Geology Reference
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experiments conducted in thermal water gave other
results; rapid formation of carbonate minerals on
copper substratum was noted. Chafetz et al.
(1991a) and Chafetz & Lawrence (1994) observed
calcium carbonate precipitation on copper substra-
tum in hot-springs in USA and Italy. Similarly,
Folk (1994) in La Zitelle spring found that carbonate
crust 0.2 - 0.3 mm thick grew on a copper tablet
within 22 hours. SI
calc.
is the main parameter diff-
ering the previously studied sites from those where
the encrustation of copper was not discerned throu-
ghout the recent experiment. Water at the studied
sites has low SI
calc.
values: 0.35 at Karw
´
w and
0.55 at Z
´
zriv
´
, in the late autumn of 2002
(Table 2). This parameter is highly elevated in the
case of previously studied thermal travertine sites,
where it reaches 1.8 (Chafetz et al. 1991a).
The results of experiments carried out in ambient
temperature water are ambiguous. Emeis et al.
(1987) and Malusa et al. (2003) did not observe pre-
cipitation on copper sponges in the Plitvice lake
system and Fossil Creek in Arizona, respectively.
Conversely, Lojen et al. (2004) detected tufa
growth on copper substratum during an experiment
carried out in the Krka river geographically close to
Plitvice. The SI
calc.
values of water were similar in
all the sites. Thus, the different times of exposition
could be responsible for differences. Exposure lasted
a few weeks in Plitvice and around three months in
Krka. Similarly, a copper substrate was covered with
travertine (tufa in terminology adopted here) in the
course of three-month experiments carried out by
Chafetz et al. (1991b) in the Honey and Falls
creeks in Oklahoma. During an experiment con-
ducted by Janssen et al. (1999) in Belgium no car-
bonate precipitates were detected on copper plates
placed in tufa-depositing streams. It might have
been caused by short exposition time and/or by
low SI
calc.
values which at some locations were as
low as 0.44. Thus, two factors appear to be relevant
for inorganic precipitation of carbonate minerals on
copper substratum - time of exposition and SI
calc.
value. Both of them stimulate precipitation of an
insulating layer or at least of small patches of car-
bonate directly on copper substratum, essential for
further algal colonization. Unless the insulating
calcite is present, algal colonization is not possible.
Growth rates of tufa deposited during the same
time in various points differed substantially. A
strong tendency is present to faster deposition
of tufa in high-energy settings. An impressive
example is provided by the Karw
´
w site. The
annual rate of tufa growth at the dam point is
0.09 mg/cm
2
/day while at the cascade, only a few
metres downstream, the rate is 1.93 mg/cm
2
/day
(Table 3). Tufa at both points includes biogenic
components. At the dam it has hemispherically
layered texture while in the cascade the texture
is mainly hemispherically layered and fibrous.
Similar difference, but not so profound, was obser-
ved at the H
´
j site, between the lower waterfall
and dam points. The net rates of growth equalled
0.69 mg/cm
2
/day and 0.34 mg/cm
2
/day, respect-
ively. The rate at the upper waterfall point is slightly
lower than that at the dam, but the waterfall is
located in the upper reaches of the stream, close to
the spring, hence the rate of tufa growth may be
affected be the length of flow too short for water
to degas (cf. Michaelis et al. 1985). Moreover, the
stream between the upper and lower waterfalls
is additionally fed by other springs, which may
change the water chemistry and make a meaningful
comparison impossible.
At the L ´
ˇ
ky site, higher annual growth of
6.43 mg/cm
2
/day was found at the L ´
ˇ
ky E point,
that is on the waterfall face, where the tablets
were constantly flushed by water falling down. In
the same time period, the tufa growth rate at the
L ´
ˇ
ky top point, located in the streambed just over
the waterfall head, was substantially slower and
reached 3.86 mg/cm
2
/day.
The examples mentioned above depict semi-
quantitatively the tendency to a faster growth of
calcite in settings with fast flow than in calm ones.
A similar tendency was earlier detected by Liu
et al. (1995) and Lu et al. (2000) in the famous
Huanglong ravine in China, by Drysdale & Gillie-
son (1997) in Louie Creek in northern Australia as
well as by Bono et al. (2001) in Tartare karst
spring in Italy. Liu et al. (1995) explained this
phenomenon by the smaller thickness of a diffusion-
boundary layer in fast-flowing water, which facili-
tates ion migration toward the growing crystals.
This phenomenon occurs particularly in waterfall
settings. Zhang et al. (2001) coined the term 'water-
fall effect' to describe it, while Chen et al. (2004)
put forward aeration, low pressure and jet-flow
effects as stimulators of calcite precipitation. Rec-
ently Hammer et al. (2008) have shown that the
most decisive mechanism governing the calcite
growth in flowing water is advection of ions
towards the crystal surface. All these mechanisms
are based on inorganically driven processes. How-
ever, the tufa textures imply that biogenic activity
may also influence tufa growth in moderate and
Differences between tufa growing at
various settings
The location of various study points along the
course of the same stream allowed to observe differ-
ences in the tufa growth and texture related to
microenvironmental conditions. All the study sites,
except for Z´zriv´, provide a good opportunity to
discuss this difference.
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