## 3 Results and Discussion
### Influence of Wetlands on Water Quality
#### 3.5.3 Total Nitrogen Assessment  
An increase in TN values was observed over 7 years between the input and output in the wetland area of the Pantanal. In the years 2005, 2007, and 2015, there was stability in the trend; however, for the years 2007, 2009, 2013, and 2014, there was a reduction in concentrations. Thus, it is observed that there is no clearly defined pattern of behavior for nitrogen in the studied Pantanal wetland areas. It is also noted that, in general, the highest concentration values occur during the rainy seasons (Figure 12).  
[PERSON] et al. [45] estimated the performance in the input and output of a wetland area in removing nitrogen loads originating from upland pastures in the watershed in Waikato, New Zealand. The authors found that the concentrations of TN were consistently lower at the outlet of the wetland area, regardless of flow conditions or seasonality. This is due to water infiltration through saturated layers of anoxic organic sedimentary material and plant debris with high denitrification potential, so that high denitrification rates are common in wetlands and riparian zones rich in organic matter [45]. [PERSON] & [PERSON] [12] also observed the reduction in TN in the wetland area of Riacho Fundo, Brasilia, Brazil. The authors found an average retention of 36.7% for TN between the inlet and outlet of the wetland area.  
In the literature review conducted by [PERSON] and [PERSON] [13] on the nitrogen retention capacity in wetlands around the world, the authors confirm that most wetlands retain nitrogen; however, about 13% of the wetlands studied showed an increase in Nitrogen in the aquatic environment. Nitrogen can also be deposited in wetlands through atmospheric processes of molecular nitrogen (N\({}_{2}\)) fixation, carried out by fixing bacteria. Additionally, the decomposition of dead organic matter can also release nitrogenous forms into the  
Figure 12: Spatial variation of the mean Total Nitrogen (mg/L) at the monitoring stations of the Pantanal (IA07, IA14, IA15, IA16, IA17).  
water mass. Most wetlands can function as effective reservoirs of nitrogen in tropical zones, accounting for two-thirds of all globally fixed atmospheric nitrogen [46]. [PERSON] and [PERSON] [46] highlighted that some factors affect nitrogen fixation in wetlands such as low N:P ratios in sediment, inputs of wastewater, reducing conditions (redox potential), photosynthetic activity, availability of molybdenum, iron, and dissolved organic matter. On the other hand, nitrification reactions, denitrification, ammonia volatilization, and plant absorption help to keep nitrogen levels low in the water column. The contribution of each of these reactions will depend on a series of environmental factors, which can effectively optimize or minimize the relative rates of each reaction in soil and wetland areas [46].  
The capacity of wetlands to remove nutrients from water varies with climatic seasonality, increased nutrient loads, and different types of vegetation. Vegetation production and seasonality influence the amounts of organic matter and carbon in wetland sediments and the oxygen concentration in sediment [47]. Therefore, the variability of nitrogen concentrations in the studied area can be explained by the regime of wetland areas during dry and flood periods and by the nitrogen cycle that occurs fully in wetlands, thanks to the presence of air, water, sediment, land, and live biomass. Additionally, the nitrogen cycle occurs jointly with the other biogeochemical cycles of carbon, phosphorus, and oxygen [47].