Geology Reference
In-Depth Information
hidrogr
´
fica del Ebro (Zaragoza) and the Agencia
Estatal de Meteorolog
´
a (Table 1).
(2) Areas of slow flowing to standing water:
these appeared upstream and downstream of water-
falls and small barrages along the river (Fig. 3d).
Water velocity ranged between almost 0 (although
at the sites monitored the minimum was 32 cm/s)
to 55.33 cm/s, and water depth from 10 to 30 cm.
Lime mud, diverse carbonate grains and in situ
coated plants in palustrine conditions were
present. Microbial filaments and tube-like bodies
appear in areas of faster flow.
(3) Stepped waterfalls and barrages with
bryophytes: these include small waterfalls and bar-
rages (up to 3 m high) on the river bed, and
stepped waterfalls (up to about 8 m high) (Fig. 3e,
f). All of them had a thin water lamine with turbulent
flow. They are mainly formed of mosses and fila-
mentous green algae, with minor cyanobacteria
and herbaceous plants, all of which were coated
by calcite producing porous deposits. These
included trapped coated phytoclasts and hanging
coated plants.
(4) Spray and splash areas beside waterfalls,
with mats of mosses, cyanobacteria and filamentous
algae coated and impregnated by calcite. These con-
stituted thin, generally non-laminated deposits.
(5) Waterfalls with vertical drops (e.g. waterfalls
Caprichosa and Cola de Caballo, 10 and 35 m high)
(Fig. 3c). Herbaceous hanging plants and moss mats
that grew in parts of the river section with low water
flow were coated by calcite constituting banded
deposits with steep inclination.
(6) Caves behind waterfalls (e.g. Cave Iris).
These were shady areas with great water seepage,
in which bryophyte and microbial mats coated
diverse cave surfaces. Stalactites developed there,
sometimes from hanging plants coated by calcite.
In addition, in most fluvial deposits diatoms,
aquatic
Hydrochemistry
The River Piedra water is of calcium-bicarbonate
type, with pH values always between 8 - 8.5
(except for two values c. 7.4 in September 2000),
conductivity between 630 - 670 mS/cm, alkalinity
between 250 - 310 mg/L and Ca concentration
between 85 - 102 mg/L (for detailed hydrochemical
data, see V´zquez-Urbez et al. in press).
Alkalinity and calcium concentrations showed a
more or less gradual decrease from the upstream site
to the downstream site, indicating the effective
precipitation of calcium carbonate. The water is
permanently saturated with respect to calcite, with
saturation index [log IAP/K(T)] values close to
þ1 (without clear downstream variations) and,
therefore, at levels sufficient to overcome the car-
bonate kinetic precipitation barrier (Jacobson &
Usdowski 1975; Dandurand et al. 1982; Drysdale
et al. 2002). All these trends are similar to those
observed in other tufa-depositing rivers and
streams (Herman & Lorah 1987; Lu et al. 2000;
Drysdale et al. 2002; Malusa et al. 2003).
Differences in the hydrochemical data between
warm and cool periods only were clearly seen for
calcium and alkalinity (Os´car et al. 2003;
V´zquez-Urbez et al. in press), with a steeper
decreasing pattern along the river in the warm
periods. These differences indicate a more intense
calcite precipitation process in warm periods. This
seasonal pattern related to temperature changes
has also been observed in similar fluvial systems
(e.g. Kano et al. 2003; Kawai et al. 2006).
insects,
worms
and
crustaceans
were
Sedimentary subenvironments of the
fluvial system
present.
Analysis of sedimentation patterns
Topographic features, flow characteristics and bio-
facies of the River Piedra in the Monasterio de
Piedra Natural Park allowed V´zquez-Urbez et al.
(in press) to distinguish several tufa sedimentation
subenvironments, some of which have been
described from other fluvial systems (e.g. Pedley
1990,
To carry out the analysis of the seasonal variations
of sedimentological (thickness, structure, texture)
and geochemical (stable isotopes) features, data
of sedimentation rates obtained from six-monthly
thickness measurements with the MEM on tablets
were used to identify seasonal intervals of the
tufa deposited on the tablets installed from
August 1999 - March 2003. Data on sedimentation
rates for a longer period and their relationships
to environmental factors, such as hydrology,
hydrochemistry, climate and biological activity,
are dealt with in detail in the paper by
V´zquez-Urbez et al. (in press). The following
section is based on the information of that paper
that is essential for comprehension of the present
research.
2009).
The
main
characteristics
of
the
several
subenvironments
in
the
Monasterio
de
Piedra are summarized as follows (Fig. 3):
(1) Areas of fast flowing water, including steeper
stretches of the river bed (e.g. small jumps and
stepped falls up to 2 m high) (Fig. 3a, b, c). Mean
water velocity ranged between 109.33 and
215.67 cm/s, and depth between a 3 and 10 cm.
The sediment consisted of dense laminated tufa
mostly formed of microbial tube-like bodies made
of calcite crystals.
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