**2.4 Traditional environmental problems in the LRF**

Traditionally, both the LRF and its surroundings have been densely populated in recent decades, and this urbanization has been accompanied by several harmful environmental effects, such as those arising from numerous landfills and silting that have sharply reduced its water features. According to Soares et al. [1], at the beginning of the 1970s, there occurred a spate of particularly aggressive property speculation in the district surrounding the Lagoon, which had experienced landfills since 1808 and lost almost a half of its original area. Despite the fact that Municipal Decree 130/1975 had stipulated the boundaries of the surface area of the water features, it was only finally protected definitively by Decree 9.396/1990.

Another serious impact, which is still prevalent, is closely bound up with the continuous discharges of sanitary effluent into its waters. This is generally caused by illegal sewerage networks for the rainwater drainage system that pours into the Lagoon and the affluent rivers and canals [15]. For this reason, the quality of the water of LRF greatly deteriorated in the period 1970–2000, as a result of the installation of drainage pipes, through the water supply system, as well as through contact with the tributaries of the rivers that contained a considerable polluting load when they reached the entry of the floodgates of the General Garzon Canal [6, 16].

For several years, the situation was aggravated by the presence of two craters at the bottom of the Lagoon: one between the Caicaras and Flamengo Clubs and the other in front of Cantagalo. These depressions arose from the withdrawal of material for landfills and led to the accumulation of a good deal of organic matter in anaerobic decomposition, where it produced toxic gases such as sulfidic ores and methane. It was found that the pit that was less deep (Caicaras) was completely filled with silt sediment at one part of the bed of the Lagoon. This discovery was made in the period preceding the Olympic Games of 2016, when an attempt was made to attain a minimum depth of 3 m in the whole region used for the competition. With regard to the deepest pit (Cantagalo), there is no information about its current depth, because no bathymetry was employed after these proceedings. Mello [17] states that the filling of the pits could be regarded as a positive effect of the silting mentioned above, since it could operate as an anaerobic biodigester and lead to an increase of the area of water circulation (albeit on a small scale).

## *2.4.1 Evolution of fish mortality in the LRF*

The first studies on the stagnation of the water and the mortality of fish in the LRF were reported in 1877 by the Baron of Lavradio and in 1880 by the Baron of Teffe. According to a survey carried out by Andreata [18], there are about 60 species of fish in the LRF and, hence, different degrees of sensitivity and tolerance to a wide range of factors such as temperature, dissolved oxygen, pH, and salinity.

The mortality rate of the fish recorded in the Lagoon can mainly be attributed to the following causes: a lack of renewal of the waters, algae toxicity, the disposal of wastewater, the stirring up of soil, and the anoxic sediment layer at the bottom [1]. It has been argued that the serious problem of the mortality rate of the fish in the Rodrigo de Freitas Lagoon was not caused by the installation of a sewage system but rather by the current stock of nutrients that can be found today which result from a combination of the older sewage systems *in natura* and the rainfall drainage and

**29**

*Environmental Monitoring of Water Quality as a Planning and Management Tool: A Case…*

the fact that there is an ineffective outlet to the sea [19]. However, what has been observed by the monitoring is that the influence of the sewage system is essential

The entry of this organic load as well as the stirring up of the sediment at the bottom has made available a large number of nutrients for the water column. This can allow algae to flourish and lead to phenomena of natural or anthropic origin which can be defined as an explosive growth that is self-limiting and confined to

Lima [5] notes that even gentle breezes can prevent the stratification of the water column and lead to the horizontal uniformity of the water mass. He stresses the fact that, when in a condition of instability, the ecosystem in question is more vulnerable at nighttime since at this time there is no primary production (i.e., photosynthesis),

There is no doubt that the situation in the LRF has improved, as can be confirmed by the reduction in the mortality rate of the fish. This improvement has also been demonstrated by the results of the analyses conducted to monitor the quality of the waters of the LRF and also by the decreasing rates of the parameters such as mortality and DBO shown by CEDAE itself. The Sustainability Management Plan for the Olympic Games in Rio (2016), published in 2013, recorded an improvement in the quality of the water. However, the situation is still far from being effectively remedied, and these mass deaths continue to occur, although they are less frequent

The region is served by infrastructural facilities of a good standard which include telephones, electricity, a transport system and a road network (with streets and a cycle path), a water supply system, a public drainage system, and sanitary sewage system, as well as a completely separate system operated by CEDAE. Nonetheless, it is still possible to find polluted water being discharged into the Lagoon through a network of drains and through the rivers that flow into the LRF, even in periods of serious drought. Thus, it can be proven that there is still a link between the public sewerage system and the installation of drains in the streams themselves. These installations end up by reaching and polluting the water in the rivers and the Rodrigo de Freitas Lagoon itself. This is the case, for example, of the pollution witnessed in the Macacos Canal, which is connected to the river with the same name, as well as

On the basis of the analysis conducted by INEA [6], the Macacos River was found to be in an excellent condition above the Forest of Tijuca but began to be extremely polluted after it had passed the Jardim Botânico. The analysis of its water revealed that at certain times the Macacos River records a high level of pollutants. Researchers and officials at the Jardim Botânico found that some animals had symptoms of diseases that could be linked to this pollution and contaminated water. According to Bess D'Alcântara et al. [15], the occurrence of problems in the sanitary sewage system in the LRF basin resulted in large amounts of waste in the water feature of the Lagoon, which further impaired the indicative parameters of

In recent years, the region has been the object of several projects and public measures aimed at reducing, or even eradicating, this problem of wastewater and hence improving the environmental conditions of the Lagoon. These include an

but only the absorption of oxygen that is dissolved through respiration.

*DOI: http://dx.doi.org/10.5772/intechopen.88687*

for the nutritional intake in the Lagoon [17].

just one or a few species of microorganisms [20].

than was found in the past, as explained above.

the Rainha and Cabeca rivers, before flowing into the Lagoon.

**2.5 Urban infrastructure**

the quality of its waters.

*2.5.1 System of culverts for the LRF protection*

*Environmental Monitoring of Water Quality as a Planning and Management Tool: A Case… DOI: http://dx.doi.org/10.5772/intechopen.88687*

the fact that there is an ineffective outlet to the sea [19]. However, what has been observed by the monitoring is that the influence of the sewage system is essential for the nutritional intake in the Lagoon [17].

The entry of this organic load as well as the stirring up of the sediment at the bottom has made available a large number of nutrients for the water column. This can allow algae to flourish and lead to phenomena of natural or anthropic origin which can be defined as an explosive growth that is self-limiting and confined to just one or a few species of microorganisms [20].

Lima [5] notes that even gentle breezes can prevent the stratification of the water column and lead to the horizontal uniformity of the water mass. He stresses the fact that, when in a condition of instability, the ecosystem in question is more vulnerable at nighttime since at this time there is no primary production (i.e., photosynthesis), but only the absorption of oxygen that is dissolved through respiration.

There is no doubt that the situation in the LRF has improved, as can be confirmed by the reduction in the mortality rate of the fish. This improvement has also been demonstrated by the results of the analyses conducted to monitor the quality of the waters of the LRF and also by the decreasing rates of the parameters such as mortality and DBO shown by CEDAE itself. The Sustainability Management Plan for the Olympic Games in Rio (2016), published in 2013, recorded an improvement in the quality of the water. However, the situation is still far from being effectively remedied, and these mass deaths continue to occur, although they are less frequent than was found in the past, as explained above.
