Starting from spatial-temporal distribution of nitrogen and phosphorus species in Ocoí river Sub-basin, Itaipu's tributary, this work evaluated the environmental impact in surface waters. After rain, non-point sources are predominant, presenting higher levels of total phosphorus and nitrogen. In the case of phosphorus, trophic states varied from ultraoligotrophic to mesotrophic. Even though Brazilian legislation is obeyed for surface and drinking water, total nitrogen showed values above background levels, and nitrite concentration, 0.06 mg L-1 NO2--N, lies above the recommended value meant to protect aquatic life, according to the Canadian Water Quality Guidelines. Non-point and point sources control is advisable to minimize environmental phosphorus and nitrogen species impact, increasing the water support capacity and minimizing its discharge into Itaipu Reservoir.
Ocoí River; Itaipu Reservoir; phosphorus and nitrogen; principal component analysis; trophic index
