lake on top

gt 4 m deep
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Moat mires
So Sphagnum magellanicum appears to be
dominant at slightly lower EC then Astelia.

• Going down

60
110
75
125
97
110/135
135
126
297
15
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
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Moat mires
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).