Geology Reference
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is efficiently removed. Pedley (1992), following the
experimental work by Lorch & Ottow (1985), stated
that even bacterial biofilm can be damaged and
scrubbed off when water flow is too fast. Mineral
grains transported in traction substantially enhance
this process.
Tufa deposited on the tablets exposed in water-
falls and in fast-flowing sections of the streams,
includes also commonly porous tufa composed of
highly encrusted algal filaments. Orientation of the
filaments is governed by energy of the stream. In
higher energy conditions, the filaments are aligned
with the flow, parallel to each other and more or
less parallel to their substrate. Both Vaucheria and
cyanobacteria filaments display such orientation
(Figs 10e & 20a, e). The dependence of Vaucheria
filament orientation on the current direction was
noted earlier (Wallner 1934b; Golubi´ et al.
2008). It seems to be a rule applying to all filamen-
tous algae. Whitton (1975), for instance, described
Cladophora, an alga commonly found in tufa-
depositing milieu, forming elongated structures,
exhibiting parallel orientation to the flow, in con-
ditions of higher current velocity.
Some filaments in the studied samples form
laminae loosely cemented with the basement,
which indicates that cementation proceeded within
a cyanobacterial or algal mat partly floating in the
current. This was probably forced by shear stress
of flowing water and vulnerability of the upper
part of the algal mat to dislodgement because the
lower part of the mat looses its ability to support
the overlying part, as a result of senescence,
shading or metabolic processes (Allan 1995, 96).
The tufa which grew on the tablets at the L ´ˇky E
point exhibits such a structure (Fig. 24).
Conversely, in a lower-energy setting, such as
the L´ˇky top and W points or in places where
water is supplied only as small rivulets, as at the
Karw´w cascade, the filaments are not stuck by
water, which results in their random orientation.
Tufa rich in micrite forms in low energy settings.
It displays clotted or hemispherically layered
texture. In the former case the micritic crystals
grow within or on the EPS. Hence, its origin prob-
ably reflects conditions suitable for production of
the copious amount of EPS (Pedley 1992, 2000).
The diatoms which accompanied the EPS are prob-
ably their main producer (Winsborough 2000).
However, diatoms were detected also in other
samples. They accompany the filaments that build
the porous tufa growing in fast-flowing water.
Diatoms are able to withstand high-velocity cur-
rents; hence they also inhabit high-energy milieus
(Allan 1995, 95). Therefore, the presence of
diatoms is not limited to the conditions in which
micrite tufa forms (see Winsborough & Golubi´
1987; Arp et al. 2001).
The extreme situation favouring the origin of
clotted micrite rich in diatoms and their EPS is
slowing down of water flow, coupled with systema-
tic drying up of the stream. Such a process took
place in the summer of 2003, when the upper
segment of the stream in H´j dried up completely
and the water level in its lower segment lowered
substantially, resulting in subaerial exposition of
tablets at the H´j upper waterfall and dam points.
The occurrence of layers abounding in diatoms
formed during the drought was noted from Cuatro
Ci´negas
area
in
Mexico
by
Winsborough
&
Golubi´ (1987).
The growth form of upward-radiating filaments
of cyanobacteria, most probably Phormidium
sp., controls the hemispherically layered texture
(Figs 11a, 12d - f, 19). It dominated at the Karw ´w
dam and Karw´w cascade points where minute
water rivulets seeped or trickled down. Thus, this
textural type seems to be connected with different
energy conditions but in a relatively small stream.
However, it occurs also commonly in bigger
streams (Golubic et al. 1993; Freytet & Plet 1996;
Freytet & Verrecchia 1998 and references herein).
Interestingly, the sparite bushes connected with
the calcification of Oocardium stratum originate in
sluggish flow condition. At the earlier described
localities, this desmid alga inhabits fast-flowing
water. Wallner (1935b) mentioned, based on his
experiments, that in the sluggish flow colonization
of Oocardium stratum was not observed. Conver-
sely, he found vigorous growth of Oocardium tufa
in relatively fast-flowing water. Similarly, Pentecost
(1991), describing two sites with Oocardium
stratum from Great Britain and one from Belgium,
pointed out that each of them experienced moder-
ately fast flow.
Temperature. The temperature of water influences
principal physicochemical conditions governing
SI
calc.
values, which in turn rules the tufa growth
rate (Pedley et al. 1996; Pentecost 2005).
However, the temperature at all the studied sites
changes within narrow range and thus any effect
of temperature may be overridden by the influence
of other factors (Merz-Preiß & Riding 1999). Never-
theless, temperature increase probably contributes
to SI
calc.
elevation in summer seasons, for instance
at the Z´zriv´ site (Fig. 4). Conversely, the substan-
tial decrease of SI
calc.
at this site in cold seasons
resulted probably from temperature decline. This
was
possible
because
of
the
relatively
small
amount of water feeding the discussed site.
In some cases, higher temperatures between
spring and autumn may favour development of
tufa with abundant moulds of cyanobacterial or
other organism (except diatoms), because these
algae seem to prefer slightly higher temperature
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