Geology Reference
In-Depth Information
Methods
(Micro-Erosion Meter, MEM) consisted of a 5 10
point coordinate on a rectangular framework on
which a digital micrometer was installed, allowing
sediment height to be measured at 50 coordinates
(Fig. 2). The tablets were removed from the river
at the end of the warm (end of March) and cool
(end of September) periods. In the laboratory, the
tablets were first air-dried for 5 days, and then
measurements of sediment accumulation by the
aforementioned device were made. About a week
after their removal, the tablets were put back in
their original position. The differences in sediment
height (mean of the 50 points per tablet) between
consecutive measuring times represented the six-
monthly sedimentation rates at each site. Measure-
ments are expressed as millimetres per six-monthly
period.
Up to 14 tablets were monitored at 13 sites from
August 1999 - March 2003. By March 2003 all
tablets were definitively removed. In the laboratory,
the tablets were cut perpendicularly to the accumu-
lation surfaces by means of a power saw. Cross-
section cuttings were made coinciding with one of
the ten five-point rows of measurement. In each
case, one of the two parts was used to obtain thin
sections and samples for scanning electron micro-
scopy and stable isotope analysis.
Prior to sediment sampling, each tablet section
was analysed to identify the several seasonal sedi-
mentation intervals. Each tablet section was
scanned and then the six-monthly measured
accumulation data of the five-point row that
coincided with the section were plotted on the corre-
sponding scanned tablet cross-section. Once the
different six-monthly accumulation periods were
identified, textural analysis and sampling of sedi-
ment for stable isotope analyses and Scanning Elec-
tron Microscopy observations were made.
Textural observations of the sediment were
made using a petrographic microscope (employing
thin sections of the deposits on the tablets) and by
scanning electron microscopy performed at the
Electron Microscope Service of the University of
Zaragoza (using a JEOL JSM 6400).
Sediment samples for stable isotope analysis
(d 18 O and d 13 C) were selected from each six-
monthly interval with a punch, then ground and
sieved (32 mm). The samples were reacted with
103% phosphoric acid at 25 8C, following standard
methods (McCrea 1950). Sediment stable isotope
determinations were made by the Stable Isotope
Analysis Service of the University of Salamanca
(Spain). The analytical precision was better than
0.1‰ for d 18 O and d 13 C. The results are expressed
in d ‰ units and compared against VPDB.
Additionally, water discharge of the Piedra
River, rainfall and air temperature data of the
studied area were obtained from the Confederaci ´ n
Several sites that represent different fluvial sub-
environments (mostly defined by the physical flow
characteristics and biofacies) within the Monasterio
de Piedra Natural Park were choosen for periodic
monitoring from August 1999 onwards. This contri-
bution deals with data obtained between August
1999 - March 2003. The study comprised six-
monthly monitoring of properties and parameters
of water and sediment. In this study, spring/
summer was the warm period and autumn/winter
the cool period. These periods correspond to the
astronomical seasons. During the first year of moni-
toring, the warm period included October.
Some physical and chemical parameters of the
water (e.g. velocity, depth, temperature, conduc-
tivity and pH) were measured in situ in five selected
sampling sites along the river at the end of June and
December from 1999 to March 2003. At the same
time, water samples were taken at those sites for
chemical (alkalinity, Cl, SO 4 , Ca, Mg, Na and K)
determinations and d 18 O analyses. Water analyses
were carried out at the Petrology and Geochemistry
Laboratory of the University of Zaragoza.
Speciation - solubility calculations (e.g. to calculate
pCO 2 , Total Disolved Inorganic Carbon, and calcite
saturation index) were performed with the code
PHREEQC (Parkhurst & Appelo 1999) and the
WATEQ4F thermodynamic database (Ball & Nord-
strom 2001) (see details of procedures in
V ´ zquez-Urbez et al. in press). Determinations of
d 18 O in water were based on the CO 2 -H 2 O equili-
brium according to Epstein & Mayeda (1953)
method, adding pure CO 2 and keeping at 25 8C
during 12 hours. Water stable isotope determi-
nations were made at the Stable Isotope Analysis
Laboratory of the University of Salamanca
(Spain). The results are expressed in d ‰ units
and reported against V-SMOW.
In addition, tufa sediment was sampled every six
months (end of June and end of December) in areas
adjacent to the tablets that had identical physical
flow and sediment characteristics to those of the
tablets. The most recent parts were selected, then
ground and sieved (53 mm) for mineralogical ana-
lyses and determination of Mg content (x-ray dif-
fraction with a Phillips PW 1729 diffractometer)
at the Mineralogy and Cristallography Laboratory
of the University of Zaragoza.
Sediment characteristics (texture, flora, mineral-
ogy, d 13 C and d 18 O) and sedimentation rates were
obtained from sediment deposited on limestone
tablets (25 15 2 cm) installed in different sub-
environments along the River Piedra, laying par-
allel to the floor. The tablets and mesurement
device were based on those designed by Drysdale
&
Gillieson
(1997).
The
measurement
device
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