4. Results and discussion

#### 4.1 Climatological scenario and environmental descriptors

During the sampling period, an atypical pattern was observed, with annual rainfall amounts ranging from 995 mm (2012) to 2530 mm (2011), which was the result of a combination of the effects of the El Niño–Southern Oscillation (ENSO) [42].

The characteristics of the estuarine waters of the Jansen lagoon are summarized in Table 6 and Figure 3, with significant differences in environmental variables occurring between the rainy and dry seasons.

The water temperature is typical of environments near the equator, and regarding the salinity values, the waters of Jansen lagoon during the study period were


#### Table 6.

Seasonal variation of environmental variables in Jansen lagoon, São Luís-Maranhão.

Figure 3. Seasonal variation of environmental variables during the study period in Jansen lagoon, São Luís-Maranhão.

classified as brackish waters. Total chlorophyll a concentrations showed higher values in the dry season. The TP showed higher values in the rainy season. For toxic substances, phenol and surfactants also showed higher values in the rainy season.

The water samples from the Jansen lagoon did not show any acute effect for the Poecilia sphenops juveniles during 96 hours of exposure, without water renewal and in stable physicochemical conditions (temperature, salinity, oxygen, and pH), considering 100% of survival during acute toxicity tests.

#### 4.2 Water quality indexes

### 4.2.1 Index of minimum parameters for the protection of aquatic communities (IMPAC)

According to the results obtained for the essential parameters and the toxic substances, the IMPAC was calculated for the Jansen lagoon waters with weightings ranging from 2 to 9, being 5.13 during the dry season and 3.3 in the rainy season. In general, the quality of the water in Jansen lagoon was considered bad in 56.66% (Figure 4).

Regarding the seasonal variation of IMPAC, the waters had the pattern shown in Table 7. During the study period, the presence of dead fish was not observed. However, some species that are possibly the ones that could adapt and remain in that environment were observed.

Due to the decomposition of the organic matter in the lagoon, the bad smell from the release of the hydrogen sulfide gas was constant. Besides that, blooms of indicator phytoplankton (Microcystis aeruginosa) and Ruppia maritima specimens were observed at the study area, resulting in a mass of greenish-dark coloration [26, 43].

The surfactants were the main toxic substances that determinate the classification of water quality in the Jansen lagoon. July 12 was the period in which the lagoon had the lowest water quality. In that period, all sampling sites were classified as very bad where dissolved oxygen and surfactants reached the highest weightings, indicating that the whole environment was very much compromised.

Phytoplankton Biomass and Environmental Descriptors of Water Quality of an Urban Lagoon DOI: http://dx.doi.org/10.5772/intechopen.87955

#### Figure 4.

Representation of the index of minimum parameters for the protection of aquatic communities (IMPAC) in Jansen lagoon, São Luís-Maranhão.


#### Table 7.

Spatiotemporal distribution of IMPAC mean values according to Zagatto et al. [17] in Jansen lagoon, São Luís-Maranhão.

This scenario was favored by the season. In the beginning of the dry season, the confined waters presented a typical oxygen profile of that environmental scenario and the increase of surfactants could be expected due to the fact that it is a holiday season, which means that people will stay longer in their residences and consequently there will be a greater use of cleaning products, which are sources of these substances, and that will be released to the sewage system.

The quality of the lagoon waters ranged from regular to very bad. For this index, the most important elements for classification of the Jansen lagoon were the dissolved oxygen in the group of essential parameters, and the surfactants in group of toxic substances. These parameters presented high values, being above the allowed by CONAMA Resolution 357/05 [30], evidencing a high degree of pollution caused by the disordered occupation that occurs in the area and by problems of sanitary sewage that still persist.

The heavy metals were detected in small quantities; however, even when quantified above the limit allowed by the federal legislation, their weightings did not have the same weighting as the other indicators in the calculation and final values of IMPAC.
