Limnological Characterization of Gravataí River, Rio Grande do Sul
State, Brazil.
SALOMONI 1 , S . E . ; R O C H A 2 , O . & L E I T E 3 , E . H .
1
Pos-graduate Program
PO
Box
676,
Via
in
Ecology
Washington
and
Luis
Natural Resources. Federal University of São Carlos.
km
235,
CEP:
13.565-905,
São
Carlos,
S P,
Brazil.
[email protected]
2
Department of Ecology and Evolutionary Biology. Federal University of São Carlos. PO Box 676,
V i a W a s h i n g t o n L u i s k m 2 3 5 , C E P : 1 3 . 5 6 5 - 9 0 5 , S ã o C a r l o s , S P, Brazil. [email protected]
3
S t a t e F o u n d a t i o n o f E n v i r o n m e n t a l P r o t e c t i o n ( F E PA M ) o f R i o G r a n d e d o S u l . C a r l o s C h a g a s 5 5 .
CEP: 90030-020, Porto Alegre, RS, Brazil.
[email protected]
ABSTRACT: Limnological Characterization of Gravataí River, Rio Grande do Sul State, Brazil. A
limnological study of Gravataí River, RS, Brazil (29° 45’ - 30° 12’S and 50° 27’- 51° 12’W) was
carried out in order to characterize the spatial and temporal changes of physical, chemical,
climatic and microbiological variables along its course attempting to explain its functioning
as a lotic system, in terms of current theories. A set of meteorological, hydrological,
physical, chemical and microbiological variables were monitored each month at six selected
locations along the Gravataí River, between September 2000 and August 2002. The variables
analyzed were: water temperature, pH, transparency, conductivity, OD, BOD-5, COD, total
nitrogen, organic nitrogen, orthophosphate, total phosphorus, chloride and faecal coliforms.
Air temperature, rainfall, and river discharge data were also recorded. The results showed
that there is a continuum from the headwater to the middle course of the river, characterized
by a gradual decrease in dissolved oxygen concentration and rising turbidity, nutrients,
conductivity, chlorides, and biochemical oxygen demand. A discontinuity in the gradient,
caused by the input of large amounts of organic matter was found, where many variables
increased or decreased abruptly with changes of one order of magnitude or more,
characterizing two distinct portions of Gravataí River: a better-preserved upper and middle
portion conforming with the river continuum model, and the polluted lower portion, a
discontinuity imposed by the heavy input of organic wastes. A comparison of the present
limnological conditions in Gravataí River with information available from earlier years reveals
that significant changes have occurred over the last decade, indicating an accelerated
process of eutrophication.
Key- words: Gravataí River, river ecology, river pollution, eutrophication.
RESUMO: Caracterização Limnológica do Rio Gravataí, Rio Grande do Sul, Brasil. Variações espaciais e temporais das características físicas, químicas e microbiológicas no rio Gravataí,
RS (29° 45’ a 30° 12’S e l50° 27’ a 51° 12’W), foram analisadas visando entender seu funcionamento, em decorrência das alterações ocorrentes em sua bacia. Variáveis climáticas,
hidrológicas e características físicas e químicas da água foram avaliadas mensalmente,
em seis estações de amostragem selecionadas ao longo do rio, da nascente à foz, no
período de setembro de 2000 a agosto de 2002. As variáveis avaliadas foram: temperatura
d a á g u a , p H , t r a n s p a r ê n c i a , c o n d u t i v i d a d e , O D , D B O 5, D Q O , n i t r o g ê n i o t o t a l , n i t r o g ê n i o
orgânico, ortofosfato, fósforo total, cloretos e coliformes fecais, temperatura do ar, precipitação e vazão. Os resultados evidenciaram que da nascente até o trecho médio do rio há
um contínuo, caracterizado pelas diminuições graduais nas concentrações de OD, e aumento da turbidez, da condutividade, dos cloretos e da DBO. Evidencia-se, no entanto
uma descontinuidade no gradiente, ocasionada por elevada entrada de material orgânico,
em que os valores das diversas variáveis aumentam ou decrescem bruscamente com
variações de uma ou mais ordens de magnitude. Foram caracterizadas duas porções
distintas do rio Gravataí. A primeira, formada pelo trecho superior-médio do rio, mais
preservada, e que segue o modelo do contínuo fluvial e a outra, no trecho inferior do rio
formada por uma descontinuidade imposta pela entrada de despejos orgânicos de origem
antropogênica. A comparação das características limnológicas atuais do rio Gravataí com
Acta Limnol. Bras., 19(1):1-14, 2007
1
as informações existentes de anos anteriores, revela a ocorrência de grandes mudanças
na última década que caracterizam um acelerado processo de eutrofização.
Palavras-chave: rio Gravataí, ecologia de rios, poluição de rios, eutrofização.
Introduction
Freshwaters
have
suffered
great
changes in its physical, chemical, and
biological characteristics all over the world,
as a result of antropic alterations in
hydrographic basins. Some of these
changes come from direct intervention, as
in the case of dams, reservoirs, and canals,
however the largest changes come from the
inadequate land use, increasing the
amounts of suspended matter in the water,
both dissolved and particulate. Non-point
sources as the agricultural runoff and point
sources from industrial and domestic
effluents considerably alter the water quality
in most populated and industrialized
regions.
Rivers
are
very
individualized
ecosystems,
each
with
its
own
characteristics, mainly influenced by
climatic, geomorphological and hydrological
factors occurring and interacting within the
hydrographic basin. Other factors vary
temporally and between heterogeneous
spaces differing from basin to basin, or from
region
to
region,
depending
on
anthropogenic interferences (Neves, 2002).
According to Neiff (1990), rivers behave
like systems in permanent non-equilibrium,
where spatial and temporal variation is a
complex function of the energy and material entering and leaving distinct locations of
the hydrographic basin, and also of
interactions
determining
population
abundances and distributions. After the
introduction of the River Continuum
Concept (RCC) by Vannote et al. (1980),
there was a renewed interest in the study
of rivers. Although interesting, the RCC does
not apply to most tropical rivers, as pointed
out by Junk et al. (1989), who found that
flood pulses are more important to the
functioning of low-land tropical rivers, as
the Amazon and Paraná-Paraguai basins.
In the present study the longitudinal
and seasonal changes of chemical, physical,
and microbiological variables, along the
course of the Gravataí River, were analyzed
aiming
to
provide
a
limnological
characterization of this important water
resource in the Guaíba hydrographic basin.
2
SALOMONI, S.E. et al.
Material and methods
The climatic data was provided by the
Instituto de Pesquisas Agronômicas do Rio
Grande do Sul (IPAGRO) (Rio Grande Do Sul
Agricultural Research Institute), having been
recorded at the nearest meteorological
station to field site 4 (29 o 57’ 16”S and 51 o
07’37” W), on the Gravataí River.
The
physical,
chemical,
and
microbiological data were obtained by the
Fundação Estadual do Meio Ambiente do
Estado do Rio Grande do Sul (FEPAM) (Rio
Grande do Sul State Foundation for the
Environment) and the Departamento Municipal de Água e Esgoto (DMAE) (Municipal
Water and Sewage Department), which have
been conducting monthly monitoring of the
water quality in this river, as past of the
Pró-Guaíba project. Data was collected, on
a single day each month, between
September 2000 and August 2002, at six
sampling sites along the Gravataí River,
marked in Fig. 1.
The water and air temperature, depth
of water at sampling site, pH, transparency,
dissolved oxygen (DO) and conductivity
were measured in situ and water was
collected and transferred immediately to
glass and polyethylene flasks, for turbidity ,
biochemical oxygen demand (measured
a f t e r 5 d a y s i n c u b a t i o n ( B O D5) ) ; c h e m i c a l
oxygen demand (COD), total nitrogen,
organic nitrogen, ammoniacal nitrogen,
orthophosphate, total phosphate, chloride
and faecal coliform counts. Samples were
kept in ice, transported to the laboratory
and analysed immediately on arrival. The
techniques used in both sampling and
analysis followed the procedures described
in APHA (1992).
Data Analysis
Mean values of each variable in each
season, between September 2000 and
August 2002, were subjected to cluster
analysis. The following environmental
variables were analysed: water and air
temperature, conductivity, turbidity, pH,
dissolved oxygen (DO), biochemical oxygen
d e m a n d m e a s u r e d a f t e r 5 d a y s ( B O D 5) ,
chemical
oxygen
demand
(COD),
ammoniacal nitrogen, organic nitrogen,
Limnological characterization of Gravataí River ...
orthophosphate, total phosphate, chloride,
and faecal coliforms.
Discriminant and Cluster Analysis
were carried out on the transformed data
with the program Pcord 4.0 using the
similarity matrix of Euclidean distances.
According to Digby & Kepton (1987), the
Euclidean distance may be a poor measure
of similarity when the values range over
many decades, but this effect can be
reduced by applying a logarithmic data
transformation
before
the
distance
calculations, as performed here.
The results obtained in both analyses
were represented graphically. Data for
discriminant analysis were standardized
using
the
squared
Mahalanobis‘s
distances between groups.
Figure 1: L o c a t i o n o f t h e h y d r o g r a p h i c B a s i n o f t h e G r a v a t a í R i v e r , i n t h e s t a t e o f R i o G r a n d e d o S u l ,
Brazil, and the six sampling stations along the Gravataí River. 1 = Chico Lomã Stream,
District of Santo Antônio da Patrulha; 2 = Juca Barcelos’ Farm, District of Glorinha; 3 = Passo
dos Negros bathing pool, of Gravataí town; 4 = Pumping station, city of Porto Alegre/Canoas;
5 = Areia Stream, city of Porto Alegre/Canoas; 6 = Gravataí River mouth, city of Porto Alegre.
Acta Limnol. Bras., 19(1):1-14, 2007
3
Results
Climatic Variables
Monthly rainfall between January 2000
and October 2002 is represented in Fig. 2.
The precipitation registered in January 2001
(298.9 mm) represents a large inflow of
water into the system.
During the winter precipitation was low,
averaging 88.5 mm, and the highest reported
v a l u e w a s 1 4 6 . 2 m m , i n J u l y. A n n u a l
precipitation was 1,323.2 mm in the year
2000; 1,536.3 mm in 2001 and 1,496.8 mm
in 2002.
Minimum
and
maximum
monthly
temperatures (°C) variation between January
2000 and October 2002 are presented in
Fig. 3. The highest mean maximum
temperature registered was 33.6 °C in March
2002 and the lowest was 5.1 °C in July 2000.
350
Precipitation (mm)
300
250
200
150
100
50
jul
/02
se
p/0
2
jul
/0
1
se
p/0
1
no
v/0
1
jan
/02
m
ar
/02
m
ay
/02
jul
/00
se
p/0
0
no
v/0
0
jan
/01
m
ar
/01
m
ay
/01
jan
/00
m
ar
/00
m
ay
/00
0
months of the year
Figure 2: The monthly variation of precipitation (mm) during the period January 2000 - October 2002.
Source: Instituto de Pesquisas Agronômicas do Rio Grande do Sul (IPAGRO – the Rio Grande
do Sul Agricultural Research Institute), located in Gravataí River basin, Porto Alegre, RS.
Temperature (oC)
40
35
30
25
20
15
10
5
jan
/00
m
ar
/00
M
ay
/00
jul
/00
Se
p/0
0
no
v/0
0
jan
/01
m
ar/
01
M
ay
/01
jul
/0
1
Se
p/0
1
no
v/0
1
jan
/02
m
ar
/02
M
ay
/02
jul
/02
Se
p/0
2
0
Max
Min
Figure 3: Monthly maximum and minimum temperatures (°C) from January 2000 to October 2002. Source:
I n s t i t u t o d e P e s q u i s a s A g r o n ô m i c a s d o R i o G r a n d e d o S u l ( I PA G R O ) ( T h e R i o G r a n d e d o S u l
Agricultural Research Institute) station located in Gravataí River basin, Porto Alegre, RS.
Environmental Variables
Spatial and seasonal changes of
physical, chemical and microbiological
variables in the water along the course of
4
SALOMONI, S.E. et al.
the river are presented in Figures 4 to 8.
Water temperatures varied from 27.5 ±
0.52°C during the summer of 2002 and the
summer of 2002 16.7 ± 0.65°C) in the winter
Limnological characterization of Gravataí River ...
of 2002, both in the lower stretch of the
river (Figs.4A and 4B). Water turbidity was
variable and generally high in both portions
of the river. There is a seasonal pattern of
variation with higher turbidities in the
spring and summer and a lower levels
d u r i n g f a l l a n d w i n t e r, i n b o t h a n a l y s e d
years (Figs 4C and 4D).
B
AA
35
35
Temperature (º C)
30
Temperature ( OC)
E1,2,3
25
20
15
10
25
20
15
10
5
5
0
0
S1
S2
S3
S4
S5
Sp/00 S/01
S6
A/01
sampling stations
S/02
D
D
140
A/02
W/02
E1,2,3
E4,5,6
120
120
100
Turbidity (NTU)
Turbidity (NTU)
W/01 Sp/01
annual seasons
CC
140
100
80
60
80
60
40
40
20
20
0
0
E1
E2
E3
E4
E5
Sp/00 S/01
E6
A/01
20
EE
18
W/01 Sp/01 S/02
A/02
W/02
annual seasons
sampling stations
20
18
Chlorides (mgL -1 Cl)
16
Chloride (mgl-1Cl)
E4,5,6
30
14
12
10
8
6
4
F
E1,2,3
F
E4,5,6
16
14
12
10
8
6
4
2
2
0
S1
S2
S3
S4
S5
sampling stations
S6
0
Sp/00
S/01
A/01
W/01
Sp/01
S/02
A/02
W/02
annual seasons
F i g u r e 4 : Values (mean ± s t a n d a r d d e v i a t i o n [ S D ] ) o f t h e m e a s u r e d p h y s i c a l a n d c h e m i c a l v a r i a b l e s o f
temperature (°C), turbidity (NTU) and chloride (mg L – 1 Cl), at each sampling station (S1=station 1,
S2= station2, S3=station3, S4=station 4, S5=station 5, S6= station 6) and the seasons (S1,2,3 =
mean of stations 1,2,3; S4,5,6= mean of stations 4,5,6; Sp=spring, S=summer, A=autumn, W=winter;
00=year 2000, 01=2001, 02=2002) in the period of September 2000 to August 2002, for six sampling
stations along the Gravataí River, State of Rio Grande do Sul, Brazil.
Acta Limnol. Bras., 19(1):1-14, 2007
5
Rising concentration gradients were
observed from riverhead to the mouth for
chloride (Fig. 4E), conductivity (Fig. 5C), BOD
(Fig. 6C) and all nutrients (Figs.7 A, 7C, 7E;
8A and 8C). For all the quantified nutrients,
the concentrations in the lower river stretch
were from three to five times higher than
those reported in the upper-middle river
stretch.
As for the seasonal variation, in general,
all the nutrient concentrations during the
spring and winter were lower than those of
in summer and fall (Figs 4F; 5D; 6D; 7B, 7D,
7F; 8B and 8D).
A large degree of homogeneity was
observed throughout the Gravataí River
regarding the chemical oxygen demand
(COD), (Fig. 6E).
The density of faecal coliforms was
quantified as a biological indicator of water
quality from the sanitary point of view. The
spatial analysis reveals that the highest mean
faecal coliform values were found at station
6, 175,120 ± 186,047.5 MPN/100mL, while the
lowest values were reported at station 2, 270
± 206.9 MPN/100mL (Fig. 8).
During the two years sampled, the
highest mean faecal coliform counts were
registered in the lower river, while the lowest
counts were seen in the upper stretch during
the summer of 2002. Two distinct groups
were formed by the application of cluster
analysis to all the values from the set of
analyzed variables. The groups denote a
disruption in the gradient: the first part
representing the upper-middle stretch of the
river, and the other of corresponding to the
lower river stretch (Fig.9). All seasons were
represented in each group, with no indication
of seasonality effect.
A
BB
A
E1,2,3
8
8
7
7
6
6
5
4
pH
pH
5
3
4
3
2
2
1
1
0
0
S1
S2
S3
S4
S5
S6
Sp/00
S/01
A/01
C
250
C
Conductivity (uS cm-1)
250
W/01
Sp/01
S/02
A/02
W/02
annual seasons
sampling stations
Conductivity (uS.cm-1)
E4,5,6
200
150
100
50
0
DD
E1,2,3
E4,5,6
200
150
100
50
0
S1
S2
S3
S4
sampling stations
S5
S6
Sp/00 S/01
A/01
W/01 Sp/01
S/02
A/02
W/02
annual seasons
Figure 5: Values (mean ± standard deviation [SD]) of the measured pH and conductivity (µS cm - 1 ) at each
sampling station (S1=station 1, S2= station2, S3=station3, S4=station 4, S5=station 5, S6= station
6) and the seasons (S1,2,3 = mean of stations 1,2,3; S4,5,6= mean of stations 4,5,6; Sp=spring,
S=summer, A=autumn, W=winter; 00=year 2000, 01=2001, 02=2002) in the period of September
2000 to August 2002, for six sampling stations along the Gravataí River, State of Rio Grande do
Sul, Brazil.
6
SALOMONI, S.E. et al.
Limnological characterization of Gravataí River ...
10
8
7
7
6
5
4
3
6
5
4
3
2
2
1
1
0
0
S1
S2
S3
S4
S5
Sp/00
S6
S/01
A/01
sampling stations
C
12
W/01
Sp/01
S/02
A/02
W/02
annual seasons
C
10
8
6
E1,2,3
D D
14
BDO (mg L -1 O 2 )
BOD (mg L -1 O 2 )
14
E4,5,6
12
10
8
6
4
4
2
2
0
0
S1
S2
S3
S4
S5
Sp/00
S6
S/01
A/01
60
W/01 Sp/01
S/02
A/02
W/02
annual seasons
sampling stations
60
E E
E1,2,3
F F
E4,5,6
50
COD (mg L -1 O 2 )
50
-1
COD (mg L-1
O 2)
E4,5,6
9
8
DO (mgL -1 O 2 )
DO (mg L -1 O 2 )
9
E1,2,3
BB
10
AA
40
30
20
40
30
20
10
10
0
0
S1
S2
S3
S4
sampling stations
S5
S6
Sp/00
S/01
A/01
W/01 Sp/01
S/02
A/02
W/02
annual seasons
Figure 6: Values (mean ± standard deviation [SD]) of the measured chemical variables of DO, BOD, COD
( m g L – 1 O 2 ) , a t e a c h s a m p l i n g s t a t i o n ( S 1 = s t a t i o n 1 , S 2 = s t a t i o n 2 , S 3 =s t a t i o n 3 , S 4 = s t a t i o n 4 ,
S5=station 5, S6= station 6) and the seasons (S1,2,3 = mean of stations 1,2,3; S4,5,6= mean of
stations 4,5,6; Sp=spring, S=summer, A=autumn, W=winter; 00=year 2000, 01=2001, 02=2002) in
the period of September 2000 to August 2002, for six sampling stations along the Gravataí River,
State of Rio Grande do Sul, Brazil.
Acta Limnol. Bras., 19(1):1-14, 2007
7
7
A
6
E1,2,3
B
N)
-1
5
4
3
2
1
0
S1
S2
S3
S4
S5
5
4
3
2
1
0
Sp/00
S6
S/01
N)
-1
Organic Nitrogen (mg L
N)
-1
O r g a n ic Nitrogen (mg L
C
S1
S2
S3
S4
S5
sampling stations
A/01
W/01 Sp/01
S/02
5
4,5
4
3,5
3
2,5
2
1,5
1
0,5
0
D
E1,2,3
S p / 0 0 S/01
S6
A/01
W/01 Sp/01 S/02
E
11
E4,5,6
A/02
W/02
E4,5,6
F
-1
N)
10
Total Nitrogen (mg L
Total Nitrogen (mg L -1 N)
W/02
annual seasons
E1,2,3
11
10
9
8
7
6
5
4
3
2
1
0
A/02
annual seasons
sampling stations
5
4,5
4
3,5
3
2,5
2
1,5
1
0,5
0
E4,5,6
6
Ammonium (mg L
Ammonium (mg L -1 N)
7
S1
S2
S3
S4
S5
sampling stations
S6
9
8
7
6
5
4
3
2
1
0
Sp/00
S/01
A/01
W/01
Sp/01
S/02
A/02
W/02
annual seasons
F i g u r e 7 : Values (mean ± s t a n d a r d d e v i a t i o n [ S D ] ) o f t h e m e a s u r e d c h e m i c a l v a r i a b l e s o f a m m o n i u m ,
organic nitrogen and total nitrogen (mgL –1 N), at each sampling station (S1=station 1, S2= station2,
S3=station3, S4=station 4, S5=station 5, S6= station 6) and the seasons (S1,2,3 = mean of stations
1,2,3; S4,5,6= mean of stations 4,5,6; Sp=spring, S=summer, A=autumn, W=winter; 00=year 2000,
01=2001, 02=2002) in the period of September 2000 to August 2002, for six sampling stations
along the Gravataí River, State of Rio Grande do Sul, Brazil.
8
SALOMONI, S.E. et al.
Limnological characterization of Gravataí River ...
A
B
1,6
1,4
1,4
1,2
1,2
PO4O (mg L -1 PO 4 )
PO 4 O (mg L -1 PO 4 )
1,6
1
0,8
0,6
0,4
0,2
E1,2,3
1
0,8
0,6
0,4
0,2
0
0
S1
S2
S3
S4
S5
S6
Sp/00
S/01
A/01
Sp/01
S/02
A/02
W/02
D
PO 4 )
E1,2,3
2
E4,5,6
2
PO4T (mg L
-1
PO 4 T (mg L -1 PO 4 )
2,5
C
2,5
W/01
annual seasons
sampling stations
1,5
1
0,5
1,5
1
0,5
0
0
S1
S2
S3
S4
S5
S6
Sp/00 S/01
Faecal coliforms (NMP 100 mL)
E
100000
10000
1000
100
10
1
S1
S2
S3
S4
sampling stations
W / 0 1 Sp/01
S/02
A/02
S5
S6
E1,2,3
F
1000000
1000000
A/01
W/02
annual seasons
sampling stations
Faecal Coliforms (MPN 100 mL)
E4,5,6
E4,5,6
100000
10000
1000
100
10
1
Sp/00
S/01
A/01
W/01 Sp/01
S/ 0 2
A/02
W/02
annual seasons
Figure 8: Values (mean ± standard deviation [SD]) of the measured chemical variables PO 4 O and PO 4 T (mg
L - 1 PO 4 ) and number of faecal coliforms (MPN 100 mL) at each sampling station (S1=station 1, S2=
station2, S3=station3, S4=station 4, S5=station 5, S6= station 6) and the seasons (S1,2,3 = mean
of stations 1,2,3; S4,5,6= mean of stations 4,5,6; Sp=spring, S=summer, A=autumn, W=winter;
00=year 2000, 01=2001, 02=2002) in the period of September 2000 to August 2002, for six sampling
stations along the Gravataí River, State of Rio Grande do Sul, Brazil.
Acta Limnol. Bras., 19(1):1-14, 2007
9
Euclidean Distance
1,3E-01
1,2E+02
2,4E+02
3,6E+02
Information
10
0
75
50
25
sp1/00
sp1/01
A1/01
S2/01
W1/01
sp3/01
A3/02
S2/02
S3/02
W1/02
sp2/00
W2/01
S1/01
S1/02
sp2/01
Group I
w3/01
A2/02
A3/01
A2/01
W2/02
A1/02
Sp3/00
W3/02
S3/01
sp4/00
W4/02
W5/02
W6/02
S4/01
S4/02
A4/02
S5/01
A5/01
W6/01
Group II
A4/01
A5/02
W4/01
sp6/00
W5/01
sp4/01
sp5/01
S5/02
sp5/00
S6/01
S6/02
A6/01
sp6/01
A6/02
Figure 9: Dendrogram (Euclidean distances) resulting from cluster analysis based on s i m i l a r i t i e s a m o n g
the physical, chemical, and biological characteristics of six sampled locations along Gravataí
River, in the period of September 2000 to August 2002, sampled in eight seasonal periods
(sp=Spring, S=Summer, A= autumn, and W=Winter). Numbers 1 to 6 correspond to the sampling
stations, ordered from the head to the mouth, and 00, 01 and 02 correspond to the years 2000,
2001, and 2002.
The result of the ordination of all
environmental variables by discriminant
analysis is presented in Figure 10. Axis 1,
explaining 48% of the variability contain the
most important vectors on the positive side
as evidenced by their eingenvalues (in
parenthesis): PO4 (0.79), pH (0.67), total
10
SALOMONI, S.E. et al.
phosphate (0.59), total nitrogen (0.48) and
organic nitrogen (0.29) (Fig.2a), representing
the increase in organic pollution and
eutrophication at the stations 4, 5, and 6
(Fig.2b). Axis 2, explaining 30% of the
variability, was positively connected with
stations 1, 2 and 3, which were correlated
Limnological characterization of Gravataí River ...
with the high concentrations of dissolved
oxygen (0.51 ). A comparison of data from
the present study and those from an earlier
period is reported in Table I.
A
Variables (axis F1 and F2: 78 %)
1
0,8
0,6
DO
0,4
pH
0,2
Temp
0
Turb
orgN
CL
-0,2
FC
-0,4
NH3
NT
BOD
Cond
COD
-0,6
PO4T
PO4O
-0,8
-1
-1
-0,5
0
0,5
1
-- axis F1 (48 %) -->
B
Observations (axis F1 and F2: 78 %)
70
60
1
50
2
40
3
4
30
5
20
6
10
0
0
2
4
6
8
10
12
-- axis F1 (48 %) -->
Figure 10: Ordination by Discriminant Analysis of environmental variables (A) and ordination of the sampling
stations (S1,S2,S3,S4,S5,S6) according to the environmental variables (B), during the period of
September 2000 to August 2002, on the Gravataí River, RS, Brazil.
Acta Limnol. Bras., 19(1):1-14, 2007
11
Ta b l e I : M e a n v a l u e ( ± s t a n d a r d d e v i a t i o n [ s d ] ) a n d r a n g e o f t h e m e a s u r e d p h y s i c a l , c h e m i c a l a n d
microbiological variables monitored in the sampling stations (S1, S3, S4 and S6) along the Gravataí
River, Rio Grande do Sul State, Brazil, in the period 1992 to 2002. Source: Fundação Estadual de
P r o t e ç ã o A m b i e n t a l d o R i o G r a n d e d o S u l . ( F E PA M / R S ) .
Períods
DO
BOD
TN
PO4T
Conductivity
Faecal coliforms
mgL-1O2
mgL-1O2
mgL-1 N
mgL-1 PO4
µS cm
MPN/ 100 mL
S1 1992 - 1994
7.22 ± 1.81
4-11
1.89 ± 0.84 0.95 ± 0.34 0.10 ± 0.11
1-4
0.44-1.62
0.0097-0.55
1995 - 1998
5.13 ± 1.94
2-9
1.75 ± 0.92 1.18 ± 0.58
1-5
0.65-2.96
1999 - 2002 5.80 ± 2.53
1-11
S3 1992 -1994
1995 - 1998
60.61 ± 23.11
34-150
14.863 ± 4398.85
50-5000
0.11 ± 08
0.019-0.44
74.99 ± 39.35
10-250
1023.26 ± 2506.3
40-16000
1.74 ± 2.10 1.29 ± 0.71
1-6
0.18-3.0
0.18 ± 0.16
0.025-0.86
91.70 ± 55.92
21-340
606.16 ± 715.93
74-2500
7.66 ± 1.43
5-11
1.78 ± 1.13 1.21 ± 1.07
1-5
0.49-4,86
0.06 ± 0.05
0.0125 –
0.247
46.90 ± 15.0
30-100
401.81 ± 587.84
23-2200
6.30 ± 1.61
2 – 10
1.44 ± 0.91 1.02 ± 0.42
1–6
0.22 – 2.71
0.07 ± 0.04
0.0100 –
0.229
57.91 ± 24.31
10 – 160
581.00 ± 1424.23
23 - 9000
56.12 ± 17.71
12.4 – 94.3
6359.75 ± 36083.09
20 –9700
91.0 ± 52.23
34 - 200
27912.90 ± 37957.28
1300 - 160000
1999 - 2002 5.39 ± 2.14
1.9 –10
3.878 ±
3.544
0.10 – 20
1995 - 1998
1999 - 2002 2.65 ± 2.30
0.10 – 10.3
S6 1992 -1994
1.33 ± 0.76 1.20 ± 0.64
0.13 ± 0.11
1–5
0.48 – 4.68 0.028 – 0.208
5.44 ± 2.49 3.78 ± 3.81 3.37 ± 4.55 0.25 ± 0.17
0.60 – 13.07
1-21
0.51 – 17.8 0.017 – 0.69
S4 1992 -1994
-1
6.24 ± 10.58 4.77 ± 4.167 0.377 ± 0.281 124.59 ± 92.59
1-19
0.93 – 17.8 0.077 – 0.916
25 – 311
5.19 ± 4.26 5.59 ± 5.39 0.65 ± 0.52
2 – 18
1.07 – 21.6 0.160 – 2.32
4.59 ± 2.91 5.59 ± 4.00 4.78 ± 5.76
0.38 – 11.10
2.0 -17
0.50 – 19.6
0.43 ± 0.32
0.11 – 1.53
158.24 ± 124.8
32.2 - 560
151809.76 ± 203507.85
1600 - 860000
119.06 ± 74.68
45 – 400
66233.33 ± 60856.92
3000 - 170000
1995 - 1998 2.42 ± 2.285 8.38 ± 7.40 5.34 ± 3.26 0.538 ± 0.356 149.88 ± 87.49
0.0 – 6.90 2.00 – 31.0 1.32 – 14.8
0.14 – 1.42
29 - 460
1999 - 2002 3.33 ± 2.32 6.94 ± 4.42 5.42 ± 2.98
0.2 – 8.8
1.9 - 19
1.68 – 11.72
Discussion
The interpretation of the influence of
hydrological and climatic variations on
limnological characteristics of rivers is
rather
complex,
involving
the
superposition of spatial and temporal
factors. Changes over different timescales, such as seasonal and inter-annual
fluctuations, are superimposed, making
the identification of recurrent patterns
difficult, except in long-term studies. The
data obtained for Gravataí River basin have
showed for example, great inter-annual
changes regarding the total rainfall
between the years of 2000 and 2002, and
also
changes
in
the
monthly
rain
12
SALOMONI, S.E. et al.
1.36 ± 1.14
0.18 – 4.69
171626.410 ± 374008.4
1300 – 900000
141.28 ± 66.70
94 -297
176290.323 ±
220520.021
5000 - 900000
1880000 ± 188407.51
1900 - 660000
distribution. Some months had higher
rainfall, like January, April, and September.
In several countries, rivers located
near dense human agglomerations or in
highly industrialized areas do suffer large
alterations in their physical and chemical
characteristics, jeopardizing the water
quality and representing a significant risk
to human health (Sabater et al. 1996; Agatz
et al. 1999; Sonnemann et al. 2001).
A comparison of the data in the
present study and those reported for an
earlier period (Leite et al., 1992/1994)
shows that over the last decade there
have been significant changes, revealing
an accelerated eutrophication of the
Gravataí River water in recent times.
Limnological characterization of Gravataí River ...
One of the most striking limnological
changes observed refers to the dissolved
oxygen concentration in the water, which
suffers a marked decrease in the upper and
middle stretch due to oxidative degradation
o f o r g a n i c m a t t e r. O t h e r v e r y a p p a r e n t
changes were the rise in the concentrations
of ions (electrical conductivity) and
phosphorus, particularly in the middle and
lower stretches, except at the mouth. The
almost anaerobic conditions in the site
nearest to the disturbance and gradual
recovery follow the pattern usually found
for many rivers submitted to heavy organic
pollution (Margalef, 1983) and well described
by Mirande et al. (1999) in the Gastona River,
Argentina.
The
continuum
concept
model
foresees a gradual rise in conductivity and
turbidity from the source to the mouth of a
river, due to the gradual loading of fine ionic
and particulate material contributed by
effluents
and
surrounding
terrestrial
ecosystems.
The present limnological
study shows that Gravataí River thus not
conform to the usual river model. The
headwater region has a semi-lentic character
and a higher nutrient concentration than
subsequent stretch, although still somewhat
preserved and presenting oligotrophic
characteristics.
The statistical analysis confirmed the
existence of two distinct portions in the
river: The first, comprising the upper and
middle stretches, from the headwater until
Passo dos Negros where the expected
increase in the mineral content and ionic
concentrations occurs along the river. The
second part comprising the inferior stretch
of
the
river
has
hypereutrophic
characteristics, only comparable with those
of highly polluted rivers.
The absence of seasonal variation was
striking for some variables like temperature,
conductivity and the concentration of
nutrients. It appears that the effect of
eutrophication is so strong that it masks
the seasonal changes. A similar situation
was found for the higher portion of Tietê
River by Tundisi & Matsumura-Tundisi (1990)
due to heavy inputs of domestic and industrial wastes from São Paulo city
discharged into the river. Moretto & Nogueira (2003), have also shown striking
differences between Lavapés and Capivara
Rivers in the Paranapanema River basin
related to the land uses and human impacts
in the watershed.
At the middle of Gravataí River,
between Passo de Negros and Air-base
Pumping Station, there is a great change in
the water quality caused by discharge of
domestic and industrial sewage from the
n o r t h p a r t o f P o r t o A l e g r e c i t y. T h e r e i s
noticeable increase in labile organic material, characteristic of residual water dumped
in natura , that is also reflected in the BOD
values and in faecal coliform numbers which
increased by 3 to 50 times. Near the rivermouth, nutrient concentrations and coliform
densities become even greater, increasing
by about 10 and 100 times, respectively.
G r a v a t a í R i v e r i s a t y p i c a l p l a i n r i v e r,
with a sinuous course, low flow-rate and
mean of 5.14 m 3 /s (IPH, 2002) resulting in
reduced re-aeration and pollutant dilution
capacity. The impact of organic pollution
by the city of Porto Alegre promotes a severe
water quality deterioration, characterizing
the so-called serial discontinuity. Chemical
and physical parameters and the density of
faecal coliforms indicate that the lower part
of the river can be classified as eutrophic
and polysaprobic with low sanitary quality.
Multiple uses of the Gravataí River water
are jeopardized in its lower portion and
strong
remedial
action
are
urgently
necessary in order to revert this condition.
Acknowledgements
The authors would like to thank the
research Foundation Agency of Rio Grande
d o S u l S t a t e ( FA P E R G S ) , t h e B r a z i l i a n
National Research Council (CNPq). Also,
great appreciation is extended to the Museu de Ciências Naturais da Fundação
Zoobotânica do Rio Grande do Sul (MCNF Z B ) f o r t h e i n f r a s t r u c t u r e g r a n t e d . To
Haywood Dail Laughinghouse IV and to Tim
Roberts for reviewing the English text.
References
Agatz, M., Asmus, R.M. & Deventer, B. 1999.
Structural changes in the benthic diatom
community along eutrophication gradient
on a tidal flat . Helgol. Mar. Res., 53:92101.
American Public Health Association - APHA.
1992.
Standard
methods
for
the
examination of water and wastewater. 18 th
ed. APHA, Washington. 1316p.
Digby,
P. G . N .
&
Kepton,
R.A.
1987.
Multivariate
analysis
of
ecological
Acta Limnol. Bras., 19(1):1-14, 2007
13
communities. Chapman and Hall, London.
206p.
Instituto de Pesquisas Hidráulicas – IPH.
2002. Identificação das alternativas possíveis e prováveis para a regularização
das vazões do rio Gravataí. IPH, Porto
Alegre. cap.7.
Junk, W.J. Baylet, P.B. & Sparks, R.E. 1989.
The flood pulse concept in riverfloodplain systems. In: Dodge, D.P. (ed.)
Proceedings of the International Large
River Symposium. Can. Spec. Publ. Fish.
Aquat. Sci., 106:110-127.
L e i t e , E . H . , H a a s e , J . F. , P i n e d a , M . D . S . ,
Cobalchini, M.S. & Silva, M.L.C. 1992/1994.
Qualidade das águas do rio Gravataí. Fundação Estadual de Proteção Ambiental FEPAM, Porto Alegre. 65p. (Relatório Final).
Margalef, R. 1983. Limnologia. Omega, Barcelona. 1010p.
Mirande, V., Romero, N., Barrionuevo, M.A.,
Meoni, G.S.B., Navarro, M.G., Apella, M.C.
& Tracanna, B.C. 1999. Human impact
on some limnological characteristics of
the Gastona River (Tucumán, Argentina).
Acta Limnol. Bras., 11(2):101-110.
Moretto, E.M. & Nogueira, M.G. 2003.
Physical and chemical characteristics of
Lavapés and Capivara rivers, tributaries
of Barra Bonita Reservoir (São Paulo –
Brazil). Acta Limnol. Bras., 15(1):27-39.
Neiff, J.J. 1990. Ideas para la interpretación
del rio Paraná. Interciencia, 15:424-441.
Neves, I.F. 2002. Diversidade da comunidade zooplanctônica em trechos do rio
Cuibá
impactado
por
atividades
antropogênicas. São Carlos, UFSCar, 146p
(Master Thesis).
Sabater, S., Guasch, H., Picón, A., Romaní,
A.M. & Muñoz, I. 1996. Using diatoms communities to monitor water quality in a
river after the implementation of a
s a n i t a t i o n p l a n ( r i v e r Te r, S p a i n ) . I n :
Whitton, B.A. & Rott E. (eds.) Use of algae
for monitoring rivers II. Institut für Botanik,
Universität Innsbruck, Innsbruck. p.97103.
S o n n e m a n , J . A . , W a l s h , C . J . , B r e e n , P. F. &
Sharpe, A.K. 2001. Effects of urbanization
on streams of the Melbourne region,
Victoria, Australia. II. Benthic diatom
communities. Freshwater Biol., 46:553565.
Tundisi, J.G. & Matsumura-Tundisi, T. 1990.
Limnology and eutrophication of Barra
Bonita Reservoir, São Paulo State,
14
SALOMONI, S.E. et al.
Southern Brazil. Arch. Hydrobiol. Beih.
Ergeb. Limnol., 33:661-667.
Vannote, R.L., Minshall, G.W., Cummins, K.W.,
Sedell, J.R. & Cushing, C.E. 1980. The river
continuum concept. Can. J. Fish. Aquat.
Sci., 27:130-137.
Received: 26 May 2006
Accepted: 12 March 2007
Limnological characterization of Gravataí River ...