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Keywords: Poluição hídrica;  Bacia de drenagem;  Nitrogênio;  Óxido nitroso;  Water pollution;  Watershed;  Nitrogen;  Nitrous oxide
Issue Date: 15-Feb-2012
Abstract: Human activities are causing substantial changes in the nitrogen cycle. These changes result in an increase in reactive forms, the distribution of its various forms in aquatic systems and the generation of gases N, considered important regulators of chemical and physical processes in the atmosphere. A greenhouse gas generated is N2O, which besides being one of the greenhouse gas, contributes to the consumption of stratospheric O3. The present study was to evaluate the impacts caused in the distribution of species of dissolved N, N loads and emissions of N2O from the discharge of untreated urban wastewater of the Paquequer basin (Teresópolis, RJ). The river rises in a Paquequer Unit of Environmental Conservation, PARNASO, however, the impacts begin when the river leaves the park and goes toward the urban perimeter, where it receives high load of wastewater. Later, through areas where rural activities are developed, before flowing into the Preto river. Samples were collected in august (2010), a period characterized by drought, along the basin river Paquequer and its main tributaries. In situ measurements of pH, conductivity, temperature and the analysis of NH4+, NO2-, NO3-, NTD, N2O concentration and flow were made in that region. The NTD ranged from 580 to 9996 μg N L-1, respectively these values are found within the conservation area and the urban perimeter. In the four sampling points located in areas subject to little direct influence of human activities (3 in the conservation unit) predominated in NOD compared to inorganic forms of N, and NO3- these predominated over the others. In these four points, the levels of NO2- and NH4+ were less than 20 μg N L-1. In the most polluted parts of the Paquequer basin predominate NH4+ and NOD. N2O emissions ranged from 0.7 to 201 μg N m-2 h-1 in the main channel of Paquequer and from 1.1 to 9.9 μg N m-2 h-1 in three tributaries investigated. In places within the boundaries of Parnassus and Principe stream , not sectors, or very little, subject to the discharge of sewage, emissions ranged from 0.7 to 6.1 g N m-2 h-1. The highest emissions occurred within and just outside the city limits lower, with values ranging from 68 to 201 μg N m-2 h-1. The concentrations of NH4+ and N2O show a statistically significant correlation (r2 = 0.73), suggesting that the production of oxides in the polluted waters of the Paquequer basin may be predominantly associated with the process of nitrification, which arises as a byproduct in the oxidation step NH4+.
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