REVISTA DE BIOLOGIA E CIÊNCIAS DA TERRA
ISSN 1519-5228
Suplemento Especial - Número 1 - 2º Semestre 2006
Vertical and nictemeral dynamics of limnological variables in
a tropical Brazilian Dam
Paulo Roberto de Medeiros1, José Etham de Lucena Barbosa2, Ana Maria Alves da Silva3, Maria Cristina Basílio Crispim4
ABSTRACT
Nictemeral studies are important to assess information about the variations of ecological factors in
short periods of time. With the aim of studying the vertical and nictemeral variations in the Bodocongó
dam, located in the Northeast of Brazil, samples were taken from four depths (Subsurface, 50% Io, 1%
Io and Bottom) at a single sampling station with a depth of 5 meters in four-hour intervals (1pm, 5pm,
9pm, 1am, 5am, 9am and 1pm), during the dry period in November 2003. The following variables were
sampled: water transparency, water temperature, electric conductivity, dissolved oxygen, pH, ammonia,
nitrite, nitrate, orthophosphate and total phosphorus. Overall, no significant vertical or nictemeral
variation was found for any of the variables, which is probably be related to the shallow depth of the
dam. However, there was a trend towards a day/night shift in the values of water temperature, electric
conductivity, pH, alkalinity and dissolved oxygen. Nutrient’s values showed no distinct pattern of
distribution.
Key words: Nictemeral, limnological variables, dam, Northeast Brazil.
RESUMO
Estudos nictemerais são importantes para se obter informações sobre fatores ecológicos em curtos
períodos de tempo. Com o objetivo de estudar as variações verticais e nictemerais no açude de
Bodocongó localizado no Nordeste do Brasil, amostras foram coletadas de quatro profundidades (Subsuperfície, 50% Io, 1% Io e Fundo) em uma única estação de coleta com 5 m de profundidade, em
intervalos de 4 horas (13:00, 17:00, 21:00, 01:00, 05:00, 09:00 e 13:00), durante o período seco, em
Novembro de 2003. As seguintes variáveis foram amostradas: transparência da água, temperatura da
água, condutividade elétrica, oxigênio dissolvido, pH, alcalinidade, amônia, nitrito, nitrato, orto-fosfato
e fósforo total. Não houve variação vertical ou nictemeral significante para nenhuma das variáveis
analisadas, o que pode estar relacionado com a profundidade rasa do açude. No entanto, temperatura da
água, condutividade elétrica, pH e oxigênio dissolvido mostraram uma tendência para uma variação
dia/noite. Para os valores dos nutrientes não foi observado um padrão de distribuição distinto.
Palavras-chave: Nictemeral, variáveis limnológicas, açude, Nordeste brasileiro.
1 INTRODUCTION
Diurnal rhythms are usually studied to
assess information about the short-period
variations of ecological factors in any kind of
ecosystem (Ramirez, 1996). These nictemeral
studies (from the Greek Nychthémeron: one day
and one night) are very useful as an attempt to
understand the physical, chemical and biological
interactions that occur in short periods of time
(diurnal cycles) on aquatic ecosystems. Also,
studying the dynamics of an ecosystem is an
important way of understanding how the physical
and chemical variables shift during the day/night
73
cycle and how these differences can influence
the life cycles of the organisms that dwell in it.
Nictemeral studies are particularly
important on the tropics since there is a broader
variation of the ecological variables in a diurnal
cycle (24 hours) than there is in a seasonal cycle
(12 months) (Ganf & Horn, 1975). In a diurnal
cycle, periodic vertical reorganizations occur
and this complex characteristic, particularly in
shallow aquatic ecosystems, is still poorly
understood (Gavilán, 1990). Also, nictemeral
studies are important not only from a conceptual
point of view, but also for the application of a
management plan in different environments
(Barbosa, 1996).
Many relevant studies
emphasize the importance of nictemeral
researches in tropical freshwater environments
(Barbosa, 1981; Melack & Fisher, 1983;
Simonato, 1986; Esteves et al., 1988; Alves et
al., 1988; Toledo et al., 1988; Barbosa &
Tundisi, 1989; Gavilán, 1990; Bozeli et al.,
1990; Bozeli et al., 1992; Huszar et al., 1994
and Ramirez, 1996), where they all agree that
these tropic aquatic ecosystems are more
influenced by a 24 hours cycle than by an
annual cycle.
The present research aimed at studying
the vertical and nictemeral variations of
limnological variables in a tropical Brazilian
dam during the dry period.
2 MATERIAL AND METHODS
2.1 – Study area
The Bodocongó dam (7º 13' 11" S, 35º 52'
21" W) is located in the city of Campina Grande,
Paraiba state in the northeast of Brazil at an altitude
of about 508 meters above the sea level. It has an
average depth of 3 meters and a maximum depth of
6,5 meters. Historically, the first limnological
researches of Brazil were carried out in the
Bodocongó dam and so, it’s considered today the
birthplace of Brazil’s limnology
2.2 – Sampling procedures and data analysis
The water samples were taken from four
depths (Subsurface, 50% Io, 1% Io, and Bottom) at a
single sampling station with a depth of 5 meters at
four-hour intervals during 24 hours (1pm, 5pm, 9pm,
1am, 5am, 9am and 1pm) in the dry season on the 17th
and 18th of November 2003. Water temperature
samples were also taken at three additional depths
(75% Io, 25% Io and 10% Io). Water transparency
samples were taken in five intervals (1pm, 5pm, 5am,
9am and 1pm). All the samples were collected using a
Van Dorn bottle with a five liters capacity. Table 1
summarizes the variables and the methods used.
The resulting values were submitted to a
basic descriptive statistical analysis: arithmetic
mean as a central position measurement and
Pearson’s coefficient of variation (CV) as relative
dispersion measurement. To detect significant
differences a one way Analysis of Variance
(ANOVA) was used. Also, Pearson’s coefficient of
correlation was used among all variables. All
statistical analysis and graphs were built with the
use of Statistica 5.1 and Surfer 5.0 for Microsoft
Windows.
Table 1. Material and/or methods, with the respective units, used to estimate the limnological variables in the
Bodocongó dam, Paraíba, Brazil
Variables
Water transparency
Water temperature
Electric conductivity
Dissolved oxygen
pH
Alkalinity
Ammonia
Nitrite
Nitrate
Orthophosphate
Total phosphorus
Material and/or Method
30 cm Secchi disk
0,5º precision thermometer
Cole Palmer conductivimeter
Winkler method
Hanna HI 9224 pHmeter
Golterman et al. (1978)
Mackereth et al. (1978)
Mackereth et al. (1978)
Rodier (1975)
Mackereth et al. (1978)
Apha (1995)
Unit
m
ºC
µ.S.cm-1
mg.L-1
mg.L-1
µg.L-1
µg.L-1
µg.L-1
µg.L-1
µg.L-1
74
3 RESULTS
The lowest and highest values of water
transparency were 0.54 m (5am) and 0.65 m
(1pm), respectively with a CV of 6.35 %.
No significant vertical variation was
observed for the water temperature (p = 0.89;
d.f = 6; α = 0.05). The greatest amplitude
between the first depth (Subsurface) and the last
(Bottom) was of 1,4 ºC at 5pm, but traces of
stratification were observed in the middle of the
water column during the shift from the morning
to the beginning of the afternoon (9am to 1pm)
(Fig. 1). Although no significant nictemeral
variation of the water temperature values was
observed (p = 1,62; d.f = 6; α = 0.05), the lowest
values were observed at night and dawn (22 to
24º C) and the highest values were observed in
the morning and in the beginning of the
afternoon (27 to 34º C) (CV = 12.2 %) as shown
in Fig. 1.
The electric conductivity values varied
from 904 (5am; 1% Io) to 2810 (1pm; Subsurface)
µ.S.cm-1 (CV = 45.41%) and the pH from 6.81
(5am; 50% Io) to 7.68 (1pm; Subsurface) (CV =
4.18%). There was also no significant vertical
variation for the electric conductivity (p = 0.99;
d.f = 3; α = 0.05) and the pH values (p = 0.83;
d.f = 3; α = 0.05) and these two variables
showed similar patterns of distribution (Fig. 2).
This was confirmed since these two variables
were also positively significantly correlated (r =
0.88; α = 0,05). Although no significant nictemeral
variation was observed for electric conductivity (p
= 1.06; d.f = 6; α = 0.05) or pH (p = 4.24; d.f = 6; α
= 0.05), the higher values were observed during the
first three hours sampled (1pm, 5pm and 9pm) and the
lowest values were observed in the subsequent
hours (1am, 5am, 9am and 1pm) for these two variables
(Fig. 2).
High values of dissolved oxygen were
observed in both vertical and nictemeral scales. The
concentrations oscillated from 3.8 (1pm; Bottom) to
12.95 mg.L –1 (1pm; 50% Io) (CV = 18.53 %). These
corresponded to a saturation percentage that varied
from 45.2 to 154.1 %. However, no significant
vertical (p = 0.13; d.f = 3; α = 0.05) or nictemeral
(p = 0.23; d.f = 6; α = 0.05) variations were found
for this variable. Thus, with the exception of the
first time sampled (1pm), which showed traces of
vertical stratification, the distribution of the
dissolved oxygen was relatively homogenous (Fig.
3). There was a significant negative correlation
between dissolved oxygen and ammonia (r = - 0.50;
α = 0.05).
The alkalinity concentrations varied from 67
(1pm; Subsurface) to 95 mg.L –1 (5am; 1% Io) (CV =
7.74 %) and although there was no significant
vertical variation (p = 0.82; d.f = 3; α = 0.05), ,
there was a significant nictemeral variation (p =
0.01; d.f = 6; α = 0.05). Thus, a small trend towards
an increase in the concentration of alkalinity in the
last hours of the study was observed (Fig. 4).
Negative significant correlations between alkalinity
Figure 1. Values of water temperature (ºC) from 7 depths (m) sampled in a daily cycle in the Bodocongó dam,
Northeast of Brazil.
75
Figure 2. Values of electric conductivity (µ.S.cm-1) and pH from 4 depths (m) sampled in a daily cycle in the
Bodocongó dam, Northeast of Brazil.
Figure 3. Values of dissolved oxygen (mgO2.L –1) from 4 depths (m) sampled in a daily cycle in the Bodocongó dam,
Northeast of Brazil.
and electric conductivity (r = - 0.61; α = 0.05)
and between alkalinity and pH (r = -0.52; α =
0.05) were detected.
Values of ammonia, nitrite, nitrate,
orthophosphate and total phosphorus are shown
in Fig. 5. No significant vertical or nictemeral
variations were observed. Overall, the nutrient’s
concentrations were relatively homogenous,
showing no remarkable pattern of distribution (Fig.
5).
4 - DISCUSSION
No significant vertical or nictemeral
variation was found in the dam for the variables
sampled (alkalinity was the only exception). This
76
Figure 4 Mean (■) plus one standard deviation (─) of alkalinity (mg.L –1) from 7 hours and 4 depths sampled in the
Bodocongó dam, Northeast of Brazil.
can be related, at least partially, to the shallow
depth of the dam, which increases the capacity
of the wind in mixing the water and
consequently makes it more homogenous.
The water transparency values were very
homogenous with the lower and higher values
found in the beginning of the morning (less sun
radiation) and the beginning of the afternoon
(more sun radiation), respectively. Values of
water temperature were considerably high and
although no significant variation was found, a
trend for a day/night shift was observed. This
was expected since the waters of the dam
absorbed heat from the radiation of the sun
during the day and diffused heat to the
atmosphere during the night. Since the values of
alkalinity significantly increased during the
period of study, it would be expected that the
higher values of pH would also be found in
these corresponding times. However, the
opposite happened. Since there was a
resemblance in the distribution of the electric
conductivity and the pH values, the higher
levels of dissolved ions in the water during the
first half of the study and the lower levels
during the other half, may have caused a
corresponding increase and decrease in the
levels of the pH, respectively. The resemblance
in the distribution of the values of these two
variables was also confirmed by Pearsons’
coefficient of correlation, as seen above.
Alternatively, the increasing values of
alkalinity show the capacity of the carbonates,
bicarbonates and hydroxides in neutralizing the
increasing acids in the water during the same
period (Cole, 1983; Wetzel, 1993). Thus, the
significant negative correlation obtained between
alkalinity and pH and between alkalinity and
electric conductivity in this study can be related to
the neutralizing capacity of this variable. The
dissolved oxygen values were considerably high in
the dam indicating high levels of primary
productivity.
Although the distribution was significantly
homogenous, traces of stratification observed in the
beginning of the study showed that there is a trend
towards lower levels of oxygen in the bottom. This
can be related to the lower primary productivity and
to the higher rates of nutrients metabolism in the
sediment in these depths. The significant negative
correlation between ammonia and dissolved oxygen
observed in this study showed that there is a
significant use of oxygen in nitrogen’s metabolism.
The nutrients values were considerably high
(specially total phosphorous) and showed no
significant variation along the depths and times
sampled. Distribution of nitrate in tropical lakes can
be directly related to the concentration of oxygen in
the environment (Barbosa, 1981) as it was observed
in this study from the negative correlation obtained
between ammonia and dissolved oxygen. It can also
be related to bacteria activity (nitrification) (Lopes,
1999). Along with oxygen concentration, water
temperature is another important variable that
influences the nitrogen cycle (Schäfer, 1985). These
relationships show how dynamic and interrelated
these variables are, especially when considering
tropical environments in short periods.
Although it is out of the scope of this study
to assess the trophic condition of the dam, the high
values of nutrients obtained shows the level of
degradation of this environment. Ceballos (1995)
77
Figure 5. Mean (■) plus one standard deviation (─) of ammonia (µg.L –1), nitrite (µg.L –1), nitrate (µg.L –1),
orthophosphate (µg.L –1) and total phosphorus (µg.L –1) from 7 hours and 4 depths sampled in the Bodocongó dam,
Northeast of Brazil.
studying the Bodocongó dam also found high
values of nutrients, although they were
considerably lower than the ones observed in the
present study.
78
The results of the present study clearly
showed that the Bodocongó is a considerably
homogenous environment with no significant
vertical or nictemeral variation. However, the
water temperature values showed a remarkable
day/night shift, which confirms the hypothesis
of a broad nictemeral variation of this variable
in tropical environments (Ganf & Horn, 1975).
Electric conductivity, pH and alkalinity showed
important relationships. The high amounts of
dissolved ions observed, can be a consequence
of the elevated metabolism of the nutrients
(Sawyer et al., 1994), the domestic sewage
(Blundi, 1998) or it can be related to the
elevated evaporation rates and salty soils, which
are common in the northeastern region of Brazil
(Barbosa, 2002). An important relationship was
also observed between dissolved oxygen and
ammonia and the high amounts of oxygen in all
depths may indicate high primary productivity
rates and little vertical variation of the
photosynthetic organisms in the water column.
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_________________________________________
[1] Biólogo. Mestrando em Zoologia pela
Universidade Federal da Paraíba, João Pessoa, PB.
[email protected]
[2] Doutor, professor da Universidade Estadual da
Paraíba, Campina Grande, PB.
[3] Bióloga pela Universidade Estadual da Paraíba,
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