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ABSTRACT
Master Thesis
Post-Graduation Program in Geography and Geosciences
Federal University of Santa Maria
RELATIONS BETWEEN THE VARIABLES SPECTRAL AND LIMNOLOGICAL OF
DONA FRANCISCA/RS’S HYDROELETRIC POWERHOUSE RESERVOIR
AUTHOR: ROSANA CORAZZA
ADVISER: WATERLOO PEREIRA FILHO
Date and Place of Defense: Santa Maria, May the 6th of 2010.
Continental water systems have main importance to a variety of living beings. The terrestrial
remote sensing has been efficient for the study of such systems, since it allows their detailed
monitoring by means of field spectroradiometers. Inserted in this context, the aim of this
study was to analyze the relation between spectral variables and limnological of Dona
Francisca’s Hydroelectric Powerhouse reservoir, using spectroradiometry field data collection
and limnology. Concerning methodology, the first stage of the study is constituted by
limnological data collected in February, March, April, June, July, August and October of the
year 2009, and in the obtaining of reflectance specters in October of 2009. For this aim one
used 22 sample points that were defined a priori. In field and in laboratory, one determined
the following limnological variables: chlorophyll-a, total suspended solids, dissolved organic
carbon, Secchi disk depth, water temperature, electric conductivity and pH. The reflectance
specters were acquired by field portable spectrometers FieldSpec® HandHeld. The original
specters were qualitatively analyzed and one applied first order derivation technique, mapping
the spectral angle, continuum removal and band reason with the aim of identifying features of
absorption due to active optical components. Finally, limnological and spectral data were
related by the use of correlations, dispersions and significance tests. Concerning limnological
results, one found variation in the space-time distribution during the research period. The
chlorophyll-a variable presented statistically significant correlations (99.9% of trust) with
Secchi disk, with the total suspended solids, dissolved organic carbon and the temperature.
Besides, limnological variables evidenced relationship with pluviometric precipitation regime
and the consequent carrying of particled material and nutrients from the capturing bays to the
hydric body. In spectral results, the maximum reflectance tax was 16% in green spectral level,
approximately in 590 nm. One verified the absorption bands around 610 nm and 675 nm.
According to the literature, the absorption band in 610 nm occurs because of the absorption of
ficocyanine, an auxiliary photosynthetic pigment of chlorophyll-a, that is present in
cyanobacterias, which indicates the existence of such organisms in the phytoplanktonic
extract of the reservoir. The absorption band in 675 nm occurs due to chlorophyll-a, and it has
shown to be more prominent as the pigment concentration increased. The techniques that
were applied on specters made easier the interpretation and identification of the three distinct
spectral groups, which were located in different sections of the reservoir: one in Jacuí River
section (extreme amount), another in the Jacuizinho River section (tributary), and the other
beyond the confluence of these two rivers (intermediate section until the dyke). The statistical
tests evidenced that in the month of October of 2009 the reflectance was significantly
statistically related to chlorophyll-a, which constituted the main optically active component
that was active in Dona Francisca’s reservoir water.
Key-words: Dona Francisca’s Reservoir, Water Spectral Behavior, Limnology, Chlorophyll-
a.