Avaliação integrada da Bacia de drenagem do Rio Parnaíba através de fatores de emissão de cargas de nitrogênio e fósforo e índices de qualidade de águas

Abstract

The main purpose of this thesis was to present environmental management tools for an integrated and systemic analysis of the Parnaíba River basin with regard to the inputs of nitrogen (N) and phosphorus (P), their effects on the quality and trophic status of the main rivers of the different sub-basins, and their flows to the coastal zone. This was done through the assessment of the different natural and anthropogenic vectors and transfer mechanisms along the continent-ocean continuum. Loads and emission factors associated with different land uses were estimated. The use of the minimum quality index (IQAmin) and of the Trophic State Index (IETPt) showed the potential effects the transfer of loads may have on the water quality conditions in the region. The estimated total load was 76,033 t N.year-1 and 36,533 t P.year-1, while the estimated factors were 229 kg N.km-2.year-1 and 110 kg P.km-2.year-1. The mid sector of the basin has the largest nitrogen emissions, while the High Parnaíba responds for the highest emissions of phosphorus. Diffuse sources related to agricultural and livestock farming activities were predominant. However, the Mid and Lower Parnaiba showed to have a growing number of point sources of domestic effluents due to an increased urbanization. The estimated loads and factors were compared to spot concentrations . The probability curves of the limnological variables showed that total phosphorus, total nitrogen, turbidity and total suspended solids were the critical water quality variables in the region, which allowed the determination of the IQAMin. Regular to good conditions prevailed in the High Parnaíba while the mid and lower sectors of the river showed bad conditions. On the other hand, IETPt showed higher trophic levels in the sub-basins of the mid and lower sections of the basin. The coastal region of the Parnaíba River Delta presented quality conditions that were Regular to Good, and its trophic status was defined as oligo-mesotrophic, except for the Igaraçu River (eutrophic) during the dry season, indicating the strong influence of urban phosphorus inputs from the coastal cities. N and P load estimates obtained through emission factors and the adjustment of indices to the regional conditions represent an important management tool for the systematization of information, being useful as well to identify and rank the main nutrient pollution vectors and their effects on the quality of surface waters thorughout the Parnaíba River basin.