vers?o impressa ISSN vers?o On-line ISSN
Braz. J. Biol. v.65 n.4 S?o Carlos nov. 2005
http://dx.doi.org/10.-00017
Limnological and ecotoxicological
studies in the cascade of reservoirs in the Tiet& river (S&o Paulo,
Estudos limnol&gicos e ecotoxicol&gicos
na cascata de reservat&rios do rio Tiet& (S&o Paulo, Brasil)
Rodgher, S.I; Esp&ndola,
E. L. G.I; Rocha, O.II; Frac&cio, R.III;
Pereira, R. H. G.I; Rodrigues, M. H. S.I
ICenter of Water Resources and Applied
Ecology, S&o Carlos School of Engineering, University of S&o Paulo,
USP, Av. Trabalhador S&o Carlense, 400, C.P. 292, CEP , S&o
Carlos, SP, Brazil
IIDept. of Ecology and Evolutionary Biology, Federal University of
S&o Carlos, Rodovia Washington Luiz, km 235, C.P. 676, CEP ,
S&o Carlos, SP, Brazil
IIIDept. of Hydrobiology, Federal University of S&o Carlos,
Rodovia Washington Luiz, km 235, C.P. 676, CEP , S&o Carlos,
SP, Brazil
An evaluation was made of the quality of samples
of water and sediment collected from a series of reservoirs in the Tiet&
River (SP), based on limnological and ecotoxicological analyses. The samples
were collected during two periods (Feb and Jul 2000) from 15 sampling stations.
Acute toxicity bioassays were performed using the test organism Daphnia similis,
while chronic bioassays were carried out withCeriodaphnia dubia and Danio
rerio larvae. The water samples were analyzed for total nutrients, total
suspended matter and total cadmium, chromium, copper and zinc concentrations,
while the sediment samples were examined for organic matter, granulometry and
potentially bioavailable metals (cadmium, chromium, copper and zinc). The results
obtained for the limnological variable, revealed differences in the water quality,
with high contribution of nutrients and metals for Tiet& and Piracicaba
rivers, besides the incorporation and sedimentation, consequently causing a
reduction of materials in Barra Bonita reservoir, thus promoting the improvement
of the water quality in the other reservoirs. The toxicity bioassays revealed
acute toxicity for Daphnia similis only in the reservoirs located below
Barra Bonita dam. On the other hand, chronic toxicity for Ceriodaphnia dubia
and acute for Danio rerio showed a different pattern, decreasing
in magnitude from Barra Bonita to Tr&s Irm&os, demonstrating an
environmental degradation gradient in the reservoirs.
Keywords: reservoirs ecology, limnology,
ecotoxicology, Tiet& River.
O presente trabalho visou avaliar a qualidade
de amostras de &gua e sedimento dos reservat&rios em cascata do
rio Tiet& (SP) atrav&s de an&lises limnol&gicas e
ecotoxicol&gicas. Foram realizadas coletas de &gua e sedimento
em dois per&odos (fevereiro e julho de 2000) e em 15 esta&&es
de amostragem. Foram realizados bioensaios de toxicidade aguda para Daphnia
similis, de toxicidade cr&nica para Ceriodaphnia dubia e para
larvas p&s-eclodidas de Danio rerio. An&lises de nutrientes
totais, material em suspens&o total e c&dmio, cromo, cobre e zinco
foram realizadas para as amostras de &gua e an&lises de mat&ria
org&nica, granulometria e metais biodispon&veis (c&dmio,
cromo, cobre e zinco) para o sedimento. Os resultados obtidos para as vari&veis
limnol&gicas, revelaram diferen&as na qualidade da &gua,
com elevado aporte de nutrientes e metais pelos rios Tiet& e Piracicaba,
al&m da incorpora&&o, da sedimenta&&o e da
redu&&o de materiais no reservat&rio de Barra Bonita, promovendo
a melhoria da qualidade da &gua nos demais reservat&rios. Os bioensaios
revelaram toxicidade aguda para Daphnia similis somente nos reservat&rios
localizados & jusante da barragem de Barra Bonita, por&m os bioensaios
de toxicidade cr&nica com Ceriodaphnia dubia e com Danio rerio
revelaram toxicidade decrescendo em magnitude de Barra Bonita & Tr&s
Irm&os, evidenciando um gradiente de degrada&&o ambiental
nos reservat&rios.
Palavras-chave: ecologia de reservat&rios,
limnologia, ecotoxicologia, Rio Tiet&.
INTRODUCTION
The construction of reservoirs for a variety
of purposes represents one of the greatest human experiences in the modification
of the natural ecosystems. Making use of rivers by building a series of reservoirs
is a common practice in large Brazilian rivers. In the state of S&o Paulo
(southeastern Brazil) this system is commonly adopted for maximum exploitation
of hydroelectric energy potential. Numerous consecutive dams create a group
of reservoirs that receive and accumulate organic and inorganic matter from
adjacent systems. Exemplifying this kind of system, along its length, the Tiet&
River comprises the reservoirs of Barra Bonita, &Alvaro de Souza Lima
(Bariri), Ibitinga, M&rio Lopes Le&o (Promiss&o), Nova
Avanhandava and Tr&s Irm&os.
These six reservoirs were built between the 1960's
and 90's. The first of the series was concluded in 1964 (Barra Bonita reservoir)
and the last one in 1991 (Tr&s Irm&os reservoir). They were built
in response to the growing demand for electric energy in southeastern Brazil,
as well as for urban, industrial and agricultural use, including recreation
and navigation. According to the National Environmental Council (CONAMA – Resolution
20/1986), which establishes Brazil's water quality standards based on predominant
usage, the water in the middle and lower Tiet& reservoirs was classified
under Category 2 (water suitable for domestic consumption, recreation, irrigation,
and protection of aquatic communities).
An important point for consideration in the evaluation
of this system is the reservoirs' cascade-like arrangement, since any modification
in the reservoirs upstream affects the ones downstream. Studies developed by
Armengol (1977), Margalef (1983), and Stra?kraba (1994) demonstrated that
this physical arrangement should result in increasingly improved water quality,
since part of the nutrients and pollutants may be retained in the uppermost
portion of the system. Matsumura-Tundisi et al., (1981) observed
decreasing eutrophication in the Tiet& River's reservoirs from Barra Bonita
to Nova Avanhandava. However, this pattern was not observed by Barbosa et
al. (1999) in the Tiet& system. The latter authors demonstrated that
approximately 20 years after the Matsumura-Tundisi et al. (1981)
study, the reservoirs downstream of Barra Bonita had a higher trophic level
than that reported in the earlier study.
Increased agricultural and industrial activity
allied with intensive use and occasional spillage of agrotoxic and toxic substances
in general in the vicinity of aquatic ecosystems have caused river, dam and
pond contamination worldwide. In response, several water quality programs have
been implemented, involving methods of chemical, physical, and biological analysis.
While such analyses reveal the contents of chemical substances in absolute quantities,
they cannot identify fractions responsible for toxic effects in organisms. To
expand these studies, ecotoxicological evaluations have been made in recent
decades to investigate the effects of pollutants on the aquatic biota (Rand
et al., 1995).
The present work was designed to evaluate the
water and sediment quality of the Tiet& River's series of dams through
limnological analyses and toxicity bioassays with microcrustaceans and fish
larvae as test organisms, in order to better evaluate the impacts currently
affecting this system.
MATERIAL AND METHODS
Our study involved an evaluation of 15 sampling
stations (see ): station 1 (Tiet& River) and
station 2 (Piracicaba River); stations 3 and 4 upstream and downstream,
respectively, from the Barra B stations 6 and 7 (Bariri); stations 9
and 10 (Ibitinga); stations 10 and 11 (Promiss&o); stations 12 and 13
(Nova Avanhandava); and stations 14 and 15 (Tr&s Irm&os). Samples
were also taken from the Bauru River (station 5), a highly impacted tributary
and, consequently, a significant source of pollutants for the water of Bariri
Reservoir.
Sampling was carried out in two different periods:
February and July of 2000, representing, respectively, the rainy (February)
and dry (July) seasons. Water transparency was measured using a Secchi disk.
A single vertically integrated sample of water was collected with a suction
pump from each sampling station. Temperature, pH, conductivity and dissolved
oxygen were measured at 0.5 m depth intervals using a Horiba U-10 field
meter. Water samples were transferred to previously washed and dried plastic
bottles and stored at 4 °C until the moment they were analyzed. Total organic
nitrogen (Golterman et al., 1978), total phosphorus (Standard Methods,
1995), total cadmium, chromium, copper and zinc (Standard Methods, 1995),
as well as total suspended matter (Teixeira et al., 1978) were analyzed.
Sediment samples were collected with an Eckman
dredge and immediately stored in plastic containers inside styrofoam boxes containing
ice until their analysis in the laboratory. Analyses were made of the organic
matter (Fonseca, 1997), granulometry (ABNT, 1968), and concentration of potentially
bioavailable metals (Cd, Cr, Cu and Zn) (Tessier & Campbell, 1987).
For the bioassays, the sediment samples were
kept refrigerated at 4 °C prior to the experiments. The toxicity bioassays were
conducted with the test organisms Daphnia similis and Ceriodaphnia
dubia (Crustacea, Cladocera) neonates and with Danio rerio (Cypriniforme,
Cyprinidae) larvae. The test organisms used in the toxicity bioassays were kept
according to the recommendations of CETESB (1991a).
The acute toxicity bioassays were conducted with
water samples collected at different sampling stations. Newborn Daphnia similis
were exposed to undiluted water and the immobile organisms counted after
48 h. Acute toxicity bioassays were considered valid when the immobile individuals
among the organisms in the control treatment did not exceed 10% (CETESB, 1991a).
For the chronic toxicity bioassays of water samples, newborn Ceriodaphnia
dubia, 1 per test tube, were exposed to 15 mL of undiluted water in 10 test
tubes for each sampling station. The bioassay lasted from seven to ten days,
the period required for the third brood to hatch, and the number of newborns
produced throughout the experiment was recorded (CETESB, 1991b).
The acute toxicity bioassays were conducted with
Daphnia similis in sediment samples. Chronic toxicity bioassays were
done with Ceriodaphnia dubia and Danio rerio larvae (24 h after
hatching), following the protocol of Burton & Macpherson (1995), which
calls for a 1:4 ratio of sediment and water. The duration and the parameter
evaluated in the acute and chronic toxicity bioassays with zooplankton were
similar to those described for the water samples. The fish larvae bioassays
lasted seven days, during which the organisms fed on nothing but their own vitelluses.
The following criteria were adopted to evaluate
the results of the acute toxicity bioassays with Daphnia similis: a)
nontoxic sample: immobility in the test organisms ranging from 0 to 10% b) toxicity trace: immobility ranging from 10 to 40% in test organisms,
and c) toxic: immobility equal to or above 40% of the organisms (Barbosa, 2000).
The results of the chronic toxicity bioassays for Ceriodapnhia dubia
were analyzed for normality. Tukey's test (parametric) was applied for normal
distributions, while the Kruskall-Wallis test (nonparametric) was applied to
verify the occurrence of each sample's significant differences in relation to
the control.
As for the organism Danio rerio, the toxicity
evaluation of the environmental samples was based on the mortality percentage
proposed by Prater & Anderson (1977), which considers that mortality percentages
of 1 to 25% indicate low en 26 to 50%: medium toxicity,
and 51 to 100%: high toxicity.
Pearson correlation analyses were applied to
detect correlations between metal concentrations in the water and sediment,
and between the results of acute and chronic toxicity bioassays.
lists the results
of physicochemical variables monitored in the reservoirs' water samples. The
water temperature revealed two very defined stations during the study period.
The temperatures during the rainy period (Feb 2000) were higher, i.e., a minimum
of 24.48 °C in the Piracicaba River and a maximum of 28.03 °C in Tr&s
Irm&os upstream. During the dry period (Jul 2000), the lowest temperature
was 19 °C in the Piracicaba River and the highest temperature recorded was 22.78
°C in Tr&s Irm&os upstream.
With regard to pH, the lowest values were found
in Feb 2000, varying from 5.65 to 6.70, respectively, in Ibitinga and Promiss&o,
both downstream, while the lowest pH in July 2000 was 6.07 (Ibitinga downstream)
and the highest was 7.13 (Promiss&o downstream). The pH values below
or close to the lower limit established by CONAMA 20/1986 were found in the
rainy season in the Tiet&, Piracicaba and Bauru rivers and in Bariri and
Promiss&o reservoirs. Water conductivity showed the highest values in
July 2000, with a minimum of 51 uS/cm (Tr&s Irm&os downstream)
and a maximum of 411 uS/cm (Tiet& River). The lowest values were recorded
in the rainy period, with a minimum of 58 uS/cm in Tr&s Irm&os
downstream and a maximum of 178 uS/cm in Ibitinga upstream.
The dissolved oxygen concentrations were higher
in Feb 2000 at most of the sampling stations, with a minimum concentration of
7.17 mg/L (Tr&s Irm&os downstream) and a maximum of 8.33 mg/L
(Bariri downstream). In July 2000, the lowest concentration was 1.25 mg/L (Piracicaba
River) and the highest was 9.98 mg/L in Bariri upstream. In July 2000, low dissolved
oxygen concentrations were also found in the Tiet& (3.31 mg/L) and
Bauru (2.63 mg/L) river water and in Barra Bonita reservoir upstream (5.85 mg/L).
These values fell below those established by CONAMA Resolution 20/1986 for category
2 (5-9 mg/L) rivers.
As for the Secchi disk results, the best visibility
at most of the sampling stations was found in the dry period, with a minimum
of 0.35 m in the Piracicaba River and a maximum of 9.3 m in the Tr&s
Irm&os reservoir. The lowest values were recorded in the rainy season
(0.1 m to 3.5 m) in the Piracicaba River and upstream and the downstream, respectively,
from Nova Avanhandava dam. The values of total suspended matter were inversely
related to the visibility obtained by Secchi disk: higher concentrations of
total suspended matter in the rainy season caused lower visibility values obtained
by Secchi disk ().
As for total organic nitrogen, the Tiet&
River water consistently showed the highest concentrations, and the highest
values were generally found in July 2000, varying from 0.093 mg/L to 5.32 mg/L
(Nova Avanhandava upstream and in Tiet& River, respectively). The lowest
concentrations were found in Feb 2000 (from 0.05 mg/L to 1.77 mg/L, in
Nova Avanhandava and Tr&s Irm&os reservoirs and in the Tiet&
River, respectively) ().
indicates, the
highest total phosphorus concentrations were recorded in the wet season (Feb
2000), with values varying from 0.02 mg/L to 0.23 mg/L (Tr&s Irm&os
upstream and Barra Bonita downstream, respectively). The concentrations in most
of the sampling stations were lowest in July 2000 (from 0.01 mg/L to 0.75 mg/L,
Promiss&o downstream to Piracicaba River, respectively). In Feb 2000,
all the values exceeded the limit established by CONAMA Resolution 20/ mg/L)
except for Tr&s Irm&os upstream, while in July 2000, total phosphorus
exceeding the limit included the sampling stations of the Tiet& River
downstream to the Ibitinga reservoir.
As for the total metal concentrations in the
water (), cadmium exceeded the limit established
by CONAMA Resolution 20/1986 for Category 2 rivers. Higher values were recorded
in July (0.004 mg/L to 0.013 mg/L, for Ibitinga and Promiss&o reservoirs
and the Piracicaba River, respectively) and the lowest concentrations (0.002 mg/L
to 0.009 mg/L) were found in the Tiet& River and Barra Bonita reservoir,
respectively) in Feb 2000. Chromium exceeded the limit established by CONAMA
in Feb 2000 in the Piracicaba River (0.056 mg/L), while copper concentrations
were lower than the legal limit. The lowest zinc concentration was 0.035 mg/L
in the Tiet& River and the highest – 1.215 mg/L – was found in Feb 2000
in the Piracicaba River (exceeding CONAMA's limit for Class 2 rivers, i.e.,
above 0.18 mg/L).
The lowest concentrations of organic matter in
sediment were found in Feb 2000, varying from 0.1% (in Nova Avanhandava reservoir
downstream) to 15.34% (in the Bauru River). In July 2000, these concentrations
varied from 0.5% (upstream and downstream from the Tr&s Irm&os
Dam) to 16.73% (in Promiss&o reservoir upstream). As for granulometry,
there was a prevalence of clay and silt in the Tiet& and Piracicaba Rivers
and in the Barra Bonita to Promiss&o reservoirs, while sand was prevalent
in the Nova Avanhandava and Tr&s Irm&os reservoirs ().
Our findings for potentially bioavailable metals
in the sediment are listed in . In July 2000,
the highest values were found for cadmium (1.67 mg/Kg to 5.00 mg/Kg (in the
Tiet& and Bauru rivers, respectively), copper (3.33 mg/Kg to 97.57 mg/Kg,
in Nova Avanhandava and Bariri reservoirs, respectively), and zinc (1.60 mg/Kg
to 224.93 mg/Kg, in Tr&s Irm&os reservoir and the Tiet& River,
respectively). In Feb 2000, the highest chromium concentrations detected varied
from 3.60 mg/Kg (Barra Bonita reservoir) to 11.40 mg/Kg (Piracicaba River).
In Feb 2000, Daphnia similis showed acute
toxicity when exposed to a water sample from downstream Bariri and upstream
Nova Avanhandava, as was the case in July 2000 with the water samples from upstream
Promiss&o to downstream Nova Avanhandava. A statistical analysis of reproduction
data from the chronic toxicity bioassays with Ceriodaphnia dubia revealed
chronic effects on the test organisms exposed to water samples from the Tiet&
(Feb and Jul 2000), Piracicaba River (Feb 2000), upstream Barra Bonita
reservoir (Feb and Jul 2000), downstream Barra Bonita (Feb 2000), Bauru River
(Feb 2000), upstream Bariri (Feb and Jul 2000), downstream Bariri (Feb 2000),
upstream Ibitinga (Feb 2000) and upstream Promiss&o (Feb and Jul 2000)
The toxicity bioassays on sediment samples showed
acute toxicity for D. similis in sediment from downstream Ibitinga and
upstream Promiss&o reservoirs in Feb 2000, and chronic toxicity for C.
dubia exposed to sediment from the Tiet& river (Feb and Jul 2000)
and the reservoirs from Barra Bonita to Ibitinga (Feb 2000). Danio rerio
displayed acute toxicity in sediments from the Tiet& and Piracicaba
rivers (Feb and Jul 2000) and the Bauru (Jul 2000), and from Barra Bonita reservoir
upstream and downstream (Feb and Jul 2000), Bariri upstream (Feb and Jul 2000)
and Ibitinga downstream (Jul 2000) ().
An analysis of the correlation between metal
concentrations and bioassayed toxicity revealed that cadmium, copper and zinc
concentrations in the sediment correlated positively (r & 0.5 and p & 0.05)
with the data from chronic toxicity bioassays on sediment samples. However,
no correlation was found between metal concentrations and acute and chronic
toxicity in water samples (r & 0.5 and p
DISCUSSION
Reservoirs built in cascade arrangements to generate
electricity are usually operated as simple units, but from the standpoint of
physical, chemical and biological characteristics, each reservoir can behave
as a separate unit with unique characteristics, e.g., residence time, tributaries
and usage of its hydrographic basin. However, understanding the limnology of
a specific reservoir is not easy, particularly if it is one of a series, without
first understanding the processes that take place in the chain of reservoirs
located upstream from it (Stra?kraba, 1994).
According to Tundisi (1999), the main components
and forces that govern the conditions in a reservoir operation, whose measuring
is essential, include the area's climatic characteristics, the time of residence
of the water, and the position of the reservoir (since a reservoir causes and
receives effects from other reservoirs up and downstream from it).
In the reservoirs of the middle and lower Tiet&
river, for example, the contribution of suspended matter coming from the Tiet&
and Piracicaba rivers (precise sources) and from the reservoirs' banks (diffuse
sources) in the wet season (Feb 2000) exceeds that of the dry season (Jul 2000).
This seasonalness of matter generated by rainfall produces a pulse of nutrients
and inorganic matter within the reservoirs, which is confirmed by the highest
concentrations of suspended matter in the wet season causing the lowest Secchi
disk visibility values in the reservoirs. The decreasing penetration of light
revealed by Secchi disk measurements was attributed to the greater dispersion
of suspended particulate matter (Wetzel, 1993).
With respect to spatial variations, a generally
increasing gradient of water transparency was found along the cascade of reservoirs
in the two sampled periods. This finding coincides with that of Tundisi et
al. (1991) and G&ntzel (2000) in the middle and low Tiet& reservoirs.
According to Stra?kraba (1994), in the upper reservoirs of the cascade system,
the presence of abundant suspended matter causes decreased light penetration
and, hence, lower visibility of the Secchi disk, which is not the case in the
lower reservoirs, thanks to the sedimentation of suspended matter in the system's
upper portion.
In terms of water temperature, the study period
showed two well-defined seasons, with higher temperatures in the wet season
(summer) and lower temperatures in the dry season (winter). The dissolved gas
concentration in water is one of the most important environmental variables
in the dynamics and characterization of aquatic ecosystems. This variable is
influenced by seasonal alterations in rainfall, temperature, water flow, and
retention time indices. The low dissolved oxygen concentrations found in the
Tiet&, Piracicaba and Bauru rivers and Barra Bonita reservoir in July
2000 indicated anoxia resulting from intensive decomposition of organic matter,
which reduces oxygen concentrations.
Persistent anoxia is a negative factor in water
quality because, under such conditions, the chemical compounds in sediment,
as well as toxic gases, e.g., methane and hydrosulfide, tend to be released
into the water (Esteves, 1988). In the Segredo reservoir, the second of a series
of four reservoirs in the middle Igua&u river (Paran& State),
Thomaz et al. (1997) found anoxia occurring throughout most of the year,
when the reservoir was thermally stratified. According to these authors, anoxic
conditions can favor the release of phosphorus from sediment, contributing to
the reservoir's eutrophication.
The values of pH were close to the limit established
by CONAMA Resolution 20/1986 for Category 2 rivers in Feb 2000 in the Tiet&,
Piracicaba and Bauru rivers and in the Bariri and Promiss&o reservoirs.
Aquatic ecosystems with low pH show high concentrations of organic acids. The
lowest pH values were recorded in the wet season, demonstrating the seasonal
influence on the system's pH, since rainwater is usually acid (pH 5-6) and can
also affect the pH of aquatic ecosystems (Esteves, 1988).
Conductivity was higher in the dry season, with
the lowest values recorded in the wet season. Seasonal variations in this variable
were attributed to diluted ion concentrations resulting from higher rainfall
in the wet season, resulting in the lowest conductivity values, a phenomenon
not found in the dry season. G&ntzel (2000) found high conductivity values
in the 1998 rainy season in the same reservoirs, ascribing this finding to greater
input of nutrients and sediment, resulting in higher dissolved ion concentrations
in the water. A generally high concentration of ions was found in the Tiet&
River and in the first two reservoirs of the cascade (Barra Bonita and Bariri),
and high deposition and consumption along the series of reservoirs in Jul 2000,
although some intermediary reservoirs showed higher values than those found
in February in the Tiet& River.
Thomaz et al. (1997) found low electric
conductivity values in July and August and high values in January in the Segredo
reservoir (Paran& River), which ranged from 20 uS/cm to 50 uS/cm. In
the cascading reservoirs of the S&o Francisco River, Severi et al.
(2000) found conductivity values varying from 62 uS/cm to 74 uS/cm.
Nutrient concentrations were also related to
conductivity. The total organic nitrogen concentrations were generally higher
in the dry season, which may be attributed to greater water retention in the
reservoirs and, hence, to higher nitrogen compound concentrations. The lowest
values were found in the wet season, evidencing the diluting effect of rainwater
flowing into the system. During the period of this study, high total organic
nitrogen concentrations were detected in the reservoirs of the middle and lower
Tiet&, in the Tiet&, Piracicaba and Bauru rivers, and in the cascade
system's upper reservoirs. In the wet season of 1999, Barbosa et al. (1999)
also found lower nitrogen concentrations in the Tiet& River than in the
Barra Bonita Reservoir.
As for total phosphorus, the wet season showed
higher concentrations than the dry season. The highest concentrations were found
in the Tiet& and Piracicaba rivers and in the reservoirs from Barra Bonita
down to Promiss&o. Thus, a comparison of the legal limits and the values
found in this study indicates that most of the latter exceeded the limit, mainly
in the upper and middle portion of the cascade system, indicating the reservoirs'
eutrophication.
As for the absence of a decrease in total phosphorus
concentrations found throughout the cascade system studied here, Sandes (1990)
also found higher phosphorus concentrations in the Bariri reservoir than in
Barra Bonita reservoir. The presence of easily identifiable sources (domestic
and industrial waste) and diffuse sources (agricultural activities) of discharge
into the drainage basin, as well as favorable conditions for sediment resuspension,
likely contributed to this finding. Barbosa et al. (1999) noted high
total phosphorus concentrations in the Tiet& River (0.28 mg/L), and
a decrease in this nutrient in the first reservoir of the series (0.06 mg/L),
followed by an increase in the second reservoir (0.09 mg/L) and a decrease throughout
the other reservoirs.
In the cascade reservoirs of the lower San Francisco
River, Rocha et al. (2000) found retention of nutrients in the lateral
however, the central body did not show such retention due
to the low retention time and to suspended matter. According to these authors,
the system as a whole acts to conserve the physical, biological and chemical
characteristics, and visible alterations in the water were not seen from the
beginning to the end of the cascade. However, that was not the case in the middle
and lower Tiet& reservoirs.
Metals are extremely important elements in aquatic
ecosystems because, albeit essential in small concentrations, many are toxic
at high levels, and can bioaccumulate and biomagnify in food webs, ultimately
presenting risks to predators at the top of the food chain, including humans.
In the present study, total metals concentrations in water were close to or
exceeded the limits established by CONAMA Resolution 20/1986 for Category 2
rivers. Our findings indicated metal contamination in both water and sediment
caused by domestic sewage and industrial and agricultural effluents flowing
into these aquatic ecosystems.
Metals are also significant pollutants of aquatic
sediments. The highest potentially bioavailable metal concentrations were found
in the Tiet&, Piracicaba and Bauru rivers, demonstrating anthropic influence
and foreshadowing its consequences on the environmental quality of the Tiet&
reservoirs. These values showed a rising tendency over time, indicating that
these reservoirs are undergoing a process of deterioration (Esteves et al.,
1981). The Pearson correlation revealed a significant correlation between cadmium,
copper and zinc in the sediment and in the chronic toxicity bioassays.
As for potentially bioavailable metals in the
sediment, the cascade of reservoirs showed a decreasing gradient of zinc concentrations.
On the other hand, cadmium and chromium were found to increase from Barra Bonita
reservoir towards Nova Avanhandava and Tr&s Irm&os reservoirs,
likely because of diffuse sources of pollution in the lower reservoirs.
Another important factor is the bioavailability
of metals. The prevalence of clay and silt fractions over sand and the higher
percentages of organic matter in the cascade's upper reservoirs may lead to
a large number of connection loci to metals. Because of their large superficial
area to volume ratio, fine-textured sediments (containing high percentages of
clay and silt) have a greater capacity to retain chemicals than do thicker-textured
sediments containing fewer metals connection loci (Rand et al., 1995)
The toxicity bioassays indicated that a large
proportion of the water and sediment samples collected in Feb 2000 caused toxic
effects in the test organisms, possibly resulting from the input of abundant
matter from the surrounding areas into the reservoirs. Despite the high total
metal concentrations in the water and potentially bioavailable in the Tiet&
and Piracicaba river sediment and in that of the upper reservoirs of the Tiet&
cascade system, no acute effects on Daphnia similis were recorded for
those stations, while the chronic toxicity tests with Ceriodaphnia dubia
and Danio rerio indicated a decrease in toxicity along the cascade.
According to Cooney (1995), really significant differences have been found among
different groups of organisms, and many authors have recently suggested that
pollutants should be tested on algae, on one or more invertebrate groups, or
on fish in order to get the most complete picture of existing toxicity.
Using Ceriodaphnia silvestrii (a native
species) and Daphnia similis to evaluate the quality of water in the
Piracicaba River basin, Fonseca (1997) also found considerable differences
among the tested species when exposed to a water sample with high zinc content.
Fonseca (1997) found no effect on Daphnia similis, while Ceriodaphnia
silvestrii showed a chronic effect. In an evaluation of sediment quality
at a sampling station in the Piracicaba River basin, Melleti (1997) identified
a sign of toxicity in a fish species (Prochilodus scrofa), which was
not observed in Ceriodaphnia silvestrii and Daphnia similis when
exposed to the same sample by Fonseca (1997).
The results of our acute toxicity bioassays with
Daphnia similis refute the theory that the quality of the water improves
along the cascade of reservoirs, possibly because of the presence of pollutants.
According to Weltens et al. (2000), many pollutants are retained in suspended
solids present in water, which may decrease their toxicity. Metals in water
are commonly analyzed by atomic absorption spectrometry, which leads to findings
that sometimes contradict those of toxicity bioassays, which can express equivalent
toxicity in much lower concentrations of metal due to the complexity of those
elements (Conney, 1995). No significant correlation was found between the metals
in the water samples and the acute and chronic toxicity test data.
Another important class of ecosystem pollutants
is persistent organic pollutants (POPs), such as dioxins and organochloric pesticides,
which were not evaluated in this study. In their analysis of water samples from
38 reservoirs in 7 hydrographic basins in the state of S&o Paulo (Paranapanema,
Paran&, Iguape, Tiet&, Para&ba, Pardo and Grande rivers),
C&ceres et al. (1987) found BHC and DDT residues (organochloric
pesticides) in all of them.
According to Larsson et al. (2000), eutrophic
lakes contain a great phytoplanktonic biomass due to the excess of nutrients,
causing POP retention and greater sedimentation of these pollutants, unlike
oligotrophic lakes, where POP is more readily transferred to the food web. Thus,
in the Tiet& reservoirs, possible organic pollutants would not be totally
available in the waters of the Tiet& and Piracicaba rivers and in the
first reservoir of the cascade (Barra Bonita), which are considered eutrophic,
unlike the reservoirs downstream (mesotrophic and oligotrophic). The high values
of total suspended matter found in the Tiet& and Piracicaba river water
and in the upper reservoirs of the cascade may have prevented the availability
of certain metals and other pollutants from affecting Daphnia similis and,
hence, from causing a toxic effect in these organisms.
The study reported here found that water quality
in the middle and lower Tiet& watershed is degraded. Large amounts of
pollutants such as heavy metals, pesticides and barely degradable organic compounds
can affect water quality in reservoirs. Toxicity bioassays are important in
evaluating the degree of environmental toxicity. However, once toxicity is proven,
the Toxicity Identification and Evaluation (TIE) approach must be incorporated
into water resources monitoring because of its importance in identifying compounds
responsible for toxicity (Paschoal, 2002). The TIE method is a tool serving
to isolate and characterize the physicochemical nature of toxicants in complex
samples based on knowledge of how factors such as pH and hardness modify toxicity
(Rand et al., 1995).
Acknowledgments ? The authors would like
to thank the Higher Education Improvement Council (CAPES) for the scholarships
granted, the PROBIO MMA/CNPq Project and the technicians of the Center for Water
Resources and Applied Ecology (CRHEA), the S&o Carlos School of Engineering
(USP), and the Federal University of S&o Carlos Department of Ecology
and Evolutionary Biology (DEBE).
REFERENCES
ARMENGOL, J., 1977, Tipologia dos embalses espa&oles,
p. 3 6. In: Seminario sobre medio ambiental y embalses. Anais, Tomo
I, Montevideu.&&&&&&&&[  ]ASSOCIA&C&AO BRASILEIRA DE NORMAS
T&ECNICAS, 1968, MB 32 An&lise Granulom&trica de Solos M&todo
Brasileiro, 7 p.&&&&&&&&[  ]BARBOSA, F. A. R., PADIS&AK, J., ESP&INDOLA,
E. G. L., BORICS, G. & ROCHA, O., 1999, The Cascading Reservoir Continuum
Concept (CRCC) and its application to the River Tiet& – Basin, S&o
Paulo State, Brazil, pp. 425-437, In: J.G TUNDISI & M STRA?KRABA
(eds), Theoretical Reservoir Ecology and its Applications. Brazilian
Academy of Sciences and Backhuys Publishers, Rio de Janeiro. &&&&&&&&[  ]BARBOSA, R. M., 2000, Avalia&&o
do impacto de lodo de esta&&es de tratamento de &gua &
biota aqu&tica atrav&s de estudos ecotoxicol&gicos.
Tese de Doutorado, Escola de Engenharia de S&o Carlos, Universidade de
S&o Paulo, S&o Carlos, 200 p.&&&&&&&&[  ]BURTON, G. A. JR. & MACPHERSON, C., 1995,
Sediment toxicity testing issues and methods. In: D. J. HOFFMAN, G. A.
RATTNER., G. A. JR. BURTON, JR CAIRNS (eds), Handbook of Ecotoxicology,
Lewis Plublishers, Boca Raton Fl. New York.&&&&&&&&[  ]C&ACERES, O., TUNDISI, J. G., & CASTELLAN,
O. A. M, 1987, Residues of organochloric pesticides in reservoirs in S&o
Paulo States, Ci&ncia e Cultura, 39: 259-264.&&&&&&&&[  ]COMPANHIA DE TECNOLOGIA DE SANEAMENTO AMBIENTAL,
CETESB, 1991a, &Agua e teste de toxicidade aguda com Daphnia similis
Claus, 1876 (Cladocera, Crustacea). Norma T&cnica, L5.018,
S&o Paulo, 33 p.&&&&&&&&[  ]COMPANHIA DE TECNOLOGIA DE SANEAMENTO AMBIENTAL,
CETESB, 1991b, &Agua e teste de toxicidade cr&nica utilizando Ceriodaphnia
dubia Richard, 1894 (Cladocera, Crustacea). Norma T&cnica
L5.022, S&o Paulo, 30 p.&&&&&&&&[  ]CONSELHO NACIONAL DO MEIO AMBIENTE, 1986, Legisla&&o
ambiental brasileira. Resolu&&o do Conselho Nacional do Meio
Ambiente, CONAMA 20/1986. IBAMA, Bras&lia.&&&&&&&&[  ]COONEY, J. D., 1995, Freshwater test, pp. 71-98.
In: G. M. RAND (ed), Fundamentals of aquatic toxicology: effects,
environmental fate, and risk assessment. Taylor & Francis, Washington.
&&&&&&&&[  ]ESTEVES, F. A., FERREIRA, J. R., PESSENDA, L.
C. R. & MORTATTI, J., 1981, An&lises preliminares sobre o teor e
a distribui&&o de metais em sedimentos de represas do Estado de
S&o Paulo, pp. 323-342. In: II Semin&rio Regional de Ecologia.
S&o Carlos, Anais, UFSCar, S&o Carlos.&&&&&&&&[  ]ESTEVES, F. A., 1988, Fundamentos da Limnologia.
Interci&ncias FINEP, Rio de Janeiro. 602 p.&&&&&&&&[  ]FONSECA, A. L., 1997, Avalia&&o
da qualidade da &gua na Bacia do Rio Piracicaba atrav&s de testes
de toxicidade com invertebrados. Tese de Doutorado, Escola de Engenharia
de S&o Carlos, Universidade de S&o Paulo, S&o Carlos, 211
p.&&&&&&&&[  ]GOLTERMAN, H. L, CLYMO, R. S. & OHNSTAD,
R., 1978, Methods for physical and chemical analisys of freshwater, 2?
ed, Blackwell Science, IBP Handbook, London, 213 p.&&&&&&&&[  ]G&UNTZEL, A. M., 2000, Varia&&es
espa&o-temporais da comunidade zooplanct&nica nos reservat&rios
do m&dio e baixo rio Tiet&/Paran&. Tese de Doutorado,
Universidade Federal de S&o Carlos, S&o Carlos, 445 p.&&&&&&&&[  ]LARSSON, P., ANDERSSON, A., BROMAN, D., NORDB&ACK,
J. & LUNDBERG, E., 2000, Persistent organic pollutants (POPs) in pelagic
systems, Ambio, 29: 202-209.&&&&&&&&[  ]MARGALEF, R, 1983, Limnologia, Omega.
S.A, Barcelona, 1010 p.&&&&&&&&[  ]MATSUMURA –TUNDISI, T., HINO, K. & CLARO,
S., 1981, Limnological studies at 23 reservoir in southern part of Brazil. Verh.
Internat. Verein. Limn., 21: 47.&&&&&&&&[  ]MELETTI, P. C., 1997, Avalia&&o
da qualidade da &gua na bacia do rio Piracicaba atrav&s de testes
de toxicidade aguda com peixes. Disserta&&o de Mestrado, Escola
de Engenharia de S&o Carlos, Universidade de S&o Paulo, S&o
Carlos, 148 p.&&&&&&&&[  ]PASCHOAL, C. M. R. B., 2002, Avalia&&o
ecotoxicol&gica de sedimentos em reservat&rios da bacia do Rio
Tiet&, SP, com &nfase na aplica&&o e identifica&&o
da toxicidade. Tese de Doutorado, Escola de Engenharia de S&o Carlos,
Universidade de S&o Paulo, S&o Carlos, 146 p.&&&&&&&&[  ]PRATER, B. L. & ANDERSON, M. A., 1977, A
96 hours bioassay of Duluth and Superior Harbor Basins (Minnesota) using Hexagenia
limbata,Aselus communis, Daphnia magna, and Pimephales promelas as
test organisms. Bull. Environm. Contam. Toxicol, 18: 159-169.&&&&&&&&[  ]RAND, G. M, WELLS, P. G., & McCARTY, L. S.,
1995, Introduction to Aquatic Toxicology, pp. 3-66. In: G.M. RAND (ed),
Fundamentals of aquatic toxicology: effects, environmental fate, and risk
assessment, Taylor & Francis, Washington,&&&&&&&&[  ]ROCHA, O., ESP&INDOLA, E. L. G., REIS,
R. & SEVERI, W., 2000, Aspectos estruturais e funcionais das cascatas de
reservat&rios do baixo rio S&o Francisco, Brasil, pp 40. In:
Semin&rio Internacional. Represa do Lobo-30 anos de Pesquisa em Limnologia,
Gerenciamento e Participa&&o da Comunidade e Bases Cient&ficas
para o Gerenciamento da Eutrofiza&&o. Resumos. UFSCar-USP,
S&o Carlos.&&&&&&&&[  ]SANDES, M. A. L., 1990, Flutua&&es
e fatores ecol&gicos, composi&&o e biomassa do fitopl&ncton
em curto per&odo de tempo no reservat&rio de &Alvaro de
Souza Lima (Bariri, S.P). S&o Carlos. Disserta&&o de
Mestrado, Escola de Engenharia de S&o Carlos, Universidade de S&o
Paulo, S&o Carlos, 111 p.&&&&&&&&[  ]S&AO PAULO (ESTADO), 1982, Coordenadoria
da Ind&stria e do Com&rcio. Diretrizes para a Pol&tica
de Desenvolvimento e Desconcentra&&o Industrial. Governo do
Estado de S&o Paulo.133 p.&&&&&&&&[  ]SEVERI, W., REIS, R., ROCHA, O. & ESP&INDOLA,
E. L. G., 2000, Caracter&sticas limnol&gicas de reservat&rios
do subm&dio rio S&o Francisco. pp. 42, In: Semin&rio
Internacional. Represa do Lobo-30 anos de Pesquisa em Limnologia, Gerenciamento
e Participa&&o da Comunidade e Bases Cient&ficas para o
Gerenciamento da Eutrofiza&&o. Resumos. UFSCar-USP, S&o
Carlos. &&&&&&&&[  ]STANDARD METHODS FOR THE EXAMINATION OF WATER
AND WASTEWATER, 1995, For examination of water and wastwater. In: A. D. Easton
et al (eds), 19th ed. American Publish Health Association,
Washington, 1269 p. &&&&&&&&[  ]STRA?KRABA, M., 1994, Vltava cascade as teaching
grounds for reservoir limnology. Wat.Sci.Tech., 30: 289-297.&&&&&&&&[  ]TEIXEIRA, C., TUNDISI, J. G. & KUTTNER, M.
B., 1978, Plankton studies in a mangrove. II. The standing – stock and some
ecological factors. Bol. Inst. Oceanogr., 24: 23-41.&&&&&&&&[  ]TESSIER, A. & CAMPBELL, P. G. C., 1987. Partitioning
of trace metals in sediments: relationships with bioavailability. Ecological
effects of in situ sediment contaminants, Hidrobiol, 149: 43-51. &&&&&&&&[  ]THOMAZ, S. D., BINI, L. M & ALBERTINI, S.
M., 1997, Limnologia do reservat&rio de Segredo: padr&es de varia&&o
espacial e temporal, pp. 19-37. In: A. A. AGOSTINHO & L. C GOMES
(eds), Reservat&rio de Segredo: bases ecol&gicas para o manejo.
Eduem Maring&.&&&&&&&&[  ]TUNDISI, J. G., 1999, Reservat&rios como
sistemas complexos: teoria, aplica&&es e perspectivas para usos
m&ltiplos, pp. 19-38. In: R. HENRY (ed), Ecologia de Reservat&rios,
FUNDIBIO FAPESP, Botucatu.&&&&&&&&[  ]TUNDISI, J. G. MATSUMURA –TUNDISI, T. CALIJURI, M. C.
& NOVO, E. M. L., 1991, Comparative limnology of five reservoirs in the
middle Tiet& River, S&o Paulo State. Verh. Internat. Verein.
Limn., 24: .&&&&&&&&[  ]WELTENS, R., GOOSSENS, R. & VAN PUYMBROECK,
S., 2000, Ecotoxicity of contaminated suspended solids for filter feeders (Daphnia
magna). Arch.Environ.Contam.Toxicol., 39: 315-323.&&&&&&&&[  ]WETZEL, R. G., 1993, Limnologia. Funda&&o
Calouste Gulbenkian, Lisboa, 919 p.&&&&&&&&[  ]&
Correspondence to
Suzelei Rodgher
Center of Water Resources and Applied Ecology
S&o Carlos School of Engineering, University of S&o Paulo, USP
Av. Trabalhador S&o Carlense, 400, C.P. 292
CEP , S&o Carlos, SP, Brazil
Received January 8, 2004 – Accepted May 10, 2004
 – Distributed November 30, 2005
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