Emission Characteristics of Nitrogen and Phosphorus in a Typical Agricultural Small Watershed in Tuojiang River Basin

The emission of nitrogen and phosphorus via non-point source pollution from a small watershed has become the main pollution source of river waters, while climatic conditions and human activities directly affect the changes in rainfall-runoff and types of land use that are closely related to nitrogen and phosphorus pollution. In this study, we explore the runoff loss, nitrogen and phosphors concentration, and nitrogen and phosphorus emission in Huajiaogou small watershed on the upper reaches of Yangtze River. The rainfall, runoff, and temporal changes of nitrogen and phosphorus were analyzed using the continuous position monitoring data. The results showed that:① the runoff volumes were 10.05×105 m3 and 3.34×105 m3 from July 1st to September 30th, accounting for 76.58% and 56.51% in 2012 and 2013, respectively, and they were positively correlated to rainfall. The peak concentrations of ammonia nitrogen (NH4+-N) from April 1st to June 30th were 11.51 mg ·L-1 and 4.44 mg ·L-1in 2012 and 2013, respectively. ② The NH4+-N emission risk period was from July 1st to September 30th, accounting for 78.45% and 62.24% in 2012 and 2013, respectively. The peak concentration and emission risk period of total nitrogen (TN) and nitrate nitrogen (NO3--N) were from July 1st to September 30th, and NO3--N was the main form of the total nitrogen emission. The peak concentration of NO3--N was 6.06 mg ·L-1 and 11.43 mg ·L-1in 2012 and 2013, respectively, and the loss in NO3--N from July 1st to September 30th accounted for 88.74% and 65.55% in 2012 and 2013, respectively. ③The emission risk period of total phosphorus (TP), dissolved total phosphorus (DTP), and particulate phosphorus (PP) was also from July 1st to September 30th, and the particulate phosphorus was the main form of the total phosphorus emission. The particulate phosphorus emission from July 1st to September 30th accounted for 36% and 68% in 2012 and 2013, respectively, and the ration of particle phosphorus to total phosphorus was easily affected by rainfall.