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296
A. R. GHIDINI ET AL.
composed mainly by pastureland (Andreoli &
Carneiro 2005).
Iraí Reservoir was built in 2001 and its
morphometrical and hydrological features have been
causing Cyanobacteria proliferation since its filling,
complicating water treatment and reducing water
quality (Andreoli & Carneiro 2005).
One of the four main tributaries (Timbú
River) is characterized by an elevated nutrient load,
especially of phosphorus and nitrogen, due to the
disordered urban occupation of the drainage basin.
This fact, associated to the high residence time and
low dept of the reservoir favored the development of
blooms of Cyanobacteria, as Anabaena sp.,
Cylindrospermopsis sp., and Microcystis sp.,
promoting significantly changes in the water quality
of the reservoir (Bollmann & Andreoli 2005).
Field work, samples and data analyses.
The samples were obtained monthly from
March/2002 to July/2003 in six stations in the
reservoir, totalizing 102 samples. Stations 1, 2 and 3
were located in the dam axis (stations 1 and 3, Z max =
4 m; station 2, Z max = 8 m), and the others were in the
main body the reservoir (stations 4, 5, and 6, Z max = 3
m) (Fig. 1).
Two-hundred liters of sub surface water
(due to low depth) were filtered in a conical
plankton net (55 µm mesh size), using a motorized
pump. The samples were narcotized with 4 %
buffered formalin. Countings were made through
subsamples of 1 mL using Stempel pipette, and a
minimum of 200 individuals were counted per
sample in a Sedgewick-Rafter chamber under optical
microscope. Cladocerans are usually quantified in
acrylic gridded Petri dishes using stereomicroscope.
However, in this study, countings in Sedgewick-
Rafter were possible due to the elevate number of
small organisms. Identification of species was based
in specialized literature, as Matsumura-Tundisi
(1984), Elmoor-Loureiro (1998; 2007), Hollwedel et
al. (2003) and Elmoor-Loureiro et al. (2004).
Abundance data were expressed as individuals.m -3 .
Figure 1. Localization of Iraí Reservoir (Paraná State) and of sampling stations
Non-parametric tests were used after
Shapiro-Wilk normality test have indicated a not
normal distribution. Organism’s richness and
abundance were analyzed using H Kruskal-Wallis
ANOVA test (p < 0.05) to detect significant
variations between sampling stations and months.
Biotic and abiotic variables for limnological
characterization were not different among the
stations (p > 0.05). It was used data of station 2, in
middle dam zone. Biotic and abiotic variables were
related to the cladocerans abundance. Phytoplankton
species abundance and cladocerans abundance
interactions were analyzed using the Spearman
correlation (p < 0.05). Due to the elevate number of
statistical analyses applied, multiple comparisons
tests between the means of analyzed categories were
used to avoid error type I on null hypothesis.
Multiple comparisons analyses of “p” values (Z, p >
0.05) were performed on the significance tests of H
Kruskal-Wallis ANOVA and Bonferroni correction
(β, p > 0.05) on Spearman correlations. Despite the
corrections, infringements about null hypothesis
Pan-American Journal of Aquatic Sciences (2009), 4(3): 294-305