**5.6 Ammonia nitrogen**

Ammonia nitrogen is formed by ammonia species (NH3) and ion ammonia (NH4+), which is the most toxic species in the aquatic organisms [39]. The CONAMA Resolution 357/2005 stipulates 0.70 mg/L N as the limit of total ammonia nitrogen for the brackish waters of class 2, regardless of the pH [40]. Nitrogen is regarded as one of the most important elements in the metabolism of aquatic ecosystems for directly protecting aquatic life. This is also due to its role in the formation of proteins and chlorophyll [33].

The values of ammonia nitrogen showed a wide variation in 2018, although the seasonal fluctuations were not defined (**Figure 10**). However, it should be pointed out that, generally speaking, in summer the averages were reduced, while spring showed the highest maximum values, with the detection of a considerable increase in the parameter after heavy rainfall, mainly on October 15 and November 26. This rise in ammonia nitrogen can be attributed to the entry of organic matter and other substances into the Lagoon.

The inorganic forms of nitrogen, mainly ammonia nitrogen and nitrate, are ideally assimilated by phytoplankton [41–43]. During the period of phytoplanktonic blooming which took place between December 10 and 17, 2018, there was a reduction in the values of ammonia nitrogen, with a subsequent rise of the parameter at the end of the blooming period.

**Figure 10.** *Ammonia nitrogen on the surface of the LRF in 2018.*


#### **Table 11.**

*Average Ammonia nitrogen at the LRF during the monitored spring seasons.*

When compared with the springs of 2014, 2015, and 2016 in **Table 11**, the parameter in 2018 was between 0.071 mg/L and 0.119 mg/L above the others.

CETESB [26] establishes that the control of eutrophication by reducing the intake of nitrogen was adversely affected by the numerous sources, some of which are hard to control like the fixation of atmospheric nitrogen on the part of the algae. In this way, an investment was made in controlling the sources of phosphorus.

### **5.7 Dissolved oxygen**

Dissolved oxygen (DO) is the main element in the metabolism of aerobic aquatic organisms such as fish and planktonic microorganisms. It is because of its importance in the maintenance of aquatic life that the DO is used as the main parameter for the quality of the water. CONAMA 357/2005 stipulates a minimum value of 4.00 mg/L of DO for class 2 brackish water.

The principal sources of oxygen for the aquatic ecosystem are the atmosphere and the photosynthesis of the algae, while its consumption is related to the decomposition of organic matter, the respiration of aquatic organisms the oxidation of ions, and losses to the atmosphere [39]. Low concentrations of dissolved oxygen in the water can cause delayed growth, a reduction in efficient feeding practices, and an increase in the incidence of diseases and the mortality of fish [44].

Polluted water tends to have low concentrations of dissolved oxygen owing to its consumption in the oxidation of the organic compounds, whereas clean water displays higher concentrations of DO [34]. However, systems with eutrophication can have supersaturated conditions, with concentrations of oxygen higher than 10 mg/L, even in temperatures above 20°C. According to CETESB [26], this mainly occurs in lakes with low speeds where algae soil crusts are formed on the surface.

#### *5.7.1 Dissolved oxygen during blooming and fish mortality*

During the year that was analyzed (2018), there was a wide variation in the concentrations of DO on the surface of the Lagoon (**Figure 11**). Esteves [33] points out that the rise in temperature and salinity reduces the capacity of the oxygen to dissolve in water. For this reason, summer (the season which showed the highest values in these parameters) recorded the lowest average concentrations of DO. However, it should be noted that the lowest minimum concentrations of DO occurred in spring, after the senescence. Then there was a sharp reduction and consequent aerobic decomposition of the phytoplanktonic population of *Synechocystis* spp., which was in bloom, leading to records of the mortality of fish by anoxia in the LRF, from December 20 to 23, 2018.

Esteves [33] states that owing to high temperatures, the decomposition of organic matter in tropical waters occurs 4–10 times more rapidly than in temperate climates, which involve a proportionally greater intake of oxygen. In the case of shallow water bodies, like the case of LRF, the concentration of organic matter combined with high temperatures is a decisive factor in determining the degree of deoxygenation.

**47**

**Table 12.**

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

When compared with the springs of 2014, 2015, and 2016 in **Table 12**, the

Organic matter is rich in nutrients like nitrogen and phosphorus which, in excess, can cause an imbalance with regard to the production and consumption of biomass, a condition known as eutrophication [45]. According to Esteves [33], phosphate is cited as being responsible for the artificial eutrophication of continental waters, the most important artificial sources being the sewage systems and the

Although the legislative regulations of CONAMA (357/2005) define the maximum limit of 0.186 mg/L for total phosphorus and separate phosphate fractions, it is the monitoring of the orthophosphate in water bodies that is most important

No significant differences were observed in the average levels of total phosphorus between the different points (**Figure 12**). Although the highest values were found in spring, it was only in point LRF6 that the limit of 0.186 mg/L (that was established by CONAMA Resolution 357/2005) was surpassed for brackish water of class 2. It was

Averages at sampling points 2014 2015 2016 2018

6.4 6.9 7.0 7.6

since it is the main means of assimilating primary end consumers [33].

The amount of oxygen can either increase through the intensification of photosynthetic production or decline if there is greater respiration among the local communities and/or a greater oxidation of organic matter. Temperature has a direct influence on both the respiration of the organisms and the other oxidative processes like the decomposition of organic matter by aerobic microorganisms and hence has

parameter in 2018 was between 0.6 and 1.2 mg/L above the others.

an effect on the levels of dissolved oxygen.

*Dissolved oxygen in the surface of the LRF in 2018.*

**Figure 11.**

**5.8 Total phosphorus and orthophosphate**

particle material of industrial origin.

**Dissolved oxygen (mg/L)**

*Average water DO at the LRF during the monitored spring seasons.*

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

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

#### **Figure 11.**

*Lagoon Environments Around the World - A Scientific Perspective*

*Average Ammonia nitrogen at the LRF during the monitored spring seasons.*

**5.7 Dissolved oxygen**

**Ammonia nitrogen (mg/L)**

**Table 11.**

4.00 mg/L of DO for class 2 brackish water.

When compared with the springs of 2014, 2015, and 2016 in **Table 11**, the parameter in 2018 was between 0.071 mg/L and 0.119 mg/L above the others. CETESB [26] establishes that the control of eutrophication by reducing the intake of nitrogen was adversely affected by the numerous sources, some of which are hard to control like the fixation of atmospheric nitrogen on the part of the algae. In this way, an investment was made in controlling the sources of phosphorus.

Averages at sampling points 2014 2015 2016 2018

0.203 0.155 0.166 0.274

Dissolved oxygen (DO) is the main element in the metabolism of aerobic aquatic organisms such as fish and planktonic microorganisms. It is because of its importance in the maintenance of aquatic life that the DO is used as the main parameter for the quality of the water. CONAMA 357/2005 stipulates a minimum value of

The principal sources of oxygen for the aquatic ecosystem are the atmosphere and the photosynthesis of the algae, while its consumption is related to the decomposition of organic matter, the respiration of aquatic organisms the oxidation of ions, and losses to the atmosphere [39]. Low concentrations of dissolved oxygen in the water can cause delayed growth, a reduction in efficient feeding practices, and

Polluted water tends to have low concentrations of dissolved oxygen owing to its consumption in the oxidation of the organic compounds, whereas clean water displays higher concentrations of DO [34]. However, systems with eutrophication can have supersaturated conditions, with concentrations of oxygen higher than 10 mg/L, even in temperatures above 20°C. According to CETESB [26], this mainly occurs in lakes with low speeds where algae soil crusts are formed on the

During the year that was analyzed (2018), there was a wide variation in the concentrations of DO on the surface of the Lagoon (**Figure 11**). Esteves [33] points out that the rise in temperature and salinity reduces the capacity of the oxygen to dissolve in water. For this reason, summer (the season which showed the highest values in these parameters) recorded the lowest average concentrations of DO. However, it should be noted that the lowest minimum concentrations of DO occurred in spring, after the senescence. Then there was a sharp reduction and consequent aerobic decomposition of the phytoplanktonic population of *Synechocystis* spp., which was in bloom, leading to records of the mortality of fish by anoxia in the LRF, from

Esteves [33] states that owing to high temperatures, the decomposition of organic matter in tropical waters occurs 4–10 times more rapidly than in temperate climates, which involve a proportionally greater intake of oxygen. In the case of shallow water bodies, like the case of LRF, the concentration of organic matter combined with high

temperatures is a decisive factor in determining the degree of deoxygenation.

an increase in the incidence of diseases and the mortality of fish [44].

*5.7.1 Dissolved oxygen during blooming and fish mortality*

**46**

December 20 to 23, 2018.

surface.

*Dissolved oxygen in the surface of the LRF in 2018.*

When compared with the springs of 2014, 2015, and 2016 in **Table 12**, the parameter in 2018 was between 0.6 and 1.2 mg/L above the others.

The amount of oxygen can either increase through the intensification of photosynthetic production or decline if there is greater respiration among the local communities and/or a greater oxidation of organic matter. Temperature has a direct influence on both the respiration of the organisms and the other oxidative processes like the decomposition of organic matter by aerobic microorganisms and hence has an effect on the levels of dissolved oxygen.

## **5.8 Total phosphorus and orthophosphate**

Organic matter is rich in nutrients like nitrogen and phosphorus which, in excess, can cause an imbalance with regard to the production and consumption of biomass, a condition known as eutrophication [45]. According to Esteves [33], phosphate is cited as being responsible for the artificial eutrophication of continental waters, the most important artificial sources being the sewage systems and the particle material of industrial origin.

Although the legislative regulations of CONAMA (357/2005) define the maximum limit of 0.186 mg/L for total phosphorus and separate phosphate fractions, it is the monitoring of the orthophosphate in water bodies that is most important since it is the main means of assimilating primary end consumers [33].

No significant differences were observed in the average levels of total phosphorus between the different points (**Figure 12**). Although the highest values were found in spring, it was only in point LRF6 that the limit of 0.186 mg/L (that was established by CONAMA Resolution 357/2005) was surpassed for brackish water of class 2. It was


**Table 12.**

*Average water DO at the LRF during the monitored spring seasons.*

#### **Figure 12.**

*Total phosphorus in the surface of the LRF in 2018.*

noted that this failure in compliance occurred on December 19, or in other words, at the end of the phytoplanktonic bloom that took place in the Lagoon in the spring of 2018.

When compared with the springs of 2014, 2015, and 2016 in **Table 13**, the parameter in 2018 was 0.026–0.055 mg/L above the others.

Similarly, no significant differences in the average levels of the orthophosphate were found between the points (**Figure 13**). A similar behavior for the total phosphorus was noted with higher values in spring.

When the springs of 2014, 2015, 2016, and 2018 are compared in **Table 14**, it was only in the last that average values of orthophosphate were recorded above 0.016 mg/L, suggesting there was a rise in the input of nutrients in this particular spring.

The rise in total phosphorus and the more significant orthophosphate was recorded on December 3 and could have resulted in the entry of a large amount of organic matter and other substances into the Lagoon after the rainfall that occurred between November 26 and December 8. The significant rise of the parameters on December 19 might be owing to the decomposition of the phytoplankton, which was in bloom, which means these nutrients were replaced and made available in the environment. In the same way, the higher values recorded in December 26 may have resulted from the decomposition and the return to the environment of the components after the mortality of about 89 tons of fish which took place in the LRF between December 20 and 23, 2018.

It should be noted that Lopes and Magalhães [34] point out that the growth, death, and decomposition of aquatic organisms have a harmful interference on the quality of the water owing to alterations in the levels of nitrogen, phosphorus, pH, and dissolved oxygen.


**49**

**Figure 13.**

**Table 14.**

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

**6. Conclusion and recommendations for further study**

*Average orthophosphate at the LRF during the monitored spring seasons.*

most alterations in the parameters that were analyzed.

rainfall which led to a large input of nutrients going to the Lagoon.

In the analysis that has been conducted which adopted an approach from a seasonal standpoint, it was not evident from the results of the parameters used for monitoring that there was a considerable variation in the results between the different collection points (LRF1 to LRF6). On the other hand, it can be argued that in general (with regard to all the points monitored), the spring of 2018 was the season of the year that had the most significant alterations. When compared with the previous springs (those of 2014, 2015, and 2016), it was also shown to have undergone

Averages at sampling points 2014 2015 2016 2018

0.016 0.016 0.016 0.022

It is worth stressing that the blooming of the algae occurred in December 2018, as the result of the combination of two factors: the availability of nutrients and the suitable conditions with regard to temperature and salinity. High temperatures were found in this period, which favored lower levels of oxygen in the water column, as well as heavy

In addition, there was a period of failure in the floodgate management which affected the entry of water from the sea and hence heightened the problem of the reduction of the values of salinity, which is an important (if limited) parameter for the establishment of *Synechocystis* spp. At the end of the blooming period of these algae, there was a large fish mortality caused by anoxia. In view of this, attention should be paid to the influence of the Rua General Garzon Canal (notorious for its contamination) in the LRF when its floodgates are opened. For this reason, there is a serious need for a suitable management of floodgates that comply with the guidelines of the protocol of the Municipal Contingency Planning of the Rodrigo de

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

*Orthophosphate in the surface of the LRF in 2018.*

**Orthophosphate (mg/L)**

**Table 13.**

*Average total phosphorus at the LRF during the monitored spring seasons.*

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

#### **Figure 13.**

*Lagoon Environments Around the World - A Scientific Perspective*

**48**

**Table 13.**

**Total phosphorus (mg/L)**

and dissolved oxygen.

between December 20 and 23, 2018.

*Average total phosphorus at the LRF during the monitored spring seasons.*

Averages at sampling points 2014 2015 2016 2018

It should be noted that Lopes and Magalhães [34] point out that the growth, death, and decomposition of aquatic organisms have a harmful interference on the quality of the water owing to alterations in the levels of nitrogen, phosphorus, pH,

noted that this failure in compliance occurred on December 19, or in other words, at the end of the phytoplanktonic bloom that took place in the Lagoon in the spring of 2018. When compared with the springs of 2014, 2015, and 2016 in **Table 13**, the

Similarly, no significant differences in the average levels of the orthophosphate were found between the points (**Figure 13**). A similar behavior for the total phos-

When the springs of 2014, 2015, 2016, and 2018 are compared in **Table 14**, it was only in the last that average values of orthophosphate were recorded above 0.016 mg/L,

The rise in total phosphorus and the more significant orthophosphate was recorded on December 3 and could have resulted in the entry of a large amount of organic matter and other substances into the Lagoon after the rainfall that occurred between November 26 and December 8. The significant rise of the parameters on December 19 might be owing to the decomposition of the phytoplankton, which was in bloom, which means these nutrients were replaced and made available in the environment. In the same way, the higher values recorded in December 26 may have resulted from the decomposition and the return to the environment of the components after the mortality of about 89 tons of fish which took place in the LRF

suggesting there was a rise in the input of nutrients in this particular spring.

0.045 0.016 0.036 0.071

**Figure 12.**

*Total phosphorus in the surface of the LRF in 2018.*

parameter in 2018 was 0.026–0.055 mg/L above the others.

phorus was noted with higher values in spring.

*Orthophosphate in the surface of the LRF in 2018.*


#### **Table 14.**

*Average orthophosphate at the LRF during the monitored spring seasons.*
