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
Fig 2 Part of central Rio de Janeiro with the Sugar Loaf, Pão de Açúcar (390 m), east of Botafogo Bay. 1974.
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.
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.
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
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
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
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
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.
Björk, S, Lettvall U. & Ripl W. 1975. The Lagoa Rodrigo de Freitas Restoration
Project. - United Nations Development Programme, World Health Orgnization.