Överkörd Natur

Brasilien

Sven Björk

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Lagoa Rodrigo de Freitas Rio de Janeiro

Summary (mainly from Ambio 17, 1988)

Fig 1 The southeastern part of Rio de Janeiro with Lagao Rodrigo de Freitas and Botafogo. The canal connecting the Lagoa with the Atlantic, Canal Jardim de Alà, has its outlet between tho Leblon (to the west) and Ipanema beaches. From the map Estado da Guanabara. 1973.

Landwards from the Copacabana and Ipanema beaches in Rio de Janeiro the Lagoa Rodrigo de Freitas (2.5 km2, maximum depth 4.5 m) constituted a problem in the densely built-up city. Pollution by sewage in combination with high temperatures, salinity stratification as well as the high speed in the development and collapse of dense phytoplankton populations were the prerequisites for repeated total-oxygen deficiency and sudden fish-kills. The residents around the lake complained about the nasty smelling environment and the blackish water was not suitable for recreational activities.

The objectives for the restoration of Lagoa Rodrigo de Freitas were the elimination of the environental problem and the transformation of the lake section of the city into an environmental asset, suitable for recreational purposes.

The redevelopment of the area started with the removal of favela constructions (partly pile-dwellings), diversion of sewage and tracing of clandestine sewage outlets.

The restoration program comprised

  • 1) the removal of sewage-sludge deposits,
  • 2) renewal (pumping) with ocean water to such an extent that the lake is kept unstratified, and
  • 3) the tidying-up of the shores and putting them in order as green areas, playgrounds and promenades.

Fig 2 Part of central Rio de Janeiro with the Sugar Loaf, Pão de Açúcar (390 m), east of Botafogo Bay. 1974.
Fig 3 Lagoa Rodriga de Freitas, the western part. 1974.
Fig 4 Lagoa Rodriga de Freitas. th eastern. The Jardim de Alà canal, visible to the right of the island, Ilha Carçara´s, at the upper (southern) shore, 1974.
Fig 5 Rio Janeiro. Incineration of garbage in recidential quarters. 1975.

Fig 6 Sampling for investigations of sediment stratification and quality. 1974.

For economical reasons the restoration program had in 1988 not yet been fully accomplished. Part of the sewage-sludge sediment had been removed and the connection with the ocean (the Canal Jardim de Alá) had been opened up. Gates had been installed in the canal to regulate water flow. Thus, the tide promotes water renewal to such an extent that the lake is kept unstratified except during rainy periods. Furthermore, the shores have been upgraded.

Fig 7-8. Suction dredging of sewage sludge sediment. 1977.
Fig 9. Shore restauration close to the Jardim de Alà canal. M. Enell. 1978

These measures had already in 1988 resulted in a much more attractive environment. The lake, therefore, contains a diverse fauna and flora (including macrophytes); is used for sport fishing, for canoeing etc. and the redeveloped section of the city has gained aesthetically. Until the whole of the recommended program for complete restoration has been put into practice (e.g. water renewal secured through pumping) the risk for short, occasional ecosystem collapses remains.

Fig 10-11. Improved function of the Lagoa ecosystem.
Te revitalized Lagoa Rodrigo de Freitas. M. Enell 1978 and Granéli 2007

The project, which began operation in February 1974, was financed by the World Health Organization (WHO) and carried out as a cooperation between the Fundaça o Estadual de Engenharia do Meio Ambiente (FEEMA) and the Institute of Limnology, University of Lund.



Lago Paranoa Brasilia

Fig 1. The drawing by Mats Lind for the Swedish National Encyclopedia gives a concentrated impression of the connection between the shape of the man-maid  Lago Paranoa and the architectural design of the city Brasilia.

The original upland landscape

Fig 2. Typical landscape within the Brasilia region
Fig 3-4. Almost undistubed drainage systems. 1975.

In connection with the scientific program 1975-76 at Lagoa Rodrigo de Freitas, the Lund team of limnologists was also asked to make limnological investigtions in Lago Paranoa, Brasilia, and to structure a restoration plan for the lake. Also in this case the project was financed by WHO. The studies were made 1975-1977, in cooperation with Companhia de Água e Esgotos de Brasília (CAESB).

The city of Brasilia

Fig 5. The centre line of Brasilia seen from the east. Lago Panoia in the background. 1974.
Fig 6. Part of the city and Lago Panaora. Note the typical terra rossa. 1974
Fig 7. Suburban area illustrating the rapid growth of the Brasilia population. 1975.

Lago Paranoa (40 km2, maximum depth 37 m, catchment area 10 km2, 1000 m.a.s.l., hydraulic retention time one year, mean water temperature in epilimnion 23o C) is a man-made lake, filled with water in 1960. Unfortunately the bottom of the lake was not cleaned from vegetation (including trees and bushes) before the valley was filled with water. Lago Paranoa was created for aesthetic and recreational purposes, as an asset for the inhabitants of the new capital of Brasil. Sewage discharge transformed it from a nutrient-poor lake to a water body characterized by heavy blooms of cyanobacteria ("blue-green algae"). Within the Brasilia region the soils are characterized by being extremely poor in nutrients. The natural conditions for a healthy, pleasant environment are, therefore, excellent, but eutrophication made, after a short period with clear water, the utilization of the lake impossible for the recreational purposes it was intendet to serve.

Erosion within the catchment area of Lago Paranoa

Fig 8-9. Initiated and expanding erosion. 1975.
Fig 10. Inflow of eroded matter in Lago Paranoa. 1975.

Hardly any organic sediments had been deposited in Lago Paranoa according to investigations in the late 1970s. It was, therefore, then still possible to redevelop the lake simply through the diversion of sewage. This should have been done in connection with the construction of efficient treatment plants and diversion of treated sewage to a river as the receiving body. Part of the treated sewage could have been used for irrigation. However, according to studies made 10 years later, the overloading by nutrients of the lake ecosystem had resulted in deposits of organic sediments, now covereing the bottom with the exception of part of the central area. Thus, the delay in sewage diversion and treatment was making it much more difficult to restore the lake.

The pollution of Lago Paranoa

Fig 11. The south treatment wastewater plant of Brasilia, with Lago Paranoa as the Recipient. 1975. Fig 12. Lago Paranoa characterized by heavy water bloom. Club premesis on the shore. 1975.

Unfortunately, the continued pollution prevented the use of Lago Paranoa for the purposes for which it was intended in the large-scale planning of the Brasilia region. Addition of copper sulfate in order to reduce plankton growth, already carried out in this lake, is an unjustifiable cosmetic treatment of the symptoms of serious degradation. The longer a lake is overexploited, the more grave will the danger become that an internal loading of nutrients will be added to the external one.

Further reading

Björk, S, Lettvall U. & Ripl W. 1975. The Lagoa Rodrigo de Freitas Restoration Project. - United Nations Development Programme, World Health Orgnization. Geneva
Björk, S. 1979. The Lago Paranoa restoration project, Brasilia, Brazil. - Project UNDP BRA/75/033 WHO Bra-2341. Incl. the following references:
    Hilmer A. 1978. Loading and budget calculation. - Final report.
    Enell M. 1978. Water chemistry and sediment stratigraphy. - Final report.
    Cronberg G. 1978. Phytoplankton ecology and taxonomy. - Final report.
    Lindmark G. 1978. Bioassays - Field and laboratory experiments - and phytoplankton productivity. - Final report.
Björk, S. 1988. Redevelopment of lake ecosystems - A case-Study approach. - Ambio 17.
Somlyódy, L. 1987. Assessment of sanitary and environmental characteristics of the Sao Bartolomeu River and Lake Paranoa Basins. - Report Project BRA/UNDP.

Sidan uppdaterades januari 2013
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