[Spatial dstribution of the net anthropogenic phosphorus input (NAPI) to the Dongting Lake basin, China.]

Based on the net anthropogenic phosphorus input (NAPI) model, we estimated the NAPI of the Dongting Lake basin and its sub-basins from 1985 to 2015, and analyzed the spatio-temporal distributions and variations. The results showed that there was an increasing trend at first and then a decrease in the Dongting Lake basin. The NAPI values in the area in 1985, 1995, 2005 and 2015 were 7.00, 9.20, 10.33, 10.01 kg·hm^-2·a^-1, respectively. The largest input source changed from the net food and feed import in 1985 to phosphorus fertilizer during 1995-2015. The mean annual input of phosphorus fertilizer, with an average value of 6.01 kg·hm^-2·a^-1 accounting for 65.8% of NAPI; followed by the food and feed import, the annual average value was 2.65 kg·hm^-2·a^-1, accounting for 29.0%, and the least was non-food phosphorus, with an average annual value of 0.47 kg·hm^-2·a^-1, accounting for 5.2%. Spatially, the distribution of NAPI in the Dongting Lake basin showed the characteristics of high in the northeast region and low in the west, which was mainly consistent with distribution of local agriculture. The average annual NAPI values in sub-basin from high to low ranked as following: Dongting Lake area, Xiangjiang River downstream, Zijiang River upstream, Xiangjiang River upstream, Lishui River area, Yuanjiang River upstream, Yuanjiang River downstream and Zijiang River downstream. The highest NAPI was found in the Dongting Lake area, increasing from 13.01 kg·hm^-2·a^-1 in 1985 to 24.14 kg·hm^-2·a^-1 in 2015. Agricultural production and population growth were the main contributors to the current input of net phosphorus, and the negative ecological effects of which could not be ignored.