Dados oficiais de concentração de nutrientes e vazão do Rio Jaguari, foram utilizados na avaliação das contribuições difusas, com origem rural, às águas superficiais de uma sub-bacia do Rio Jaguari, SP. Modelos de cargas médias diárias de Ntotal e Ptotal foram gerados a partir de regressão estatística aplicada a dados de campo obtidos entre 1999 e 2002. A validação dos modelos foi feita utilizando-se dados de campo obtidos entre 1996 e 1998. O modelo mostrou que, em média, 68,2% das cargas anuais de Ntotal e 77,3% das cargas anuais de Ptotal foram transportados pela sub-bacia no período chuvoso. Partindo-se de cargas de base diárias de 1706,5 kg Ntotal e de 165,7 kg Ptotal, determinou-se que 55,1 e 69,4% das cargas anuais totais de Ntotal e Ptotal, respectivamente, transportadas pela sub-bacia, provieram de fontes difusas. As taxas de exportação de nutrientes por carga difusa, obtidas pela aplicação do modelo, foram iguais a 230 kg Ntotal km-2 ano-1 e 40 kg Ptotal km-2 ano-1. Concluiu-se que o controle das fontes difusas de Ptotal, a partir de áreas rurais, deverá diminuir as concentrações deste nutriente no Rio Jaguari.

Official water quality and flow data from Jaguari River were used to assess the diffused loads of nutrients from rural areas into surface waters. Mathematical models of mean daily loads of total nitrogen (TN) and total phosphorus (TP) were generated through the application of simple statistical procedures to field data collected from 1999 to 2002. The models obtained were validated with field data collected from 1996 to 1998. The application of the model showed that, on average, 68.2% of the TN annual loads and 77.3% of the TP annual loads were transported through the sub-basin during the raining season. Assuming the mean baseflow loads as 1706.5 kg TN d-1 and 165.7 kg TP d-1, the annual diffused loads obtained - primarily from rural sources - were equivalent to 55.1 and 69.4% of the total annual loads of TN and TP transported through the sub - basin, respectively. The mean export coefficients from diffused loads for TN and TP were equal to 230 and 40 kg km-2 year-1, respectively. In may be concluded that controlling the diffused loads of TP from rural areas should decrease the high concentrations observed.