Seasonal behavior of the Upper Rio das Velhas benthic

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Seasonal behavior of the upper Rio das Velhas benthic macroinvertebrate
communities (Minas Gerais, Brazil)
Junqueira, M.V.* & Natividade, J. F. I. L.
Fundação Centro Tecnológico de Minas Gerais-CETEC/Setor de Recursos da Água
Belo Horizonte-MG CEP 31170-000.
*[email protected]
Abstract
Seasonal behavior of the upper Rio das Velhas benthic macroinvertebrate communities (Minas
Gerais, Brazil)
This study aims at evaluating the behavior of the zoobenthic communities as regards its
diversity and abundance in relation to seasonal variation, which allows for the identification of the
period of the year when those communities are more representative at the Rio das Velhas basin. The
freshwater macroinvertebrate communities found in both the epifauna and in the infauna had been
sampled along the edge of the watercourses and in river beds through the "kicking" method (Macan
1958), with the aid of a 0,3mm mesh net fish trap, ISO 7828 (1985), during three minutes. The samples
were kept in formol at 10%, and later sifted with a 0.3 mm-mesh sieve. The material was then selected
under a stereomicroscope, and the organisms stored in alcohol at 80%, for further quali-quantitative
classification. The structure and composition of the zoobenthonic communities present clear
differences in relation to the rainy and dry seasons, as shown in the results of the qualitativequantitative taxonomic analysis. The January campaign registered an average taxa of 4.8 of
macroinvertebrates, while April showed 5,4 and July reached 9.3. In October the average was 11.2.
These results confirm previous biomonitoring studies developed by CETEC at the Rio das Velhas basin
(Junqueira & Campos 1998).
Our conclusion is that the variety and amount of zoobenthonic
community organisms are drastically reduced during the rainy season. This is due to the effects of the
rainy season over the aquatic biota, mainly related to increased outflows and the carriage of sediments
to the rivers
Resumo
Comportamento sazonal da comunidade de macroinvertebrados bentônicos na bacia do
alto rio das Velhas (Minas Gerais, Brasil).
O estudo proposto visou avaliar o comportamento da comunidade zoobentônica com relação à
variação sazonal no que diz respeito a sua diversidade e abundância permitindo identificar e confirmar
o período do ano em que a comunidade zoobentônica se torna mais representativa na Bacia do Ato Rio
das Velhas. As comunidades de macroinvertebrados aquáticos presentes tanto na epifauna como na
infauna bentônica foram amostradas às margens do curso d’água ou no leito do rio, segundo o método
de “kicking” (Macan, 1958), com o auxílio de puçá com tela de 0,3mm de poro, ISO 7828 (1985),
durante um período de três minutos de coleta. As amostras foram fixadas em formol a 10% e
posteriormente triadas com peneira de 0,3 mm de malha. Em seguida procedeu-se a seleção do material
através do estereomicroscópio, acondicionando os organismos em álcool a 80%, para posterior
classificação quali-quantitativa. Os períodos de chuva e estiagem apresentam diferença na estrutura e
composição das comunidades zoobentônicas, mostrada no resultado da análise taxonômica qualiquantitativa. A campanha de janeiro apresentou uma média de 4,8 taxa de macroinvertebrados e a de
abril uma média de 5,4 de taxa. Já na coleta de julho obteve-se uma média de 9,3 de diferentes taxa e
em outubro esse número subiu para 11,2 taxa coletadas por estação. Tais resultados vêm confirmar os
obtidos em trabalhos de biomonitoramento executados anteriormente pelo CETEC no alto Rio das
Velhas (Junqueira & Campos 1998). Através do trabalho conclui-se que as comunidades zoobentônicas
sofrem acentuada queda tanto na sua variedade quanto na quantidade de organismos nos meses de
chuva. Isto decorre de diversos distúrbios provocados pelo período chuvoso sobre a biota aquática,
relacionados principalmente ao aumento acentuado das vazões e ao carreamento de sedimentos para os
rios.
INTRODUCTION
The upper Rio das Velhas basin has been used by the Minas Gerais Technology Center Foundation CETEC since 1985 as a pilot basin for studies about the development of lotic ecosystem water quality
bioindicator methodologies (Junqueira et al. 2000). These studies were aimed at supporting watershed
control and supervision in the state of Minas Gerais. However, despite the increased knowledge
resulting from use of bioindicators in this basin , for routine biomonitoring it was necessary to
investigate a few other aspects of the seasonal behavior of the aquatic benthonic fauna so as to
determine the best time of the year to collect biologic samples. Therefore, this work is aimed at
determining the veracity of the assumption that the dry season is the most adequate to be used as
reference for the biomonitoring of the water quality of rivers as it is during this season that the
zoobenthic communities are expanded. To accomplish this task, we investigated the behavior of the
zoobenthic communities of the Upper Rio das Velhas with a focus on their seasonal abundance and
varieties during the year of 2003.
The seasonal changes of the biological communities are well known. (UNESCO/WO/UNEP 1992) and,
according to Friedrich, com.pess. and “Standard Methods for German Rivers” - DIN (1990), many
studies have been developed on how to find the best period of the year for zoobenthic collection aimed
at biomonitoring German rivers. Those studies will also set up the adequate frequency of the collection
for future biomonitoring.
It is also worth noting that even in the wealthiest European countries the evaluation of the river water
quality takes as reference the biomonitoring data obtained from samples collected during the periods
when the macroinvertebrate community is more representative thus being valid for the whole year. The
data obtained is used in the elaboration of the annual classification of water (LAWA 1982). This
approach allows for cost reduction and the optimization of collection and analysis efforts, without
affecting the quality of results but entirely meeting the objectives of water quality monitoring.
STUDY AREA
The area studied covers the entire upper Rio das Velhas basin, from the neighborhood of its source on
the Antônio Pereira mountain range, in the city of Ouro Preto, district of São Bartolomeu, to the
neighborhoods of its confluence with the Ribeirão da Prata, in the city of Raposos. The area surveyed
covers over 70 km. This region presents a very typical landscape and the sampling site upstream was
located at an altitude of 980m, while at downstream it was located at an altitude of 693m. The weather
in the region is generally between 18oC and 20oC (annual isothermal lines), the coldest in the state. The
southern area, near the city of Ouro Preto, is an isolated nucleus of high rainfall rates, with very high
levels of humidity – around 1800-2000mm annually.
The exact location of the sampling network stations for the biomonitoring in the upper Rio
das Velhas basin can be seen in the map.
MAP
MATERIALS and METHODS
The sampling method used for this study is in line with the one biomonitored by CETEC for the Minas
Gerais Water Management (IGAM Instituto Mineiro de Gestão das Águas 2005) in the upper Rio das
Velhas basin. Sample gathering was carried out seasonally during the months of January, April, July
and October, thus covering the four seasons of the year.
The network comprised 14 sampling sites, considered of major relevance in terms of anthropogenic
effects for the evaluation of water quality at the upper Rio das Velhas basin. All the areas selected for
the zoobenthonic community sampling were similar in terms of habitat, all of them presenting a stony
substratum and riffles. These selection criteria were aimed at providing maximum homogeneity for
the physical features of the habitat so that the results could be properly compared. The list of sites
included in this network, with its respective geographic location is presented in Table I.
TABLE I - Biological sampling network sites of the upper Rio das Velhas basin.
Coordinates (UTM)
Station
code
Latitude
Longitude
Height
(m)
AV005
7753142.67
648719.04
980
Rio das Velhas upstream from São Bartolomeu
AV010
7754204.58
644614.55
984
Rio das Velhas upstream from the Rio de Pedras
dam
AV040
7765067
630940.76
760
Rio das Velhas downstream from the Rio de
Pedras dam
AV050
7748112.68
614977.6
996
Ribeirão do Silva upstream from Ferteco company
AV110
7765743.26
624742.94
800
RCBC*
7786976.05
607910.01
734
Rio Itabirito downstream from the city of Itabirito
and Ribeirão do Onça
Córrego Capão do Boi at COPASA water station
AV200
7774310.99
618189.41
785
Rio do Peixe downstream from Peixes village and
from Usina.
AV210
7778301.43
626553.05
716
Rio das Velhas downstream from Córrego Mingú,
at the seat of Rio Acima.
AV240
7780859.01
608506.02
1140
Córrego Seco at COPASA Fechos Reservation
AV250
7785099.59
622644.47
746
Ribeirão dos Macacos near the confluence with
Rio das Velhas
AV300
7790627.92
619026.56
736
Córrego do Cardoso at the city of Nova Lima.
AV320
7790385.76
623367.51
726
Córrego da Mina Dágua downstream from Morro
Velho reservoir
AV330
7789868.96
623714
729
AV345
43047'46''S
19058'25''W
740
AV340
779917.73
625949.6
709
Rio das Velhas downstream from Rio Água Suja
and Córrego da Mina Dágua
Ribeirão da Prata upstream from the city of
Raposos.
Ribeirão da Prata at Barracão Amarelo district
near the mouth of the river
Description
AV350
7798558.27
623747.64
693
Rio das Velhas downstream the city of Raposos.
* CETEC code
 Sample collection and analysis
The sample collection at the benthic macroinvertebrates communities was performed along the banks
of the water courses and/or in the central channel of the river bed, wherever depth made it possible.
The “kicking” technique (Macan 1958) was used to sample the macroinvertebrates communities
found in the epifauna and in the benthonic infauna. The collection was made with the help of a 0.3mm
mesh net during three minutes, as established by the International Standard ISO 7828 (1985), and
later fixed in a formaldehyde solution, 10%. Specimen collected manually were fixed in alcohol,
80%.
A set of sieves with various mesh sizes was used to wash and screen the material collected, separating
the organisms contained in the samples. The material was then sorted by stereomicroscopy and kept
in 10 and 20 ml bottles filled with alcohol 70º, for further qualitative and semi-quantitative analysis.
This analysis involved the taxonomic identification of the organisms with the help of dichotomic keys
(Domingues, et al. 1992; Merrit & Cummins 1996; Heckman 2000a;2000b), comparisons of
illustrative plates and the usual optical microscopy techniques. Blade assemblage techniques were
also used to allow for better visualization of the anatomical structure of some of the taxonomic groups
thus facilitating their identification through microscopy.
Concurrently with the biological sampling, water samples were collected for analysis of various
physical and chemical parameters. For evaluation, only those parameters with the most meaningful
seasonal variations were used, that is, residues in suspension and turbid. The water sample collection
were made on the surface of the water, in compliance with the “Standard Methods for Examination of
Water and Waste-Water” (APHA 1995).
RESULTS AND DISCUSSION
Table II shows the results obtained from the taxonomic analysis of the zoobenthonic communities
collected during the campaigns carried out in the months of January through April (rainy season), and
July through October (dry season) in the biomonitoring sampling network stations of upper Rio das
Velhas basin.
TABLE II - Composition and total abundance of organisms found in the zoobenthonic communities
of the sampling network of the upper Rio das Velhas basin between January and October 2003.
(arquivo separado)
Due to of the impossibility to reach the borders of some collection stations as a result of floods which
occurred in the rainy season, to the collection was made in six stations only during the first campaign,
in January. All the fourteen pre-selected stations were available for collection in April, and for the
third campaign, in July, two experimental stations were added to the network making a total of
sixteen stations. The experimental stations were Córrego Capão do Boi and the Ribeirão do Prata,
upstream Raposos).
The results obtained indicated a clear difference between the structure and the composition of the
samples collected in the zoobenthonics communities at the peak and end of the rainy season (January
through April), and during the dry season (July through October). The pluviometric data provided by
the CEMIG meteorological station located in the upper Rio das Velhas basin, in the city of Rio das
Pedras, in the proximity of the study areas, shows values ranging between 443mm in January, 18mm
in April, 1 mm in July and 84mm in October. Fig. I shows this data, which was obtained during the
periods of zoobenthonic sample collection in the basin.
The average taxa of macroinvertebrates per station reached 4.8 in January, 5.4 in April, 9.3 in July and
11.2 in October. The first campaign showed 21 distinct taxa against 19 in the second collection and
30 different taxa in the third collection. Finally the fourth collection showed a total of 32 taxa of
benthonic macroinvertebrates, therefore a growth in the variety of organisms by the end of the rainy
season and throughout the dry season, a figure inversely proportional to that obtained at the peak of
the wet season. Similar results had been obtained before in the works developed by Junqueira &
Campos (1990), in the Rio Grande and Rio Paranaíba basins (Junqueira et al. 1992).
The above mentioned taxa were treated as family levels, the class Oligochaeta, Collembola and
Hidracarina being considered as one single family.
The abundance of macroinvertebrate organisms was obtained per station, and indicated average values
of 21 organisms in the first campaign, 62 individuals in the second campaign, and between 344 and
359 individuals in the third and last sampling campaign, demonstrating that the abundance of
organisms was raised in the dry season. These qualitative and quantitative findings can be better seen
in Figs. I and III.
The structure and composition of the benthonic communities observed in the dry season confirm the
findings of previous biomonitoring works developed by CETEC at the upper Rio das Velha
(Junqueira 2000 op. cit.). Studies by Paprocki (1997) performed in open streams of the Cipó mountain
range, which have substratum characteristics similar to those of the upper Rio das Velhas basin
stations also showed that the most variety and density of the zoobenthonic fauna is found in the dry
season. (June).
Besides the effect of the carriage of organisms, this may be associated to the modifications of various
abiotic and biotic factors resulting from disturbance caused mainly by the increase of sediments in the
water on the aquatic biotics resulting from floods. According to the "Water Resource Management
Manual" (FATMA 1999), these flood have a negative impact on the aquatic life as they prevent
proper breath and absorption of light. This disturbance is primarily related to the accentuated increase
of the outflows of the rivers, caused by the lack of vegetation in their catchment areas, as is the case of
the basin herein described. The floods do not allow for proper zoobenthonic collection in some
stations and leave many zoobenthonic organisms adrift (Bohle 1995). Another negative factor for
aquatic organisms is the great carriage of sediments through flash floods during this period of the
year.
The lixiviation of sediments carried to the rivers in the wet season may increase the amount of solids
dissolved in the water and consequently increase its turbidity. The findings obtained for turbidity and
solids in suspension in the water analyzed in the studied stations reached average values of 250,66
NTU and 190,3 mg/l respectively between January and April, as compared to 6,62 NTU and 11.21
mg/l registered between July and October. High levels of solid contents dissolved in the water may
result in the decrease of the oxygen dissolved in the water, thus affecting the photosynthetic
organisms which are dependent on the transparency of the water, and having an indirect impact on the
whole aquatic community (UNESCO/WHO/UNEP op. cit.).
Additionally, as Wantzen (1997) states, the solids dissolved in the water may have a negative abrasive
affect on aquatic macroinvertebrate organisms. High concentrations of solids endanger the organisms
which filter the water to feed, predators depending on water visibility to catch their prey and the most
sensitive organisms depending on branquial breathing (Bohle op. cit.)
mm
FIG. I - Monthly pluviometric data obtained in the CEMIG meteorological station of Rio das Pedras,
in the upper Rio das Velhas basin, 2003.
500
450
400
350
300
250
200
150
100
50
0
433
84
1
18
January
April
July
October
Concerning the composition of the benthonic fauna, the following taxa: Ceratopogonidae, Dytiscidae,
Psephenidae,
Veliidae,
Gomphidae,
Glosossomatidae,
Hydroptilidae,
Hydrobiosidae,
Polycentropodidae, Leptoceridae, Physidae, Hidracarina and Nematoda occurred only in the samples
collected between July and October, the dry season. Coenagrionidae, Hydropsychidae, Pyralidae,
Collembola and Glossiphoniidae were only observed in the collection which started in April, by the
end of the rainy season and in the beginning of the dry season.
FIG. II - Composition of the number of taxa found in benthonic macroinvertebrates during the sampling
campaigns carried out between January and October, 2003 in the upper Rio das Velhas basin.
12
11,2
taxa number
10
9,3
8
6
5,7
5,4
4,8
4,2
4,6
número de taxa
desvio padrão
4
2
1,3
ct
ob
er
O
Ju
ly
pr
il
A
Ja
nu
ar
y
0
FIG. III - Average of the absolute abundance of benthonic macroinvertebrates per station found
between the months of January and October, 2003 in the upper Rio das Velhas basin.
number of organisms
400
344
359
300
200
100
0
62
21
january
April
July
October
CONCLUSION
Although the data sampling presented in this work is representative of only one interval of one
hydrologic year 2003, it made it possible to detect and evidence that the benthonic communities
presented an accentuated decrease in variety and quantity of organisms in the first two collections
carried out during wet season. The data provided evidences that the partial absence of rain, typical of
the dry season, provides the stability of the climatic conditions necessary to favor the settling of the
zoobenthonic community colonies and the growth of its populations, which enriches the fauna and
makes it more abundant. This data attests the validity of previous data obtained in the historical series
of CETEC projects developed in the upper Rio das Velhas basin (CETEC 1994; 1998). Under these
conditions the samplings become more representative and more adequate for the bioindication of
water quality for biomonitoring, as a bigger number of zoobenthonic representatives serve as
bioindicators of the water quality. Besides, the fact that dissolved substances were found to be more
concentrated in the water during the dry season strengthens the advantages of using the samples
collected during that period as reference for biomonitoring, for that season is the most adequate to
reflect the most critical conditions of the physical and chemical characteristics of the water and the
most stable conditions of the coriótopos of lotic ecosystems.
We can conclude that in the upper Rio das Velhas basin the best periods to obtain samples of the
benthonic fauna are probably between May and October. Such results, which indicate the dry season
as the most adequate for collecting benthonic macroinvertebrates of lotic environments, are in
agreement with studies previously made in other hydrographic basins of the State, like the one
developed by Campos et al. (2002) in the Córrego Rico basin, and comply with the norms of the
"Water Resource Management Manual" (op. cit.) These studies also confirm that the periods of
collection adopted by CETEC during the development of their water quality biomonitoring
methodology were correct and will support the collection plan of future biomonitoring to be made by
the CETEC/SEMAD/IGAM in the upper Rio das Velhas basin.
However the best period for sample collection in the dry season can be identified by performing a
survey of a longer series of historical data about the seasonal behavior of the benthonic communities
of this area in shorter intervals. As 2003 was a typical hydrologic year, the findings presented in this
work can be considered very representative.
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ACKNOWLEDGEMENTS
The financial support that made this work possible was provided by the Minas Gerais Research
Support Foundation (FAPEMIG), the Minas Gerais Water Management Institute (IGAM) and the
Minas Gerais Technology Center Foundation (CETEC). Thanks are also due to Rosa Maria Neves da
Silva for proofreading and editing the English text.
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