In the semiarid region of Brazil, the construction of water reservoirs has the human supply as the main purpose. By climatic and management factors, the population of this region faces serious problems with the water deficit. Still, the lack of sanitation affects the quality of the water of this spring, which are launched domestic effluents daily.
The reservoir under study is located in the city of Nossa Senhora das Dores in the state of Sergipe. It belongs to the sub-basin of Rio Siriri, integrating the list of municipalities in the semiarid region of Brazil. According to the Atlas of Sanitation 2011, the city of Nossa Senhora das Dores does not have sewer collectors.
The collection period was the period from February 2014 to January 2016, considering the dry and rainy seasons in the region.
The methodology for the analysis of parameters was established according to Standard Methods for the Examination of Water and Wastewater, American Public Health Association (1998). Data were worked by descriptive statistics methods in Excel ™ spreadsheet.
The average dissolved oxygen concentrations ranged from 6.9 to 8.4 mg L-1 in the dry period, and 4.8 to 8.3 mg L-1 in the rainy season. According to CONAMA Resolution No. 357/2005, these sections would be framed as Class 3.
In the analysis of the total phosphorus, dry and rainy season, showed the following average values 0.1031 and 0.054 mg L-1, respectively. However, these values are above limit 0,025 mg L-1 established by CONAMA Resolution No. 357/2005, for watercourses in condition Class 3. There is a high average value of Chlorophyll a 77,81μg.L-1 for the dry season, and 127.08 μg.L-1 for the rainy, exceeding the limit set by CONAMA Resolution No. 357/2005, Chlorophyll a equals to 60 μg.L-1.
According to the Nitrogen results in the form of Nitrate and Nitrite is worth mentioning the maximum values of these parameters. In the dry period, the nitrate showed maximum concentration of 11.11 mg L-1, getting above the limit of 10 mg L-1, defined by CONAMA Resolution No. 357/2005. For nitrite, the maximum value was <0.002 mg L-1.
The recent pollution is characterized by the presence of nitrogen in its ammonium form. In the analysis performed, the variations found in the dry period were 1.522 to 0.406 mg L-1 for the rainy season, the variations remained constant with maximum and minimum values of 0.839 mg L-1, both values within the limits established by CONAMA Resolution No. 357/05, for freshwaters Class 2.
The maximum values of turbidity were 204.15 and 150.81 NTU for the dry and rainy season, respectively. For Total Dissolved Solids, the figures showed no disagreement with the law during the monitored period. The Ministry of Health Ordinance No. 518/04 determines a concentration up to 500 mg L-1 SDT as the standard of potability of water intended for human consumption.
The monitoring of water quality in time and space, allows the implementation of management tools for the conservation of this wealth, prioritizing aquatic life and health of its surrounding population.