Variation of net anthropogenic phosphorus inputs (NAPI) and riverine phosphorus fluxes in seven major river basins in...

The riverine phosphorus (P) import resulting from human activities is always a worldwide concern for environmental management due to the effect of eutrophication. In this study, we made modification of the NAPI method to make the results closer to the actual situation. We collected the data of seven major outflow rivers in China to have a comprehensive understanding of P export and P inputs and build the quantitative relationship between them. We estimated the net anthropogenic phosphorus inputs (NAPI), including fertilizer P (P_fert), net food and feed import P and non-food P using by human (P_im+nf), in seven major river basins in China and the corresponding riverine total phosphorus (TP) fluxes. The relationship between NAPI and riverine TP flux was also explored. NAPI in seven river basins presented an obvious uneven distribution. Huaihe River basin showed the highest NAPI of 4005.09 kg P km^-2 yr^-1 due to its highest intensities of human-activities, and the lowest NAPI was observed in Songhua River basin as 334.36 kg P km^-2 yr^-1. P_im+nf occupied a larger proportion of NAPI in the Pearl River and Liaohe River basins (> 65%), while P_fert contributed more to NAPI in the other basins (nearly 60%) with an exception of the Yangtze River basin (where P_im+nf and P_fert approximately contributed the same). Different contributions of NAPI components were mainly attributed to the different land uses. The total TP flux of all the seven rivers was 117.10 × 10³ t P yr^-1, with the highest flux in the Yangtze River (77.42 × 10³ t P yr^-1), contributed 72.88% to the total TP fluxes in China. Change in riverine TP flux could be well described by NAPI, river discharge, and percentage of lake area in the basin and this provided an effective way to predict TP fluxes in rivers.