Walia Special Edition on the Bale Mountains (2011) - Zoologische ...

occurrence above 4000 m. Rainfall is highly seasonal on the northern slopes of the mountains, with
most of the mean annual rainfall occurring between July and September. Annual precipitation rises
with altitude from 925 mm at Goba (2720 m) to 1086 mm at Chorchora (3500 m) and 1061 mm
at Koromi (3850 m), but is markedly lower at the highest altitudes (852 mm at Konteh, 4050 m).
Mean annual rainfall on the southern slopes is less (848 mm at Rira, 3000 m) but is more evenly
distributed through the year (Miehe and Miehe 1994; Umer et al. 2007). At present, no permanent
snow can be discovered, but precipitation in the form of hail may occur. The Bale Mountains, like
other tropical mountains, exhibit discrete vegetation belts distributed across the altitudinal gradient
(Hedberg 1951, 1955; Friis 1986; Uhlig and Uhlig 1991; Miehe and Miehe 1994). Differences in
rainfall seasonality between the northern and southern slopes give rise to a corresponding difference
in their vegetation (for details, see Umer et al. 2007). According to Messerli et al. (1976), the Bale
Mountains represent the largest area in Ethiopia glaciated during the Pleistocene, occupying all of
the plateau, with the snowline as low as 3600 to 3800 m.
Material and Methods
In January 2009 (dry season) and May 2010 (short wet season), we surveyed virtually all (12)
permanent lakes situated between 3900 and 4200 m on the Sanetti Plateau. In order to maximize use
of collected materials and field data in a variety of studies, lakes were explored following a fixed
procedure, which includes:
1. General characterization of topography and vegetation in the drainage basin.
2. Determination of lake bathymetry by depth measurements (i.e. GPS and echo-sounding)
along cross-lake transects. We also mapped wet season and dry season shorelines as to
estimate seasonal water loss.
3. Recovery of continuous depth profiles of temperature, conductivity (salinity), pH and oxygen
at the principal sampling station, as to determine the stratification and thus temperature
regime. Transparency was measured using a secchi desk.
4. Collection of water samples in lakes and inflowing rivers to determine their general water
chemistry including anions, cations, dissolved organic carbon, nutrients and pigment
concentration (for sampling and analysis protocols, see Eggermont et al. 2007)
5. Collection of an intact surface-sediment samples for analysis of various climate-proxy
indicators (fossil chironomids, cladocera and ostracods; fossil diatoms; algal pigments;
geochemistry; biomarkers and pollen) along environmental gradients
6. Sampling of the modern (living) aquatic algae, insects and micro-crustacea in littoral,
pelagic, benthic, epibenthic and epiphytic habitats.
7. Recovery of a short sediment core (~50 cm) of recent sediments in Garba Guracha for a
multi-proxy reconstruction (i.e. reconstructions using various biological, geochemical and
sedimentological indicators) of the ecological and limnological response to climate change.
<strong>Walia</strong>-<strong>Special</strong> <strong>Edition</strong> on the Bale Mountains 173