4.2.2 State trophic index (TSI)

With the TSI based on two partial indexes (TSI-TP and TSI-Chl a), the trophic state of Jansen lagoon showed a variation of 190.69 μg L<sup>1</sup> in the dry season and 191.04 μg L<sup>1</sup> in the rainy season, and Jansen lagoon was classified as hypereutrophic (Figure 5). When the parameters are analyzed individually, the environment is classified as very eutrophic, and when they are aggregated for the final calculation of this index, the result obtained corroborates this pattern, with a weighting of 5.

Combining the two partial indexes, it was possible to observe that the TSI-TP showed higher weighting with regard to the increase of the degree of eutrophication in Jansen lagoon, considering that the total TSI showed an intermediate quantification in relation to the one observed in the TSI-TP and in the TSI-Chl a; however, all of them had the same weighting and classification. When that happens, it is inferred that the system is already under eutrophication, since the trophic state indicated by the TSI-TP coincided with TSI-Chl a.

#### Figure 5.

Representation of the trophic state index (TSI) in Jansen lagoon, São Luís-Maranhão: ultraoligotrophic (blue), oligotrophic (green), mesotrophic (yellow), eutrophic (orange), supereutrophic (red), and hypereutrophic (purple).


#### Table 8.

Spatial-temporal means of TSI values according to Lamparelli [18] in Jansen lagoon, São Luís-Maranhão.

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

Comparing the values obtained in the final TSI, it was possible to observe a small variation in the degree of eutrophication. In this perspective, in a general average for the sites, L1 was considered the most eutrophic and L5 as the less eutrophic (Table 8). Regarding the sampling campaigns, Mar-12 was the most eutrophic because it had maximum values of the TSI (TP) and the TSI (Chl a) and the least eutrophic was set/12 because it had high values for the TSI (TP) only.

This scenario is explained by the high concentration of total phosphorus available in the system and because it has not been considered as a limiting element for photosynthetic organisms, since even though it was being consumed, there was still a large amount of it.

Regardless of the sampling site or campaign, Jansen lagoon was classified as hypereutrophic, because according to the classification of Lamparelli [18], all sites obtained a weighting of 5, which equals TSI values above 67.

The trophic level observed in this study through the use of the TSI showed to be very high, being even higher than what is reported for other environments that also suffer from cultural eutrophication as verified by Knoppers et al. [44] in six coastal lagoons in Rio de Janeiro (Brazil), Herrera-Silveira et al. [45] in three coastal

#### Figure 6.

Representation of the aquatic life protection index (ALPI) at Jansen lagoon, São Luís-Maranhão.


#### Table 9.

Mean values of the aquatic life protection index (ALPI) according to Zagatto et al. [17] modified by CETESB [32] in Jansen Lagoon, São Luís-Maranhão.

lagoons in Yucatán (México), and Fia et al. [46] in Mirim lagoon (Brazil). These authors also observed that cultural eutrophication plays an important role in the determination of water quality, besides influencing the self-purification capacity of the environment, leading to loss of water quality and intensification of the eutrophication process.

Therefore, the use of these waters for any secondary contact activity (recreation and amateur fishing-subsistence) is not appropriate, as for these purposes, the acceptable trophic state in environments such as lakes is mesotrophic or even slightly eutrophic [15].

#### Figure 7.

Representation of IMPAC (index of minimum parameters for the protection of aquatic communities),TSI (state trophic index), and ALPI (aquatic life protection index) classification categories at Jansen Lagoon, São Luís-Maranhão.

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

### 4.2.3 Aquatic life protection index (ALPI)

The general characterization of water quality in the Jansen lagoon from the ALPI interpretation was classified as bad, with values of 11.16 in the dry season and 9.0 in the rainy season (Figure 6).

Knowing that the first two indexes have already shown that water quality in Jansen lagoon is not suitable for the activities indicated for class 2 brackish waters, according to CONAMA 357/05 [30], it is confirmed by the ALPI which classifies this environment as inappropriate. The weightings obtained from the ALPI calculation were above 6.8 resulting in a very bad classification. It can be observed that the poor water quality was more critical at the site L4 and in the July-12 campaign, with average weightings of 10.8 and 14.4 (Table 9), respectively.

Comparing the weightings obtained from the first two indexes with the weightings obtained from the ALPI calculation, it was observed that the higher IMPAC weightings were responsible for raising the weightings of the ALPI in 30% of the sites monitored, mainly in July-12, being again the campaign with a higher degree of impairment of water quality. Thus, it was verified that the worst weightings defined the final value of the index [9]. The result obtained through the ALPI index for the Jansen lagoon was much higher when compared to the environments studied by Coelho [47] and Barbosa [9]. Besides, they do not have a constant classification pattern in relation to the TSI as verified in this study.

Based on CONAMA Resolution [30], which was used to classify the waters of the Jansen lagoon, the preponderant conditions verified through the application of the indexes and the limits established for each environmental parameter analyzed showed that this lagoon environment is very much affected by a loss of water quality and decreased protection of aquatic life.

In this scenario, the application of IMPAC and TSI showed that the renewal of the water of Jansen lagoon by the spring tides is not enough to improve its quality. According to Schettini [48], this deterioration in coastal lagoons is favored by their morphometry that makes them more susceptible mainly due to the exchange with the ocean and the increase in the time of renovation; for this environment, the ideal would be around 90% every 28 days if all polluting sources were eliminated. In view of this situation, the Jansen lagoon does not have a spatial and temporal difference, with poor water quality, subject to the conditions of the environmental descriptors, trophic degree, and toxic substances (Figure 7).
